MIT researchers say a hybrid solar-thermoelectric system they’re working on would provide a big advantage over conventional solar cells or solar thermal systems, particularly for household use: the ability to produce heat and electricity simultaneously. They propose accomplishing this mean feat through a clever reconfiguration of the standard parabolic trough.
In a typical parabolic system (like the one pictured below), a curved mirror reflects sunlight onto a liquid-filled tube, and the hot water produced in that tube is used either to drive a turbine to produce power, or for heat for industrial uses or space heating. The MIT team – Professor Evelyn Wang and grad student Nenad Miljkovic – is working on hybridizing the system to do both at once by modifing that tube with a series of concentric tubes within it.
Their first tube-within-the-tube would contain the thermoelectric material, which would take advantage of a temperature gradient to produce power. This thermoelectric system would have pretty low efficiency, the researchers say – but that’s OK, because homes generally don’t need too much electricity. They need some, but they need a lot more heat – and the MIT design produces that by using an even narrower tube at the center of their device containing what’s called a thermosiphon. This is a device that “draws heat away from the ‘cold’ part of a thermoelectric system,” according to MIT, “passively transferring heat from the thermoelectric cold side and alleviating the need to pump cooling fluid as in a conventional parabolic-trough system.”
The heat carried away by the thermosiphon could then be used to heat water for, well, hot water, but also space heating and industrial processes.
Abraham Kribus, a professor of mechanical engineering at Tel Aviv University in Israel who was not involved in this research, told MIT that in their paper on their work, Wang and Miljkovic describe a “a fresh approach to solar energy conversion” but that some questions remain – as would be expected. “This is the situation at early stage with every nonconventional idea,” Kribus said. “Overall, the paper shows a nice start and a very capable team behind it.”