THERMAL SOLAR POWER PLANT

Title

Thermal solar power plant

Field of the invention The present invention relates to the field of energy transformation, and particularly to a thermal solar power plant according to the preamble of the independent claim.

Background of the invention

Sun energy is generally referred to as the direct transformation of solar radiation into electricity and heat, and may be performed in solar cells, sun panels or on a large scale in solar power stations. Solar cells may locally actuate electric apparatuses or small plants outside the ordinary electricity supply network, or may be connected in large numbers for connection to the electricity supply network. Sun panels on rooftops may produce hot water for consumption in houses or operate larger plants to heat up great amounts of water that may be stored seasonally.

Solar power stations use sun energy to generate electricity with turbine actuated generators (thermal solar power stations) or by means of solar cells. In thermal solar power stations the sunlight is used to generate electricity with conventional steam turbine technology. To reach high temperatures, large sun following mirrors on stands may be used which reflect and concentrate the direct solar radiation to an absorber on top of a sun tower. The water is heated to a high temperature and forms steam. The steam is then conveyed to a steam turbine connected to a generator, where the electricity finally is produced.

Another kind of solar power station makes use of stationary or sun following solar cells, in which solar radiation is directly transformed into electricity.

Many thermal solar power stations use some kind of coolant water source for the coolant water to be used in the steam condensing process, and in the absence of natural heat sinks, cooling systems for the coolant water. By using evaporative cooling, heat is removed from the coolant water, but then replacement water has to be added. Their open construction also permits pollution of the coolant water, and also pollution of the environment if the coolant water is contaminated or comprises environmentally dangerous elements.

Another solution to cool down the coolant water is to use dry cooling towers, which makes use of heat exchange between air and the coolant water in a closed system. There are no losses to the environment, but it is a less efficient method than evaporating cooling.

From the international application WO 2007/104080 A, a thermal power plant incorporating subterranean cooling of condenser coolant is known. To cool down the coolant fluid, a subterranean heat exchanger is used through which the coolant fluid is recirculated when cycling through the condenser. The power plant is thus fairly complex and includes excavating work to be installed.

There is thus a need for a thermal power plant that may be more easily installed at distant, rural places with no or little access of coolant fluid.

Summary of the invention

The object of the present invention is to replace environmentally dangerous production of electricity with an environmentally friendly and secure process. A further aim is to provide a power plant that is more adapted to be used in harsh environment to provide electricity at distant rural places.

The above-mentioned object is achieved by a thermal solar power plant comprising a sun panel system for transferring of solar energy to a fluid, a first accumulator tank which is connected to the sun panel system, whereby the fluid is arranged to circulate via tubes and valves between the first accumulator tank and the sun panel system. A turbine is connected to the first accumulator tank by means of at least one pressure regulated valve, and an electricity generator is connected to the turbine, for generation of electricity. The power plant further comprises a second accumulator tank which is connected to the sun panel system, whereby the fluid is arranged to circulate via tubes and valves between the second accumulator tank and the sun panel system. The second accumulator tank is connected to the turbine by means of at least one pressure regulated valve, whereby the sun panel system alternately heats up fluid which circulates between the first accumulator tank and the sun panel system, and fluid which circulates between the second accumulator tank and the sun panel system.

The invention achieves a solution to the problem of producing energy in an environmentally friendly way, by using only solar power and transforming it into electricity. The electricity is produced without environmentally unfriendly discharge into the nature.

Preferred embodiments are set forth in the dependent claims.

Short description of the appended drawings Figure 1 illustrates a first embodiment according to the invention. Figure 2 illustrates the relationship between temperature and saturation pressure. Figure 3 illustrates a second embodiment according to the invention. Figure 4 illustrates a third embodiment according to the invention. Figure 5 illustrated the circulation of fluid between an accumulator tank and a sun panel system.

Detailed description of preferred embodiments of the invention

The invention will now be explained in conjunction with the figures. Figure 1 illustrates a thermal solar power plant 1 according to the invention. The power plant 1 comprises a sun panel system 2 for transferring of solar energy to a fluid and a first accumulator tank 3 which is connected to the sun panel system 2, whereby the fluid is arranged to circulate via tubes and valves 6 between the first accumulator tank 3 and the sun panel system 2. The power plant 1 also comprises a turbine 4 connected to the first accumulator tank 3 by means of at least one pressure regulated valve 5, 6, and an electricity generator 8, connected to the turbine 4, for generation of electricity. The power plant 1 further comprises a second accumulator tank 7 which is connected to the sun panel system 2, whereby the fluid is arranged to circulate via tubes and valves 6 between the second accumulator tank 7 and the sun panel system 2. The second accumulator tank 7 is connected to the turbine 4 by means of at least one pressure regulated valve 5, 6, whereby the sun panel system 2 alternately heats up fluid which circulates between the first accumulator tank 3 and the sun panel system 2, and fluid which circulates between the second accumulator tank 7 and the sun panel system 2.

The thermal solar power plant 1 may be constructed in large units as well as small units. The electricity may be used for production of hydrogen gas or production of other kinds of power accumulators, or alternatively be delivered directly to power consumers. The power plant 1 may produce electricity to the existing power network for industrial and private use. The power plant 1 may further replace existing power stations and produce environmentally friendly electricity at an acceptable cost.

Preferably, the first and second accumulator tanks 3, 7, respectively, are arranged to receive condense, condense fluid and gas from the turbine 4 via tubes and valves 5, 6. The fluid may thus be used again and no refilling of fluid to the thermal solar power plant is needed. No fluid or gas is given off to the environment, which makes it possible to use fluids that transforms into gas at a relatively low temperature, which would otherwise contaminate the environment if given off from the power plant 1. The thermal solar power plant 1 according to the invention may thus replace existing production plants which do not meet environmental demands according to present and future needs, as the thermal solar plant 1 does not release any environmentally dangerous elements, as the process is completely closed. The same fluid is thus continuously used.

Advantageously, the valves 5 from the accumulator tanks 3, 7 are pressure regulated two- way valves. The fluid is heated up to desired temperature, whereby the valve 5 opens and the fluid is transformed into the form of gas, according to the curve illustrated in figure 2, and is directed via a further valve 6 to the turbine 4, which is put into rotation. Thus, when the temperature in the accumulator tank 3 reaches a desired level, a valve 5 connected to the accumulator tank 3 is opened and gas is conveyed via a tube to a valve 6, which according to one embodiment is a pressure regulated three-way valve. The valve 6 then opens, and gas is conveyed to the turbine 4. The rotation of the turbine 4 is transformed into electricity by means of an electricity generator 8. Electricity is produced and is fed to a predetermined consumer. The thermal power plant according to the invention accordingly takes advantage of the relation between the saturation pressure and the boiling point temperature. When the fluid has been adequately heated and desired pressure suitable for the turbine 4 has been reached, a preferably pressure regulated valve 5 (e.g. expansion valve) is opened whereby the fluid as a result of the lowering of the pressure is transformed into the form of gas. The gas flows to the turbine 4 and puts the turbine 4 into rotation. The gas is then condensed because of the lowering in temperature and is stored in the next accumulator tank 7.

The gas is thus condensed and is fed to the second accumulator tank 7 via valve(s) 6 (from the turbine and according to one embodiment also from the other accumulator tank 3). The valve 6 is according to one embodiment a pressure regulated three-way valve. When the fluid in the first accumulator tank 3 has reached certain conditions, the sun panel system 2 is coupled to the newly filled second accumulator tank 7, via the tubes and valves 6 between the sun panel system 2 and the newly filled second accumulator tank 7, and is reheated. When desired temperature of the fluid is reached, the control valve 5 connected to the second accumulator valve 5 is opened whereupon the fluid is transformed into the form of gas and is conveyed to the turbine 4 which is put in rotation whereby electricity is generated. The condensed gas from the turbine is conveyed from the turbine 4 to the first accumulator tank 3. When the fluid in the second accumulator tank 7 has reached certain conditions, the sun panel system 2 is coupled to the newly filled first accumulator tank 3 and fluid is reheated.

This process continues as long as there is sun energy accessible. It may be necessary to dimension the plant such that alternation to the other, not used, accumulator tank 3, 7 is made when the sun goes down. The power plant may be dimensioned for different needs, whereby the volume of accumulator tanks 3, 7, the dimensions and number of the sun panels in the sun panel system(s), as well as the number of accumulator tanks 3, 7 may be varied according to required performance. Many accumulator tanks 3, 7 and sun panel systems 2 may be connected to a common turbine. Fluid is chosen with care such that the temperature range from started heating to finished heating is adapted to the efficient operating range for the geographical location in question for the power plant 1. There is a plurality of different fluids that may be used. For example may oil or water with an additive be used as a fluid. Other examples of fluids are trichlorofluormethane, dichlorofluoromethane, dibromotetrafluoromethane, isopentane, methylformate and dichloromethane. Several other fluids may be used in the present invention, the fluids here mentioned should not be seen as limiting the scope of the invention as defined by the appending claims.

A fluid may thus circulate through the sun panel system 2 and the first accumulator tank 3 or second accumulator tank 7. The fluid may according to one embodiment, illustrated in figure 5, independently circulate as the fluid density is changed by the heating of sun panel system 2, whereby the change in fluid density causes the circulation of fluid between respective accumulator tank 3, 7 and the sun panel system 2. The fluid will expand as the fluid is heated, and this expansion makes the fluid lighter. The tubes conveying fluid from the accumulator tanks 3, 7 to the sun panel system 2 are then preferably connected to the sun panel system 2, such that fluid is conveyed from the accumulator tanks 3, 7 to the lower part of the sun panel system 2. The tubes conveying fluid from the sun panel system 2 back to the accumulator tanks 3, 7 are then preferably connected from the uppermost part of the sun panel system 2 to the accumulator tanks 3, 7. Two columns of fluid A and B with the same height h, but with different density will then be obtained (shown schematically as side A and side B in the figure 5). h is the height from the fluid level in an accumulator tank 3, 7 to the lowermost level of the tube conveying fluid from an accumulator tank 3, 7 to the sun panel system 2. The column of fluid B including the sun panel system 2 becomes lighter than the column of fluid A in the tube on the other side which does not include the sun panel system 2. The difference in weight of the columns of fluid A and B thus causes the circulation of fluid. It is accordingly advantageous if the sun panel system 2 is placed underneath the accumulator tanks 3, 7.

According to another embodiment, the fluid is pumped through the sun panel system 2 and the first accumulator tank 3 and second accumulator tank 7, respectively, by means of at least one circulation pump 9 which causes the circulation of fluid. The pump 9 may be energized by solar power.

According to one embodiment, the alternation of heating of fluid circulating between one of the accumulator tanks 3, 7 and the sun panel system 2, to heating up fluid circulating between the other accumulator tank 3, 7 and said sun panel system 2 is actuated when the pressure measured by a pressure sensor 11 in the former accumulator tank 3, 7 decreases below a certain threshold value. Thus, the accumulator tanks 3, 7 may thus comprise a pressure sensor 11 each which gives sensing signals to a control unit 12, which in turn compares the signals with the threshold value and controls the preferably pressure regulated valves 6 accordingly, to alternate the heating of fluid. This control scheme is illustrated in figures 1 and 3 by dotted lines to and from the control unit 12, and the valves 6 and sensors 11.

According to an other embodiment, the alternation of heating of fluid circulating between one of the accumulator tanks 3, 7 and sun panel system 2, to heating up fluid circulating between the other accumulator tank 3, 7 and the sun panel system 2 is actuated when the amount of fluid measured by a level sensor 11 or a weight sensor 11 in the former accumulator tank decreases below a certain threshold value. Thus, the accumulator tanks 3, 7 may thus comprise a level sensor 11 or weight sensor 11 each, which generates sensing signals to a control unit 12. The control unit 12 in turn compares the signals with the threshold value and controls the preferably pressure regulated valves 6 accordingly, to alternate the heating of fluid. This control scheme is also illustrated in figure 1 and 3 by dotted lines to and from the control unit 12, and the valves 6 and sensors 11.

According to a further embodiment, the alternation of heating of fluid circulating between one of the accumulator tanks 3, 7 and sun panel system 2, to heating up fluid circulating between the other accumulator tank 3, 7 and the sun panel system 2 is actuated when the temperature of the fluid measured by a temperature sensor 11 in the former accumulator tank decreases below a certain threshold value. Thus, the accumulator tanks 3, 7 may thus comprise a temperature sensor 11 each which gives sensing signals to a control unit 12. The control unit 12 in turn compares the signals with the threshold value and controls the preferably pressure regulated valves 6 accordingly, to alternate the heating of fluid. This control scheme is also illustrated in figure 1 and 3 by dotted lines to and from the control unit 12, and the valves 6 and sensors 11.

In some embodiments, pressure equalization is needed between the sun panel system 2 and accumulator tanks 3, 7. This is made to facilitate replenishment of fluid in the sun panel system 2. According to one embodiment, fluid pressure differences between the sun panel system 2 and accumulator tanks 3, 7 are equalized by using pipes between the sun panel system 2 and the accumulator tanks 3, 7 (not shown in the figures). This to eliminate that gas bubbles stays in the tubes between the sun panel system 2 and the accumulator tanks 3, 7. Pipes and valve are placed such that the gas is conveyed out of the sun panel system 2 into the accumulators 3, 7. In these cases the uppermost part of the fluid level in the sun panel system 2 should be in level with the fluid level in the accumulator tank 3, 7.

According to one embodiment shown in figure 3, the turbine 4 is connected to a condense accumulator 10, which in turn is connected to the accumulator tanks 3, 7 via valves 5. Thus, by having a condense accumulator 10 it is possible to further avoid fluctuations levels in the power plant system 1.

According to a further embodiment, the power plant 1 comprises more than two accumulator tanks connected to the sun panel system 2. Thus, it is possible adapt the power plant for different circumstances and needs. The valves denoted 6 in the figure 1 and 3 are then preferably adapted to the number of accumulator tanks in the power plant, i.e. four accumulator tanks gives a need for five-way valves 6. According to a further embodiment, some of the accumulator tanks are connected to at least one more sun panel system, but are connected to the same turbine 4, whereby the turbine 4 has several turbine wheels to render it possible to receive gas from different tubes and valves 6. The possibility to drive the turbine 4 continuously is obtained, without any interruptions because it takes time to heat the fluid in the accumulator tanks.

Figure 4 illustrates one example of a power plant 1 with three accumulator tanks 3, 7, 13 connected to the same sun panel system 2. The valves denoted 5 and 6 are here two-way valves. As a start fluid is added to the power plant 1. Fluid in the accumulator tank 3 is heated (when the fluid circulates between the tank 3 and the sun panel system 2). Gas is then conveyed to the accumulator tank 13, and air is then pressed out of the tubes. Then air is pressed out of the other accumulator tanks such that a great surface is obtained for the steam formation. The power plant 1 according to the embodiment illustrated in the figure 4 then functions as follows: One accumulator tank, e.g. 3, with fluid is heated, and when desired pressure has been obtained, the top valve 5 of the accumulator tank 3 is opened and gas is conveyed to the turbine 4, and condense and condense fluid (and not already condensed gas) is conveyed to accumulator tank 13. At the same time the bottom valves 5 between accumulator tank 13 and 7 opens, and fluid (condense, condense fluid and gas) is then conveyed to both accumulator tank 13 and 7. When the accumulator tank 3 is empty, the pressure in the tank 3 is lower than a certain threshold, or when the weight or temperature of the fluid/gas in the accumulator tank 3 has reached a certain threshold, the heating of fluid in the accumulator tank 13 is started. When a desired pressure in accumulator tank 13 is obtained, the top valve 5 of the accumulator tank 13 is opened and gas is conveyed to the turbine 4, and condense and condense fluid (and not already condensed gas) is conveyed to accumulator tank 7 (which already contains some fluid). At the same time the bottom valves 5 between accumulator tank 7 and 3 opens, and fluid (condense, condense fluid and gas) is then conveyed to both accumulator tank 7 and 3. When the accumulator tank 7 is empty, the pressure in the tank 7 is lower than a certain threshold, or when the weight or temperature of the fluid/gas in the accumulator tank 7 has reached a certain threshold, the heating of fluid in the accumulator tank 3 is again started. As the fluid is conveyed to two interconnected tanks, the cooling of the gas/condensed fluid is improved. This process may function continuously. Various modifications of the invention within the scope of the claims are of course possible.

According to one embodiment, the sun panel system 2 comprises at least one sun panel, and advantageously several. The amount of sun panels may thus be adjusted according to size of the power plant and the solar energy during the day at the intended localization for the power plant 1. The accumulator tanks 3, 7, 13 may also be dimensioned such that alternation between the accumulator tanks 3, 7, 13 occurs in accordance with the amount of solar energy during the day. The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.