$/watt Cost Of Vaccum Tube Solar Collectors

Q: Does anyone have a figure for how much vaccum tube solar collectors cost relative to their output, say in full sun? Thanks, I see. Does anyone know their cost per unit area then? I was thinking whether it would be possible to use these for a solar A/C by driving an absorption chiller, or whether it would be better to use PV panels connected to a conventional chiller.

A: A pure "$/Watt" figure (or just Watts) is problematical for thermal systems because there's nothing "pure" about it - to give the maximum watts out, you heat vast amounts of water (or air, or other working fluid) a very low temperature rise (1/2 a degree F or so), and that gives the most possible Watts out. It's also pretty useless, but it's still perfectly valid Watts. Do it for an hour and it's some number of Watt*hours. As your temperature rise goes up, and the difference between ambient and the collector output goes up, your effienecy (and thus the Watts out) goes down, even though the heat gained is now more useful. At the opposite end of the spectrum, you get no heat out (no Watts) with no flow and the highest possible temperature. So "Watts out in full sun" depends greatly on what temperature rise you are seeking. It is a function of the whole system, not just the collector and the sun. I have seen many posts in this and other places that would have you reconsider using the rankin cycle A/C systems unless you purchase a turnkey gas system. To try to run one with a non standard source of heat is to open a can of worms you may regret. According to input from those experienced in that area, they are fraut with problems even in the production models.

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