Abstract:
Provision of electricity to an electrical grid is controlled such that the electricity supply from the power plant is reduced to the current electric power demand by charging a thermal energy store(s). As a result, the provision of electricity by renewable energy sources to the electrical grid can be given precedence. The power plant can be connected to a heat pump and/or a refrigeration unit by the thermal energy store(s). The thermal energy store(s) can be used for district heating/cooling networks.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national stage of International Application No. PCT/EP2014/054122, filed Mar. 4, 2014 and claims the benefit thereof. The International Application claims the benefit of German Application No. 102013209681.1 filed on May 24, 2013, both applications are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    Described below are energy conversion and storage systems for balancing full-load and part-load periods of operation of power plants. 
         [0003]    Although there is a great desire to replace conventional fossil-fuel power plants, owing to the excessively high CO 2  emissions and their impact on the climate, and also nuclear power plants, owing to the various risks associated with them, by renewable sources of energy in order to ensure a safer, more environmentally-friendly supply of electricity in future, ensuring an above all independent supply of power solely on the basis of renewable sources of energy nevertheless still remains a requirement. The conventional generation of electricity by, for example, fossil-fuel and nuclear power plants, at least in Germany, still represents over 50% of the power generated. 
         [0004]    In order to expand renewable sources of energy such as, for example, biomass, photovoltaics or wind energy in addition to reliable independent power generation, these very different forms of energy generation need to be fed into the power grids in parallel. However, solar and wind power have the great disadvantage of being able to make available only a highly fluctuating supply of power to the power grid. Up until now it has been possible for power to be stored only in very small quantities, as happens for example in batteries or pumped-storage power plants or by flywheels. Depending on geographical conditions, potential energy stores such as, for example, pumped-storage power plants are used, for example in Norway, but in most other countries they do not offer an economically attractive solution, at least in the near future, and in addition the storage quantity is limited. 
         [0005]    In order to provide power flexibly to power grids, up until now for example power plants with gas turbines or alternatively gas-and-steam power plants are known and are used because they can adjust their output upward and downward relatively quickly. However, the number of such power plants is still very small. Moreover, the climate is further impacted by burning natural gas and there is also a dependence on gas imported from other countries. Moreover, it is questionable to what extent no-load and part-load periods of operation of these power plants are still economical. 
         [0006]    A different approach provides load management on the consumer side of the network which for this purpose needs to be a smart grid. The expansion of such smart grids so that they are comprehensive and reach a sufficiently large number of users will, however, only solve part of the problem and also reach its limitations. 
         [0007]    Conventional power plants which are designed for a long-term foreseeable power demand can be switched from full-load to part-load periods of operation only very slowly and only with high losses, or are switched off altogether. Depending on the power plant, this would take from at least a few hours up to several days. 
         [0008]    It is therefore a technical requirement to enable adjustable provision of power by conventional power plants. 
         [0009]    Solutions from the related art here relate to thermal storage solutions such as, for example, those known from DE 26 15 439 A1, DE 10 2008 050 244 A1, FR 2 922608 A1, U.S. 2012/0047 891 A1 or U.S. 2013/0118170A1. 
         [0010]    It is, however, a disadvantage of these solutions known from the related art that the thermal stores are not suitable or provided for efficient storage of waste heat. In particular, the solutions known from the related art disclose energy storage at a relatively high temperature level, which can also result in relatively high heat loss and hence inefficiencies. 
       SUMMARY 
       [0011]    In this respect, a technical storage solution is desired which not only allows thermal energy storage at a low temperature level but also makes it possible to make profitable use of waste heat of a power plant which would otherwise not be used further. 
         [0012]    In addition to a power plant, at least one thermal energy store and at least one energy conversion device are provided. The energy conversion device(s) is/are configured so as to charge the thermal energy store during a period of excess power supply, wherein a first heat store is coupled to a condenser of the power plant. This has the advantage that excess power supply is not wasted and instead can be stored, and this solution has the advantage that, in order not to generate any excess power, the power plant does not need to be run unnecessarily expensively at part load or even switched off. 
         [0013]    The coupling of the thermal store to a condenser of the power plant makes it possible to discharge thermal energy, as a result of which the cooling demand in the condenser of the power plant is reduced. At the same time, this coupling permits thermal storage, at a low temperature level, of waste heat which would otherwise not be used further. 
         [0014]    According to a further embodiment, it is provided that the thermal store is coupled to the condenser of the power plant in such a way that it can be charged with heat by the latter. 
         [0015]    In an advantageous embodiment, an adjusting device for the provision of power to a power grid is also included. The adjusting device is configured so as to reduce the supply of power by the power plant by charging the thermal energy store to the power demand that applies during this period so that the provision of power from renewable sources of energy to the power grid is prioritized. This has the advantage that even individual inflexible conventional power plants can be used at full-load operation for compensating adjustment behavior within a smart power grid. The power plants can in particular be fossil-fuel power plants which, in constant full-load operation, operate most efficiently without reducing the fuel mass flow, and at the same time the use and expansion of renewable sources of energy can be increased. 
         [0016]    The power plant is here in particular designed for constant full-load operation. 
         [0017]    In a further advantageous embodiment, at least one thermal energy store is a heat store, and at least one energy conversion device is a heat pump, wherein the heat store is discharged via a district heating grid. 
         [0018]    In an alternative advantageous embodiment, at least one thermal energy store is a cold store, and at least one energy conversion device is a refrigerating machine configured to discharge the cold store via a district cooling grid. 
         [0019]    This has the advantage that the heating or cooling demand within the vicinity of the site of the power plant can be met in an energy-efficient fashion. 
         [0020]    Furthermore, the first thermal store can be thermally coupled to an evaporator of a heat pump and/or to a condenser of a refrigerating machine. The thermal store can thus discharge heat to the evaporator of the heat pump or be charged additionally with heat by the condenser of the refrigerating machine. Especially when the evaporator of the heat pump is connected to the condenser of the power plant in such a way that thermal energy is removed from there after the at least one turbine of the power plant, the total cooling demand of the power plant, especially the cooling demand in the condenser, is reduced very advantageously. 
         [0021]    In a further advantageous embodiment, at least one energy conversion device is a heat pump and a second thermal store is thermally coupled to a condenser of the heat pump. In particular, it is coupled to the condenser in such a way that it can be charged with heat by the latter. This second thermal energy store can particularly advantageously be used to supply a district heating grid because a higher amount of thermal energy can be stored as a result of the thermal coupling to the condenser of the heat pump. 
         [0022]    For example, at least one energy conversion device is a refrigerating machine, the evaporator of which is thermally coupled to a third thermal store such that this third thermal store is charged with cold by the evaporator of the refrigerating machine and serves as a cold store. This cold store can be used particularly advantageously to provide cooling in a district cooling grid. As a result of the thermal store, the cooling grid can be operated at staggered intervals. 
         [0023]    Likewise, the district heating grid can be operated at staggered intervals via the second thermal store. For example, it is also possible to decouple a part heat flow from the power plant directly and hence to feed the district heating grid, which corresponds to the previous combined heat and power procedure, in order to compensate for any peak loads in the district heating grid when, owing to the requirements of the power grid and the power supply which is, for example, provided from renewable sources, the heat pump should not be put into operation. The connection of the condenser of the power plant to the evaporator of the heat pump is particularly energy-efficient because the waste heat of the power plant for use in the district heating grid can be brought to a much higher temperature level by the heat pump and simultaneously the cooling capacity of the power plant can be reduced. The use of water for cooling and the electrical fan capacity are thus reduced in the power plant. It is, for example, also conceivable to use the waste heat of compressors, for example via water cooling circuits, to charge the second thermal store. 
         [0024]    Water stores or phase change material stores are, for example, suitable as thermal stores. 
         [0025]    In particular, the power plant can be connected to a district heating grid and simultaneously to a district cooling grid via a heat pump and a refrigerating machine, respectively, and both thermal grids can be operated at staggered intervals via the respective thermal store. In this situation, a further connection can be made of the condenser of the refrigerating machine to the first thermal store which is connected to the condenser of the power plant and the evaporator of the heat pump, and the waste heat of the refrigerating machine can thus be used at staggered intervals for the evaporator of the heat pump. This is a particularly advantageous energy-efficient synergy of the system of multiple components described herein. 
         [0026]    It is particularly advantageous to couple a generator of the power plant and a compressor of at least one energy conversion device to the same shaft. 
         [0027]    Alternatively, the compressor or multiple compressors can also be operated by indirect power transfer, for example via belts or without any direct power transfer at all, for example via the power grid. The advantageous embodiment of coupling compressors and the generator or turbine of the power plant on a common shaft reduces any power transfer losses. The coupling and decoupling of a rotating machine in ongoing operation is known and does not contain any new technical requirements. 
         [0028]    Both a refrigerating machine and a heat pump, or both of them at the same time on the same shaft, can be operated like the generator of the power plant. For example, in the combination with a refrigerating machine and with a heat pump too, in each case only one energy conversion device can be operated and it is thus possible to switch, for example, from winter to summer operation. 
         [0029]    All possible conventional power plants for power generation can be considered as a power plant in one of the described systems, for example nuclear power plants, coal-fired power plants, biomass power plants, gas-fired or oil-fired power plants, etc. The respective power plant used can be operated at a constant fuel mass flow and nevertheless adjustable flexible electrical power can be provided using the heat pump or the refrigerating machine. These power plants can thus also be used within smart grids into which the feeding-in of renewable sources of energy can be prioritized. 
         [0030]    In the method for the adjustable provision of power by a power plant, in which at least one thermal energy store which is thermally coupled to a condenser of the power plant and in particular is designed as described above and below is charged by an energy conversion device during a period of excess power supply, the power supply to a power grid by the power plant is reduced by charging the at least one thermal store to the power demand applied during the period, so that the provision of power to the power grid from renewable sources of energy is prioritized. In particular, the power plant here runs at constant full-load operation. In an embodiment of the method, a heat store is used as a thermal energy store which is discharged via a district heating grid, in particular during a period in which there is no excess power supply from the power plant. Alternatively or additionally, a cold store is used as a thermal store which is discharged via a district cooling grid, in turn in particular during a period in which there is no excess power supply from the power plant. In the method, in particular at least one heat store is charged by a heat pump and at least one cold store is charged by a refrigerating machine. This embodiment has the advantage of covering three different power demand periods. Multiple different power demand periods can also be covered by multiple heat pumps or by multiple refrigerating machines. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0032]      FIG. 1  is a schematic block diagram of a power plant, thermal store, heat pump and refrigerating machine, 
           [0033]      FIG. 2  is a schematic block diagram of a power plant combined with a refrigerating machine, and 
           [0034]      FIG. 3  is a schematic block diagram of a power plant, thermal store, heat pump and refrigerating machine. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0035]    Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0036]      FIGS. 1 to 3  show in each case flow diagrams for a power plant process with the charging and discharging of thermal energy stores T 1  to T 3 , energy conversion processes  20 ,  40  which also exist, and energy consumption grids  30 ,  50  connected to the stores T 1  and T 3 . In each case, the power plant process  10  is shown on the left-hand side in the drawing. The power plant in each case includes a generator  11  which is driven by a turbine  12 . Furthermore, the power plant includes a condenser  15 , a feed pump  14 , and a steam generator  13 . All three drawings show the most common type of power plant  10  with a steam circuit. Power plants such as gas-and-steam power plants or a gas engine can, however, also be coupled accordingly to a refrigerating machine  40  or also to a heat pump  20 . According to the example of a gas-and-steam power plant, its air compressor, gas turbine, and steam turbine could be arranged on a common shaft. 
         [0037]    In  FIG. 1 , the power plant  10  is coupled to a heat pump  20 . The latter has a compressor  21 , an evaporator  22 , an expansion valve  23 , and a condenser  25 . Particularly advantageously, on the one hand a mechanical power connection needs to be produced between the power plant  10  and the heat pump  20  in such a way that the generator  11  and the turbine  12  of the power plant  10  and the compressor  21  of the heat pump  20  are coupled on a common shaft W. Furthermore, the power plant  10  and the heat pump  20  are interconnected via the first thermal store T 1 , a heat store. The latter is charged by waste heat of the condenser  15 , and the evaporator  22  extracts the heat again from the thermal store T 1 . The condenser  25  of the heat pump  20  is additionally connected to a second thermal store T 2 , in turn a heat store, which is charged to a significantly higher temperature level as a result of the thermal coupling to the condenser  25  of the heat pump  20 . This is particularly suitable for being discharged via a district heating grid  30 . The temperature level of the first thermal store T 1  is, for example, between 50° C. and 90° C., and the temperature level of the second thermal store T 2  is, for example, between 80° C. and 130° C. 
         [0038]      FIG. 2  shows an example for a steam power plant  10  with a refrigerating machine  40 . The power plant  10  and the refrigerating machine  40  are here again connected via a common shaft W to which the generator  11  of the power plant  10  and the steam turbine  12  are coupled, in exactly the same way as the compressor  41  of the refrigerating machine  40 . The uncoupling and coupling of the rotating machines takes place in ongoing operation in order to connect or disconnect the refrigerating machine  40  to the power plant  10 . The refrigerating machine  40  moreover includes an evaporator  42 , an expansion valve  43 , and a condenser  45 . The evaporator  42  is advantageously connected to a cold store T which is charged to a temperature level, for example between −20° C. and 15° C. and which can discharge its cooling via a district cooling grid  50 . Waste heat again also occurs at the condensers  15 ,  45  of the refrigerating machine  40  and of the power plant  10 , at a temperature level between 30° C. and 90° C., and can be charged for example to a further thermal store. 
         [0039]    The charging of a thermal store T 1  by the condenser  15  of the power plant  10  and by the condenser  45  of the refrigerating machine  40  is shown in  FIG. 3 , in which the power plant  10  is coupled to a heat pump  20  and a refrigerating machine. In this combination, a first heat store T 1  is charged with heat by the condensers  15 ,  45  of the power plant  10  and of the refrigerating machine  40 . This first heat store T 1  may be used to operate the heat pump  20  by discharging its heat to the evaporator  22 . The condenser  25  of the heat pump  20 , which makes waste heat available at a significantly higher temperature level, loads in particular a second heat store T 2  which is available to supply a district heating grid  30 . The refrigerating machine  40  shown again supplies a district cooling grid  50  which can be operated at staggered intervals by the cold store T 3 . This combination is particularly effective in terms of energy efficiency when the rotating components  11 ,  12 ,  21 ,  41  again are all operated on a common shaft W because any transfer losses are thus avoided. It is shown in  FIG. 3  that the generator  11  and the steam turbine  12 , as well as the compressors  21  and  41  of the heat pump and refrigerating machine, are arranged on a common shaft W. 
         [0040]    A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).