> Heat has generally been successfully extracted from the lower convective zone (LCZ) of solar ponds by two main methods. In the first, hot brine from the LCZ is circulated through an external heat exchanger, as tested and demonstrated in El Paso and elsewhere. In the second method, a heat transfer fluid circulates in a closed cycle through an in-pond heat exchanger, as used in the Pyramid Hill solar pond, in Victoria, Australia.
They use the hot brine to vaporize a motive fluid such as liquid pentane in the heat exchanger, when the liquid is converted to gas it creates a high pressure environment and is piped into a turbine which spins the generator. Then they condense the motive fluid back to a liquid so they can vaporize it again. It's the same way binary geothermal power works, with the Organic Rankine Cycle.
>This means that the temperature at the bottom of the pond will rise to over 90 °C while the temperature at the top of the pond is usually around 30 °C.
Can that really be right, it seems like a very high gradient.
Water has quite low thermal conductivity (~0.6 W/(m*K)). If you exclude convection you can easily have such a temperature difference. For example with heat flux of 100 W/m2 you have 60 K temperature difference over a 36 cm thick layer of water.
http://www.sciencedirect.com/science/article/pii/S0038092X10...
> Heat has generally been successfully extracted from the lower convective zone (LCZ) of solar ponds by two main methods. In the first, hot brine from the LCZ is circulated through an external heat exchanger, as tested and demonstrated in El Paso and elsewhere. In the second method, a heat transfer fluid circulates in a closed cycle through an in-pond heat exchanger, as used in the Pyramid Hill solar pond, in Victoria, Australia.