A flexible coal-fired power generation system includes a thermal system for coal-fired power generating unit and a high-temperature heat storage system connected in parallel, wherein: the heat storage system includes a heat storage medium pump (17), a cold heat storage medium tank (18), a hot heat storage medium tank (20), multiple valves, and a heat storage medium and feedwater heat exchanger (21). A heat storage medium heater (16) locates in the boiler (1) and is connected with both the cold heat storage medium tank (18) and the hot heat storage medium tank (20). Through the heat storage medium pump (17), the flow of heat storage medium that enters the heat storage medium heater (16) is adjusted to reduce the output of the steam turbine when the boiler (1) is stably burning.

A flexible coal-fired power generation system includes a thermal system for coal-fired power generating unit and a high-temperature heat storage system connected in parallel, wherein: the heat storage system includes a heat storage medium pump (17), a cold heat storage medium tank (18), a hot heat storage medium tank (20), multiple valves, and a heat storage medium and feedwater heat exchanger (21). A heat storage medium heater (16) locates in the boiler (1) and is connected with both the cold heat storage medium tank (18) and the hot heat storage medium tank (20). Through the heat storage medium pump (17), the flow of heat storage medium that enters the heat storage medium heater (16) is adjusted to reduce the output of the steam turbine when the boiler (1) is stably burning.

A system for readying sub-critical and super-critical steam generator, a servicing method of the sub-critical and the super-critical steam generator and a method of operation of sub-critical and super-critical steam generator is provided. The steam generator includes a first auxiliary heating device disposed on at least one water-steam separator for heating the at least one water-steam separator, and/or a second auxiliary heating device disposed at least on a part of furnace top-end piping for heating the furnace top-end piping. The auxiliary heating devices are heating steam producing components of the steam generator and thus allowing to keep them above the temperature in which materials creating the steam producing components are brittle. The method includes recirculation of the water through the steam generator.

A system for readying sub-critical and super-critical steam generator, a servicing method of the sub-critical and the super-critical steam generator and a method of operation of sub-critical and super-critical steam generator is provided. The steam generator includes a first auxiliary heating device disposed on at least one water-steam separator for heating the at least one water-steam separator, and/or a second auxiliary heating device disposed at least on a part of furnace top-end piping for heating the furnace top-end piping. The auxiliary heating devices are heating steam producing components of the steam generator and thus allowing to keep them above the temperature in which materials creating the steam producing components are brittle. The method includes recirculation of the water through the steam generator.

A CHP system includes a combustor (heat source), a Rankine cycle apparatus, and a second heat exchanger. The Rankine cycle apparatus includes, as an evaporator, a first heat exchanger that absorbs thermal energy produced in the combustor. The second heat exchanger is located closer to the combustor than is the evaporator, absorbs thermal energy produced in the combustor, and transfers the thermal energy to a heat medium.

A system for readying sub-critical and super-critical steam generator, a servicing method of the sub-critical and the super-critical steam generator and a method of operation of sub-critical and super-critical steam generator is provided. The steam generator includes a first auxiliary heating device disposed on at least one water-steam separator for heating the at least one water-steam separator, and/or a second auxiliary heating device disposed at least on a part of furnace top-end piping for heating the furnace top-end piping. The auxiliary heating devices are heating steam producing components of the steam generator and thus allowing to keep them above the temperature in which materials creating the steam producing components are brittle. The method includes recirculation of the water through the steam generator.

A back-up boiler system for a solar thermal power plant (201) for transferring solar energy into electricity, said back-up boiler system comprising a combustion chamber (70) and a convection section (80) in fluid connection with said combustion chamber (70), wherein in the convection section (80) at least a first heat exchanger (92) is provided for heating a molten salts mixture of the solar thermal power plant and a second heat exchanger (90) for pre-heating boiler feed water of the solar thermal power plant, wherein the back-up boiler system (25) is configured to allow selection between only providing heat to the first heat exchanger (92), only providing heat to the second heat exchanger (90) and providing heat to both heat exchangers (90, 92), preferably dependent on availability of solar radiation and/or dependent on demand of power generation. The invention also relates to a solar thermal power plant (201) for transferring solar energy into electricity and a method for operating a solar thermal power plant.