I believe so :)
Min temp a panel heats is mains cold water temp, maybe 5C in winter. In an ideal world one would optimise a system by using flat panel to raise cool w ater temp, then vac tubes to get it hot. In a large system this maximises r eturn. In a small system the cost of a 2nd pump, piping, control etc isnt n ecessarily justified.
NT
Thats answered my questions, Thanks to all, for the info and calculations
Moonlight will generate almost the full voltage, although limited to just enough current to electrocute someone.
Tubed panels aren't any worse than flat panels once you have a reflector behind the tubes. In the winter you really need tubed panels to get much heat.
NT
The main thing that flat plate excels at is a small temperature rise which is damn all use for hot water or heating bulk space unless you have designed in huge low temperature difference fan assisted radiators.
Vacuum tube designs have the merit of producing water that is usefully hot when the sun is actually shining even in winter.
Since you are generally dealing with weak or diffuse sunlight in winter and not very much of it you ideally want non focusing flux concentrator designs rather than simple half cylinder mirrors.
The simplest of these is a part parabola with the focus of one side at the base of the other. Every ray entering the aperture will hit the back plate collector in finite time. Real ones can be optimised a bit more to take account of the shape of the pipe.
Another is a sort of spiral these designs have never really caught on.
You can double the output of a PV array by surrounding it with mirrors as a crude variant of this game (though the plastic bits may cook).
sun |||||| \||||/ \__/ 60
All lengths the same. Mirrors are cheap PV cells are not. Light incident on the mirrors hits the PV array after reflection. Mainly of interest for portable solar chargers.
When hot water is heated, it starts stone cold, and progresses up to piping hot. Flat plate work better at the cold to warm region, tubes work better in the warm to hot region. Hence the upside of using both together with 2 water zones, one hot one warm.
Yes, the same trick can be done with flat plate too, if not quite so easily.
Yes, so long as you get even lighting on the PV. What the higher temp does to panel life I don't know.
NT
I have tubes, with a compound reflector behind them, I can see no reason why a flat plate of the same area would work any better. I can see several reasons why flat panels wouldn't work as well.
t makes me wonder what panels were being compared and what assumptions were made.
But then you always were rather dense.
Assuming the same grade of absorber with efficiency 1-a (a were made.
That the mirrors are not perfect ones - which is *very* true.
A typical production mirror scatters or absorbs about 8% of the incident light where as a decent matt black paint scatters less the 4%.
The concentrators allow you to trade some minor loss of efficiency for a much higher output temperature which is usually worth it.
There are additional losses off the air-glass surfaces of the front cover plate as well but they are common to both designs.
Well, it was addressed further upthread and explained on the link given. Its not just energy out over energy in, its also financial efficiency, ie power out per pound in. That's a prime issue for system choice.
IRL flat plate is far lower due to losses, in fact its normal for them to work all the way down to 0% as they approach their stagnation temp. But as the graph illustrates, at low temps they beat tubes on efficiency, at high temps tubes win.
NT
In message , A snipped-for-privacy@anonymous.invalid writes
But scientists have come up with a new way to combat global warming caused by excessive CO2 emissions by shooting salt crystals into the atmosphere to create more cloud to reflect the suns heat back into space thereby screwing solar panels even further - and causing us to fall back on gas power stations which in turn will pump more CO2 into... Ah!!
Grow firewood trees in your garden and buy a wood stove. You can collect a lot of firewood for free if in a rural area.
Is that a peasant's right? What does the Lord of the Manor require in return?
Generally it's theft. But I've not noticed anyone complaining. I would advise against carrying a chainsaw, however.
A nominal 4kW array in Yorkshire can produce 25ish kWh on a good day in mid summer. Around Christmas it struggles to make 1kWh Forget the idea or as others have said it can contribute to heat water/aircon to cool in summer.
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