GB2058935A - Solar power generating system - Google Patents

Abstract

A d.c. voltage generated by a solar collector 1 comprising photovoltaic cells is used to decompose water into hydrogen gas and oxygen gas, these two propellant components being fed, via separate storage tanks 3, 4 to the combustion chamber 5 of a gas turbine plant (driving, for example an electrical generator 16) which has a closed cycle, whereupon, after the mixture of the working medium (e.g. air or helium) and water vapour formed during combustion has been cooled, the water vapour is withdrawn from the gas turbine cycle via a condenser 9 and recycled for decomposition into oxygen and hydrogen. <IMAGE>

Description

SPECIFICATION Solar powered installation This invention relates to a solar powered installation. Known solar powered installations fall into three types. These are: A) A solar powered "tower" installation util izing a tracking reflector system to con centrate the solar energy onto an ab sorber or receiver mounted on a tower, a heat vehicle circuit for transporting heat from the receiver to an energy converter, for example, turbo-machine and generator and energy storage devices where appli cable.

B) A solar "farm" installation utilizing para bolic tubular collectors for concentrating incident solar energy, through which flows a heat carrier such as oil. This oil can be heated to about 320"C via a primary thermal circuit comprising a steam generator and an energy converter such as a steam machine or turbine for converting steam into mechancial energy which is then converted into electrical energy and, if need, stored in any conve nient manner. A large number of collec tors may be disposed on the ground, or, alternatively, the collectors may be mounted on a platform arranged to follow the sun along a circular track.

C) Direct conversion installations using pho tovaltaic cells which are connected either in parallel or in series to generate a d.c.

of voltage, a d.c. to a.c. converter and energy storage devices where applicable.

installations of type A) are especially suitable for large scale plants of up to 20 MW.

The resulting thermal efficiency (generator terminal/incoming solar energy) which it will be possible to achieve with materials available in the forseeable future, is 8 to 15% taken as an average over the seasons and days. This relatively low thermal efficiency is a considerable contributory factor towards the high costs of the collector and receiver the most expensive parts of the complete installation, since they have to designed for a very high heat output.

Another considerable disadvantage is the close coupling between solar radiation and the power output, so that the required flexible power supply needed by the consumer is initially unattainable. In principle this disadvantage can be reduced by thermal or hydraulic storage means or by varying the supply of energy derived from fossil fuel. However, the former involves considerable capital expenditure and in the latter case the additional supply of energy by burning fossil fuel is a problem.

Installations of type B) were hitherto considered only for low power, particularly since the thermal efficiency is very low and it is difficult to provide for the collection of the quantity of saturated steam required for a large-scale plant. As regards the lack of flexibility of power output and the necessary energy storage, the same remarks apply as to installations of type A).

Because of the extremely high costs of photovoltaic cells, installations of type C have hitherto been used only for space travel purposes. The efficiency of photovoltaic cells depends greatly on the material used, efficiencies (electrical power/solar radiation) of up to 28% appear feasible although experimental results obtained to date show a maximum of 18%. More recent developments have shown that the previous specific (power-related) costs for photovoltaic cells can be greatly reduced while the efficiency of these cells can be brought much nearer the theoretically possible value. With regard to storage facilities, basically the same remarks apply to installations of the types A) and B) referred to above, although in this case storage necessitates prior conversion of the surplus electrical energy into thermal or hydraulic energy.

In view of the desirable disconnection between the solar radiation and power output, and in respect of the energy storage problem, it must be remembered that on average there is solar radiation for only 1 2 hours each day while on the other hand: a) the power output staggered in accordance with known cycles continues throughout the day (24 hours); b) the power output differs considerably from day to day; and c) Any fluctuations in solar radiation (e.g.

passing clouds) should have the minimum effect on power output.

A basic assumption is therefore made that is the power output is to be satisfactorily flexible, i.e. if the plant loading is to be fully adapted to consumer requirements, an energy storage means is required to take up about 100-1 50% of a normal daily energy production. The storage of thermal or hydraulic energy in this order of magnitude would involve a very high capital expenditure and therefore appears unrealistic. In the known system in which solar radiation is complemented by additional fossil fuel heating, the above discrepancy between radiation and the power output which varies with the time can be eliminated in principle but this solution is not in keeping with elimination of dependency on fossil fuel, and it also requires additional infrastructure because of the need to store and supply the fuel.In addition, it is not a simple matter to accommodate variations indicated under (c) above by additional fossil fuel heating, in view of the unstable thermal loading of sensitive components (receiver, heat vehicle circuit, gas turbine).

One object of the invention, therefore, is to obviate the above mentioned disadvantages of known installations and provide a solar plant which provides optimum disconnection between solar radiation and the power output required at any time.

According to this invention we propose a solar installation comprising a solar energy collector in which voltaic cells are used to generate a d.c. voltage and connected to means for decomposing water to form hydra gen and oxygen, storage means for the hydrogen and oxygen so produced, a closed cycle gas turbine plant and having a combustion chamber connected to the storage means for the supply of oxygen and hydrogen thereto, a cooler for the mixture of the working medium of the closed cycle gas turbine plant and water vapour formed during combustion, and a condenser for extracting water vapour from the working medium and recycling water to the said decomposing means.

Other features of this invention are set forth in the appended claims.

The installation of the invention has the advantage that by virtue of the oxygen and hydrogen storage means, the gas turbine power output is effectively variably to meet any required power demand.

Also short-term or sudden changes in solar radiation can be accommodated by the storage means, the storage capacity required being within reasonable bounds.

Given an appropriate photovoltaic cell construction, approximately the same total thermal efficiency as with installations of type A) should be possible.

Another advantage is that the use of expensive hot-strength materials is minimized (only required for the combustion chamber and the turbine of the gas turbine plant).

Further, the high admissible turbine inlet temperature enables the gas turbine circuit heat output to be reduced to a temperature which enables this heat to be used effectively in a steam circuit.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is schematic circuit diagram of a solar installation with flexible output availability, or with the energy supply and the power output disconnected from one another.

Referring to the diagram a d.c. voltage is generated by means of a solar collector 1 built up from groups of voltaic cells, and is used to decompose water in tank 2 into hydrogen gas and oxygen gas; these two propellant components are fed via conduits a and b to two separate tanks 3, 4 in which the gases are stored under pressure. From these the hydrogen gas the oxygen gas are then fed through two other conduits c, dto the combustion chamber 5 of a gas turbine plant G, which has a closed circuit and internal combustion (hydrogen and oxygen), the outlet of the combustion chambers and the turbine inlet being interconnected via conduit k Air or helium may be used as working medium for the gas turbine plant G. In this way very high turbine input temperatures can be obtained as compared with gas turbine plants with a closed cycle and external heating by means of heat exchangers.

The gas turbine plant G also includes a compressor 10 and turbine 6 interconnected via a common shaft W, a heat exchanger 7 being incorporated in their cycle.

By means of reduction gearing not shown in the drawing, the output of the gas turbine plant G can be fed vai the output shaft W to the electrical generator 1 6.

According to the invention, the mixture consisting of air (or helium) and water vapour is first cooled in a pre-cooler 8 and then the water vapour forming from the combustion of the hydrogen and oxygen is withdrawn via a condenser 9 from the gas turbine cycle return line e between pre-cooler 8 and condenser 9 - and pumped back by pump 11 via conduit fto tank 2, in which the water is again split into oxygen and hydrogen. As a result, the water contained in the cycle is substantially maintained.

The pre-cooler 8 is connected downstream of heat exchanger 7 via conduit 1 and the mixture of air (or helium) and water vapour flows from turbine 5 via another conduit g into the heat exchanger 7 by means of which some of the heat contained in the mixture additionally heats up the compressed working medium (air or helium) before it enters the combustion chamber 5. Conduits h and i are provided for the flow of the working medium between the compressor 10 and the heat exchanger 7 on the one hand and between the heat exchanger 7 and the combustion chamber 5 on the other hand.

In a modified embodiment (not shown), the thermal energy withdrawn from the mixture of air (or helium) and water vapour after passing through the heat exchanger can be rendered usable in a steam circuit disposed downstream of the gas turbine circuit, in which case the pre-cooler is advantageously replaced by a steam generator.

The tanks 1 2 for pressure level control are incorporated in the return conduit e (between the pre-cooler 8 and the condenser 9) with interposition of compressor 1 3 and safety valves 14.

The gas turbine plant working medium circulating in the closed cycle passes to the compressor 10 from the condenser 9 via a conduit m.

Cooling water is supplied to the condenser by a pump 15.

Claims (6)

1. A solar powered installation comprising a solar energy collector in which voltaic cells are used to generate a d.c. voltage and connected to means for decomposing water to form hydrogen and oxygen, storage means for the hydrogen and oxygen so produced, a closed cycle gas turbine plant and having a combustion chamber connected to the storage means for the supply of oxygen and hydrogen thereto, a cooler for the mixture of the working medium of the closed cycle gas turbine plant and water vapour formed during combustion, and a condenser for extracting water vapour from the working medium and recycling water to the said decomposing means.

2. An installation according to Claim 1 and comprising an electrical generator driven by the gas turbine plant.

3. An installation according to Claim 1 or Claim 2 and comprising a heat exchanger connected for receiving the working medium from the turbine of the gas turbine plant, which heat exchanger acts as a preheater for the working medium before it enters the combustion chamber (5).

4. An installation according to Claim 2, and modified in that the cooler is replaced by a steam generator whereby the mixture of working medium and water vapour after passing through the heat exchanger is rendered useable in a steam circuit connected downstream of the gas turbine circuit.

5. An installation according to any one of Claims 1 to 4, and comprising pressure level control tanks associated with a compressor and safety valves, are connected between the cooler and the condenser.

6. A solar powered installation constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.