This is a concept I never fully understood. My father even sold all kinds of renewables for ~5 years until 2016, and he just said “Thermal just isn’t worth it” but never really explained how or why. And even now when all Europe is under a strong pressure into deciding how to heat our homes this winter, it seems that no one is still considering thermal solar as a solution.
Heck some governments even decided that it was better to propose PV + Heat Pumps instead of Solar heating
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Why?
In: 4
You mention heating homes in a European winter. Thermal solar works by using sunlight to heat up some material (usually a liquid), and then using the heat in that material. A problem is that heat can leak from this material back into the cold environment.
Photovoltaic systems work by using a photon to “bump” an electron out of place on one side of a solar cell, and then as the electron is forced to trickle the long way around to get back to the other side of the cell, we can extract energy from it. It doesn’t rely on a temperature difference, and indeed ordinary silicon PV cells are more efficient when they’re cold.
So thermal solar works best, paradoxically, when the environment is not particularly cold. Until recently, solar thermal domestic hot water systems were more popular in Australia than a lot of other places, partly for this reason. As other commenters have mentioned, economies of scale have now made PV cheaper, but have not had much effect on solar thermal. So for new installs PV plus heat pump is now attractively priced, whereas solar thermal systems cost as much as they always have.
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