EP1495269A1

EP1495269A1 - An autonomous unit for supplying energy

Info

Publication number: EP1495269A1
Application number: EP03725320A
Authority: EP
Inventors: Robert Leslie Young; Robert Anthony Severwright; Clive William c/o MDU Limited EFFORD
Original assignee: MDU Ltd
Current assignee: MDU Ltd
Priority date: 2002-04-11
Filing date: 2003-04-11
Publication date: 2005-01-12
Also published as: WO2003087674A1; GB0208335D0; AU2003227860A1

Abstract

An autonomous unit for supplying energy to one or more structures (402) comprising power generation means comprising an engine (404) adapted to drive a generator (406) for generating power and a power store (408) for storing said power, the unit further comprising a heat store (412) for storing heat generated by the power generation means, wherein conversion means (420) are provided for converting power stored in the power store (408) into heat, the heat being stored in the heat store (412).

Description

AN AUTONOMOUS UNIT FOR SUPPLYING ENERGY

Field of the Invention

The invention relates to units for supplying energy to structures and equipment associated with these structures. The primary structures with which the invention is concerned are houses, however, the invention relates to other structures such as swimming pools, greenhouses, business buildings, stadiums, refugee camps and public facilities requiring energy in the form of heat or electricity.

Review of Art Known to the Applicants

In conventional houses the heat requirements are often provided by a gas or oilfired boiler. These boilers - especially the gas-fired kind preferred by most householders - usually have a life-expectancy between 10 and 15 years under the best service conditions. These boilers will need to be frequently replaced during the life of the average modern house. The cost of replacing this equipment can be over the years considerable.

The average house is also usually connected to the grid for its electricity requirements. The occasional house incorporates solar panels or even wind generators to meet a fraction of its energy requirements. These can be for example in the form of solar collectors placed on the building's roof to accumulate solar energy in the form of heat in its hot water system.

The electricity grid's problems are notorious. Due to local electricity requirements, pylons, pillars and cables and numerous sub-stations stretch across every section of the country. Due to the weather or a specific technical problem, the electricity may not for a period reach some of the sections of the grid. These pylons, pillars, cables and sub-stations are often unsightly and may even be a health hazard.

In an effort to avoid being momentarily cut off from their electricity supply, certain installations such as football stadiums are often equipped with standby generators which start their operation as soon as their electricity supply is cut off and terminate their operation as soon as the electricity supply is re-established. Standard standby generators operate using a conventional engine to drive an electricity generator to meet the electricity requirement of the installation to which the generator is connected.

One of the objectives of the invention is to provide an autonomous unit capable of substituting the electricity grids. Another objective of the invention is to provide an autonomous power and heat unit for increasing the overall efficiency of power and heat supply in structures and equipment associated with these structures. By so doing it aims also to be cost-effective with a great life expectancy.

A further objective of the invention is to even substitute both the electricity and the gas supply grids.

Another objective of the present invention is to provide a unit or system which can be easily retrofit or incorporated into new buildings for dwelling or commercial purposes. The unit may be used in conjunction with existing power and heating systems.

It is a further object of this invention to provide a unit which can be transportable to remote sites to provide heat and light (for example in disaster-stricken areas or refugee camps) .

The unit of the invention also aims at doing away with unsightly electrical grid pylons, cables and sub-stations.

Summary of the Invention

The invention takes as its starting point the broad state of the art just outlined. There is no one specific prior design which, to the applicants' knowledge, suggests either a problem awaiting solution or a base for further inventive advance. The invention now to be outlined and then exemplified in detail is believed to be both new and a non-obvious development on that basis.

In its broadest aspect, the invention is embodied in an autonomous unit for supplying energy to one or more structures and/or their associated equipment, comprising one or more fuel -powered engines adapted to drive one or more electricity generators for a period, one or more optional power stores (for example batteries) for storing the electricity produced by the generator and/or any other electricity generating means with which the unit operates, means for feeding any electrical equipment to which the unit is connected; and means to transmit at least part of the heat emitted by the, or each engine and/or the or each generator and/or the, or each power store to any appropriate section of the or each structure and/or its associated equipment; and control means which determine the amount of electricity stored in the or each power store and/or the heat requirement of any appropriate section of the structure and which control the period of operation of the or each engine (for, say, one minute to several hours) . This particular combination of features is advantageous because it can substitute or even operate autonomously, not merely augment, the electricity grid. This energy-generating unit is also advantageous because it provides for a substantial portion if not the entire heating requirement of the structures with which the unit is in operation. A unit of this type also presents unforeseen aesthetic advantages as it operates without unsightly pylons, cables and sub-stations .

A subsidiary aspect of the present invention presents a unit wherein the, or at least one of the, fuel-powered engines is a diesel engine.

Although diesel engines are common in the field of self-propelled machinery, using diesel engines in a unit embodied in the invention represents a complete departure from the conventional thinking within that field, which is to use gas as the burner fuel wherever a domestic gas supply is available. The modern highly developed diesel engine has a life-expectancy which exceeds the life-expectancy of conventional boilers when operated as proposed in the system. Diesel engine fuel consumption can be very accurately monitored and is very efficient. Another advantage of this combination is that the engine can be easily adapted to only run intermittently (for say, from a minute to several hours) .

A further subsidiary aspect of the present invention presents a unit wherein the or at least one of the fuel powered engines is a gas engine.

In accordance with a subsidiary aspect of the broadest encapsulation of the present invention, means are provided to transmit heat from the sump oil of the engine to any appropriate section of the or each structure and/or its associated equipment.

The provision of these means is particularly advantageous because the heat generated by the operation of the engine is recouped by these means and therefore is not lost into the atmosphere. These means augment the heat transferred into the structure or its associated equipment and therefore reduce the overall fuel consumption necessary to meet the dwelling's energy requirements.

According to a further subsidiary aspect of the present invention means are provided to transmit heat from the exhaust to any appropriate section of the, or each, structure and/or its associated equipment.

The advantage of this arrangement is an increase in the heat recuperated from the engine and therefore maximisation of the efficiency of such a system.

According to a subsidiary aspect of the present invention, the heat generated by the unit is stored as hot water.

In another embodiment of the present invention, at least part of the heat generated by the unit is stored using a heat pump in an underground heat store .

The heat as provided by the unit is preferably transported by means of conduits which contain a fluid such as water. The fluid is heated by the oil in the engine thereby effectively cooling the engine.

We have discovered that the efficiency of the autonomous unit as herein before described is poor when the demand of the structure for heat and power are not balanced or synchronised. This situation occurs for example when there is a high demand for power or electricity and a low demand for heat which generally occurs during Summer, and when there is a high demand for heat and a relatively low demand for power which generally occurs during Winter.

If the engine of the unit as hereinbefore described is activated for prolonged periods to provide sufficient power to the structure, consequently a large amount of heat is generated. Part of this heat may stored in for example a boiler to provide hot water to the structure and part of this heat may be dissipated directly in the structure for example via the central heating system to provide heating of the structure. However, eventually the situation arises wherein the heat dissipation is maximised and heat is absorbed by the system whilst the power demand is still high thereby still producing additional heat. Then, it will no longer be possible to effectively cool the engine unless a substantial part of the heat stored in the system is discarded, for example by draining away some of the hot water and replacing it by cold water or by direct dissipation as waste heat through the use of a conventional radiator as used commonly in motor vehicles. This situation is more likely to arise in Summer than in Winter when the demand for heat is reduced whilst the power demand is still high. Obviously, the discarding of heat stored in the system is undesirable as it renders the application of the autonomous unit in these conditions inefficient and consequently uneconomic.

In order to solve this problem, the unit may comprise a heat store for storing the heat generated by the unit . In a preferred embodiment, the control means control the amount of heat stored in the heat store depending on the heat and power requirements of any appropriate section of the structure.

In a preferred embodiment, the unit may comprise means for selecting the amount of power stored and the amount of power which is directly provided to the structure. The unit or system may further comprise means for selecting the amount of heat stored and the amount of heat which is directly provided to the structure. The control means preferably controls the selection means so that depending on the demand for heat and/or power the appropriate amount of heat and/or power is extracted from the respective stores or stored in the respective stores.

In this way, dissipation of unused heat is reduced, as any heat which is not directly usable is stored in the heat store so that it is available as and when this is required. Also, in this way, overheating of the engine is prevented in all operating conditions.

Conversely, in certain operating conditions, it is desirable that heat is produced by the unit for example to heat the central heating in the structure or to provide sufficient hot water. This could for instance occur during the Winter months when the demand for heat is significantly higher than the demand for power. When heat is produced by the unit, this also results in the production of power. Some of this power is stored in the power store. However, if demand for heat is high and prolonged, the power store will be fully loaded and excess power is available.

In order to increase the efficiency of the unit and to avoid wasting the excess power, in an advantageous embodiment of the invention, the power is converted into heat by means of a suitable converter. The power may be provided directly to the structure in the form of heat by means of a converter in the form of an electric heater. Preferably, the conversion means are provided in the heat store in the form of a heating element or immersion heater so that the heat is stored for later use.

In this way, excess heat is stored in the heat store and excess power which cannot be stored in the power store can be converted into heat and subsequently stored in the heat store. This has the advantage that operation of the unit is more efficient if the heat and power requirements of the structure are not balanced.

Also, as power can be converted and effectively stored as heat, the number of batteries required to store electric power may be reduced. This significantly decreases the cost of the autonomous power and heat unit and greatly increases the efficiency of the unit. In addition, the overall size and weight of the unit is significantly reduced. This increases the number of applications of the autonomous heat and power unit.

An important advantage of the heat store is that it provides synchronisation of heat and power as provided by the engine and generator assembly independent from the actual demands for heat and power from the structure. The heat store thus allows efficient operation of the engine and generator assembly whereby little or no excess power or heat is discarded because it cannot be effectively used in the structure or stored. The heat and power store also act as buffers to allow sufficient heat and power to be supplied when demands for heat and/or power are suddenly high.

For most applications of the unit, the heat store may store heat for a number of hours whereas the power store may store power for a number of days .

The provision of a heat store in the autonomous heat and power unit as herein described greatly increases the efficiency of operation of the unit whilst significantly reducing the overall cost of the unit.

In another embodiment of the invention, the control means preferably control the conversion means depending on the heat and power requirements of any appropriate section of the structure.

In yet another embodiment of the invention there is provided a heat store for storing heat . In a further embodiment, the heat generated by the unit is stored using a heat pump in an underground heat store .

The heat store preferably comprises a material or medium adapted to change phase upon input of heat into the medium or extraction of heat out of the material.

In another embodiment of the invention, the heat store comprises input and output heat exchangers to provide heat transfer to and from the medium. In a preferred embodiment, the medium comprises a heat absorbent material such as wax or a wax like substance. Preferably, the medium has a melting point which is below the temperature of the fluid in the input heat exchanger.

In a preferred embodiment, the heat store comprises a medium in which heat is stored using latent heat of fusion which occurs when a liquid changes into a solid and vice versa.

In yet another embodiment of the invention, there is provided a heat store comprising a container comprising a medium in which heat is stored using the latent heat of phase change of the medium.

In a preferred embodiment, the heat store comprises a container or enclosure or tank, which is thermally insulated, containing a medium which changes phase (melts/solidifies/evaporates) in the region of the temperature at which the heat is to be stored. Heat is put into the store by a primary (input) heat exchanger in the form of flow of hot water (at the input temperature) through conduits within the tank. The conduits are in contact with the heat storage medium. Heat is withdrawn from the store by a secondary (output) heat exchanger in the form of the flow of water through further pipes within the tank. This secondary water flow is heated to a temperature approaching the melting temperature of the medium, in the process removing heat from the store, ultimately resulting in the medium solidifying and giving up the latent heat. Fins may be fitted to the pipes to promote the heat exchange in order to provide a high thermal conductivity.

The heat store absorbs heat from the cooling water of the engine at a temperature probably but not necessarily between 80 and 100°C, store it in a medium with a melting point probably but not necessarily around 75°C and in the process melting the medium and later to give up this heat to water probably but not necessarily forming part of a domestic central heating system at a temperature probably but not necessarily around 60 to 70°C and in the process solidifying the medium.

The fluid in the unit is thus conveyed through the unit and the structure to transport and transfer the heat whereas -lithe heat storage medium is stationary and it absorbs the heat and releases the heat to the fluid.

The main benefit from the use of this type of heat store over one using solely the heat arising from an increase in temperature is that for a given heat storage capacity, the size is dramatically reduced.

The heat store is particularly suitable for storing heat energy for later release into structures such as houses, swimming pools, greenhouses, business buildings and other places requiring heat .

In a preferred embodiment, the heat store is located underground. This has the advantage that the space required by the unit on the surface is limited. As the heat store does not contain any moving components that could malfunction, access to the heat store is not essential to ensure proper functioning of the unit.

The primary application for the heat store is anywhere that requires heat input at a temperature in the approximate range of 60°C to 80°C. The key features of the heat store are that it exhibits improved heat storage and recovery efficiency and that it exhibits a higher energy density relative to conventional water containing heat storage devices such as hot water boilers whilst avoiding the use of environmentally unfriendly materials.

The term autonomous employed in this specification is intended to mean either that the unit is self-contained or that it operates independently from the electricity grid.

Brief Description of the Figures Figure 1 shows a block diagram of a first embodiment of the present invention.

Figure 2 presents two further block diagrams of a subsequent embodiment of the invention.

Figure 3 presents a diagrammatic view of an autonomous heat and power unit according to another embodiment of the invention.

Figure 4 presents a block diagram of an autonomous heat and power unit according to yet another embodiment of the invention.

Figure 5 presents a diagrammatic plan view of a heat store according to a further embodiment of the invention.

Description of the Preferred Embodiments of the Invention

Throughout this specification, the term 'fuel powered engine' extends to engines such as diesel, petrol, gas and even so-called fuel cell engines.

In a preferred embodiment, the engine, the heat exchanger, the generator and the control means are located within a housing one of whose wall abuts against the exterior wall of the house. This housing is preferably waterproof and should be able to withstand harsh weather conditions over an extended period of time. A vent is provided in one of the walls of the housing to permit air to enter and to be fed to the engine. Apart from this vent the housing is preferably provided with an insulating layer to minimise the emission of heat and noise from the housing to its neighbouring environment. The housing will ideally also comprise a front door to allow easy access and maintenance. The unit is not limited to be mounted against the exterior wall of the house and can be easily adapted to fit within the dimensions of the neighbouring garage or within a specifically designed room of the house such as a boiler room .

The engine used in the invention's unit is advantageously a diesel engine. The size of the diesel engine will easily be selected by the person skilled in the art depending on the energy requirements of the structure to which the unit is inserted. A particularly well-suited diesel engine is a 11 kilowatt three-cylinder engine. This type of engine is capable of supplying sufficient energy to either two modern semi-detached houses or one modern four bedroomed executive detached house.

The unit 10 illustrated in Figure 1 in the form of a series of block diagrams comprises an engine 14 whose operation depends entirely on the control means 15. These control means 15 can be manual, however it is preferred that these are automatic so that the energy requirements of the dwelling to which the unit is connected, are provided without any human intervention apart from the occasional service. The control means is connected to sensors placed within the house 18 to measure the temperature of the air or of the water circulating through the radiators. The house 18 may also be equipped with a means to select the desired temperature of either the water or the air. Dependent on this selection the control means will compare the actual temperature of the various sections of the house 18 with the desired temperatures and commission the operation of the engine. It is also envisaged that during the operation of the engine and the consequential change in temperature readings within the house 18, the control means will instruct the switching off of the engine as and when the state of the heat and power stores (battery) dictate.

The heat generated by the engine 14 is transmitted to the house 18 via a heat exchanger 19 which operates by circulating fluid over the heat-emitting sections of the engine .

The circulating fluid can be water, a specific coolant or even air. When the circulating fluid is water it is envisaged that the heat is transmitted to the house 18 through conventional radiators. It is also envisaged within the scope of this invention that the hot water obtained through the heat exchanger 19 is stored in an appropriately-sized hot water cylinder to be available whenever an operator requires it.

In the case of using air to transmit heat to the house 18, a fan can be placed at any appropriate location of the unit 10 to extract the hot air. This hot air can be directly pumped into an appropriate location of the house 18 or fed to a heat pump, for example one formed of underground cavities to retain the air and to maintain it at an elevated temperature, and then the air can be extracted from these cavities to meet the house's requirements.

The electricity requirements of the house 18 are met by the electricity produced by the generator 12 which is driven by the engine. A power store in the form of a bank of batteries 16 may be provided to store via an inverter the electricity generated by the unit 10. Since damage may occur to the battery due to the elevated temperature of the operating engine and the heat exchanger 19, the bank of batteries 16 may be stored in a neighbouring compartment of the unit 10 that would be to a certain extent thermally isolated from the engine. The invention also foresees that any heat generated by the battery 16 or even the generator 12 may be captured by a circulating fluid such as water or even air over the battery 16 and the generator 12 respectively. Although the heat generated by the battery 16 and the generator 12 is not of the same magnitude as that generated by an engine, the capture of this modest source of energy may be useful to supplement the heat transferred to the house 18.

The bank of batteries 16 of the unit 10 may be additionally charged through renewable energy sources such as photo-voltaic cells and wind turbines. In the case of a wind turbine it is not uncommon that its generator 12 emits a high level of heat when it is constantly activated due to persistent winds. In this case, the invention envisages that some of the circulating fluid may pass around an appropriate surface of the turbine generator 12 to provide an additional source of heat to the house 18.

Heat exchangers may also be adapted to transmit the heat emitted by the sump oil and the exhaust of the engine - this would enable an even more efficient transmission of energy to the house 18 by even further reducing the heat loss to the environment from the engine and its constituents.

Figure 2 presents a further embodiment of the present invention where a unit 100 of the type described with reference to Figure 1 is designed to operate in conjunction with a house 102, an air-conditioning unit 104 and a swimming pool 106. The swimming pool 106 of this embodiment is an outdoor pool destined to be used primarily during the summer months . During the winter months the air-conditioning unit 104 and the swimming pool 106 are not usually required to operate in conjunction with the unit 100. The heat exchangers 108 which operate with the engine, the sump and the exhaust transmit heat to the house 102 which is stored in the house 102 as hot water. This hot water is either stored in an insulated boiler or circulated through conventional radiators appropriately placed in a variety of locations in the house. The generator 110 which is driven by the engine 112 produces sufficient electricity to meet the electricity requirements of the house 102. The control means 114 can be adapted to monitor whether heat needs to be supplemented to the swimming pool 106 and electricity to the airconditioning unit 104. The control means 114 can even be adapted to automatically identify whether the requirements of the system 100 are winter requirements or whether these are summer requirements.

During the summer months the heat requirements of the house 102 alone are generally considerably lower than during the winter. Due to longer days, the electricity requirements of the house 102 are also inferior to those similar requirements during the winter period. In the summer months, the heat exchangers 108 can be used to transmit heat to the hot water boiler of the house 102 and also to increase the temperature of the swimming pool ' s water by a few necessary degrees. The heat requirements in the summer of the house 102 plus a swimming pool 106 can be similar to those of the house 102 alone during the winter months. In order to avoid the situation where there is a surplus of electricity generated to meet the requirements of the house 102, it is advantageous to fit an air-conditioning unit 104 to the house 102.

As was described with reference to Figure 1, the generator may charge a battery, The invention also envisages that the battery may be additionally charged through photo-voltaic cells or through a wind generator. If the unit is placed in a location where the rays of the sun are easily captured, the photo-voltaic cell means can cover the exposed surfaces of the unit's housing.

The diagram in Figure 3 shows the main components of an alternative autonomous power and heat system 300. The system 300 comprises an engine-generator 302, a power store 304, a heat store 306 and an inverter 308 for converting the direct current (DC) of the power stored in the power store into alternating current (AC) . The system further comprises a control system 310 for controlling the supply of heat and power. Optionally, power is also provided by a wind generator 312 or a solar energy powered generator (not shown) . The heat can further be provided to the heat store 306 by means of a solar collector (not shown) .

In operation, the inverter 308 provides electricity as required to the structure such as a house. This power is directly provided by the power store 304.

When the control system 310 detects that the house demands heat or the heat store is low or the power store is low, it starts the engine-generator 302, which provides power into the power store 304. Whilst the engine is running, heat is provided to the structure through the heat store 306 into the existing conventional domestic hot water heating system (not shown) .

The optional wind turbine 312 represents the ability of the system to incorporate power from wind and/or solar photovoltaic (PV) panels. The basic system is capable of supplying heat and power to the house with a substantial reduction in fuel consumption and C02 emissions. The addition of solar PV or wind turbine results in an even greater reduction in fuel consumption and C02 emissions. Figure 4 presents an autonomous unit 400 for supplying energy to a structure in the form of house 402 and associated equipment comprising a fuel powered engine 404 for driving an electricity generator 406. The unit further comprises a power store 408 in the form of one or more batteries for storing the electricity generated by the generator 406. The electricity is fed into the house 402 either directly from the generator or is supplied by the power store 408. Although the electricity is stored in a DC format, the power is converted to an AC format at the appropriate voltage and current for running domestic appliances and other equipment (not shown here) .

The unit 400 further comprises a heat exchanger 410 for receiving heat from the coolant of the engine. For most applications, the heat exchanger is the secondary coolant system of the engine formed by the coolant water that is circulated to cool the oil inside the engine (commonly known as engine cooling system) . The heat provided by the heat exchanger is either supplied directly to the house 402 or it is stored in an appropriate heat store 412 for storing the heat. The unit further comprises a converter 420 for converting power stored in the power store into heat which is then stored in the heat store.

The unit further comprises control members 414 and 416 for controlling the amount of heat that is stored in the respective power and heat stores 408,412 and the amount of power and heat that is directly supplied to the house 402.

The unit 400 further comprises a controller 418 for controlling the engine, generator, heat exchanger, controllers 414, 416 depending on the heat and power requirements of the structure 402. In use, the controller 418 establishes the amount of heat and power required by the house. Depending on the amount of heat and power stored in the power and heat stores 408,412, heat and power is directly supplied to the house 402. Alternatively, if insufficient power and/or heat are available in the stores 408,412, depending upon the heat and power requirements of the house, the engine 404 is activated to generate power (by the generator 406) which is either stored in the power store 408 or directly supplied to the house 402. In addition, heat is produced by the engine cooling system which is supplied either directly to the house from the heat exchanger 410 or supplied to the heat store 412. In conditions where excess power is available and the demand for heat is high, power from the power store 408 is converted into heat and subsequently stored in the heat store 412. In this way, efficient heat and power is supplied to the structure 402 in all conditions independent of the demand for heat or power in the structure 402. Alternatively, the house is heated directly by the power supplied by the power store.

An example of a heat store 500 is presented in Figure 5. The heat store 500 comprises a dual walled tank with foam insulation which separates the tank walls 502. Heat is supplied to the store in the form a hot water which is supplied to the input heat exchanger connections 504. The tank contains a heat absorbing medium in the form of a wax-like substance with a melting point which is just below the temperature of the water that is supplied to the store 500. The water circulates through the input heat exchanger 504 and the heat from the water is transferred to the medium.

The heat store further comprises an output heat exchanger 506 for extracting the heat from the heat store. Water is circulated through the output heat exchanger 506 and this water is subsequently heated. Interlaced fins 508 on the heat exchanger promote exchange of heat from the heat exchangers to the medium.

In use, heat from the cooling water of an engine is absorbed in the heat store at a temperature of between 80 and 100°C, and the heat is stored in the medium with a melting point of around 75°C in the process melting the medium. This heat is later given up to the water at a temperature of around 60 to 70°C whereby the wax solidifies.

It is understood that the exchange of heat into and out of the heat store may also be a continuous process whereby part of the medium is solidified whereas part of the medium is melted and whereby heat is both provided to the heat store and heat is simultaneously extracted.

Claims

CLAIMS :

1. An autonomous unit for supplying energy to one or more structures and/or their associated equipment, comprising power generation means comprising one or more fuel powered engines adapted to drive one or more electricity generators for a period, and one or more optional power stores for storing the electricity produced by the generator and/or any other electricity generating means with which the unit operates;

means for feeding any electrical equipment to which the unit is connected;

means to transmit at least part of the heat emitted by the power generation means to any appropriate section of the or each structure and/or its associated equipment ; and

control means which determine the amount of electricity stored in the or each power store and/or the heat requirement of any appropriate section of the structure and which control the period of operation of the power generating means.

2. A unit according to claim 1, wherein the, or at least one of the, fuel powered engines is a diesel engine.

3. A unit according to either claim 1 or 2 , wherein the, or at least one of the, fuel powered engines is a gas engine .

4. A unit according to any preceding claim, wherein means are provided to transmit heat from the sump oil of the engine to any appropriate section of the, or each, structure and/or its associated equipment.

5. A unit according to any preceding claim, wherein means are provided to transmit heat from the exhaust to any appropriate section of the or each structure and/or its associated equipment .

6. A unit according to any preceding claim, wherein the heat generated by the unit is stored as hot water.

7. A unit according to Claims 1 to 6, wherein at least part of the heat generated by the unit is stored using a heat pump in an underground heat store.

8. A unit according to any of the preceding claims, wherein the heat generated by the unit is stored in a heat store .

9. A unit according to claim 8, wherein the control means determines the amount of heat stored in the heat store depending on the heat and power requirements of any appropriate section of the structure.

10. A unit according to any of claims 8 or 9, wherein the unit comprises a conversion means for converting the power stored in the power store into heat .

11. A unit according to claim 10, wherein the conversion means comprises a heating element provided in the heat store.

12. A unit according to any of the claims 10 or 11, wherein the control means control the conversion means depending on the heat and power requirements of any appropriate section of the structure.

13. A unit according to any of the claims 8 to 12, wherein the heat store comprises a medium adapted to store heat, the heat storage medium being adapted to undergo a phase change during storage and extraction of heat from the medium.

14. A unit according to claim 13 , wherein input and output heat exchangers provide heat transfer to and from the medium.

15. A unit according to claim 14, wherein the input heat exchanger and heat store are integrated.

16. A unit according to any of claims 13 to 15, wherein the heat storage medium is a wax like substance.

17. An autonomous unit for supplying energy to one or more structures comprising power generation means comprising an engine adapted to drive a generator for generating power and a power store for storing said power, the unit further comprising a heat store for storing heat generated by the power generation means, wherein conversion means are provided for converting power stored in the power store into heat, the heat being stored in the heat store.

18. A unit according to claim 17, wherein the unit further comprises control means for controlling the amount of power and heat stored in the respective power and heat stores depending on the power and heat requirements of the structure .

19. A method for supplying energy to one or more structures comprising the steps of: providing a power generation means comprising an engine adapted to drive a generator for generating power and a power store for storing said power, providing a heat store for storing heat generated by the power generation means, providing control means for controlling the amount of power and heat stored in the respective stores, wherein the method further comprises the step of controlling the amount of power and/or heat stored in the respective stores depending on the power and heat demand in the structure.

20. A method according to claim 19, wherein the method comprises the step of providing means for converting power into heat, the method further comprising the step of converting stored power into stored heat depending on the amount of power and heat required by the structure.

21. A heat store unit comprising a container containing a heat storage medium, the heat storage medium being adapted to undergo a phase change during storage and extraction of heat from the medium and input and output heat exchangers for providing heat transfer to and from the medium.