SOLAR POWER AND THERMAL UTILIZATION SYSTEM

Field of the Invention

The present invention relates in one aspect to systems that utilise solar energy. In other aspects the invention relates to control systems for thermodynamic systems that may optionally utilise solar energy, and associated methods.

Background to the Invention

It is known to use solar thermal collectors for water heating. Various flat plate collector designs are known and extensive deployment has occurred particularly for domestic hot water installations. However, typically gas or electric boosters are required to boost the water temperature when solar heat is not available or is inadequate for the demand at an installation.

In general, flat plate solar collectors only collect heat cost effectively at temperatures up to about 8O ⁰ C. This is satisfactory for water heating and water heating provides a relatively high value for the collected solar heat. However, solar collectors must generally be sized smaller than winter requirements, to maximise capacity utilisation throughout the year. This optimises capital cost at the expense of increased reliance on booster energy when there is not enough solar heat from the undersized panels.

Solar systems have also been designed for producing electricity. One such system is known as photo-voltaic and directly generates electricity for various purposes. Alternatively, solar collectors have been designed for high temperature thermal operations for various purposes including the production of high temperature steam. It is also known that conversion of solar thermal heat to useful electricity can be achieved in a suitable system but the development of efficient systems having an acceptable capital cost is a challenge which has not been met, at least to a satisfactory extent.

More particularly, there is a perceived need for an efficient system which can utilise solar energy to deliver heat energy for thermal systems such as water heating and which can be converted efficiently and flexibly into electricity production.

Summary of the Invention

According to a first aspect of the present invention, there is provided a thermodynamic system comprising; a first fluid circuit for circulating a working fluid; an electricity generating system operative to generate electricity using energy imparted by the working fluid in the first fluid circuit; a heat supply to heat the working fluid, the heat supply includes a first heat generator incorporating a solar collector, and a second heat generator; a thermal system arranged to receive heat rejected from the working fluid for use in the thermal system; and a control system for controlling the supply of rejected heat from the working fluid to the thermal system.

In one form, the control system controls the amount of heat supplied to the working fluid from the heat supply so as to influence the amount of rejected heat available for use in the thermal system. In one form, the control system alternatively or in addition controls the duration of the supply of rejected heat to the thermal system.

In one form, the second heat generator is arranged to supplement the first heat generator in supplying heat to the working fluid. In one form, the second heat generator (which typically may be a combustion heater) is operated under the control of the control system. At many locations natural gas is available either through a mains supply or through bottled gas distribution and embodiments of the present invention can utilise a simple gas heater to contribute to the heat output in combination with solar technology to permit electricity production on demand, even when there is an absence of solar energy available.

In one form, the supply of heat to the thermal system dictates the level of output from that system. For example, the thermal system may comprise a water heating system where the supply of rejected heat dictates the amount of resultant change in water temperature. In another form, the thermal system may be space heating or cooling for buildings or may be for heating in industrial applications.

In one form, the first fluid circuit may be described as a Rankine cycle process. In that process, the working fluid is arranged to change state in the cycle. In particular, the heat supply is arranged to heat the working fluid so as to cause the working fluid to

vaporise. Further, the electricity generating system may include an expander and an electricity generator, the expander being arranged to receive the vaporised working fluid to extract energy to drive the electricity generator.

In addition, means are included to reject heat from the working fluid after it exits the expander. In one form this may be achieved by passing the working fluid through a heat exchanger associated with the thermal system. In addition a condenser may be provided in parallel to the heat exchanger of the thermal system to also reject heat from the working fluid. The control system is in one form able to control the flow of the working fluid between the heat exchanger of the thermal system and the condenser. In this way, the condenser may provide a mechanism for dumping excess heat so that the thermal system is not overheated.

In one form, the condenser rejects heat in the working fluid at a lower temperature than in the heat exchanger associated with the thermal system. As such, embodiments may utilise the condenser in parallel with the thermal system to reject heat to maximise electricity generation efficiency. The efficiency of conversion of thermal energy to useful electricity in a Rankine cycle is strongly influenced by the temperature of the available heat (which should be as high as possible) and the temperature at which the heat can be rejected (which should be as low as possible for maximum conversion efficiency to electricity).

In this specification the invention has been described with application to a cycle known as the Rankine cycle, but the invention is not absolutely limited to incorporating such a cycle as other thermodynamic cycles of a similar character might be substituted.

In accordance with embodiments of the invention described above an integrated system is provided that can utilise solar energy for the production of electricity and for use in a thermal system (such as in a hot water system or air conditioning). The system allows for efficient use of energy through the use of the rejected heat in the thermal system as well as sensitivity in the control of the system to allow for flexibility in output to optimise its usage in different scenarios. The system allows for judicious heater boost to ensure development of the required heat to the thermal system and/or electricity output.

Further, the system can be configured to maximise electricity generation by appropriate diversion of the working fluid. It is well recognised that with electricity systems there are infrastructure issues when consideration is given to the problem of dealing with peak demand. Therefore a capital effective system which can contribute to peak demand generation is desirable.

In an embodiment, the control system comprises a processor to receive inputs indicative of requirements in relation to electricity generation and thermal system demand, and to issue instructions in response thereto to control heat supply and the flow path of the working fluid through the first fluid circuit.

In a further aspect, the invention provides a control system for a thermodynamic system incorporating a heat supply and arranged to generate electricity from energy imparted to from working fluid circulating in a first fluid circuit and to impart heat into a thermal system from rejected heat from the working fluid, the control system comprising a processor arranged to receive load inputs indicative of the requirements for at least one of electricity generation and the thermal system demand and to control the supply of rejected heat from the working fluid to the thermal system in response to the load inputs.

In yet a further aspect, the invention provides a method of generating electricity and imparting heat to a thermal system, comprising the steps of: circulating a working fluid around a first fluid circuit; heating the working fluid; generating electricity from energy imparted by the working fluid; selectively using rejected heat from the working fluid in a thermal system; and controlling the supply of rejected heat from the working fluid to the thermal system.

In one form, the working fluid is heated at least in part by solar energy.

In one form, the amount of heat supplied to the working fluid is controlled to influence the amount of rejected heat available for use in the thermal system. In addition or alternatively, the duration of the supply of rejected heat to the thermal system is controlled.

In one form, when the working fluid is caused to flow along a first path, heat rejected from the working fluid is at a first temperature and the rejected heat is used in the thermal system. When the working fluid is caused to flow through a second path, the heat is rejected from the working fluid at a lower temperature than the first temperature. In one form, the flow of the working fluid between the first and second paths is controlled. In a particular embodiment, the efficiency of generating electricity is improved by increasing the proportion of the flow of the working fluid through the second path as compared to the first path.

Brief Description of the Drawings

For illustrative purposes, embodiments of the invention will be further described with reference to the accompanying drawings wherein:

Fig. 1 is a schematic of a Rankine cycle power generator as might be applied to a solar system but without being in combination with other features to constitute an embodiment of the invention;

Fig. 2 is a schematic representation of a thermodynamic system according to an embodiment of the invention utilising a Rankine cycle and a hot water system;

Fig. 3 is a variation of the system of Fig. 2 having the heat supply disposed in the fluid circuit containing the working fluid; and

Fig.4 is a schematic representation of a thermodynamic system according to an embodiment of the invention utilising a Rankine cycle and a space air conditioning system.

Detailed Description of Embodiments

Fig. 1 illustrates a Rankine cycle utilising solar heat for a boiler which heats a working fluid in a circuit in a system aimed at generating electricity. A solar heater 10 provides energy through a heat transfer fluid to a boiler 11 which is in the Rankine cycle together

with a circulation pump 12, a condenser 13 and an expander 14 which drives a generator 15 to produce electricity.

The efficiency of conversion of solar thermal heat to useful electricity in this cycle is strongly influenced by the temperature of the available heat (which should be as high as possible) and the temperature at which the heat can be rejected (which should be as low as possible for maximum conversion efficiency to electricity).

Referring now to Fig. 2, a schematic of a thermodynamic system 100 according to an embodiment of the invention is indicated.

The schematic shows a building 20 having a roof mounted solar collector 21 connected to a heat supply circuit 22 using a heat transfer fluid (such as an oil which will not boil at operating temperatures). The circuit includes a second heat generator in the form of a instantaneous gas heater 23 and a heat exchanger in the form of a boiler 24. As discussed in more detail below, operation of the instantaneous gas heater is dependant on a request signal manually or automatically to turn on the heater when required.

The system 100 includes a primary fluid circuit 25 which operates as a Rankine cycle. This circuit 25 is designed to operate on a vaporisable working fluid such as a hydrofluorocarbon e.g. 245fa or similar suitable fluid. The circuit passes through the boiler 24 where heat exchange from the heat supply circuit 22 occurs to vaporise the fluid. The working fluid passes to an expander 30 from which energy is extracted to drive an electricity generator 31. The discharged hot gaseous fluid passes to a control valve 29 which can selectively feed the hot vapour either along a first path to a heat exchanger 27 of a thermal system (which in this case is a hot water system 50) or along a second path to a condenser 28. In either case heat is extracted so that the gaseous working fluid is condensed and passes to a circulation pump 26 which returns the working fluid to the boiler 24. However, heat can be extracted from the gaseous working fluid in the condenser 28 (which in the illustrated form is air cooled) at a temperature that is lower than if the working fluid is diverted to the first path through the heat exchanger 27. As such, for the production of electricity, it is more efficient if the working fluid is passed through the condenser 28.

An analysis of the thermodynamics of Rankine cycles leads to the conclusion that a Rankine cycle would be inefficient in producing electricity with a heat supply of only about 8O ⁰ C when rejecting heat to hot water at a temperature of about 60 ⁰ C. This effectively rules out the production of electricity utilising flat plate panel solar collectors of the type that have been developed and are economic for hot water production such as domestic hot water services. According in this embodiment, it is preferable for the system 100 to use solar collectors that operate at higher temperatures, say greater than 90 ⁰ C.

The system 100 also includes a controller 32 connected to receive an input from the hot water system 50 namely an input signal along line 33 representative of temperature conditions in the hot water storage vessel 51. The vessel 51 incorporates the heat exchanger 27 adapted to heat water from rejected heat from the working fluid of the primary circuit 25 and is connected to suitable conventional inlets and outlets. The controller 32 receives a second input on line 34 being a control signal for indication of requirement for electricity generation. The controller has two output lines namely a valve control output 35 and a control output line 36 for the gas heater 23 so that various modes as described below can be selected.

In the embodiment illustrated, four modes are possible with the gas heater having two modes, i.e. on and off and the control valve 29 having two modes either to direct the hot vaporised working fluid to the water heating system 27 or to the condenser 28. These four modes are: a. hot water has run out; b. some hot water heating is required; c. no hot water heating is required; and d. peak electricity generation is required.

Mode 1: Hot water has run out

A thermal sensor in the hot water vessel 51 is provided to detect the temperature of the water. This information is passed to the controller 32 via the input line 33. When the temperature falls below a preset value, this is deemed to be a situation in which hot

water has run out. Heat ftom the system 100, possibly the combination of solar energy collector 21 and combustion heating 23 or combustion heating alone, causes heat rejection to the hot water system to raise the hot water temperature back to acceptable levels. In the embodiment, this is achieved by diverting the working fluid through the heat exchanger 27 of the hot water system. At the same time, electricity is generated although, due to the higher heat rejection temperature required for water heating, full power can not be produced in the electricity generator.

Mode 2: Some hot water heating required When the sensed hot water temperature is above the preset low temperature value but is below a second preset high temperature value, there is deemed to be sufficient hot water available but solar hot water heating is still advantageous. The solar system is then solely used for hot water heating by diverting the working fluid through the heat exchanger 27, without utilising the combustion heater. Electricity production occurs but full power production is not achieved due to the high heat rejection temperature required for water heating.

Mode 3: No hot water heating required

When the sensed hot water temperature is above the second preset high temperature value, no hot water heating is required. The combustion heater is not required, and the air condenser 28 is utilised to reject excess heat by passing the working fluid through the condenser rather than through the heat exchanger 27 under the control of the valve 29. In this way, the solar system achieves full solar electricity production capacity from the electricity generator.

Mode 4: Peak electricity power required

In this mode, a command signal from an electricity system operator or other market participant, is detected to indicate a need to maximise electricity production due to load requirements. The combustion heating system operates alone or with the solar thermal collector to provide a boost to maximise electricity power production. This is achieved by utilising the low temperature air condenser operation to reject heat from the working fluid.

The controller is able to select between the four modes described above. It is thought that for most of the operational time, control mode 2 would be in operation to take advantage of the high value of solar heat used in water heating. By the utilisation of high temperature solar collector panels, the Rankine cycle can also operate in mode 2 to permit electricity generation without waste heat being rejected to atmosphere.

Providing the ability to switch to control mode 3 prevents overheating of the hot water and permits increased heat to electricity conversion efficiency. Once overheating is prevented, the quantity of solar, collectors can be increased to closer match heating demands in winter (rather than designing collector size for summer). This permits more electricity to be generated from the available solar heat and reduces the need for gas or electricity boost for winter water heating.

The ability to switch to control mode 1 provides security for hot water supply for consumers by a boost arrangement when hot water has run out, for example, during periods of high demand.

Furthermore, the provision of control mode 4 provides security for electricity supply when there is peak electricity demand.

Fig. 3 illustrates a thermodynamic system 200 which is a variation on the system 100. As the system 200 includes many of the features of the earlier embodiment, like features have been given like reference numerals with the exception that they have been prefaced with the numeral "2" to distinguish between the embodiments.

The system 200 differs from the earlier embodiment in the heat supply arrangement. Rather than have an indirect heat supply circuit 22, the solar collector 221 and the combustion heater 223 are connected inline with the primary circuit 225. As such the working fluid of the primary circuit 225 is heated directly from the heat generators 221 and 223. In other respects the system 200 operates in the same way as the earlier system embodiment 100.

Fig. 4 illustrates a thermodynamic system 300 which is further variation of the system

100. Again, as the system 300 includes many of the features of the earlier embodiments, like features have been given like reference numerals with the exception that they have been prefaced with the numeral "3" to distinguish between the embodiments.

In the embodiment of Fig. 4, the thermal system is in the form of an air conditioning system 350 incorporating a sorption chiller 351 (adsorption or absorption) rather than a hot water system 50. As such, the system 300 has the purpose of providing air conditioning and power for houses and commercial buildings.

In this case, heat from the working fluid in the primary circuit 325 is rejected to a heat exchanger 327 formed as part of the sorption chiller unit 351 which transforms the heat into cooling. The resulting thermal cooling energy is then supplied to (circulated around) the building by a stream of coolant fluid in a secondary heat transfer loop 352. The coolant fluid would normally be chilled water but could alternatively be a refrigerant.

In a similar manner to the earlier embodiment, the system 300 can be operated in different modes depending on the external circumstances. These can be described as follows:

Mode 1: Solar cooling is insufficient

A thermal sensor in the building is provided to detect the temperature and this is provided to the controller through the input line 333. When the temperature rises above a preset value, this is deemed to be a situation in which cooling from the solar heat source alone is insufficient. Heat from the system, possibly the combination of solar energy and combustion heating or combustion heating alone, causes increased heat supply to the sorption chiller resulting in an increased amount of cooling. In the embodiment, this is achieved by diverting the working fluid through the heat exchanger 327 of the air conditioning system 350. At the same time, electricity is generated although, due to the high heat rejection temperature required to drive the sorption chiller, full power can not be produced in the electricity generator.

Mode 2: Solar cooling is adequate

When the sensed building temperature is below the preset high temperature value but is above a second preset low temperature value, conditions in the building are deemed to be comfortable. The solar collector 321 is then solely used for building cooling, without utilising the combustion heater 323. Electricity production occurs but full power production is not achieved due to the high heat rejection temperature required to drive the sorption chiller 351.

Mode 3: No cooling required When the sensed building temperature is below the second preset low temperature value, no space cooling is required. The sorption chiller 351 is not required and the air condenser 328 is utilised to reject excess heat, so that the solar collector 321 achieves full solar electricity production capacity from the electricity generator.

Mode 4: Peak electricity power required

In this mode, a command signal from an electricity system operator or other market participant, is detected through input 334 to indicate a need to maximise electricity production due to load requirements. The combustion heating system 323 operates alone or with the solar thermal collector 321 to provide a boost to maximise electricity power production. This is achieved by diverting the working fluid through the low temperature air condenser 328.

Other similar applications and heat rejection combinations are also possible including heat rejection for building space heating, and industrial heating (solids drying, evaporation, distillation)

Embodiments of the present invention involves the combination of selected suitable solar collectors with a combustion heater boost system (e.g. gas heater) to heat a working fluid in primary fluid circuit arranged typically in a Rankine cycle. Embodiments provide for a system with a degree of flexibility, as discussed above, in various modes. In summary, embodiments of the invention can subsist in an integrated system that (1) takes advantage of the high value of hot water, or other thermal system production, (2) achieves high solar collector capacity utilisation rates, (3) delivers

higher solar heat to electricity conversion efficiencies than is possible with flat plate collectors and (4) can boost power production to respond to electricity system peak demand problems.

A reference herein to a prior art document is not an admission that the document forms part of the common general knowledge in the art in Australia.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.