[hnaccount_rng]

In addition to my sibling comment: The cost of the panels is a rather small fraction of the total cost of a typical installation. Most of that cost ist labor, some regulatory requirements and the inverter. Whether you pay a factor of 2 for the panels or not typically doesn't matter. In other words: Reusing used panels will only ever be able to safe you a minuscule amount.

[pfdietz]

The low cost of the modules themselves has led to the suggestion of cost optimized DC-coupled PV systems being used to directly drive resistive heaters. The cost per unit of thermal energy in a cost optimized system moderate scale system (> residential, < utility scale) may be in the range of $3-5/GJ, very competitive with natural gas. Low cost maximum power point trackers would be useful; inverters would not be needed.

Low cost modules allow one to do away with things like optimally tilted modules and single axis tracking. The modules can also be tightly packed, reducing mounting and wiring costs.

[maxerickson]

What's the proposed system design? For example, in January, I get about 9 hours of sunlight and have an average daily high of 25 F. I'm gonna need to store heat somehow or another.

[jopsen]

I've heard of farmers doing this, well I think they actually had an inverter. But limits on how much they could dump into the grid, meant that they had lots of surplus electricity and installing resistive heating was very cheap.

Even if they don't have surplus electricity all the time.

[alvah]

Is it worth using heat pumps in this setup (in addition to resistive elements)? I understand they can't reach the absolute temperature of resistive heating, but from an efficiency POV for the first few tens of degrees they are much more efficient.

[ericd]

Yeah, we paid more for the little bits of metal that held up the panels than for the panels themselves (aluminum, but still).

[dzhiurgis]

IDK sounds like you got ripped off. I diy'd and panels were cheap of course, but fittings were perhaps 3-5x cheaper. Inverter is typically same as your panels (hybrid, grid-tied are quite a bit cheaper).

[hinkley]

These days it’s a stack of microinverters. Which are not cheaper but do improve array efficiency outside of idea conditions. But that’s another up front cost.

[dzhiurgis]

They are still pretty unpopular. Solves niche problem (small roof, shade) for a quite a bit more money.