WO2016001369A1

WO2016001369A1 - System of a desalination plant driven by a solar power plant

Info

Publication number: WO2016001369A1
Application number: PCT/EP2015/065119
Authority: WO
Inventors: Svante BUNDGAARD; Per Jørn NIELSEN; Peter Badstue Jensen; Palle WENDELBOE
Original assignee: Aalborg Csp A/S
Priority date: 2014-07-04
Filing date: 2015-07-02
Publication date: 2016-01-07

Abstract

A system is disclosed comprising a Concentrating Solar Power (CSP) plant (1), a first thermal energy storage (TES1), and a desalination plant (18), the solar power plant (1) having a receiver part for heating a heat transfer fluid (6) by means of sunlight and a first heat transfer system with at least one heat exchanger (3, 10) arranged for transfer of thermal power from said first fluid to a first storage liquid being water for storage of said thermal power in the first thermal energy storage (TES1), the first thermal energy storage (TES1) being arranged to operate with the first storage liquid substantially at atmospheric pressure and the volume of the first storage liquid contained in said first thermal energy storage (TES1) is in the range of 300 m³ to 1,500 m³ per megawatt [MW] nominal thermal capacity of said receiver part, and the desalination plant (18) being arranged to desalinate seawater (22) driven by thermal power provided from the first thermal energy storage (TES1) in order to produce a flow of fresh water (23).

Description

System of a desalination plant driven by a solar power plant

The present invention relates to a system where a solar power plant is providing thermal energy to a thermal energy storage which again provides thermal energy to a thermal desalination plant for producing a supply of fresh water from seawater.

Background of the invention

The use of solar power to operate desalination plants for producing fresh water from seawater and optionally also for other purposes as well, such as operation of horticultural plants including greenhouses and/or other industrial plants is well known in the art.

It is known from international patent application No. WO 99/53745 to arrange solar powered heater in parallel connections with a steam turbine for producing electrical power, a desalination plant for supplying fresh water and a number of greenhouses.

In international patent application No. WO 2013/027097 a heat transfer fluid is circulated in a closed loop through a heater, such as a solar powered heater, a desalination unit and at least one further heat user before it is returned to the heater, i.e. a serial arrangement of the heat users thermally powered by one heat transfer fluid.

British patent application No. GB 2495782 discloses a system and a method for producing electricity and desalinated water. The system comprises a heliostat array and a solar tower with a heat transfer liquid circulating in a first closed loop. The heat transfer liquid is heated in the solar tower passes through a heat exchanger for heating and evaporating a secondary feed-flow fluid that supplies a steam turbine for production of electricity, from which the flow of the secondary fluid via a second heat exchanger supplies a multistage flash desalination plant. The system comprises a biofuel fired boiler to supply the steam turbine to ensure that the condition of the feed-flow input to the turbine is above a defined minimum.

However, a general problem is to provide such systems that are competitive with respect to traditional industrial plants, in particular horticultural plants, which are heated by burners fuelled by fossil fuel, due to the higher construction costs of solar powered systems.

It is an objective of this invention to provide workable solutions to such systems. Another objective is to provide improvements or alternatives to know solutions.

Description of the invention

Disclosed herein is a system comprising a Concentrating Solar Power (CSP) plant, a first thermal energy storage and a desalination plant, the solar power plant having a receiver part of a nominal thermal capacity arranged for receiving sunlight and heating a heat transfer fluid by means of the sunlight, the solar power plant further having a first heat transfer system with at least one heat exchanger arranged for transfer of thermal power from said first fluid to a first storage liquid for storage of said thermal power in the first thermal energy storage, the first storage liquid being water, the first thermal energy storage being arranged to operate with the first storage liquid substantially at atmospheric pressure and the volume of the first storage liquid contained in said first thermal energy storage is in the range of 300 m³ to 1 ,500 m³ per megawatt [MW] nominal thermal capacity of said receiver part, preferably in the range of 400 m³ to 1 ,200 m³, most preferred in the range of 500 m³ to 1 ,000 m³, and the desalination plant being arranged to desalinate seawater driven by thermal power provided from the first thermal energy storage in order to produce a flow of fresh water.

The concentrating solar power plant uses mirrors or lenses with a tracking system that follows the movement of the sun to concentrate a large area of sunlight, or solar thermal energy, onto a small area where the receiver part is situated. One option is a parabolic trough that comprises linear parabolic reflectors which concentrate light onto a receiver tube positioned along the reflector's focal line and filled with the heat transfer fluid, which may be heated to 150-350°C. An alternative is Fresnel reflectors that are made of a plurality of thin, flat mirror strips to concentrate sunlight onto receiver tubes through which the heat transfer fluid is pumped. Another option is a solar power tower that comprises an array of dual-axis tracking reflectors (heliostats) that concentrate sunlight on a central receiver atop a tower where the heat transfer fluid passes the receiver. Thus, the mentioned receiver part of the solar power plant may comprise one or more receivers, such as receiver tubes.

The heat transfer fluid may be pressurized water, which is heated or evaporated in the receiver part, or the fluid may be oil or molten salt, which subsequently to being heated in the receiver part optionally may be utilized for producing electric power, e.g. by producing pressurised steam for a steam turbine connected to an electric generator. Alternatively, the heat transfer fluid may be used as heat source for other types of electrical power generators, such as an organic Rankine cycle machine or a Sterling piston engine generator.

The term "nominal thermal capacity" is also known as rated capacity or nameplate capacity and is normally defined as the maximum heat effect produced under ideal conditions.

Regardless of whether or not the heat transfer fluid is utilised to produce electric power, it is an advantage that the thermal power production by means of the receiver of the solar power plant and the first storage liquid of the first thermal energy storage are separated by the at least one heat exchanger, so that the two media can be operating at different conditions tailored for their different operational circumstances. The heat transfer fluid is during operation of the system subjected to temperatures in the range of 140°C to 400°C in preferred embodiments of the present invention, more preferred in the range of 180°C to 350°C, whereas the temperature of the first storage liquid does not exceed 100°C as the first thermal energy storage is operating at about atmospheric pressure, which is advantageous in that it does not require tanks or equipment designed to be pressurised and the first storage fluid is water, which is inexpensive and does not require safety measures to be taken to protect the environment. However, a highest storage temperature of the first storage liquid in the first thermal energy storage of about 95°C is sufficient to supply thermal power to the desalination plant, in particular to a desalination plant operating according to the multiple-effect distillation (MED) process, which is preferred for the present invention. The volume of the first storage liquid is according to the present invention very large to allow for substantially constant operation of the desalination plant during the seasons of sufficient radiation from the sun so as to reduce the necessary nominal capacity of the installed desalination plant in the system.

The first storage liquid constitutes the heat storage medium of the first thermal energy storage together with optional particles, such as gravel submerged in the liquid, where the liquid is preferably contained in a so-called thermocline system for thermal energy storage, where a tank system is arranged to that the liquid is divided in a hot top layer and a colder bottom layer separated by a thermocline layer where the temperature gradient is steep. The position of the thermocline layer is variable to account for the varying amount of thermal energy stored. In the system according to the present invention, the temperature of the top layer is during ordinary operation of the system preferably in the range of 90°C to 98°C and the temperature of the bottom layer is preferably in the range of 70°C to 82°C. In a preferred embodiment, the system comprises a second thermal energy storage and a second heat transfer system arranged for transfer of residual thermal power from the desalination plant and to the second thermal energy storage. The second thermal energy storage is preferably an entity separate from the first thermal energy storage and is a low temperature storage compared to the first thermal energy storage and provides for utilisation of thermal power of a lower grade for further purposes, e.g. for heating or electric power generation in the system or externally to the system and thereby a more throughout use of the thermal power generated in the solar power plant. The second heat transfer system is preferably arranged for transfer of thermal power from a flow of brine out from the desalination plant, preferably arranged as a multiple-effect distillation desalination plant, and to the second thermal energy storage as the brine, which is a mixture of seawater and the surplus salt from the desalination process is heated during the desalination process.

It is preferred that the second thermal energy storage comprises water as the second heat storage medium and that the second thermal energy storage is arranged to operate with that second heat storage medium substantially at atmospheric pressure, wherein the volume of the second heat storage medium contained in said second thermal energy storage is in the range of 90 m³ to 450 m³ per megawatt [MW] nominal thermal capacity of said receiver of the solar power plant, preferably in the range of 120 m³ to 360 m³, most preferred in the range of 150 m³ to 300 m³. Such large volume of the water constituting the second heat storage medium ensures that the surplus thermal energy at a relatively low temperature as compared to the operational output temperature from the first thermal energy storage can be efficiently utilised by an internal or external plant that has varying requirement for thermal power, such as a horticultural plant that comprises greenhouses with a higher requirement for thermal power during the night than during the day period.

Hereby, the second thermal energy storage may provide in the order of 25 to 35% of the thermal power for such plant and thereby reduce the design requirement for the nominal thermal capacity of the solar power plant of the system.

The second storage liquid constitutes the heat storage medium of the second thermal energy storage together with optional particles, such as gravel submerged in the liquid, where the liquid is preferably contained in a so-called thermocline system for thermal energy storage, where a tank system is arranged to that the liquid is divided in a hot top layer and a colder bottom layer separated by a thermocline layer where the temperature gradient is steep. The position of the thermocline layer is variable to account for the varying amount of thermal energy stored. In the system according to the present invention, the temperature of the top layer is during ordinary operation of the system preferably in the range of 40°C to 50°C and the temperature of the bottom layer is preferably in the range of 20°C to 35°C.

It is preferred that the system comprises an industrial production plant, in particular a horticultural plant comprising greenhouses, which is arranged to be driven by thermal power provided from the second thermal energy storage. The industrial production plant is preferably arranged to be provided with fresh water by means of the desalination plant of the system. In a particular embodiment, the industrial production plant is furthermore arranged to be driven by thermal power provided from the first thermal energy storage, so that the second thermal energy storage provides the basic thermal power supply and the first thermal energy supply is arranged to top-up on the thermal power supply for the industrial plant.

The system comprises in a preferred embodiment a fresh water storage facility, wherein the storage volume of said fresh water storage facility is in the range of 750 m³ to 3,750 m³ per megawatt [MW] nominal thermal capacity of said receiver part of the solar power plant, preferably in the range of 1 ,000 m³ to 3,000 m³, most preferred in the range of 1 ,250 m³ to 2,500 m³ which is sufficient to level out the yearly variations in the production of fresh water for e.g. a horticultural plant being a part of the system. In a particular embodiment of the present invention, the first heat transfer system is arranged to produce a flow of steam from evaporation of water, and the system comprises an electrical power plant arranged to produce electrical power by use of said flow of steam, preferably comprising a steam turbine. It is furthermore preferred that at least one of the heat exchangers of the first heat transfer system comprises a condenser for condensation of said steam.

The nominal power of the electrical power plant is preferably in the range of 2 to 20% of the nominal thermal capacity of said receiver of the solar power plant, more preferred in the range of 3 to 8% hereof.

Brief description of the drawings

Different embodiments of systems according to the present invention are shown in the drawing of which Figure 1 is a diagram of a first system including a steam turbine and an electric generator,

Figure 2 is a diagram of a second system including a production plant, Figure 3 is a diagram of a system comprising a steam turbine as well as a horticultural production plant with the yearly energy flow indicated,

Figure 4A comprises representations of the yearly variation in solar power input, electric power output from generator and heat output from a boiler of the system according to figure 3,

Figure 4B comprises representations of the yearly variation in amount of hot water stored in TES1 and number of multi-effect distillation (MED) plants in operation in the system according to figure 3, and

Figure 4C comprises representations of the yearly variation in amount of fresh water stored and consumption of fresh water by the horticultural production plant per hour in the system according to figure 3.

Description of preferred embodiments

A diagram of a first system according to the present invention is shown in Fig. 1 , comprising a Concentrating Solar Power (CSP) plant 1 with a solar receiver and a reflection arrangement (not shown) for reflecting a solar field to the receiver. The receiver is arranged to evaporate water at pressure of about 12 atmosphere directly to produce a flow of pressurised steam 2. In an alternative embodiment, the receiver heats up oil that flows to a boiler for evaporating pressurised water in order to produce steam 2. The steam 2 may optionally be partly led to a first heat exchanger 3 for heating up a water flow 4 for the first thermal energy storage (TES1 ), depending on the operational circumstances of the system. The first heat exchanger 3 lowers the temperature of a part of or optionally the whole of the flow of steam 2 before it reaches the steam turbine 5, in case only a part of the flow of steam 2 is led to the first heat exchanger 3, the flow of steam 6 leaving the heat exchanger 3 is admixed with the remaining flow of steam 2 before reaching the turbine 5.

In an alternative embodiment, the first heat exchanger 3 is designed to be operating as a condenser. The steam turbine 5 is connected to an electric generator 7 for producing electric power to operate the system, which for all ordinary operation is designed to be a stand-alone system that is not depending on supply of electric power or fresh water from the exterior of the system. The electric generator 7 is optionally connected to an electric storage (not shown) to provide electrical power to the system in the periods where the solar power plant cannot produce sufficient power for the system to operate. At the low pressure side 8 of the turbine 5, the steam flow 9 at a pressure of about 1 atmosphere is led to a condenser 10 where the flow of steam 9 is condensed to a flow of water 1 1 which is pressurised by a pump (not shown) to a pressure of 12 atmosphere and is led back to the solar power plant 1. The condenser 10 heats up a flow of water 12 from the cold outlet 13 of the first thermal energy storage (TES1 ), from where the water flow 4 for the first heat exchanger 3 is also taken. The heated water flow 14 from the first heat exchanger 3 and the condenser 10 is led to warm inlet 15 of the first thermal storage (TES1 ).

The first thermal energy storage (TES1 ) is a thermocline system, which is a well- known heat storage arrangement, comprising water at atmospheric pressure in an amount that allows storage of about 12 hours of heat production of the solar power plant 1 at normal operating conditions, where the water flow 16 from the hot water outlet 17 is provided to the desalination plant 18 at about 96° C and is returned to the cold water inlet 19 at about 76° C. The first thermal energy storage (TES1 ) is in principle a large water tank provided with means, such as horizontal baffles and/or solid objects that allows for permeation of water between top and bottom of the tank, to prevent vertical admixing of the water and thus promote the formation of a hot top layer and a cold bottom layer of water separated by the so-called thermocline, a layer of water where the temperature changes rapidly in the vertical direction.

The desalination plant 18 is a thermal, multiple-effect distillation plant which is well- known in itself which is powered by a flow 16 of hot water from the hot water outlet 17 of the thermal energy storage (TES1 ) which is returned as a flow 20 of cold water to the cold water inlet 19 of the thermal energy storage (TSE1 ). The thermal power is used to desalinate an inflow 22 of sea water and produce a flow 23 of fresh water for a fresh water storage 24 and an outflow 25 of brine, which is a heated flow of seawater which an increased content of salts corresponding to the amount of salts removed from the fresh water flow 23.

In an alternative embodiment, the desalination plant 18 may be employed to produce a flow of pure water from an inflow of water that is contaminated with other contaminants than salts. A diagram of an alternative embodiment of a system according to the invention is shown in Fig. 2, where the steam turbine 5 and the electric generator 7 have been omitted. The heat transfer fluid for the receiver of the solar power plant 1 is in this embodiment oil that is heated to a temperature of 400 to 700° C. The flow 26 of heated oil is led to the first heat exchanger 3 from where it is returned to the receiver of the solar power plant 1 after having emitted heat to the flow 12 of water from the cold outlet of the first thermal energy storage (TES1 ).

Optionally, the system may be provided with a Sterling motor connected to an electric generator for producing electrical power to the operation of the system without requiring generation of steam as disclosed with respect to Figure 1.

The outflow of brine 25 at a temperature of about 45° C is led to a third heat exchanger 27 where it heats up a flow of water 28 taken from the cold water outlet 29 of the second thermal energy storage (TES2) to produce a flow 30 of heated water that is fed back to the warm water inlet 31 of the second thermal energy storage (TES2). The second thermal energy storage (TES2) is employed to provide at least a part of the thermal power required to operate a production plant 32, in this case a horticultural plant where the thermal power from the second thermal energy storage (TES2) provides the basic heating of the greenhouses. Fresh water for operation of the horticultural plant 32 is provided by the desalination plant 18 via the fresh water storage 24. Surplus heating for the greenhouses of the horticultural plant 32 is provided by means of a hot water flow 33 from the hot water outlet 17 of the first thermal energy storage (TES1 ). The second thermal energy storage (TES2) provides during normal operational conditions about 30 to 35% of the thermal energy consumption of the horticultural plant 32 and is thus enabling a substantial reduction in the required capacity of the solar power plant 1 to provide thermal energy for the horticultural plant 32. The energy flow over a year in a system according to the present invention is shown in the diagram in Fig. 3, comprising a solar power plant 1 driving a steam turbine 5 and a first thermal energy storage TES1 , which provides thermal power to a multi- effect distillation (MED) plant 18 and to the greenhouses of a horticultural production plant 32. The MED 18 also provides thermal energy for the second, low temperature thermal energy storage TES2, which provides basic heating for the greenhouses of the horticultural plant 32.

In this particular embodiment there is added a backup thermal power source in the form of an oil fired back-up boiler 35 so as to avoid damages to the plants in the greenhouses during a possible malfunction of the solar power plant 1 and to supply thermal energy during seasonal variations in the heat production from the solar power plant 1 .

The thermal power from the solar power plant 1 constitutes 96% of the total input of thermal energy, whereas the boiler only supplies about 4%. The thermal power mainly transferred to the first thermal energy storage TES1 , that is nearly 96%, whereas only 4.2% is powering the steam turbine 5 driven electric generator. The first thermal energy storage TES1 , which provides high temperature storage for thermal energy of which about 70% is used by the thermal desalination plant 18 for the production of fresh water for the greenhouses of the horticultural plant 32. The remaining 30% of the thermal energy from the first energy storage TES1 is supplied to the horticultural plant 32 as a top-up on the thermal energy provided by the second thermal energy storage TES2, which receives its supply of thermal energy from the outlet of brine at about 45° C from the multi-effect distillation (MED) desalination plant 18.

The second thermal energy storage TES2 provide low temperature thermal energy storage and provides thermal power to the industrial plant 32 in the form of a horticultural plant comprising greenhouses. The second thermal energy storage TES2 provides the base-load thermal power and the first thermal energy storage TES1 provides the thermal power that controls the operating temperature of the greenhouse. The first thermal energy storage TES1 comprises 20,000 m³ of water whereas the second thermal energy storage TES2 comprises 6,000 m³ of water. At a start-up situation where the thermal energy storages TES1 , TES2 are fully discharged it will take approximately 14 hours of operation of the solar power plant 1 at the nominal thermal capacity of the receiver of 30 MW and without any thermal energy consumption of the system to fully charge the first energy storage TES1 .

In this embodiment water is supplied to the first thermal energy storage TES1 near its boiling point at atmospheric pressure, i.e. close to 100° C from the solar power plant 1 and water at about 95° C from the top layer of the first thermal energy storage TES1 is supplied from the hot outlet 17 of the first thermal energy storage TES1 to the desalination plant 18 and the greenhouses of the horticultural plant 32. The return water 20 from the desalination plant 18 and the greenhouses 32 is approximately 78° C and is provided to the first thermal energy storage TES1 at the bottom layer thereof through the cold inlet 19.

The brine 25 leaves the desalination plant 18 at a temperature of about 48° C and is applied to heat the water in the top layer of the second thermal energy storage TES2 to a temperature of about 43°C from which it is provided to heat the greenhouses of the horticultural plant 18 and is returned to the cold inlet of the second thermal energy storage TES2 at a temperature in the range of 23 to 34°C, depending on the operational conditions of the horticultural plant 18.

Figures 4A to 4C illustrates the variations during one year of various features of the operation of the system showed in figure 3.

Figure 4A shows on top the thermal input into the system from the receiver of the solar power plant 1 , in the middle the electric output power from the steam turbine 5 driven electric generator 7 and at the bottom the additional thermal power input from the boiler in the winter season, where the thermal power from the solar receiver is lowest and the electric power output from the generator for the same reason is zero and is replaced with external electric power supply. From this figure it is evident that the system is not designed to be a 100% stand-alone system but is dependent on a minor input of electric power.

Figure 4B shows on top the storage mass of the top layer of water at 95° C in the first thermal energy storage TES1 and on the top the number of MED-units of the desalination plant 18 in operation. At the season with lowest thermal input to the system from the receiver of the solar power plant 1 , the stored mass of hot water is reduced and the number of MEDs in operation and thus the production of fresh water is reduced or zero.

The consequence is shown in Figure 4C where on the top is shown the stored volume of fresh water and on the bottom the corresponding consumption of fresh water by the greenhouses 32. The storage of fresh water builds up during the high season for thermal input to the system from the receiver of the solar power plant 1 so that the requirements for fresh water from the greenhouses 32 can be met throughout the whole year.

References

1 Solar power plant

2 Flow of pressurised steam from solar power plant 3 First heat exchanger

4 Water flow from first heat exchanger

5 Steam turbine

6 Flow of steam from first heat exchanger

7 Electric generator

8 Low pressure side of turbine

9 Steam flow at low pressure side of turbine 10 Condenser

1 1 Flow of water from condenser

12 Flow of water from cold outlet of TES1

13 Cold outlet of TES1

14 Flow of water to warm inlet of TES1

15 Warm inlet of TES1

16 Flow of water from hot water outlet of TES1 17 Hot water outlet of TES1

18 Desalination plant

19 Cold water inlet of TES1

20 Flow of cold water to cold water inlet of TES1 22 Inflow of sea water

23 Flow of fresh water

24 Fresh water storage

25 Outflow of brine

26 Flow of heated oil

27 Third heat exchanger

28 Flow of water from cold water outlet of TES2 29 Cold water outlet of TES2

30 Flow of water to warm water inlet of TES2 31 Warm water inlet of TES2

32 Production plant

33 Flow of water from hot water outlet of TES2 34 Flow of water to cold inlet of TES2 35 Back-up boiler

TES1 First Thermal Energy Storage

TES2 Second Thermal Energy Storage MED Multi-effect distillation desalination plant

Claims

1. A system comprising a Concentrating Solar Power (CSP) plant (1 ), a first thermal energy storage (TES1 ), and a desalination plant (18),

the solar power plant (1 ) having a receiver part of a nominal thermal capacity arranged for receiving sunlight and heating a heat transfer fluid (6) by means of the sunlight, the solar power plant (1 ) further having a first heat transfer system with at least one heat exchanger (3, 10) arranged for transfer of thermal power from said first fluid to a first storage liquid for storage of said thermal power in the first thermal energy storage (TES1 ), the first storage liquid being water,

the first thermal energy storage (TES1 ) being arranged to operate with the first storage liquid substantially at atmospheric pressure and the volume of the first storage liquid contained in said first thermal energy storage (TES1 ) is in the range of 300 m³ to 1 ,500 m³ per megawatt [MW] nominal thermal capacity of said receiver part, preferably in the range of 400 m³ to 1 ,200 m³, most preferred in the range of 500 m³ to 1 ,000 m³, and

the desalination plant (18) being arranged to desalinate seawater (22) driven by thermal power provided from the first thermal energy storage (TES1 ) in order to produce a flow of fresh water (23).

2. System according to claim 1 , wherein the desalination plant (18) is arranged to operate by a multiple-effect distillation (MED) process.

3. System according to claim 1 or 2, comprising a second thermal energy storage (TES2) and a second heat transfer system (27) arranged for transfer of residual thermal power from the desalination plant (18) and to the second thermal energy storage (TES2).

4. System according to claim 3, wherein the second heat transfer system (27) is arranged for transfer of thermal power from a flow of brine (25) out from the desalination plant (18) and to the second thermal energy storage (TES2).

5. System according to claim 3 or 4, wherein the second thermal energy storage (TES2) comprises water as the second heat storage medium and is arranged to operate with the second heat storage medium substantially at atmospheric pressure, and wherein the volume of the second heat storage medium contained in said second thermal energy storage (TES2) is in the range of 90 m³ to 450 m³ per megawatt [MW] nominal thermal capacity of said receiver of the solar power plant (1 ), preferably in the range of 120 m³ to 360 m³, most preferred in the range of 150 m³ to 300 m³.

6. System according to any of claims 3 to 5, further comprising an industrial production plant (32), which is arranged to be driven by thermal power provided from the second thermal energy storage (TES2).

7. System according to claim 6, wherein the industrial production plant (32) is arranged to be provided with fresh water (23) by means of the desalination plant (18) of the system.

8. System according to claim 7, wherein said industrial production plant (32) is a horticultural plant comprising greenhouses.

9. System according to any of claims 6 to 8, wherein the industrial production plant (32) furthermore is arranged to be driven by thermal power provided from the first thermal energy storage (TES1 ).

10. System according to any of the preceding claims, further comprising a fresh water storage facility (24), wherein the storage volume of said fresh water storage facility is in the range of 750 m³ to 3,750 m³ per megawatt [MW] nominal thermal capacity of said receiver part of the solar power plant (1 ), preferably in the range of 1 ,000 m³ to 3,000 m³, most preferred in the range of 1 ,250 m³ to 2,500 m³.

1 1. System according to any of the preceding claims, wherein said first heat transfer system is arranged to produce a flow of steam (2) from evaporation of water, and wherein the system comprises an electrical power plant (5, 7) arranged to produce electrical power by use of said flow of steam (2).

12. System according to claim 1 1 , wherein the electrical power plant comprises a steam turbine (5).

13. System according to claim 1 1 or 12, wherein the nominal power of the electrical power plant (5, 7) is in the range of 2 to 20 % of the nominal thermal capacity of said receiver of the solar power plant (1 ), preferably in the range of 3 to 8% hereof.

14. System according to any of claims 1 1 to 13, wherein at least one of the heat exchangers (3, 10) of the first heat transfer system comprises a condenser (10) for condensation of said steam (9).