camelot-forum.co.uk

(nowtyexperiment for searching)
I was on the phone yesterday with a fellow Camelot’ier and I was chastised for using my heatpump for a couple of hours early morning to keep the chill off the house for when I get up. The conversation went somewhere along the lines of,

You run your heating at this time of the year ?, your adding extra heat to the planet.

No, I run my heatpump from my batteries, solely charged from my solar, there was no fossil fuel import.

Your still heating your house and the planet !

No, I am transferring heat via a heatpump so I am cooling the planet and transferring the heat to my house.

But it still requires energy to run the heatpump.

Yes, but the energy I’ve used in charging the batteries would have otherwise heated the planet anyway as the Solar Panel would have run slightly cooler as it was transferring circa 18% of the sun’s energy from the solar panel to the battery.

Then there was an argument about, that’s just photons and temperature is from infra red, etc, etc. Anyway, I was pretty much convinced about my belief that disconnected solar panels run hotter. So I did some googling and could not find anything, so today I conducted a Nowty Towers experiment.

I have the results, but I will refrain from publishing them for a few hours as I would like to know peoples gut feeling or empirical knowledge on this.

So, in full sun, with identical panels and same orientation, what do you think the answer will be ?

1) Both panels are the same temperature,
2) The disconnected one with no current flow is cooler.
3) The disconnected one with no current flow is hotter.

3

I'll admit I have no real idea, so just a fun guess, that the one with a leccy flow will be hotter, since (and don't laugh at me) wires running a current get warmer?

So my wild guess is 2.

But ........ covering my bases here, I can't get my head around the issue of removing some of the sun's energy, does it matter that the heat may be infra-red, and the PV uses ultra violet? So the PV panels in use aren't cooler, but less likely to get skin cancer?

I may have lost the plot!

I choose 2 and really like the almost Pythonesqe quality of the question. European migrating swallow and a coconut anyone? Love it!

3

I’d guess 2 but it is probably marginal.

Worth an experiment surely?

Conservation of energy, init?

If you're taking energy out of the panel how can that increase its temperature if the energy input (sunlight) doesn't change? Sounds like a perpetual motion machine in the making...


Is the 18% figure for the total light input (i.e. including IR & UV) or just visible light? I'd guess that the visible light is a small part of the whole energy in sunlight so 18% of that may only make a very small difference to the temperature. I guess you could work out total energy input from the temperature rise if you knew mass, specific heat capacity, time and how much it re-radiates, loses to convection... - i.e. you probably couldn't work it out!

Stig wrote: ↑Thu Sep 16, 2021 3:39 pm Conservation of energy, init?

If you're taking energy out of the panel how can that increase its temperature if the energy input (sunlight) doesn't change? Sounds like a perpetual motion machine in the making...


Is the 18% figure for the total light input (i.e. including IR & UV) or just visible light? I'd guess that the visible light is a small part of the whole energy in sunlight so 18% of that may only make a very small difference to the temperature. I guess you could work out total energy input from the temperature rise if you knew mass, specific heat capacity, time and how much it re-radiates, loses to convection... - i.e. you probably couldn't work it out!

Stig, sounds like your sitting on the fence, please at least guess. 1, 2, or 3.

I would guess 1, as I don't think a significant proportion of the total incomung energy gets turned into electrons...
A

3, but only just.