Normally, power tower CSP heats molten salts by aiming concentrated sunlight up to a receiver on a tower that has molten salts flowing through pipes in the receiver to be heated and sent down the tower to store the sun’s energy as heat in a hot tank below.
A 2021 paper Dispatchable solar power using molten salt directly irradiated from above describes the first on-sun outdoors trial of such a setup at a scale of 600 kWh at the Khalifa University Masdar Institute Solar Platform testing site. A bath of molten salts sits on the ground, and concentrated sunlight is beamed up to an inverted mirror above the tank, and then reflected down into the molten salts bath on the ground.
This reversed setup which combines collection and storage has many thermal efficiency advantages. It is much more convenient to install and maintain and operate because the receiver is not at the top of 140 meter high tower; it’s on the ground.
“You save all the pumping energy. You don’t have to move the salt to the top of a tower, because instead of moving the salt, you move the light,” commented Dr. Nicolas Calvet, lead author of the study.