Solar water heating

[fleetfootmike]

Solar water heating
Originally uploaded by fleetfootmike.

We've gone all green :)
On the roof of our music room is this little contraption - a panel of heat exchangers that do a very efficient job of converting light to heat, that then pre-heats the water coming into our tank.

We actually get a two-fold saving - first, because obviously it takes less heat to get the water up to a desirable temperature. More interestingly, because we have temperature sensors on the panel, and the top and bottom of our hot tank, we're much more aware of whether we need to heat it or not.

Yesterday was nice and sunny - it certainly wasn't more than 10°C out, but the panels were at 34-37°C, and doing a decent job of preheating our hot water.
.

If anyone else is interested in doing this in the UK, do get in touch with us, as we get a referral bonus :)

Comments

[adrianclark.livejournal.com]

Ooh!

That's an idea that has been tempting me for ages. Unfortunately, all of our heating and hot water comes direct from the supply, via a combi boiler, so we have no hot water tank. The boiler will need replacing before long, though, so that might be an opportunity to rejig things slightly...

[fleetfootmike.livejournal.com]

They did replace our hot water tank - it has to be said that this won't hurt either - the lagging on the old one left a little to be desired.

[thunderbox.livejournal.com]

I feel sure you will have done the numbers for ROI, so what was the payback time?

[fleetfootmike.livejournal.com]

We think about 8-10 years. However, it wouldn't surprise me if it's a little shorter, given a) inflation and b) that we're consciously using the boiler less.

The panels will get up to 60°C+ in summer, at which point we basically won't use the boiler at all.

[stevieannie.livejournal.com]

This is a very YMMV situation.

When we looked at this option, we found it easy to work out our payback times, as we are on a pre-filled oil system, and thus know *exactly* what our hot water costs us (the cost of an oil tank in the summer) - £193 for over six months.

That worked out as a payback of over 15 years on a £6,000 system, assuming 100% water heating from the system, with no boiler usage for hot water at all.

A Clear Skies grant, will, obviously, bring this down.

I would suggest that anyone looking at this option shop around a LOT. We have since found similar systems for £1500+ (to get them this cheap requires a certain amount of DIY involvement, though), which was rather a big difference from the £8,000-dropped-to-£6,000-just-for-you deal which we were offered.

Vacuum water heater tubes still remain the 2nd most effective green strategy for reducing commercially generated energy usage, though.

Well done, Mike!

[muninnhuginn]

I'll bear that in mind.

At some point, when we re-roof, we'll probably go for one, tho' I'm still dithering about whether to go for solar panels for water or electricity (especially now we don't have the water cylinder on a passive feed from the Esse).

[fleetfootmike.livejournal.com]

We considered both - electricity's a tad inefficient still, from what I gather, and hellish pricey still.

[thunderbox.livejournal.com]

The ROI on photovoltaics is still in "and you should wish you'll live that long" territory, as I understand it. It's better as you get closer to the equator, of course, but this far north it's pretty dire.

There's also the controversy as to whether current tech photovoltaics are net energy positive. That is if they produce as much energy in their working life as was consumed to produce them.

[stevieannie.livejournal.com]

25 years is the current expected payback on a 3KW PV system.

[thunderbox.livejournal.com]

Hence my "live that long" comment (I'm 50 in January).

[stevieannie.livejournal.com]

Quite. I also note that most of the PV systems also carry 15 year guarantees... Not adding up in my book!

[keristor.livejournal.com]

And how big is a 3kW PV system? At the equator as I recall total solar illumination is about 1kW per square metre maximum, here I'd be surprised if it's half that even in the summer, and will of course drop off drastically morning and afternoon, and the efficiency og PV cells is a long way from 100%.

Suitable for factories with flat roofs, but for houses with limited area I'm wondering whether a 3kW system would fit...

[stevieannie.livejournal.com]

Couldn't tell you, as it wasn't one of the stats we looked at. Once we found out how energy negative and expensive it was, we killed the idea before we flew any further with it.

[filkergem.livejournal.com]

I think I remember that commercially available photovoltaics run about 10-15% efficient, and you guys are so far north that the intensity will be far less than 1kW/m^2 - I would believe the half that you mention. If I'm doing the math right, this means that we'd expect 15-20 square meters per kW electric - 5 meters by 3 or 4. Sounds plausible, with these numbers.

[katyhh.livejournal.com]

Great!!!
Out of curiosity ... which brand are those solar panels, i.e. which company did you buy them from? SHARP (the company I work for *g*) is increasing the business with solar panels a lot in Europe now, as well ...

[fleetfootmike.livejournal.com]

We bought them from Smart Energy, I dunno what make.

[sdorn.livejournal.com]

Good for you! Our energy-saving device here in the Land of Hellish Five Months (in which you have a timeshare now, I believe) was installed when we replaced the heat pump: whenever it's on, a certain proportion of the transferred heat goes into the water. So in the summer we get free hot water. There are also heat pumps that you can attach directly to the tank, and the cold air then gets pumped into the space where the water heater is (brrrr!).

The general lesson is that heating water is simpler than making electricity and you chose the right focus for your efforts. Or maybe the general lesson is that my brain is made of horehound drops, but it's 5:30 am, so it's hard to tell the difference. In any case, cool water-heating devices are cool.

[vaurien.livejournal.com]

I like the idea. It had not occurred to me to use the heat in such an immediate way. Nice one, Mike.

[tattercoats.livejournal.com]

I believe it's what gets referred to as 'passive solar power' rather than PV technology. When are you building the windmill, Fleetfoot? (Yes, Vaurien, when we have the workshop sorted...)

I've heard of folk reusing old radiators painted black to directly utilise the sun's heat too - basic, but it works.

[filkerdave.livejournal.com]

When I was in high school (not sure what the UK equivalent is, but between 16 and 18 years old), we build a similar thing using old Coke cans and PVC pipes, with black spraypaint over it. More as a proof of concept and it wasn't used for anything practical, but it IS very easy tech.

[aunty_marion]

Nearly every house in Cyprus (where my older sister lives) has this sort of solar panel water heating - as for Mike, they use it as a main hot water supply for short-term, and have an immersion heater or similar for a top-up or if more hot water's needed than the panels can supply. Yes, I realise that in Cyprus you get more sun than over here. :-} But the principle's the same!

[filkerdave.livejournal.com]

Nice!

[pbristow.livejournal.com]

"We've gone all green :)"

(Ob.Who:) Don't worry, a nice big plateful of Prof. Jones' fungus pudding will see you right. =;o}