About this blog

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Wales, United Kingdom
In autumn 2010, my husband Ian and I both quit our jobs, sold our house and left the flatlands of the east for the mountains of Wales. Our goal is to create a more self-sufficient lifestyle in a place we actually like living. Whilst Ian will continue to earn some money as a freelancer, my part of the project is to reduce how much we spend by growing and making as much of what we need as possible. The purpose of this blog is to keep friends updated with how the grand project is progressing, but all are welcome here. If you're not a friend already, well perhaps you might become one.

Saturday, 24 May 2014

Solar panels - planning and preparation

This is the biggie; this is the project I've been meaning to do for the last three years or so but haven't actually quite got down to doing. This was always part of the heating project grand plan and the thermal store (big water tank) was made with an extra coil to take the water from the solar panels when they were in place. We've probably had our heating operating below its capacity for the last three winters due to that empty coil.

Being me, we're not talking about a simple matter of buying solar panels and getting them installed, or even installing them myself. Oh no, I'm proposing to make them. Household radiators are usually filled with hot water and radiate the heat out into a room, but they'll work pretty well the other way round too. If filled with cold water and placed in sunlight, the water will heat up. This isn't a new idea, it made it into the Telegraph over a decade ago*. They obviously won't be as efficient as manufactured panels but they are a great deal cheaper, and the efficiency difference isn't as huge as you might expect.

I dithered over the project for some time because I was worried about constructing a roof that would support it. We have a south-facing gable end to this house, and I thought the obvious place for solar panels would be a lean-to roof against this wall, under which we'd store wood. However, a full radiator is very heavy and I doubted my ability to build a structure that would support several of them. Then one day my friend Gill asked if we had any plans for using the area above the conservatory.

Odd bit of hillside that's not much use for anything

I can't remember whether Gill suggested it or whether I thought of it myself, but that's a potential site for solar panels. It's east facing, not south, but that's not such a drawback as it might be. We have hillside and trees to the west of this property, so even the south facing wall gets shaded by about 4pm, and this spot gets shaded only about an hour earlier in the day. On the other hand, it gets the morning sun much earlier, even with the roof to the east. It's higher than the tank, so I wouldn't be able to use the thermosyphon system I'd been thinking of, but between this spot and the tank there's only one wall of the extension, as opposed to the three two foot thick walls I'd have to drill through to get to the other site. Also, being on the ground, this is much more accessible. On balance, this seems like a much better site than the other one, and avoids the danger of the whole construction collapsing due to my inadequate construction skills.

OK, so... DIY solar panels... what do I need? Radiators, obviously.

Radiators - check.

A sheet of glass over the top will improve the effectiveness considerably - the original greenhouse effect. I have acquired a selection of windows, from Gill's old house...

... and from Jasper's old caravan.

Glass - check

They'll need some kind of box to contain them. Um, what have I got? I have some floorboards...

... and a sheet of plywood that used to be the back of a wardrobe.

Wood for a box - sort-of check

Insulation behind the radiator would be a good idea, too, so the heat doesn't radiate straight into the ground.

Bags of insulation

My friend Ellie gave me some of that reflective stuff that goes behind radiators

and here's some insulation that's also shiny.
Yes, I think I can check the insulation box.

I'll obviously need pipes to plumb this all in, and I have some of those left over from the old central heating, too.

Copper pipes - check

And then because this won't be the thermosyphon system I originally wanted, I'll need a pump. Ah, hm, yes. I'll tell you about the pump in another post.


* I don't know whether the author has revised his views on global warming in the last ten years.


  1. I can't wait to see how this project progresses. For years I've had a dream about building a solar space heater. It's essentially a big box that collects hot air. You mount it on the south side of the house with an input on the bottom and an outflow into the house on the top and it uses convection currents to circulate the air. I'm just afraid of drilling holes into the house because then I'm really committed. Or perhaps I should be committed! :-) Anyhow, I might try to construct something that's mounted between the upstairs and garden level windows and uses the windows as the vents, that way I don't have to deal with the issue of holes.

    But enough about my crazy idea, I can't wait to see how this works out! And I'm so glad you posted pictures of the radiators... in my world a radiator is something that goes in a car so I was having a really hard time picturing how it could work!

    So my one thought... this may not be true in your part of the world, but here, most windows (anything made in the past 20 years or so) are constructed with low-e glass - in other words it has a metal oxide coating to reduce heat transfer. I'm not sure how you can tell the difference, but if you're using old windows you'd want to be sure that you're not getting low-e glass because that would throw a wrench in the whole deal!

    I also have a question about permits and regulations. I really wanted to get a solar hot water heater a while back, but our state requires the connections on any solar water heating project to be welded rather than braised. I don't know enough about that sort of thing to really understand the difference. But in practical terms it made the installation costs astronomical and turned what should be a money saving project into something where you'd never be able to recoup your investment. Do you have any of those sorts of issues to deal with?

    1. I also thought about a similar solar space heater, but was similarly put off by drilling holes in the wall, mainly because the wall in question is two foot thick. Also, I reminded myself sharply that I'm supposed to be focusing on the water heating project.

      I haven't heard of low-e glass. Double and triple glazing are more of a thing here - we're more concerned with keeping heat in than with reflecting it out. Bearing in mind that domestic air conditioning is almost unknown in this country (in cars, yes... in shops, yes... in hotels, yes, but not in houses) I think it's fairly unlikely that I have low-e glass, especially as I think both sets of windows are over 20 years old. But thanks for the thought.

      I've come across advice that solar water heaters should be connected with compression joints instead of solder, for fear of overheating. I guess that's the same concern that's addressed by the regulations for welding instead of braising. I've considered whether that should be a concern for my system, and decided on a low tech solution to the problem of overheating, should it arise. It's a solution that requires human intervention, so it wouldn't meet regulations (which always have to be idiot proof) if there are any. I haven't checked ... OK curiosity got the better of me and I had a quick look just now. In one fairly decent-looking set of guidance notes the only relevant point was that materials and workmanship should be fit for purpose. The work should also be carried out by a competent person. Hmm.

    2. And by the way, what kind of central heating do you have in your neck of the woods? I've learnt that American homes have furnaces instead of boilers, and now you tell me that you don't have radiators. How is the heat distributed around the house? Is it ducted hot air?

    3. Sounds like you should be safe in terms of the glass, and now you've totally got me curious about building regulations there. Here, if you're gonna do any meaningful project you have to pull a permit from the city and an inspector has to come out and make sure everything you've done is up to code. I've flown under the radar with a few DIY projects, so hopefully there won't be any issues if I ever decide to sell the house!

      Anyhow, here in Colorado most homes including mine have gas forced air heating with air ducts into each room. There are some older buildings - like the music school where I used to work, that have steam heat which uses radiators, but they don't look anything like the ones in your picture. The older ones are usually big cast iron things like this:

      And the newer ones usually run along the baseboard like this:

      Some parts of the country (usually back east and up north) they use "heating oil" but I'm not really sure how those systems work - don't know if the oil is used to heat water or air or what.

      I've often thought that one of those systems with water running under the floor like you installed would be the way to go. Just the thought of having warm floors in the winter time sounds wonderful! But I wonder how water based systems work in the summer. Do you just shut off the boiler? Seems like you'd have to or else you'd have a big tank of hot water radiating heat into an already overheated space. In the music school we had three giant boilers in the basement - and for some reason we had to let them run all summer so the room next to them was like an OVEN!

    4. What to do with a tank full of hot water in the summer? Insulate it! Ours has about five inches of insulation sprayed on at manufacture (at least, I assume it's sprayed) and that's pretty effective. This is only necessary if the system needs a body of water to supply hot water to the taps (faucets); for other systems it can be turned off. One common, modern design is known as a 'combi' boiler. It heats water for both radiators and taps on demand, so there's no stored hot water at all. I've had them in three houses, and I don't think they're very durable.

      I recognize those big old cast iron radiators, we used to have them in the school I went to as a child. I remember sitting on the pipes warming my hands on them in the winter.

      Round here, "heating oil" means oil that is burned to heat water. It's used in rural areas that don't have mains gas (the usual fuel for heating) and is delivered to large tanks in the garden. That said, we do have a small, freestanding radiator that's filled with oil and heated by an electric element. I'm not sure why it's filled with oil instead of water - maybe corrosion issues.

      Building regs are much the same here, except that perhaps the list of minor, non-notifiable projects may be a bit longer. If you're really curious have a look at this government website, which has lots of information on both planning and building regulations. There's a certain degree of bias evident in this website, e.g. "should" does not necessarily mean "must".

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