GB2462913A

GB2462913A - Renewable energy system for reducing dependence on mains power

Info

Publication number: GB2462913A
Application number: GB0914703A
Authority: GB
Inventors: Miles John Dudle Postlethwaite; David Postlethwaite
Original assignee: TURBINE SERVICES
Current assignee: TURBINE SERVICES
Priority date: 2008-08-28
Filing date: 2009-08-24
Publication date: 2010-03-03
Anticipated expiration: 2029-08-24
Also published as: GB0914703D0; GB0815589D0; GB2462913B

Abstract

Apparatus and method for gaining maximum economic benefit from micro or small scale locally generated electrical power is disclosed. The apparatus includes a generator 8, a connection to the electrical mains 2, a diverter 7 to measure electrical parameters and switch power, and an energy storage means. When excess power is generated by local generator 8, it is stored, in preference to supplying the grid 2 at a credit rate much less than that at which power has to be bought, thus benefiting the local generator. The excess power may be stored either as electricity in batteries, heat in storage heaters or as hot water or as potential energy as pumped storage. The power energy stored may be used at a later date, when the power being generated locally is less that that required so that the shortfall does not have to be purchased from the grid. A key feature of the invention is that means are provided to utilise only small quantities of excess power, which would not be economic on larger scale generating plants. The excess power increments / decrements, which can be used due to changing generating levels, are equally small thus maximising the benefits for micro / small power generators.

Description

APPARATUS AND METHOD FOR THE EFFICIENT UTILISATION

OF RENEWABLE ENERGY

This specification relates to renewable energy, such as may be generated at a domestic, commercial, industrial or community property, and to the efficient use of the energy produced to maximize the economic benefit of that energy for the people or organisation(s) occupying that property.

There is a great need for energy from renewable sources and, at many domestic, commercial and industrial properties, apparatus has been installed to generate electrical power. Wind, hydro and solar power are the most common sources of such micro and small scale generation. Power generated from the wind is highly variable, that generated from hydra is more reliable and, with the advent of global warming and clean air legislation, photovoltaic solar power is becoming ever more viable in higher latitudes. Whatever form of micro / small scale generation is adopted, there will be occasions when the power demand is greater than that available and this shortfall must be supplied from the national, or local, grid or a diesel grid in some remote locations. There will also be occasions when the power generated is greater than the demand and, in some countries, it is possible to sell the excess power back to the grid. However, the price paid by the grid is usually significantly less than that at which power must be bought, i.e. when demand exceeds that being generated. A typical example of the rates charged by one elecincity supplier in the UK in June 2008 was a sale price of 10.Op per unit and re-purchase at 7.64p per unit, i.e. a difference of 2.36p per unit or an effective loss' of 23.6% for the customer.

In some countries, such as Eire, excess power may be supplied to the grid but no payment is made or credit given for the power supplied.

There is thus a need for a means by which excess electrical power can be preferentially stored at the production site so that it may be available for subsequent use at that site, rather than having to sell it cheaply, or give it away for nothing, and subsequently purchase electricity at a more expensive rate. It is also necessary that the means of storing the excess power is commensurate with the type in installation, so that, on micro or small scale power generation installations, micro or small quantities of excess power can be economically stored.

According to the invention, there is provided a means of gaining maximum economic benefit from locally generated electrical power by storing excess electrical energy produced at a location for subsequent use at that location comprising:-i) a means for generating and supplying electrical power; ii) a connection to the electrical mains / grid able to provide electricity to the location; iii) a diverter having means to measure electrical power parameters and of switching power(s) according to predetermined criteria; iv) storage means to store either one, or a combination, of electrical energy, thermal energy or potential energy; and v) a means to export electrical energy back to the mains I grid; charactensed in that the diverter is able to measure the quantity of electrical power supplied by the generating means and comparing it with the electrical demand at the location and, when supply exceeds demand, diverting the excess to a storage means and, when demand exceeds supply, drawing the shortfall either from the / one of the storage means or from the mains / grid and the diverter having further means to measure the state of the storage means and, when the storage means is / are full or at a predetermined capacity, diverting excess power back to the mains I grid.

According to a first variation of the apparatus of the invention, the diverter also has means of accessing the / a storage means where that storage means is in the form of electrical power or a means that can be converted into electrical power and using the stored power to supply all, or a part, of the electrical demand from said location.

According to a second variation of the apparatus of the invention, the storage means provides space and I or water heating at the location.

According to a third variation of the apparatus of the invention, the diverter is provided with means to measure the excess power accurately and essentially continuously and to divert the excess to the storage means in small incremental steps, commensurate with the output of the power generation system.

According to the invention, there is provided a method of gaining maximum economic benefit from locally generated electrical power by storing excess electrical energy produced at a location for subsequent use at that location comprising:-I) generating and supplying electrical power ii) using the electrical mains / grid power connection to provide power to the location; iii) using a diverter having means to measure electrical power parameters and switching power(s) according to predetermined criteria; iv) using a storage means to store either one, or a combination, of electrical energy, thermal energy or potential energy; and v) using a means to export electrical energy back to the mains / grid; characterised in that the diverter is used to measure the quantity of electrical power supplied by the generating means and to compare it with the electrical demand at the location and, when supply exceeds demand, to divert the excess to a storage means and, when demand exceeds supply, to draw the shortfall either from the I one of the storage means orfrom the mains I grid and further using the diverter to measure the state of the storage means and, when the storage means is I are full or at a predetermined capacity, diverting excess power back to the mains I grid.

According to a first variation of the method of the invention, electrical power the storage means are used, either directly or indirectly to provide electrical power to supply some I all of the electrical power demand of the location.

According to a second variation of the method of the invention, the storage means is I are used to provide space and I or water heating at the location.

According to a third variation of the method of the invention, the diverter is used to measure the excess power accurately and essentially continuously and to divert the excess to the storage means in small incremental steps, commensurate with the output of the power generation system.

In a preferred application of the invention, a wind turbine (or hydro or photovoltaic power generator) supplies electrical power to the location and, when the wind is strong, its output exceeds the normal demand of the location. Under these circumstances, the turbine supplies the whole demand and the diverter passes the excess power to a storage means, such as a battery, heat storage or pumped storage.

When the wind drops and the turbine output falls below demand, the diverter can take electrical power from the battery or pumped storage to make up the shortfall. If the battery or pumped storage cannot make up the shortfall or when the stored power has run out, the diverter will make up the shortfall from the mains. In this way, the surplus power from the windy days is used to substitute full price mains electricity and so produce an economic benefit for the people or organisations occupying the location.

Where the energy stored is in the form of heat, this is available either for space heating or as domestic hot water.

If, after a long period of windy days, the capacity of the various storage means is all full, surplus power will then be passed by the diverter back to the grid. This will earn a reduced a reduced rate of income for the occupiers of the location.

For a clearer understanding of the invention and to show how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawing which shows a diagrammatic representation of the principle of the invention.

Referring to the Figure, a domestic, commercial, industrial or community property 1 receives electrical power from the grid 2 via a transformer 3 and cable 4. Cable 4 feeds into a diverter 7, which supplies property 1 via connection 6. Property 1 has a wind turbine 8, supplying power via connection 5 into diverter 7. Diverter 7 has an electrical connection 11 to one, or more, of a number of storage means 12, of which four are shown for diagrammatic purposes.

Of these four, possible examples are battery storage 12A, space storage heater 12B, domestic hot water storage, (or heating a swimming pool) 12C or pumped water storage 12D. Other forms of storage are also possible.

A loop connection 10, 1 OA is provided to connect the output 5 from wind turbine 8 to mains 4 to supply excess power, via export meter 9, back to grid 2.

A number of dashed lines are shown between diverter 7 and the various electrical connections and storage items. These connections are as follows:- * 20 monitors the power used by property 1; * 21 monitors the power produced by wind turbine 8; * 22 monitors the power being supplied by grid 2; * 23 monitors the power being supplied to connection 11 and thence to one, or more, of storage means 12; * 24, 24A-D monitors the state of the storage items 12, 1 2A-D; and * 25 monitors the power being supplied from wind turbine 8, via meter 9 to grid 2.

All these monitoring connections supply data to a controller (not shown) forming part of diverter 7. The data is supplied several times a second and so is effectively monitored on a continuous basis by the controller (not shown) to assess the power demand and supply situation. Diverter 7 is provided with switching means (not shown) to connect cables 4 to 6, 5 to 6, 5 to 11 (including 1 1A-D), 11 to 6 and 5 to 4 via 10, 1OA and meter 9.

In a real situation, turbine 8 may be supplying nothing, or a small amount of power, or its full design capacity, e.g. 6kW. Clearly, if no power is being generated, the whole of demand 20 must be supplied 22 from grid 2. However, if some power 21 is being supplied from turbine 8, it makes sense to use this in property 1 and draw any balance required from mains 2, i.e. in this case diverter 7 would draw 21 all the power available from turbine 8 and draw only the balance 22 from grid 2. If the wind velocity increased and the power 21 provided by generator 8 grew, the balance 22 drawn from the grid would decrease accordingly.

If either the wind velocity increased further or demand 20 dropped, e.g. overnight, it would be possible to export the surplus power through connections 10, bA, via meter 9. However, it would be more beneficial if this excess power could be stored for subsequent use on site 1. In this case, the excess 23 would be passed preferentially via connection 11 to one of the storage means 12. As an example, excess power 23 might be passed 11, 1 IA to battery storage I 2A.

Monitoring connection 24A, 24 would inform diverter 7 of the state of charge of battery 1 2A so that, when fully charged, the power 23 may be diverted from battery(ies) 12A to, say, storage heater 12B. Diverter 7 would be programmed with appropriate algorithms to priontise how excess power 23 was stored in the various means 12 A -0.

Storage 120 represents a pumped water storage system, whereby water is pumped up to a storage means at a higher elevation so that it may subsequently be released to run back through the pump to generate electrical power. (Neither the combined pump / generator nor the storage facility are shown separately.) The storage facility may be a tank at an elevated point in property 1 or, if property I is in a hilly area, the storage tank may be located on an adjacent hill or be a tam on the adjacent hill. Clearly, a pump / generator must operate with its designed power input so that pumped storage 120 could be operated only if excess power 23 was greater than this design value. Diverter 7 would assess the power available 23 and divert it to the appropriate storage means I 2A-D, as appropriate. It is possible that excess power 23 could be simultaneously diverted to more than one of the storage means 1 2A -0.

If the wind velocity fell somewhat, so that there was a shortfall between the turbine output 21 and demand 20, diverter 7 would draw electrical power from the storage means, i.e. from battery(ies) 12A or from pumped storage 12D. This would substitute mains power 4, which would otherwise have to be used and bought at the full selling price. Over a period of time in windy areas of the UK, the apparatus of the invention would make considerable saving and, for long periods, could replace mains power entirely. Power 23 transferred to storage heating I 2B and water heating 12C would substitute some! all of the mains electricity 22 required for space heating or hot water at site 1, i.e. giving further cost savings.

If an extended period of strong winds was experienced, such that all the various storage means were filled to capacity, further surplus electricity would be exported 10, 1 OA via meter 9 back to grid 2.

When dealing with microcurrents, it is possible to divert them through solid state systems as and when required, without any problems, e.g. in computers, etc. However, when dealing with larger power levels, e.g. several kilowatts, this is not so simple and it is necessary that special systems are built in to diverter 7so that, for example, power levels may be ramped up rather than switched backwards and forwards at random. For example, the power output from wind turbine 8 may vary according to gusty conditions and the power demand 20 may vary as lights are turned on and off and power systems come into use and are switched off. Ideally, diverter 7 could react immediately to the net power surplus or deficit 23, i.e. 121 -201, so that power 23 being stored 12 is always maximised. (The term 121 -201 indicates the algebraic difference between power levels 20 and 21 and may be positive, negative or zero, i.e. power 23 may be being stored in storage means 12 or drawn from them.) However, as had been taught, pump generator 1 2D would require a minimum power before it could be operated and, clearly, it could not be turned on and off at random or in quick succession if the power 23 was only marginally above that required 12D and would occasionally drop below this value. Thus, diverter 7 would preferentially pass power 23 into one or more of the other means 1 2A -C and only use 1 2D when power 23 was well above the level required by pump/generator 12D. Each of the storage means 12A-D might operate properly only if supplied with a certain power level. Thus, the controller (not shown) in diverter 7 would be programmed in such a way as to maxirnise the power storage according to what level of surplus 23 was available.

The key to the invention is the means by which the monitoring and switching is achieved. The principle of this lies in creating a proportional, integrated feedback loop using the values 20, 21 and 23.and progressively supplying power 11 to one / more of the storage means 12, i.e. ramping up the currents rather than using simple ON I OFF switching, which might de-.stabilise other parts of the system, e.g. computers operating in site 1.. For example, the heating provided by an electrical resistance heater is given by 12R, where I is the current and R the resistance. While such a heater would have a nominal rating, e.g. I kW, equivalent to a current of about 4 Amps at 240 Volts, a reduced level of heating would be produced by a smaller current. Thus, all spare power, 121 -201, is potentially usable. The feedback monitors 24 would indicate what storage capacity was available where.

A person without knowledge of electrical systems might think that this key aspect of the invention was similar to a bucket under a tap, in that, whether the tap was off, only dripping or full on, the bucket would catch everything. Unfortunately electrical systems are not like this.

As an example of this key aspect of the invention, equipment in diverter 7 would continuously monitor 21 the power output 5 from generator 5 and its variability. Assume that this varied between 5.4 and 5.6kW, i.e. 5.5 � 0.1kW and that demand 6 was 3kW. Under these conditions, diverter 7 would measure a surplus of 2.5 � 0.1kW, i.e. from 2.4 to 2.6kW. To ensure that demand 6 was always met, diverter 7 would take a constant 2.3kW for storage 11.

This might be divided up as 2kW to the pumped storage I 2D, as the pump (not shown) required a constant 2kW supply. 0.3kW could be allocated to heat storage 12B or 1 2C. The variable balance of 0.1-0.3kW, which is small enough to be switched by semiconducting means, could either be used as a trickle charge into batteries 12A or sent 10, IOA to the grid 2.

(This is equivalent to the dripping tap' in the analogy.) In this way, the economic value of all the power generated 5 would gained. If the wind speed increased, generating, say, 5.5-5.7kW, diverter 7 would recognise 2.4kW of constantly available surplus and re-allocate power 11 as 2kW to pumped storage 12D, 0.4kW to heating 1 2B or I 2C and the variable balance of 0.1-0.3 to batteries 1 2A or the grid 2. By being able to adapt to such small power changes and use these changes incrementally, the apparatus of the invention maximises the benefits to the greatest degree practicable.

Systems are known for larger power generation I local supply systems, where the surplus power is stored for subsequent use locally. However, such systems, with much larger generating capacities, can only store power in relatively large steps', e.g. 5 or 10kW intervals.

Even if such a system was scaled down to, say, 1kW intervals, in the example given, it would only be able to store 2kW, i.e. 0.3 or 0.4kW would be returned to grid 2; this represents a loss' of 15-20% -this loss' could be up to 0.9kW or 45% in the example.

Refemng back to the dripping tap' analogy, the known systems might be equivalent to collecting water only when the tap was at, say, % a turn, one full turn, etc. In comparison, the invention might be equivalent to, say, 100 turn increments, e.g. 100, 200, etc. This represents disproportionately large economies for micro or small power generation systems. Electrical equipment has been developed in the apparatus of the invention to accommodate the small increments taught.

Progressive changes in the supply of power, are preferable in maximising the lives of the electrical components of diverter 7 and storage means 12A-D would have very short lives if the currents 24A-D were continuously switched on I off or up / down every time a light or kettle was used in property 1.

When the surplus power 121 -201, was well in excess of the power required by the pump (not shown) of pumped storage 1 2D, power 24D could be switched to pumped storage I 2D. This might only be done if the programming of diverter 7 was such that other major uses of power were unlikely, e.g. in the small hours of the morning. If a major power consuming device was switched on during this period, diverter 7 would take the shortfall from grid 2 for a brief period, until diverter 7 could restore a positive position, i.e. switch off pumped storage I 2D and re-allocate any surplus 23 to battery 12A or hearting storage 12B or 12C.

When no power is being drawn from grid 2 and either power 21 from turbine 8 fluctuates or variations in usage 20 occur, any transient surplus 25 can be exported 10, 1OA via meter 9. In this way, the export facility 9 can be used as the equivalent of a safety valve', rather in the same way that a flare is used on an oil production to allow for fluctuations in flow.

The skilled person will appreciate the principle taught above and all the variations of its applications, all failing within the scope of the invention.

Claims

Claims:- 1. Apparatus for gaining maximum economic benefit from locally generated electrical power by storing excess electrical energy produced at a location for subsequent use at that location comprising:-I) a means for generating and supplying electrical power; ii) a connection to the electrical mains / grid able to provide electricity to the location; iii) a diverter having means to measure electrical power parameters and of switching power(s) according to predetermined criteria; iv) storage means to store either one, or a combination, of electrical energy, thermal energy or potential energy; and v) a means to export electrical energy back to the mains I grid; characterised in that the diverter is able to measure the quantity of electrical power supplied by the generating means and comparing it with the electrical demand at the location and, when supply exceeds demand, diverting the excess to a storage means and, when demand exceeds supply, drawing the shortfall either from the / one of the storage means or from the mains I grid and the diverter having further means to measure the state of the storage means and, when the storage means is / are full or at a predetermined capacity, diverting excess power back to the mains I grid.
2. Apparatus for gaining maximum economic benefit from locally generated electrical power, as claimed in claim 1, wherein the diverter also has means of accessing the I a storage means where that storage means is in the form of electrical power or a means that can be converted into electrical power and using the stored power to supply all, or a part, of the electrical demand from said location.
3. Apparatus for gaining maximum economic benefit from locally generated electrical power, as claimed in claim 1, wherein the storage means provides space and / or water heating at the location.
4. Apparatus for gaining maximum economic benefit from locally generated electrical power, as claimed in claim 1, wherein the diverter is provided with means to measure the excess power accurately and essentially continuously and to divert the excess to the storage means in small incremental steps, commensurate with the output of the power generation system.
5. A method of gaining maximum economic benefit from locally generated electrical power by storing excess electrical energy produced at a location for subsequent use at that location comprising:- 10. I) generating and supplying electrical power; ii) using the electrical mains / grid power connection to provide power to the location; iii) using a diverter having means to measure electrical power parameters and switching power(s) according to predetermined criteria; iv) using a storage means to store either one, or a combination, of electrical energy, thermal energy or potential energy; and v) using a means to export electrical energy back to the mains / grid; characterised in that the diverter is used to measure the quantity of electrical power supplied by the generating means and to compare it with the electrical demand at the location and, when supply exceeds demand, to divert the excess to a storage means and, when demand exceeds supply, to draw the shortfall either from the / one of the storage means or from the mains I grid and further using the diverter to measure the state of the storage means and, when the storage means is / are full or at a predetermined capacity, diverting excess power back to the mains I grid.
6. A method of gaining maximum economic benefit from locally generated electrical power, as claimed in claim 5, wherein the storage means are used, either directly or indirectly to provide electrical power to supply some I all of the electrical power demand of the location.
7. A method of gaining maximum economic benefit from locally generated electrical power, as claimed in claim 5, wherein the storage means is / are used to provide space and / or water heating at the location.
8. A method of gaining maximum economic benefit from locally generated electrical power as claimer in claim 5, wherein the diverter is used to measure the excess power accurately and essentially continuously and to divert the excess to the storage means in small incremental steps, commensurate with the output of the power generation system.
9. Apparatus and method for gaining maximum economic benefit from locally generated electrical power as described in and by the above statement, with reference to the accompanying drawing.