System for converting solar radiation into electricity
A system is provided for converting thermal energy derived from a solar field into electricity. The system is adapted to operate in accordance with at least two modes of operation, depending upon the thermal energy intake, and comprises: a first power generation sub-system comprising means to heat water into superheated steam by exchanging heat with a first heat transfer fluid being heated at the solar radiation collecting field, and a back pressure turbine for producing electricity; a second power generation sub-system comprising means to heat a second working fluid, and the second working fluid is used to operate a second turbine for producing electricity; and wherein the system is characterized in that when the thermal energy received at the first power generation sub-system exceeds a predetermined threshold of a selected criterion, both power generation sub-systems are operative to produce electricity and at least part of the heat required to heat the second working fluid is derived from exhaust steam being produced at the first power generation sub-system, whereas when the thermal energy received at the first power generation sub-system does not exceed that threshold, the thermal energy conveyed by the first heat transfer fluid is used essentially to heat the second working fluid and the electricity is generated only by the second power generation sub-system.
1. A system for converting thermal energy derived from a solar field into electricity and wherein said system is adapted to operate in accordance with at least two modes of operation, depending upon the thermal energy intake, and wherein said system comprising:
a first power generation sub-system comprising means to heat water into superheated steam by exchanging heat with a first heat transfer fluid being heated at said solar radiation collecting field, and a back pressure turbine for producing electricity;
a second power generation sub-system comprising means to heat a second working fluid, and wherein said second working fluid is used to operate a second turbine for producing electricity;
and wherein said system is characterized in that when the thermal energy received at said first power generation sub-system exceeds a predetermined threshold of a selected criterion, both power generation sub-systems are operative to produce electricity and at least part of the heat required to heat said second working fluid is derived from steam derived from said first power generation sub-system, whereas when the thermal energy received at said first power generation sub-system does not exceed said threshold, the thermal energy conveyed by said first heat transfer fluid is used essentially to heat said second working fluid and the electricity is generated only by said second power generation sub-system.
2. A system according to claim 1 , wherein said solar field comprises a plurality of heliostats or parabolic trough shaped solar tracking reflectors operative to concentrate incident solar radiation onto receivers each extending along a respective parabolic trough's focal line.
3. A system according to claim 1 , wherein when the thermal energy conveyed by said first heat transfer fluid exceeds said predetermined threshold, more than half of the total electricity production of the system is carried out by the first power generation block.
4. A system according to claim 1 , wherein said second power generation sub-system comprises an air-cooled condenser.
5. A system according to claim 1 , wherein said second working fluid is an ammonia-H 2 O mixture.
6. A system according to claim 1 , wherein said selected criterion is a member of the group consisting of: temperature of the heat transfer fluid leaving the solar field, rate of the heat transfer fluid leaving the solar field, incident solar radiation, type of the HTF and any combination thereof.
7. A system according to claim 1 , further comprising a storage means adapted to store at least part of the energy collected at the solar radiation collecting field from the incident solar radiation, and wherein said storage means is further adapted to enable the discharge of stored energy for the production of electricity by one or both of said power generation sub-systems.