GB2054128A

GB2054128A - Power generating system

Info

Publication number: GB2054128A
Application number: GB7840639A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-07-16
Filing date: 1978-10-16
Publication date: 1981-02-11
Also published as: GB2054128B

Abstract

In a power generating system, heat energy is supplied to a hot reservoir (601) from the Sun, from used power station cooling water or from any other source of low-grade heat including freshwater or seawater at temperatures down to freezing point, in which case the source of heat is the latent heat of fusion of the water. Heat energy is rejected from an energy-converter of the system to a cold reservoir at a temperature below that of the hot reservoir (601) and, by use of heat rejection means (611), radiated at night to the sky and outer space from the cold reservoir which may consist of ice and water held in high-altitude lakes at temperatures of 0 DEG C down to -60 DEG C. <IMAGE>

Description

SPECIFICATION Energy from sky heat exchange GENERAL STATEMENT OF THE INVENTION The present invention relates to world energy problems and more particularly to the generation of inexpensive electrical power. By the term "inexpensive" is meant much less expensive than nuclear, wave, wind and tidal power both in capital cost and unit electrical power cost.

In addition the present invention seeks to provide means to generate cheap electricity without the dangers to the environment and life which are associated with nuclear power and other thermal power stations which tend to cause thermal and gaseous pollution of the atmosphere and rivers, the hazards of toxic nuclear waste, and whose mines, cooling towers and slag heaps cause an unsightly impact on the landscape.

Also the present invention proposes means to generate electricity closely matched to the demands of the population, by providing more power output the colder the weather. This relationship between the coldness of the weather and the power output of the present invention is direct and immediate, its response to increased demand for power being instantaneous and closely matched in magnitude.

The present invention does not rely on any exhaustible resource and indeed consumes no terrestial material or energy, although it may be adapted to do so in the short-term transitional period whilst we await inexhaustible energy sources: for instance the present invention can use the waste heat of coalfired and nuclear power stations (which comprises about 60% of their source energy), geothermal energy or any other source of low-grade heat to generate power inexpensively. However in the long term the present invention relies only upon energy-exchange with outer space and indeed may provide cheap energy for slightly longer than the sun and the stars exist.

Finally the present invention seeks to provide synergy with most or all of the other "alternative energy sources" such as wave, wind, tidal or solar energy, by supplying a means to store the energy from such sources for long periods, upto and including inter-seasonal energy storage, whilst incidentally providing if needed very large quantities of fresh water for use in emergency drought situations or for irrigation.

DESCRIPTION OF ESSENTIALS AND DIFFERENCES FROM PRIOR ART It may already be apparent that the present invention is radical, being rooted in a fundamental reversal of conventional thinking on energy matters. To explain the present invention therefore, it may be helpful first to comment on conventional and historical concepts of energy.

The concept of energy is fairly recent in historical terms: until about 1 750 A.D. the only forms of energy available to civilisation were largely derived from horses, oxen and humans (for e.g. drawling ploughs, chariots and carriages, for lifting and carrying water, wood and other burden, for building pyramids, for rowing boats and ships, etc.); from the wind, for driving ships and windmills; from water for powering river and tide-mills: in short from any source which could pull a load, lift a weight or turn a wheel. All these were sources of mechanical energy which to this day is still known, even by thermodynamicists, as "work".

It was only about 200 years ago, that is about only 2% of the recorded history of civilisation, when another form of energy - heat - influenced conventional thinking, by providing the steam-driven pumps, railways and mills which brought about the industrial revolution which has largely re-founded present world civilisations and economies.

Virtually all energy "progress" since then (but barring hydro-electric, wind, tidal and wave energy which are all of the mechanical "work" type) has been concerned with exploiting sources of heat. Thus, since about 1900 A.D., conventional thinking has sought and developed the internal combustion engine, the steam turbine, the jet engine, the nuclear fission reactor and the hot air Stirling engine. Even now, very large sums of money are being spent in the search for more oil and coal (to burn to provide heats, for solar heating, for the hot sodium-sulphur battery for electric cars and - last but most extreme - on the nuclear fusion reactor which requires the fearfully-difficult heat of 100 million degrees centigrade in order to start work.

A second aspect of conventional thinking (and thinking is a psychological process) concerns the psychology of those concerned in the current search for energy. This psychology appears largely to be influenced and directed by the normal human reaction to a situation of need, that is, because we need something, we must find it and capture it. This human reaction is quite normal and perhaps has its roots in the need to find and capture food which was, after all, the original source of energy.

The present invention proposes that a solution lies in a reversal in these two aspects of conventional thinking. That is: firstly we need to find not heat but cold; and secondly we need not to capture but to give away instead. By taking these two apparently negative steps at the same time, a positive source of energy will become apparent.

The essentials of the present invention may be most easily understood by considering the planet Earth as a whole, and by studying some aspects of other planets. Firstly, all conventional energy comes or came from the Sun, via food, wood, coal, oil, uranium deposits, rain, wind, waves, tides, heat and light. All of these barring coal, oil and uranium are renewable and inexhaustible as long as the Sun exists approximately as it is now. The Sun provides a continuous source of radiation energy which supplies all the others.

None of the other planets have any of these sources of energy as we known them, with the probable exception of uranium deposits. They do not appear to support biological life. Nevertheless they exist and astronomers do not think the term "the life of the planet" as being a misnomer, because they are referring to its physical life - as determined by its temperature, atmosphere and physical movements including its winds and tides -- which, in conventional astronomical thinking, exists as long as the Sun keeps it in orbit and supplies it with energy.

Thus, if an observer were positioned for example inside the orbit of Venus and looked away from the Sun, he would be able to observe Venus nearest to him, then Earth, then Mars, then Jupiter, and then Saturn, Uranus, Neptune and Pluto. Using eyesight and conventional astronomical instruments such as a telescope, a spectrophotometer and a stopwatch, the observer would be able to observe and measure the rate at which radiation energy was being emitted by each of these planets and, from the Sun behind him, the rate at which radiation energy was being received by each planet.

From such measurements the observer could deduce the following with' regard to the temperature and. energy balance of the Sun, planets, Moon and the background of outer space:

Temperature K Rate* at which energy is: Is liquid water Body Night Day Swing Received Emitted present Sun 57760 5776 - None Negligible 62,493.1 None (the "source") Venus 233 720" 487- 2.590 The same Tiny bit Earth 275 295O 20 1.353 Slightly more Lots Moon 100" 365" 265O 1.353 The same None Mars 1700 300e 1300 0;583 The same None Jupiter 123- 313" 1900 0.050 Slightly more Tiny bit Background 3 3 None Negligible**~ Negligible None (the "sink") *Energy rate is measured in kilowatts per square metre.

**Negligible per square metre but, if integrated over the whole background, equivalent to the energy output of many million million million million Suns.

If this heavenly observer then came down to earth armed with the knowledge in the above table, and then observed all the features of the Earth, some of its physical properties and took measurements when viewing the sky, he could deduce the following 1. That "day" means "when able to receive radiation energy from the Sun".

2. That "night" means "when unable to receive radiation energy from the Sun".

3. That all the energy received from the Sun in daytimes is returned to outer space in night-times, 4. That a tiny surplus of man-made and other energy from Earth sources is also radiated from Earth to outer space largely in night-times.

5. That Jupiter also emits (i.e. radiates) slightly more energy than it receives, possibly because being the largest known planet and of a mass sufficient to allow gravity to compress its hot core there are nuclear processes at wdrk within it causing heat generation.

6. That the very small temperature swing of 200 on Earth (as between day and night-times), compared with swings of from 1300 for Mars, 2650 for the Moon and 4870 for Venus, is a consequence of the very large amount of liquid water on Earth, compared with its almost total absence on the other planets, the Moon, the Sun and in outer space.

7. That the small temperature swing of 200 on Earth is an average figure for the whole surface of the Earth as observed from space but, when the whole surface of the Earth is examined more closely by a terrestial observer, is found to be an average of components which in general have temperature swings much greater than or much less than 200. Thus the seas and oceans covering some 71% of the Earth's surface exhibit swings of the order of only 1 OC -- and even less than this when at the point of freezing with a little ice present -- whereas certain parts of the much smaller land area of the Earth exhibit swings much greater than 200C.

8. That in general, the regions of land which exhibit the greatest day-night temperature swings are those in good radiation-communication with the sky and with little liquid water. Thus, cloudless desert regions may reach 500C in daytime and cool to -1 00C at night swing of 600C. Again, land elevated to an altitude above haze and cloud - and not carrying much vegetation or liquid water - may reach for example 300C in daytime and -400C at night, giving an even greater swing of 700C.

9. That the desert regions which typically receive say 0.5 kilowatts per square metre (abbreviated hereinafter to kw/m2) in daytime, emit energy to space at night at just the same rate - when day and night are of equal duration i.e. at the 20th/2 1st March vernal equinox and again at the 22nd/23rd September autumnal equinox. During summer i.e. between 21st March and 22nd September, more energy is received in daytime than is lost at night and during winter i.e. after 23rd September but before 20th March, more energy is radiated to space at night than is received in daytime.These "turnaround" dates may be somewhat removed from the equinoxial dates according to the latitude and longitude of the region in question, the year, and local and transient effects such as cloud and other atmospheric properties and sunspots and other properties of outer space.

10. That the solar constant of 1.353 kw/m2 -the average rate at which solar energy falls on a surface positioned on the line of the Earth's orbit and facing directly at the Sun - is diminished to only about 0.1-0.2 kw/m2 in European latitudes at sea level, due to atmospheric attenuation and the lower elevation of the Sun at finite latitudes. By contrast, the energy rate may reach 1.0 kw/m2 near the peak of high mountains.

11. That the parts of the Earth's surface which appeared brightest to the heavenly observer when he observed the Earth from a position inside the orbit of Venus are covered with frozen water, that is, ice in the case of the polar ice caps and ice crystals in the case of the brightest clouds.

12. That the brightness of the polar ice caps and clouds means that they are very effective radiators of visible light but - and the observer would confirm this from observations on Earth - they are also very effective radiators of thermal energy. The observer would confirm this by measuring the coefficient of thermal absorption and emissivity of ice and finding that this coefficient had a value usually over 0.90 and often as high as 0.99.

13. That the brightness of the polar ice caps and clouds is a consequence also of their high reflectivity or albedo, that is, they are very effective at reflecting back into space the visible radiation and also a good deal of the thermal radiation which falls upon them from the Sun in daytime.

14. That in consequence, regions of the Earth which are covered with ice or ice-clouds tend to stay so covered and very cold compared with other regions of the Earth - so long as there is not much liquid water in close thermal communication with these very cold regions.

1 5. That the coldest of all the regions of the Earth are -- because the atmosphere around and above them is thin and clear and has been cooled by adiabatic expansion to the low atmospheric pressures which obtain at high altitudes -- the peaks of high mountains covered with ice with no liquid water present.

The present invention proposes, in its preferred embodiment, to make use of this quality of coldness of elevated or mountainous dry land, firstly because the low temperatures of such land improves the cycle efficiency of the power-generating systems proposed in the present invention; secondly because limitless energy may thereby be extracted from liquid water in the oceans, seas, lakes and rivers; thirdly because the power generated by such systems will match almost exactly in both timing and magnitude the demand for power by populations served by such systems; fourthly because the high rates of energy reception and emission of such elevated land permit reductions in size and cost of several major components of the present invention; and fifthly because elevated land allows energy generated by systems according to the present invention as well as by other power-generating systems including nuclear, wave, wind, geothermal and tidal systems to be stored for very long periods upto and including inter-seasonal periods of several months.

Before describing the present invention it may be helpful to comment on existing processes and systems which convert energy received from the Sun into useful power, work or heat.

The archetypal process for converting the Sun's radiation into combustion heat involves photosynthesis of sugar and cellulose in plants and trees which could be burned as wood to produce heat or later in history, burned as coal. This process may be represented by Diagram 1.

Referring to Diagram 1, it has been estimated that the photosynthetic process, if used as a source of heat by combustion of wood, coal or - in recent terminology -- "biomass", is only about 2% efficient, i.e. for each 100 units of the Sun's energy falling on a plant or tree only 2 units of that energy later appear as useful heat from combustion.

It is emphasised that these 2 units of heat eventually reach the biosphere (i.e. the atmosphere, land and oceans which support life) as heat from the flues or chimneys of fires, or as heat slowly lost through the walls and roof of buildings, or as heat from the expired air or bodies of people and animals, etc., etc., where they join up with the 98 units of energy not converted by plants and trees into combustible substance. Therefore making the broadly correct assumption that the temperature of the Earth and the biosphere does not increase -the original 100 units of energy received from the Sun eventually are re-radiated back to outer space.

Next if we consider the process by which (barring nuclear energy and the "alternative" sources of energy such as wind, waves and tides) the great majority of our electricity is generated -- that is by the burning of coal, gas and oil in a Rankine steam-cycle as employed in over 70% of our power stations then the process may be represented by Diagram 2.

First, the similarity with Diagram 1 is notable; the process is again based on chemical reactions (the combustion of organic matter) to produce heat; again the energy-converter (a power station now, instead of a plant or tree) accepts energy from a reservoir and rejects most of it to a reservoir (and the cold reservoir above is part of the biosphere of Diagram 1); again the balance of energy which was converted into the desired useful form (electricity now, instead of heat in Diagram 1) eventually reaches the biosphere as heat; and again the original 100 units of energy (from the fire now, instead of from the Sun) are eventually re-radiated back to outer space.

The only difference between Diagram 1 and Diagram 2 is not a difference of essential principle but merely one of proportion: the process in Diagram 2 is about 20 times as efficient in converting its source energy into the desired form. Thus, it converts 40% of its source energy (heat) to useful electricity whereas a plant or tree converted only some 2% of its source energy (solar radiation) into useful heat when burned.

However it must now be emphasized that the process by which the great majority of present and future electricity is generated involves these two processes in series. That is, 100 units of solar energy produce 2 units of heat for the power station, and these 2 units of heat produce 2 x 40% which equals 0.8 units of electricity. Therefore, strictly speaking, our present and future electricity is converted from solar radiation energy with only about 0.8% efficiency.In the case of oil or gas-fired power stations, this overall conversion efficiency is very much lower -- because only a tiny fraction of solar energy is converted into food for the small organisms which later become hydrocarbons, because only a tiny fraction of this food became tissue in those small organisms, and because only a tiny fraction of these organisms was converted into recoverable gas and oil. All in all, the overall conversion efficiency of gas and oil-fired power stations is unlikely to be greater than 0.001%.

Of course at the present time we do not see the process in these terms and generally think of an up-to-date power station -- perhaps one employing fluidised-bed combustion of coal - as being about 40% efficient. But the only reason why we can accept this conventional thinking lies in the fact that the two processes of Diagrams 1 and 2 are separated by perhaps 500 million years. 500 million years is indeed a very long time. However it is only about 1 O% of the remaining life of the planet Earth and in any case there is no prospect whatever of waiting for the Sun to produce further supplies of coal when we are already consuming it at a rate about a million times faster than the rate which it was created.

Before leaving Diagram 2 it should be mentioned that the figure of 40% conversion efficiency assumes Carnot efficiency for a heat engine working between temperatures of 5000K (i.e. 2270C) and 300"K (i.e. 270C) which gives a thermal efficiency of 0.4 from the well-known thermodynamic expression: cold reservoir temperature Thermal efficiency = 1 hot reservoir temperature 300 =1 500 =1-0.6 =0.4 The steam Rankine cycle used in most thermal power stations actually employs a highest steam temperature much higher than 5000K but, because a good deal of the heat input to the steam is at a relatively low temperature, the effective Carnot hot reservoir temperature is only in the region of 5000K when component inefficiencies and non-isentropic processes are taken into account.

Of much greater significance is the cold reservoir temperature in present power stations, i.e. about 3000K which equals 270C. It is often claimed that the reason for this choice of cold reservoir temperature is the fact that the cold reservoir is usually river or seawater or atmospheric air at about 1 20C and that a temperature difference of 1 50C from the steam condensing temperature of 270C is needed for heat transfer. Whilst this claim may be true, it is somewhat irrelevant: if there were a source of cooling agent at a temperature much lower than 1 20C it would be of little help - apart from allowing the condenser heat-transfer surface area to be reduced -- and indeed the thermal efficiency could hardly be improved, for these reasons:- 1.The steam-condensing temperature is limited by the steam-condensing pressure, which in up-to date power stations is in the region of 0.04 atmospheres -- a degree of vacuum (96%) already difficult to achieve.

2. Any reduction in the steam-condensing temperature would further lower the steam-condensing pressure and lead to: a) A rapid increase in the size of the condenser -- and condensers are already uncomfortably large.

b) Aggravation of the structural problems that already exist in large condensers designed to withstand high internal vacuum.

c) Aggravation of the air-ingress problem which already has an adverse effect on cycle efficiency.

d) Worst of all - because the specific volume of steam increases rapidly at pressures below 0.1 atmospheres -- aggravation of the design, construction, size, reliability and safety problems which are already a headache in steam turbine low-pressure blading and rotor manufacture and operation. The low-pressure blades of the steam turbine are already uncomfortably long and require careful manufacture, mounting and balancing. Furthermore they have to withstand the erosion caused by impact of high-velocity water droplets carried in the highly-expanded steam and any reduction in the condensing temperature and pressure would rapidly aggravate this problem also.

Turning now to the present invention, its general scheme is now described as follows.

GENERAL SCHEME The present invention relates to systems for generating power, usually but not exclusively where such power is generated in electrical form suitable for direct admission to a national or local electrical power grid, wherein the means to generate power includes an energy-converter such as but not necessarily a heat engine which accepts heat from a hot reservoir, converts some of that heat into power and rejects the balance of heat not so converted into power to a cold reservoir at a temperature lower than the temperature of the hot reservoir.

More particularly the invention is concerned with thermodynamic power-generating systems which term, for the purpose of this application, is defined as a system including a hot reservoir comprising material at a temperature TH; a cold reservoir comprising material at a temperature Tc lower than TH and higher than 30K; a heat source which supplies heat to the said hot reservoir; a heat sink at a temperature lower than Tc to which heat may be rejected from the said cold reservoir without causing the heat sink temperature to rise significantly; heat rejection means adapted to encourage the rejection of heat from the said cold reservoir to the said heat sink; and an energy converter adapted to accept heat from the said hot reservoir and to reject heat to the said cold reservoir and to provide an output of mechanical, electrical or other energy.

Such a system is described in my UK patent application No. 29987/77 entitled "Improvements in Stored Energy Systems" to which reference is directed and which is incorporated herein as the priority document.

The present invention describes thermodynamic power-generating systems all of which may be depicted in diagrammatic form as shown in Diagram 3.

First it will be noticed that Diagram 3 is closely similar to Diagrams 1 and 2 and indeed is the standard arrangement for a heat engine in classical thermodynamics. However it has certain novel and distinguishing features described as follows: 1. The proposed cold reservoir is at a temperature considerably lower than the 3000 K or so which obtains in conventional power stations.Heretofore virtually all the efforts towards improvement of thermal efficiency of power stations has been directed at increasing the effective hot reservoir temperature TH; however this is the last effective approach as the following example demonstrates: a) Consider the effect of raising TH by 50 from 450no to 500"K whilst holding the cold reservoir temperature T0 steady at 300"K.

Before After TH = 450" TH = 500 TC Carnot efficiency = 1 - TH 0.333 0.400 Heat supplied for 1 unit output 3.00 2.50 Therefore, saving in heat supplied - 0.50 (= 16.7%) But, Gradetvalue* of heat supplied = heat supplied x (TH -.T0) 450 500 Therefore, loss of Gradezvalue* 50 (=11.1%) *Grade-value as defined above gives a measure of the useful workproducing potential of the heat supplied.

b) Consider instead the effect of lowering TC by 50" from 300"K to 250to whilst holding TH steady at 450 K.

Before After TC = 300 TC 2 2500 TC Carnot efficiency = 1 - 0 333 0.444 TH Heat supplied for 1 unit output 3.00 2,25 Therefore, saving in heat supplied - 0.75 (= 25%) But, Gradevalue of heat supplied 450 450 Therefore, loss of Grade-value None Also, heat rejected for1 'unit of output 2.00 1.25 Therefore, reduction in heat rejected** 0.75 (= 37.5%) **This parameter is of greater importance in systems according to the present invention which is concerned more with heat rejection than heat supply.

Comparing case a) and case b) above it can be seen that lowering the cold reservoir temperature Tc is more effective than increasing the hot reservoir temperature TH, firstly in terms of the improvement in Carnot efficiency, secondly in the quantity of heat supplied where the saving rises from 0.50 units to 0.75 units, thirdly because there is no loss of grade-value and fourthly because the desirable reduction in the amount of heat rejected is increased from 0.50 units (it can be deduced from the above figures for case a)) to 0.75 units.

2. Heat rejection from the proposed cold reservoir is by direct radiation to the sky i.e. outer space which, from recent observations made in the U.S.A., has a background temperature of only 30K, that is, -2700C.

3. Because the useful energy output (E units of electricity for example) is proportional to the heat rejected from the cold reservoir (Q units of heat radiated to space), it follows that for a given cold reservoir the useful energy output is quite precisely proportional to the rate at which heat is lost from the Earth - and this is closely matched to the demand by the population for energy for heating (the largest proportion of demand) both as to timing and magnitude.

4. If the cold reservoir temperature Tc can be held somewhat below the temperature of land and water masses available nearby the system (and they will normally be above 2730 K) - by for instance reducing Tc to 2500K (i.e. -230C) which is quite possible when the cold reservoir is in direct radiation-communication with the background of space at 30K-then limitless useful energy can be generated, especially from the latent heat of fusion of water which has the unusually high value of 333 joules per gram and also an unusually high value of thermal conductivity which benefits the system.

The present invention will be more particularly described hereinafter in terms of its application to an office block whose electrical power, spaceheating, water-heating and air-conditioning may be provided by sky heat exchange according to the present invention. However that embodiment of the present invention was chosen for the priority document, UK patent application No 29987/77 dated the 1 6th July 1977, as a deliberately scaled-down application of the invention disclosed therein, for reasons of commercial security and brevity, whereas it was then known and intended that the invention should be applied to national electrical power generation.This will be apparent from the reference towards the bottom of page 1 5 of the priority document which reads: "Any other source of water at a temperature close to 300C (such as found for example in power station steam condensing equipment) may be used as shown in Figures 6, item 620". It will of course be appreciated that the amount of heat discarded from present thermal power stations is greater than the electrical energy produced by them: the present invention may be applied so as to convert a nationally-significant proportion of that presentlydiscarded heat into electrical power for the national grid; that proportion may be in the region of 10% by means of the present invention, that is, equivalent to an increase in the electrical power output of such power stations, of about one-sixth of their present electrical power output.An increase of one-sixth in the electrical power output of present UK thermal power stations would, if secured in most of them, provide a greater contribution to UK energy needs than the whole of UK nuclear power.

Accordingly the present invention will first be described in terms of its preferred and intended embodiments, which are intended to supply electrical power suitable for admission to any national or local electrical power grid. All of these preferred and intended embodiments contain the features disclosed in Figure 6 of the priority document and disclosed hereinafter in Figure 1 of this application, Figure 1 being identical to Figure 6 of the priority document apart from that one re-numbering. For that reason and for brevity, the following preferred and intended embodiments will now be described largely in words with only some occasional reference to elements or features depicted in the one accompanying formal drawing, Figure 1.

A first preferred embodiment proposes means both to generate electrical power and to store energy in the form of the potential energy (by virtue of gravitation) of a massive body, which in this embodiment is water but which may in other embodiments be any suitable massive body or massive counterweight advantageously comprising a large volume (e.g. more than 1000 cubic metres) of a solid or liquid substance. The primary purpose of such massive body, which may be lifted by the power produced according to the present invention and later lowered with a release of potential energy, is to enable useful energy produced either by the present invention or by any other source of energy including wind, waves, tidal, geothermal, solar, hydro-electric or nuclear energy to be stored until such time as it may be needed to produce electrical or other desired forms of energy.In addition this massive body may, if comprising water as in this and other embodiments, be used in emergency drought situations for e.g. drinking or irrigation.

Massive bodies of water at altitude already exist in numerous parts of the world in the form e.g. of high lakes, water reservoirs and hydroelectric reservoirs, the latter being probably the most effective manner of generating electrical power at very high conversion efficiency (e.g. greater than 85%) and with nearly instantaneous response to fluctuations in demand.

The value of this latter point has been realised and pursued in at least one pumped-storage facility, namely, the high lake at Dinorwic in North Wales to which water may be pumped using surplus to baseload electrical energy (especially that surplus produced by the increasing capacity of UK nuclear power stations which otherwise might become uneconomic if their occasionally-surplus capacity were not stored for reuse at other times) and from which water may flow through turbines installed within the Elidyr mountain down to the lower lake, Llyn Peris, 1640 feet (500 metres) below.For instance in situations such as the simultaneous ending of popular television programmes on two or three TV channels, the national grid experiences an extremely sudden increase in demand for electricity (e.g. for making tea and hot food, and for immersion heaters switched on in anticipation of baths or other washing) and the Dinorwic facility is intended to respond within 10 seconds to such demand surges, allowing typically 1300 Megawatts (abbreviated hereinafter to Mw) of extra power to be made available as water flows at a rate typically of 400 tonnes per second through the turbines.

The Dinorwic facility is expected to be in operation in 1 982 at a total capital cost of 310 million.

The electrical output of 1300 Mw therefore costs in the region of 250 per installed kilowatt, in terms of capital cost. This capitat cost is similar to the capital cost per installed kilowatt for coal or oil-fired power stations and perhaps half to one quarter of the capital cost per installed kilowatt of nuclear power stations ranging from the fairly cheap "Magnox" variety to the much more expensive AGR variety such as Dungeness 'B'. It is also in the region of one half the capital cost per installed kilowatt of projected wave-energy devices. By comparison, the capital cost per installed kilowatt of proposed Severn Barrage schemes may reach 2000 to 3000 (when interest charges over their about-20 years construction period are taken into account) i.e. about ten times as much as the Dinorwic facility. Fast-breeder nuclear stations based on the highly toxic plutonium fuel may cost perhaps 5 times as much as Dinorwic (in capital cost terms). The only other major long-term source of energy in prospect is that which may derive from the Joint European Torus ("JET") and other programmes aimed at producing electricity from nuclear fusion of hydrogen isotopes existing in traces in sea and other water.

However these fusion programmes are so costly and lengthy that, if we take the only reasonable view - namely that we should add up all the R 8 D and other capital costs which accrue before such time that nuclear fusion provides a significant contribution to energy needs, say, all those costs over the next thirty years, and then divide that cost by the installed nuclear fusion capacity that we may have in thirty years' time - it is conceivable that the capital cost per installed kilowatt of nuclear fusion capacity may be anything from 5000 to 50,000. So Dinorwic may prove to be between 20 and 200 times cheaper than nuclear fusion capacity by 2008 A.D.

But Dinorwic, as presently conceived, will not generate any new energy: it merely stores energy produced from some other source which itself cost perhaps 500 per kilowatt to instal and whose electricity cost perhaps 0.6 to 1.0 pence per unit to be generated.

The-present first embodiment proposes means to permit Dinorwic (and similar facilities) to generate new energy - even though on a fairly small scale for this quite small high lake - at very low additional capital cost and unit cost, for instance perhaps 100 to 200 per installed kilowatt and perhaps 0.2 to 0.5 pence per unit. Moreover, this proposed embodiment might allow such energy to be produced for the national grid by 1985 or thereabouts, if exploited with reasonable speed.This proposed embodiment of the present invention is now described as follows: Low-grade heat from for instance the discarded cooling water of the nuclear and other power stations within a few miles of Dinorwic is used to boil a working fluid which may be chosen from for instance those condensible gases which have normal (i.e under a pressure of one atmosphere) boiling or sublimation points between -800C and +1 00C, for example the following:: Boiling or Sublimation Condensible gas Point at 1 at Carbon dioxide, CO2 -78.50C (sublimation) Halocarbon R 116, C2F6 78.2 0 C (boiling) Halocarbon R 13B1, C Br F3 -57.70C Halocarbon R 502, an azeotrope 45.6 C " " Halocarbon R 115, C2CI F5 -38.70C Halocarbon R 500, an azeotrope 33.5 C " " Halocarbon R 22, CH Cl F2 -40.70C Halocarbon R 12, C Cl2F2 --29.80C Halocarbon R 114, C2CI2F4 +3.80C Halocarbon R 21, CH Cl2F +8.9"C The condensible gas may be chosen according to the degree of complexity it is felt economic or desirable to employ in order to recompress and condense that gas after it has been expanded to do work.Thus, in a simple system, halocarbon R 21 may be chosen so as to avoid any need to recompress it by use of additional equipment, because at the atmospheric pressure existing in the Dinorwic region (from sea level to the altitude of the high lake, Marchlyn Mawr) halocarbon R 21 can be recompressed by means of atmospheric pressure alone so as to condense at a temperature between 8.90C (at sea level and 1 atmosphere) and perhaps 30C at the altitude of the high lake.

Following boiling in heat-exchanger means or boiling means broadly similar to known types, the saturated gas is first superheated to a temperature of e.g. 1 000C by means of solar heating or other source of fairly low-grade heat. In the case of solar heating, the present first embodiment proposes that developments of currently available solar panels as used for domestic and other water heating should be employed so as to heat freshwater to a little over 1 000C (so as to be liquid under a slight gauge pressure in order to prevent ingress of air), this heated water being stored in large well-insulated containers containing or jacketed by a buffer substance which exhibits a change of state in the region of 700C to 900C for example, that change of state causing a release of latent or other heat with downward-falling temperature through the temperature at which the said change of state occurs. By this means solar heat collected at daytime in fairly cloud-free conditions may be stored and used in periods when solar radiation is at a low level.Alternatively, solar radiation may be collected and focussed onto the said solar panels or other heat exchanger means for heating the said water and contained or jacketing buffer substance, by means or large inexpensive concave reflectors constructed in concrete or other inexpensive setting material so as to have dished or arcuate concavity covered first with a coating or other filmlike layer of highly-reflective material such as aluminised MYLAR (registered trademark) or the like and then, if appropriate, covered with a coating or other film-like or curved sheetlike layer of dried water-glass (i.e. sodium silicate) or other metal silicate.

Following such superheating, the condensible gas which is at a significant gauge pressure is expanded by an expander of known positive displacement or reaction type such as a turbine to a pressure approximately equal to local atmospheric pressure, the mechanical or other e.g. electrical output (in the case e.g. where the said expander drives an electrical generator) being used to pump water from a low level e.g. the lake Llyn Peris, and to deliver the said water to the high lake Marchlyn Mawr.

The water in the high lake is maintained at a temperature only a little above or at its freezing point (especially in winter when demand for electricity is greater) by heat rejection means which may comprise one or more of the following: 1. A sheet or sheets of material covering the high lake, in which the transparency, opacity or other radiation-transmission, -absorption, -emission or -reflection property of the said material is chosen or controlled so as to assist heat rejection from the high lake.

2. As in 1. above, wherein the sheet or sheets of material contain light-sensitive additives for instance such as silver halides and other substances used e.g. in light-sensitive sunglasses such as are known by the registered trademark UMBRAMATIC, or the like, so that the said additives cause incoming solar or other radiation to be impeded in daytime but permit outward radiation from the high lake at night.

3. As in 1. above, wherein the sheet or sheets of material contain or enclose material of the type known in liquid-crystal displays of some electronic watches and calculators.

4. As in 3. above, wherein an electric potential is able to be applied to the liquid crystal material so as to modify or control its radiation-transmission or -reflectance properties.

5. As in 1. above, wherein the sheet or sheets of material are coated with titanium dioxide or similar coatings having relatively high coefficients of thermal emissivity.

6. As in 1. above, wherein the sheet or sheets of material have the property of one-way mirrors which permit outgoing radiation from the high lake but impede incoming solar or other radiation.

7. As in 6. above, wherein the one-way mirror property is achieved by the fusing (or other means of attachment) of numerous small (e.g. less than 1 mm diameter) dots or blobs of solid substance to that side of the said sheet or sheets of material which is closest to the surface of the high lake, the said dots or blobs advantagoeusly being of approximately hemispherical shape.

8 .As in 7. above, wherein the dots or blobs are comprised of a white ceramic solid substance.

9. As in 6. above, wherein the one-way mirror property is achieved by means which rely on the internal reflection and approximate reversal of direction of travel of radiation which would otherwise reach the high lake.

10. As in 9. above, wherein the sheet or sheets of material are largely transparent to outgoing thermal radiation from the high lake.

11. As in any of the above, wherein a gas or gaseous mixture interposes between the said sheet or sheets and the high lake.

12. As in 11. above, wherein the gas or gaseous mixture is at a pressure below that of the atmosphere surrounding the high lake so as to cause the said sheet or sheets and the interposed or enclosed gas or gaseous mixture to approximate the form of a concave lens or concave reflector 13. As in 11. above, wherein the gas or gaseous mixture is at a pressure greater than that of the atmosphere surrounding the high lake so as to cause the said sheet or sheets and the interposed gas or gaseous mixture to approximate the form of a convex lens or convex reflector.

14. As in any of the above, wherein a gas or gaseous mixture, for example air, flows across the surface of the high lake so as to encourage evaporation and cooling.

1 5. As in any of the above, wherein a gas or gaseous mixture, for example air, is bubbled through the water of the high lake so as to encourage evaporation and cooling.

1 6. As in any of the above, wherein ice or other frozen substance containing the hydrogen oxide known as H2O partly or completely covers the surface of the high lake at night-time at least, so as to encourage radiation to be emitted from the high lake by virtue of the high coefficient of emissivity of ice.

17. As in any of the above, wherein the water in the high lake contains particles of an additive which act as nuclei to promote freezing of the water in the high lake.

1 8. As in 1 7 above, wherein the said particles of additive are chosen by form, substance, colour or any other surface quality, either with or without ice accreted onto them, to promote the rejection of heat from the high lake by radiation, convection, conduction or other process.

The condensible gas after expansion is then condensed by local atmospheric pressure and by rejection of its latent heat of evaporation (or sublimation if appropriate) to the high lake by known or developed types of heat-exchanging or condensing equipment, and then returned by liquid feed pump to the boiling means, at a liquid pressure equal or greater than the pressure of the boiling condensible gas.

If appropriate all the methods (or any of them) are used in Rankine-cycle steam power stations to improve the cycle efficiency, such as feedwater heating, reheating, regenerative heat exchange etc., etc.

may be applied so as to increase the thermal efficiency of the cycle through which the condensible gas is repeatedly taken.

The electrical power generated by the system just described in this first embodiment (and of course the water turbines and electric generators are already available at Dinorwic -- except at those times when they may be used in reversed mode so as to use electricity from e.g. local nuclear power so as to pump water up to the high lake) is limited primarily by the rate at which heat can be rejected to space by the high lake. The high lake Marchlyn Mawr is quite small and is believed to have a surface area of only in the region of 10,000 square metres i.e. 0.01 square kilometres.

In winter the average rate at which heat may be radiated or otherwise rejected from the high lake may reasonably be expected to fall in the band 0.2 to 0.6 kw/m2 at night-time. Experiments conducted at the lower altitude of about 200 metres in the Cotswolds exhibited rates of heat rejection in April 1 977 (i.e. after the end of the winter) of 0.1 5 kw/m2 without any great sophistication in the means of heat rejection. Assuming that the higher altitude of Marchlyn Mawr, R a D of heat rejection techniques and the colder weather of winter might increase this rate to 0.4 kw/m2, then the high lake there may be expected to reject 0.4 x 10,000 = 4,000 kw to space at night-time.

The cycle efficiency is expected to be rather less than the Carnot efficiency, which is approximately 2750 1 --=15.4%.

3250 Assuming that losses and component inefficiencies reduce the cycle efficiency to 109/0 as a rough guide which means that 90% of the-heat supplied is rejected -- then the power output for the proposed Dinorwic embodiment might be in the region of 4,000 kw x 1/9 which equals 444 kw, or 0.444 Mw.

Similar cycle-efficiency calculations bringing in an assumed 40% cycle efficiency for a nuclear power station whose hot (e.g. 300 C) effluent is used in the proposed embodiment for boiling the condensible gas - and so to provide for example 50% of the total heat input -- indicate that the above 0.444 Mw requires the cooling water resulting from about 1.5 Mw of the output of the nuclear power station.

In addition the solar or other heat input for superheating would be in the region of 2.25 Mw. Now, if the heat from the nuclear power station's hot effluent is regarded for the time being as "free", then the energy-conversion efficiency of the solar input (to electricity) will be in the region of 0.444 x 1/2.25 which equals 20%. This compares with photo-voltaic conversion efficiencies usually between 5% and 1 5% - but at very much greater capital cost per installed kilowatt.

So in this first embodiment, the present invention may be regarded as an effective and very inexpensive way of generating electricity - or for storing in a readily-convertible form - the energy from the Sun.

However the above calculations are based on an equilibrium condition for the high lake's heat input and heat-rejection rates. Now if instead it is postulated that, in order to meet peaks of demand, it is permissible to allow the temperature of the high lake to rise by, say 1 OC over a period of say 100 hours, and that this rise in temperature were to cause the melting of say a 10 cm layer of ice covering its 10,000 m2 surface, then in addition to the heat rejected to space (i.e. 400 Mw-hours), the high lake would also be able to absorb: a) in latent heat: 333 kw-sec/kg x (10,000 m2 x 0.1 m) x 1000 kg/m3 = 333000000 kw-sec which, if divided by 3600 x 100 hours = 925 kw for 100 hours = 92.5 Mw-hours b) in sensible heat: 4.184 kw-sec/kg x 68,000,000 m3* x 1000 kg/m3 = 2.85 x 10" kw-sec which, if divided by 3600 x 100 hours = 790,300 kw for 100 hours = 79,030 Mw-hours Clearly this would enable the high lake to meet peak demands of up to 100 times the equilibrium power-generation rate, for periods of several days, or periods of up to 10 times the equilibrium rate for periods of several weeks.

In a second preferred embodiment of the present invention, the above techniques are applied to a high lake at an altitude of typically 2000 metres, a surface area of typically 10 km2, a high lake temperature of 2300K giving a cycle efficiency of 10% when the heat source is the latent heat of fusion of water at 2730K, which indicates a power-generation capacity in the equilibrium condition of about 500 Mw, and for period of several weeks at up to 5000 Mw.

In a third embodiment the present invention is adapted to a much lower scale for an office block.

The said embodiment designed for instance for an office block is now described by reference to the accompanying Figure 1 which is a schematic diagram in a much reduced scale of apparatus and techniques which may be used to gain benefits from a reversible stored energy system of considerably higher capacity and power than heretofore described.

A hot store 601 in the form preferably of a large chamber contains a first buffer substance 602 of high latent heat and a melting point in the region of 750C, and is enclosed at its upper end by a convex lens 604, advantageously made of a daytime-transparent elastic material such as polythene or polyurethane sheet. Inside the hot store a gas blanket 603 of methane or C02 (or other suitable gas) is provided at a pressure such as to hold the convex lens to a form suitable to focus ambient radiation (largely infra-red radiation from the sun and clouds) onto the first buffer substance so as to heat it to at least 750C.Advantageously the material of the convex lens may contain light-sensitive additives (such as are known in "UmbramaticR" and similar sunglasses) which admit infra-red radiation during daytime but which tend to bar its passage at night or, alternatively, an outer co-spherical transparent jacket (not shown) encloses a liquid such as is known in the liquid-crystal displays of some electronic watches and equipment is provided to apply an electric potential to this liquid at such times as to make it sensibly transparent to ambient radiation in daytime and sensibly opaque at night.The function of the gas blanket is two-fold: firstly methane and C02 (and other suitable gases) have indices of refraction significantly higher than that of air, especially at higher-than-atmospheric pressure, such that they will provide the quality of focussing shown in Figure 1 in order to ensure that the first buffer substance may be melted at all times of the year; secondly it is known that both C02 and methane exhibit a "greenhouse" effect and indeed the C02-rich atmosphere of the planet Venus is largely responsible for its prevailing temperature of about 4470C in daytime and, similarly, it is known that the methane-rich atmosphere of the planet Uranus absorbs about 99% of incident radiation in the near-infrared region.

The gas blanket will therefore become significantly heated, assisting the melting of the first buffer substance by conduction and convection as well as helping to insulate it from heat loss at night.

A warm store 605 rather similar to the hot store contains a second buffer substance 606 of high latent heat of fusion and of melting point in the region of 300C. The warm store is covered by a flat/convex lens 607 of material similar to that used for the convex lens 604 but may or may not require to be pressurised to a strongly-focussing shape, depending on the heat load of the office block in question and the amount of power requiring generation. A gas blanket 608 of methane, C02 or other gas (including air) is provided over the second buffer substance as may be needed to ensure it will tend to melt at all times of the year in daytime, and to insulate it at night.To both the first and second buffer substances (which are likely to be organic substances which shrink upon freezing) it is advantageous to add bouyant material in small-particulate forms (such as plastic foam or vermiculite particles suitably coloured to have a high coefficient of thermal radiation absorption) upon which will form any frozen buffer substance -- the particles acting as nuclei - so that such frozen buffer tends to float to the surface where it is exposed to incoming heat and so remelted.

A cold sink 609 rather similar to the hot and warm stores contains a third buffer substance which in this embodiment is water but which may be another substance of relatively low freezing point A concave lens 611 is provided of material rather similar to that of the hot store's convex lens, except that it is arranged to be largely opaque in daytime and sensibly transparent to infra-red radiation at night. An air blanket 612 at a pressure below atmospheric is provided in the cold sink in order to hold the concave lens to the desired form such as best to radiate heat away at night-times, and to insulate the third buffer substance from heat gain from the environment.Advantageously this low-pressure (L.P.) air is circulated gently over the surface of the third buffer substance in order to encourage it to cool by evaporation and in addition the base of the cold sink may contain a porous plate through which L.P. air is fed with the same purpose of encouraging evaporation and cooling. The use of water as the third buffer has numerous advantages, including high latent heats of evaporation and fusion, high thermal conductivity and - in the form of ice - an exceptionally high coefficient of absorptivity and emissivity of about 0.99 such that the ice (which floats to the surface) is well able to radiate heat away to space at nightime.

A liquid C02 tank 614 holds liquid C02 at OOC and 35 atmospheres and from this in daytime a boiler feed pump 615 feeds liquid C02 at about 70 atmospheres to the C02 boiler 616 where the C02 is boiled to form saturated C02 gas at a temperature close to critical (say 280 C). Heat for C02 boiling is provided by used washing or cooling water 617 stored at 20-500C in a warm water tank 61 8 and passed through a heat exchanger 619 in the second buffer substance to hold its temperature close to 300 C. Any other source of water at a temperature close to 300C (such as found for example in power station steam condensing equipment) may be used as shown in Figure 1, item 620.

The saturated C02 gas is led to a heat exchanger 621 in the first buffer substance where it is superheated to approximately 700C before being fed to the stored energy motor/compressor 622 which drives the motor/alternator 623 so as to generate electrical power for the office block, exhausting C02 at about 10 atmospheres and -400C (having an expansion ratio of about 5) to the daytime accumulator 624 which may suitably be in the form of an extensible plastic bag or bellows inside a vessel 627 with interposing polyurethane foam ball insulation as previously disclosed. The first buffer substance may perform a useful secondary function of supplying hot (600C) water for heating and washing, by means of the heat exchanger 629. Similarly the third buffer substance may also be used to supply water at about 1 OC to air conditioning equipment.

At nightime (or at other times when appropriate) C02 liquid is fed at 35 atmospheres to the nightime C02 boiler 630, the valve 631 closed and mains water used to boil the C02 at gradually increasing pressure and feed it to the space around the daytime accumulator (which is at about 10 atmospheres) squeezing it slowly so as to empty its contents at about 35 atmospheres or more (and about 400 C) using the valve 632, from where it is led first through the heat exchanger 633 to surrender heat to the second buffer substance, then through a heat exchanger (not shown in Figure 1) fed with mains water to cool it to about 10--20"C, then through the heat exchanger 634 where it partly or wholly condenses at a temperature of OOC and from where it is returned to the liquid C02 tank.A heat pump 636 may be provided in order to ensure condensation of the C02 in the C02 chiller 635, providing useful heat via the condenser 637 to mains water 638 and thence to the second buffer substance.

The C02 used to squeeze and empty the daytime accumulator is exhausted and stored at 40 atmospheres and about 50C in the night-time accumulator 638, provided with an extensible bag or bellows 639 on which bears a massive counterweight 640 guided and contained in the pressure vessel 641. Following emptying of the daytime accumulator, the night-time accumulator is also emptied (preferably before sunrise) by closing valve 642 and opening valve 643, allowing gas to flow to the same cooling/condensing circuit (634-635-614) as before.

Alternatively, the stored energy motor/compressor may be used to compress and recycle the gas in the daytime accumulator, being driven by the motor/alternator (as a motor) preferably using cheaprate night-time electricity or other suitable motive power. In this case the C02 will be compressed to approximately 800C and may be led backwards through the heat exchanger 621 so as t6 melt first buffer substance, thence backwards through the boiler 616 (which is then fed with cooling mains water by using valves 644 and 645), and finally to the cooling/condensing circuit (634-635-614) by suitable use of the valve 646 and 647. This alternative is indicated in Figure where appropriate by the words "Some nights" and arrows.

Claims

1. A system for generating power which includes 1.1. a hot reservoir comprising material at a temperature TH: 1.2. a cold reservoir comprising material at a temperature Tc lower than TH and higher than 30K; 1.3. a heat source which supplies heat to the said hot reservoir; 1.4. a heat sink at a temperature lower than Tc to which heat may be rejected from the said cold reservoir without causing the heat sink temperature to rise significantly; 1.5. heat rejection means adapted to encourage the rejection of heat from the said cold reservoir to the said heat sink; and 1.6. an energy converter adapted to accept heat from the said hot reservoir and to reject heat to the said cold reservoir and to provide an output of mechanical, electrical or other energy.

2. A system according to claim 1, wherein the said heat sink is the sky i.e. the astronomical region surrounding or above the system and usually known as "outer space".

3. A system according to claim 1 or claim 2, wherein the cold reservoir comprises material partly or completely liquid water at a temperature between 1 00C and -50C.

4. A system according to claim 1 or claim 2, wherein the cold reservoir comprises material partly or completely ice or water at a temperature of OOC or below.

5. A system according to any preceding claim, wherein the heat rejection means includes a sheet or sheets of material covering or able to cover the cold reservoir and in which the transparency, opacity or other radiation-transmission, -absorption, -emission or -reflection property of the said material is chosen or controlled so as to assist heat rejection from the cold reservoir.

6. A system according to claim 5, wherein the sheet or sheets of material contain light-sensitive additives for instance such as silver halides and other substances used e.g. in light-sensitive sunglasses such as are known by the registered trademark UMBRAMATIC, or the like, so that the said additives cause incoming solar or other radiation to be impeded in daytime but permit outward radiation from the cold reservoir at night.

7. A system according to claim 5, wherein the sheet or sheets of material contain or enclose material of the type known in liquid-crystal displays of some electronic watches and calculators.

8. A system according to claim 7, wherein an electric potential is able to be applied to the liquidcrystal material so as to modify or control its radiation-transmission or -reflectance properties.

9. A system according to claim 5, wherein the sheet or sheets of material are coated with titanium dioxide or similar coatings having relatively high coefficients of thermal emissivity.

10. A system according to claim 5, wherein the sheet or sheets of material have the property of one-way mirrors which permit outgoing radiation from the cold reservoir but impede incoming solar or other radiation.

11. A system according to claim 10, wherein the one-way mirror property is achieved by the fusing (or other means of attachment) of numerous small (e.g. less than 1 mm diameter) dots or blobs of solid substance to that side of the said sheet or sheets of material which is closest to the cold reservoir, the said dots or blobs advantagoeusly being of approximately hemispherical shape.

1 2. A system according to claim 11, wherein the dots or blobs are comprised of a white ceramic solid substance.

13. A system according to claim 10, wherein the one-way mirror property is achieved by means which rely on the internal reflection and approximate reversal of direction of travel of radiation which would otherwise reach the cold reservoir.

14. A system according to claim 13, wherein the sheet or sheets of material are largely transparent to outgoing thermal radiation from the cold reservoir.

1 5. A system according to claim 5 or any claim dependent therefrom, wherein a gas or gaseous mixture interposes between the said sheet or sheets and the cold reservoir.

1 6. A system according to claim 15, wherein the gas or gaseous mixture is at a pressure below that of the atmosphere or region surrounding or above the cold reservoir so as to cause the said sheet or sheets and the interposed or enclosed gas or gaseous mixture to approximate the form of a concave lens or concave reflector.

1 7. A system according to claim 15, wherein the gas or gaseous mixture is at a pressure above that of the atmosphere or region surrounding or above the cold reservoir so as to cause the said sheet or sheets and the interposed or enclosed gas or gaseous mixture to approximate the form of a convex lens or convex reflector.

18. A system according to any preceding claim, wherein a gas or gaseous mixture, for example air, flows across the surface of the cold reservoir.

1 9. A system according to any preceding claim, wherein a gas or gaseous mixture, for example air, bubbles through the body of the cold reservoir.

20. A system according to any preceding claim, wherein ice or other frozen substance containing the hydrogen oxide known by the chemical formula H20 partly or completely covers the surface of the cold reservoir at night-time at least.

21. A system according to any preceding claim, wherein the material of the cold reservoir is a buffer substance as hereinbefore defined.

22.. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below 400 C.

23. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below 300C.

24. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below 200C.

25. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below 1 OOC.

26. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below OOC.

27. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below -1 00C.

28. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below -200C.

29. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below -300C.

30. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below --400C.

31. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below -500C.

32. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below -600C.

33. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below 800 C.

34. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below -1000C.

35. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below 500C.

36. A system according to claim 21, wherein the change of state of the buffer substance which causes a release of heat occurs at a temperature below -2000C.

37. A system according to claim 5 or any claim dependent therefrom wherein the sheet or sheets of material contain or enclose a substance whose index of refraction is chosen so as to assist heat rejection from the cold reservoir.

38. A system according to claim 37, wherein the said substance is a solid.

39. A system according to claim 37, wherein the said substance is a liquid.

40. A system according to claim 37, wherein the said substance is a gas or gaseous mixture.

41. A system according to any preceding claim, wherein the material of the cold reservoir contains particles of an additive which act as nuclei to promote (in the case of a system according to claim 3 or claim 4 or any claim dependent therefrom) freezing or to promote (in the case of a system according to claim 21 or any claim dependent therefrom) the change of state of the buffer substance which causes a release of heat.

42. A system according to claim 41 , wherein the particles of additive are chosen so that, following freezing or other change of state of the material of the cold reservoir by accretion onto the particles, the particles together with the said material so accreted sink below the surface of the cold reservoir or otherwise move or are encouraged to move away from that region or area of the cold reservoir from which heat is rejected to the heat sink.

43. A system according to claim 42, wherein the particles of additive rise to the surface of the cold reservoir or otherwise move or are encouraged to move towards that region or area of the cold reservoir from which heat is rejected to the heat sink.

44. A system according to claim 43, wherein the movement of the particles therein described occurs when little or no material of the cold reservoir is accreted onto the particles.

45. A system according to claim 42 or claim 43 or claim 44, wherein the particles of additive with or without material of the cold reservoir accreted onto them as the case may be are chosen together with the choice of the material of the cold reservoir so as to promote the rejection of heat from the cold reservoir to the heat sink,

46. A system according to claim 45, wherein the rejection pf heat is promoted by choosing the substance, form, colour or any other quality of the particles of additive so as to provide the particles, with or without material of the cold reservoir accreted onto them as the case may be, with a relatively high thermal radiation-transmission, -emission, -reflection or other heat-rejection property.

47. A system according to claim 21 or claim 41 or any claim dependent therefrom, wherein the material of the cold reservoir is chosen so that upon freezing or other change of state which causes a release of heat the material of the cold reservoir experiences a change of density or other quality which causes it to sink or otherwise move away from the surface of the cold reservoir or that region or area of the cold reservoir from which heat is rejected to the heat sink.

48. A system according to claim 21 or any claim dependent therefrom, wherein the buffer substance is chosen so as to have a relatively high thermal radiation-transmission, -emission, -reflection or other heat-rejection quality.

49. A system according to any preceding claim, wherein the hot reservoir employs any means to promote its acceptance of heat from the heat source, the said means being hereinafter referred to as the "heat acceptance means".

50. A system according to any preceding claim, wherein the heat source is the Sun or other star or other heavenly body oF material in space.

51. A system according to any preceding claim, wherein the heat source is terrestial freshwater, seawater, salt-water or other predominantly-aqueous material.

52. A system according to any preceding claim, wherein the heat source is terrestial soil, gravel, pebbles, rock or other solid material.

53. A system according to any preceding claim, wherein the heat source is terrestial gas, vapour, steam or other gaseous material.

54. A system according to any preceding claim, wherein the heat source is lava, magma or other molten rock-like material.

55. A system according to any preceding claim, wherein the heat source is used cooling water or cooling air made available from a power station or other device, equipment or installation.

56. A system according to any preceding claim, wherein the heat source is waste heat defined herein as a source of heat above -1 00C which has conventionally been discarded.

57. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 2000C.

58. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 1 500C.

59. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 1200 C.

60. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 100 C.

61. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 800 C.

62. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 700 C.

63. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 600C.

64. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 500C.

65. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 400C.

66. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 300 C.

67. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 200 C.

68. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 1 50C.

69. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 1 20C.

70. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 90C.

71. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 60C.

72. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 40C.

73. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 20C.

74. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below 1 OC.

75. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below OOC.

76. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -1 0C.

77. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -20C.

78. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -30C.

79. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below --40C.

80. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -50C.

81. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -70C.

82. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -100C.

83. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -200C.

84. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -300C.

85. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below --500C.

86. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -1 000C.

87. A system according to any of the claims 50 to 56 inclusive, wherein the heat source is supplied to the system at a temperature below -1500C.

88. A system according to any preceding claim, wherein the hot reservoir comprises material at a temperature below 2000C which is otherwise described, in the manner of the following claim 89, as "the temperature specified in claim 57".

89. A system according to any preceding claim, wherein the hot reservoir comprises material at a temperature below the temperature specified in any one of the claims 58 to 87 inclusive when those claims are considered one at a time in numerical order.

90. A system according to claim 49 either by itself or in conjunction with any following claim, wherein the heat acceptance means is a heat exchanger of known type.

91. A system according to claim 49 either by itself or in conjunction with any following claim, wherein the heat acceptance means is novel at the time when this UK patent application is filed i.e.

16th October 1978.

92. A system according to claim 91, wherein the heat acceptance means employs any one or more of the techniques, materials, sheets of material, additives, coatings, one-way mirrors, gases or gaseous mixtures, relatively low or high pressures of such gaseous substance, lenses, reflectors, buffer substances, substance of chosen index of refraction, or particles of additive described in claims 5 to 17 inclusive, claim 21 and claims 37 to 48 inclusive, used in reversed mode as appropriate to promote acceptance and retention of incoming radiation from the Sun or other heat source by the hot reservoir in daytime especially and to impede outward radiation or other loss of heat from the hot reservoir at nighttime especially.

93. A system according to claim 91, wherein the heat acceptance means is a reflector to focus radiation onto the hot reservoir.

94. A system according to claim 93, wherein the said reflector is constructed of concrete or other inexpensive setting material covered first with coating or other film-like layer of highly-reflective material such as aluminised MYLAR (registered trademark) or the like.

95. A system according to claim 94, wherein the reflector is then covered with a coating or other film-like or curved sheet-like layer of dried water-glass (i.e. sodium silicate) or other metal silicate.

96. A system according to any preceding claim, wherein the energy converter is a heat engine employing a working fluid.

97. A system according to claim 96, wherein the working fluid is carbon dioxide, a halocarbon such as one of the FREONS (registered trademark), a known refrigerant or refrigeration working fluid, or the like.

98. A system according to claim 96 or claim 97, wherein the working fluid is condensible at climatic temperatures, such as exist from time to time and from place to place on a given body in the solar system, under the action of pressure alone.

99. A system according to claim 98, wherein the given body is the planet Earth.

100. A system according to claim 98, wherein the given body is the Moon.

101. A system according to claim 98, wherein the given body is the planet Mars.

102. A system according to claim 98, wherein the given body is the planet Venus.

103. A system according to claim 98, wherein the given body is one of the asteroids.

104. A system according to claim 98, wherein the given body is one of the moons of any one of the planets in the solar system.

105. A system according to claim 98, wherein the given body is any one of the other planets or bodies or masses of material in the compass of the solar system, including artefacts of man-made origin.

106. A system according to claim 92 either by itself or in conjunction with any following claim, wherein carbon dioxide (CO2) or methane (CH4) or a mixture of the two are present in significant quantity above the surface of the hot reservoir so as to promote the known greenhouse effect whereby these gases cause incoming radiation to cause a retention of heat.

107. A system according to any preceding claim, wherein the cold reservoir has a sensiblyhorizontal upper surface at an altitude above mean sea level, or above mean surface level of a heavenly body.

108. A system according to claim 107, wherein the said altitude is at least 100 metres.

109. A system according to claim 107, wherein the said altitude is at least 200 metres.

110. A system according to claim 107, wherein the said altitude is at least 300 metres.

111. A system according to claim 107, wherein the said altitude is at least 500 metres.

112. A system according to claim 107, wherein the said altitude is at least 1000 metres.

11 3. A system according to claim 107, wherein the said altitude is at least equal to N x 1000 metres, where N is a whole number and is specified as any number from 2 to 20 inclusive in consecutive order of increasing number. These values of the number N, taken one at a time, specify the limit of each sub-claim appendent from this main claim 11 3. The sub-claim with the lowest granted value of the number N is the one claimed as claim 113.

114. A system according to any preceding claim, wherein a heat pump or refrigerator is employed so as to chill and promote the condensation of the working fluid after expansion in the energy-converter or after cooling by means of the cold reservoir.

11 5. A system according to claim 114, wherein the heat rejected by the said heat pump or refrigerator is supplied to the hot reservoir.

11 6. A system according to any preceding claim, wherein the working fluid lifts a massive counterweight to an altitude above mean sea level, or mean surface level of a heavenly body.

11 7. A system according to claim 11 6, wherein the massive counterweight is constituted partly or completely of freshwater, seawater or other predominantly-aqueous material.

11 8. A system according to claim 11 6 or claim 117, wherein the predominantly-aqueous material or other massive counterweight is guided and contained in a pressure vessel, conduit or the like.

11 9. A system according to claim 11 8, wherein the pressure vessel, conduit or the like extends upwards to the altitude described in claim 1 6.

120. A system according to claim 119, wherein the said altitude is at least the lowest altitude which may be granted for this claim 120, when this claim 120 is tested with values of the said altitude specified as in claims 108 to 113 inclusive taken in increasing order one at a time.

121. A system according to claim 1 6 or any claim dependent therefrom, wherein the massive counterweight is employed to recompress, or to assist the recompression of, the working fluid after its expansion in the energy converter.

122. A system according to any preceding claim, wherein the or a working fluid is boiled to provide a vapour or gas for use in recompressing the main working fluid after expansion.

123. A system according to claim 122, wherein the heat supplied to boil the or a working fluid is supplied at a temperature at least 50C lower than the temperature TH of the hot reservoir.

124. A system according to claim 122, wherein the temperature of the heat supplied to boil the or a working fluid is at least NOC lower than the temperature TH of the hot reservoir and wherein the value of N is the lowest whole number that may be granted for this claim 124, when this claim 124 is tested with values of N increasing one at a time from 6 up to 100.

125. A system according to any preceding claim, wherein local atmospheric pressure is employed to recompress the working fluid after expansion in the energy converter.

126. A system according to any preceding claim, wherein the energy-converter is used in reversed mode as a compressor to recompress the working fluid after expansion in the energy converter.

127. A system according to claim 126, wherein the working fluid after expansion in the energyconverter is temporarily stored in an accumulator.

128. A system according to any preceding claim, wherein the working fluid is expanded in the energy-converter to a pressure significantly lower than the pressure at which the working fluid is recompressed so as to promote its condensation.

129. A system according to any preceding claim, wherein the working fluid is superheated to a temperature at least 50C above its saturation temperature.

130. A system according to claim 129, wherein the working fluid is superheated to a temperature at least NOC above its saturation temperature and wherein the value of N is the lowest whole number that may be granted for this claim 1 30, when this claim 130 is tested with values of N increasing one at a time from 6 up to 100.

131. A system according to any preceding claim, wherein the working fluid is boiled at a temperature less than 50C below its critical temperature and then subsequently superheated as claimed in claim 129 or claim 130.

132. A system according to claim 126 or any claim dependent therefrom, wherein cheap off-peak electricity is used to drive the energy-converter in reversed mode as a compressor, or to drive other compressor means, so as to recompress the working fluid after expansion in the energy-converter.

133. A system according to claim 132, wherein the said off-peak electricity is provided by one or more nuclear power stations when generating electricity surplus to baseload energy consumption.

134. A system according to claim 126 or any claim dependent therefrom, wherein the recompressed working fluid, being hotter than the hot reservoir, is used to deliver heat to the hot reservoir.