Does anyone know a reliable source of data for winter month's average insolation by any chance?
I am idly wondering about warming up water for heating using solar thermal panels rather than PV panels. Is it at all a doable thing?
Thanks.
MIDAS has chapter and verse by the hour if you want it.
Direct Diffuse Jan 70 40 Mar 180 130 April 170 165 June 225 250 July 185 265 Sept 205 145 Oct 155 95 Dec 70 35
Monthly in MJ/m^2 based on data from Kew 1958-68
Assumed optimum slope and S facing. Optimum roof slope for maximum annual direct yield is between 30 (1800) and 45 degrees (1735). The diffuse radiation capture is about the same.
You lose direct power capture proportional to cos(misallignment).
It is still a very decent book on the subject even though things have changed a bit since it was written thermodynamics remain the same.
It might be if you have the expensive concentrator ones rather than flat panel collectors. Only snag is needing a good antifreeze in the loop.
Cheers!
Yes. Even on an overcast day in winter, those panels will provide useful heat for a h/w cylinder with dual coils and plenty of insulation.
Do the maths though. Unless you can DIY it, the payback time could be lengthy, but if we are entering an extended period of very high energy costs .....
I've been idly wondering about this for years. I have a 7m x 4m flat roof garage with unobstructed views of the southern sun. My plan was based in lazy thinking and ignorance: radiator panels painted black, housed in glass fronted boxes. My next thought was that if that didn't provide much of a supply of warm water, then a large tank with a heat pump.
A single 2m x 1m thermal panel (in Cambs) provided enough heat in the spring/summer/autumn, and lukewarm to low heat in the winter. We still got heat on cloudy days, it was just a bit less. 7x4m would be massively oversized unless you're heating a swimming pool.
You could put up a single thermal panel surrounded by PV. But an alternative plan would be to go PV and then divert into an immersion heater when not in use for something else.
PV is fairly straightforward to install: put some of these console buckets on the roof:
If you're doing solar thermal you need a hot water cylinder with a suitable coil, a pump, some controls and a piping loop of glycol. That's more faff to install, and more to keep maintained.
Theo
There used to be a place in wales called the Centre for Alternative Technology, or something. Probably a Greenie paradise, but a cousin went there to see what they were doing about 25 years ago and came away with the firm conclusion that solar PV did not 'work' in the UK, but it was quiet easy to make your own solar water heating systems even back then and they did 'work'.
Back then PV panels were 200 Wp, now they're 400 Wp. They were also a lot more expensive. They 'worked', but economically didn't make sense. Now they do, in certain conditions.
Meanwhile the efficiency and economics of solar thermal haven't changed nearly so much in that time.
Theo
I have that book as well as the even more interesting US Portola Institute one (and McVeighs that I already mentioned). All are well worth a read before you embark on any kind of DIY solar power venture.
I'd borrow it from the library instead if it was >£20. Not worth £100!
McVeighs has some pretty advance stuff on early designs of non-focussing solar concentrators (borne of HEP photon collector designs).
Problem to watch with thermal solar is freezing in winter and potential stagnation and boiling in summer. One trick that works well is a flat panel for bulk energy capture and one of the rather smarter concentrator designs (just about DIYable if you are cunning) to boost the temperature to a useful level in winter. It doesn't have to be all that big to work although ironically they are not as subsidised as solar PV. The bizarre thing is that many domestic PV arrays have a diverter to turn their electricity into hot water (exploiting a loophole in the FIT rules).
You probably want it steeper than optimal total power capture for better winter power output and to avoid overheating in summer.
Solar cells have improved efficiency quite a bit since that era but they are still much better off deployed in sunnier climes than ours.
I wouldn't really be interested in PV as I'm looking for simple and cheap as possible. PV maybe in future, but one step at a time.
I see, thank you.
Set in a gorgeous location.
Thanks again Martin! I shall order a copy!
PV *is* simpler and cheaper.
[ Renusol bucket £60 PV panel £130-180 for 330-400Wp Connectors £5 Two bags of aggregate £6 (ballast from Wickes) ] multiplied by as many panels as you have (each panel roughly 2x1m)Inverter £100-400 depending on size (<3kW for simpler G98 paperwork) AC isolation switch £30 DC isolation switch £30 Switched FCU to tee into existing circuit £10 Reel of PV cable £40
Prices ex VAT from
Plonk the buckets on your roof, screw the inverter to the wall in the garage, wire it up (or pay sparky to do it). Send in the G98 form to your DNO, turn it on.
If that's too hard, these folks will sell you a kit:
With solar thermal I suppose you *can* make a DIY system out of cotton reels and bacofoil, but you'll spend forever tweaking it and chasing leaks. PV is a lot less invasive compared with replacing your cylinder with one with a PV coil - unless you're going to DIY your tank too. A DIY system might work on a rural property with plenty of space and resources for tinkering, but most UK homes are relatively constrained and so you have to use commercial products to fit within the space and planning limitations.
Theo
Panels of that sort are used as first stage heating in solarthermal setups. They're not good performers but are cheap. Ideally follow it up with better flat panels, then top your heat off with glass tubes with reflectors.
Oh, don't forget winter freeze. The options are to drain the thing down each winter, or drainback, or antifreeze & heat exchanger.
A basic rule of thumb with thermal is that the higher the stagnation temp, the higher the collector cost. Hence best results are had with cheap low performance panels followed by better ones rather than using all one type.
The commercial offerings I've seen drained it down every night, maybe that was just the vacuum tube version?
How long would those panels be expected to last?
Cheers.
All quite interesting Theo as I've just had my power bill at the new rate for a few days its shocked me into looking into this!
Problem is as i see it the apex of the house runs on a North South axis so one roof facing due east the other due west not ideal but..
Got a flat garage roof some 5.5 meters square reluctant to interfere with the new EPDM roof there but..
Is it worth doing overall seeing that the price of power is now an arm and two bloody legs!!..
The idea of the "bucket" mounting is that you don't need to alter the roof in any way, it just sits on top of it and is weighted down with bricks, sand, whatever ...
"On top of that they come with an extensive 25 year product warranty (on the all black versions) and 30 year performance warranty. Annual degradation is far lower than P-type modules, with output expected to be over 87% after 30 years!"
Theo
East/west is fine, the calcs come out only marginally worse than south. You can compensate for a reduced output by fitting more panels. It timeshifts the output towards morning/evening, which may or may not be advantageous.
Ignore the money side, just look at the kWh:
EPDM is pretty tough. The point load calculations for the buckets (loaded with ballast) are likely to be a lot less than the EPDM can cope with, although you'd need to make sure it's clean (no grit underneath to concentrate the loading). If in doubt, put something underneath to spread the load. The buckets aren't fastened to the roof in any way.
The main question is: do you or can you use electricity at times of high solar output? For some people yes (eg EV charging), for others their electricity load is highest when it's not sunny (eg tumble dryer, when they would dry outside on a sunny day), or in the winter (heating).
Theo
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