Dispatchable storage combined cycle power plants

1. A method of operating a combined cycle electric power plant, the method comprising:

operating a combustion turbine generator to generate electricity and produce hot exhaust gases;

storing heat from a heat source other than the combustion turbine generator in a thermal energy storage system at a temperature T1;

in a first mode of operation:

producing steam in a first boiler by heating feedwater with heat supplied at temperature T1 from the thermal energy storage system by a heat transfer fluid, thereby cooling the heat transfer fluid, and storing heat from the cooled heat transfer fluid in the thermal energy storage system at a temperature T2<T1;

heating the steam from the first boiler with heat from the combustion turbine exhaust gases to produce superheated steam at pressure P1; and

expanding the superheated steam at pressure P1 through a steam turbine generator to generate electricity;

and in a second mode of operation, after depleting the thermal energy storage system of heat stored at temperature T1:

producing steam in the first boiler by heating feedwater with heat supplied from the thermal energy storage system at a temperature of T2 or less by the heat transfer fluid;

heating the steam from the first boiler with heat from the combustion turbine exhaust gases to produce superheated steam at pressure P2<P1; and

expanding the superheated steam at pressure P2 through the steam turbine generator to generate electricity.

2. The method of claim 1 , wherein the pressure P1 and the pressure P2 are each controlled by a rate at which heat is supplied from the thermal energy storage system to the first boiler.

3. The method of claim 2 , comprising controlling a heat transfer fluid flow rate to control the rate at which heat is supplied from the thermal energy storage system to the first boiler.

4. The method of claim 1 comprising, in both the first mode of operation and the second mode of operation, preheating the feedwater with heat from the combustion turbine exhaust gases.

5. The method of claim 1 comprising:

in the first mode of operation:

producing steam in a second boiler operated in parallel with the first boiler by heating feedwater with heat from the combustion turbine exhaust gases;

mixing the steam from the first boiler with the steam from the second boiler; and

heating the mixture of steam from the first boiler and steam from the second boiler with heat from the combustion turbine exhaust gases to produce the superheated steam at pressure P1;

and in the second mode of operation:

producing steam in the second boiler operated in parallel with the first boiler by heating feedwater with heat from the combustion turbine exhaust gases;

mixing the steam from the first boiler with the steam from the second boiler; and

heating the mixture of steam from the first boiler and steam from the second boiler with heat from the combustion turbine exhaust gases to produce the superheated steam at pressure P2.

6. The method of claim 5 , wherein in the first and second modes of operation the first boiler produces steam using heat exclusively from the thermal energy storage system and the second boiler produces steam using heat exclusively from the combustion turbine exhaust gases.

7. The method of claim 1 , comprising:

in a third mode of operation:

supplying heat from the heat source to the first boiler at the temperature T1, without first storing the heat in the thermal energy storage system, to produce steam by heating feedwater with the heat supplied at temperature T1;

heating the steam from the first boiler with heat from the combustion turbine exhaust gases to produce superheated steam at pressure P1; and

expanding the superheated steam at pressure P1 through the steam turbine generator to generate electricity.

8. The method of claim 7 , comprising in the third mode of operation preheating the feedwater with heat from the combustion turbine exhaust gases.

9. The method of claim 7 , comprising in the third mode of operation:

producing steam in a second boiler operated in parallel with the first boiler by heating feedwater with heat from the combustion turbine exhaust gases;

mixing the steam from the first boiler with the steam from the second boiler; and

heating the mixture of steam from the first boiler and steam from the second boiler with heat from the combustion turbine exhaust gases to produce the superheated steam at pressure P1.

10. The method of claim 9 , wherein in the third mode of operation the first boiler produces steam using heat exclusively from the heat source and the second boiler produces steam using heat exclusively from the combustion turbine exhaust gases.

11. The method of claim 1 , comprising:

in a fourth mode of operation:

producing steam by heating feedwater with heat from the combustion turbine exhaust gases and without using heat from the heat source or the thermal energy storage system;

heating the steam with heat from the combustion turbine exhaust gases and without using heat from the heat source or the thermal energy storage system to produce superheated steam at pressure P3<P1; and

expanding only the superheated steam at pressure P3, no other superheated steam, through the steam turbine generator to generate electricity.

12. The method of claim 1 , wherein the heat source collects solar energy as heat.

13. The method of claim 1 , wherein the heat source comprises an electric heater.

14. The method of claim 13 , comprising powering the electric heater with electricity generated with photovoltaic solar cells, with a solar thermal electric power plant, with a wind turbine, with a hydroelectric power plant, using nuclear power, by combusting a fossil fuel, or by a combination thereof.

15. The method of claim 1 , wherein storing the heat in the thermal energy storage system comprises storing the heat in a low vapor pressure heat transfer fluid at a pressure of about one atmosphere.

16. The method of claim 15 , wherein:

300° C.≤T1≤340° C.;

35 bar≤P1≤75 bar;

240° C.≤T2≤290° C.; and

15 bar≤P2≤55 bar.

17. The method of claim 1 , wherein storing the heat in the thermal energy storage system comprises storing the heat in a molten salt.

18. The method of claim 17 , wherein:

350° C.≤T1≤600° C.;

65 bar≤P1≤125 bar;

250° C.≤T2≤400° C.; and

30 bar≤P2≤90 bar.

19. The method of claim 1 , wherein storing the heat in the thermal energy storage system comprises storing the heat in a solid heat storage medium.

20. The method of claim 19 , wherein:

350° C.≤T1≤600° C.;

65 bar≤P1≤125 bar;

250° C.≤T2≤400° C.; and

30 bar≤P2≤90 bar.

21. The method of claim 1 , wherein:

300° C.≤T1≤600° C.;

35 bar≤P1≤125 bar;

240° C.≤T2≤400° C.; and

15 bar≤P2≤90 bar.

22. The method of claim 1 , comprising starting operation of the first boiler and the steam turbine generator using heat from the heat source, the thermal energy storage system, or the heat source and the thermal energy storage system before starting operation of the combustion turbine generator.