Solar water heating

I am looking at building a solar water heating system for domestic hot water. I have 'Googled' and found quite a few good sites for DIY panels, does anyone in this group have any good links to panel construction and control systems?
Also has anyone (silly question!) done it and was it worth it.
I can but a system for about 2.5K but I would like to try to do some or all of it myself.
Thanks.
--
brian



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ashnook wrote:

This one on a mountain hut does not look elegant but it works like a charm. It works off tank water, and the water is so hot it needs to have a temperature limiter.
http://i2.tinypic.com/qowuog.jpg
I've always wondered why a cheapskate one couldn't be built using vast coils of cheap black plastic pipe of a type that can stand being in the sun for years, and covered with old window sashes or similar. If you are prepared to have a small electric pump, that could feed to an existing tank that does not have to be on the roof. It would need a way of releasing pressure in case the pump stopped.
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brian, look at http://www.cat.org.uk They supply kits and all the books too. If fitting a solar panel or two. Look at http://www.navitron.org.uk /
If fitting a solar system use a thermal store/heat bank, not a preheat cyldiner. Heat is input into the store via solar panels and boiler, etc. Heat is output into the DHW and CH. All in one cylidner. If you go this route, I will give you setup for the contol system to prioritise the solar heated hot water in the lower sectron of the store, and keep the burner off as long as poosible to heat the upper boioer heated section.
Further info on solar thermal store: http://www.heatweb.com/solar/solar.html
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On Sat, 4 Mar 2006 08:10:33 -0000, "ashnook"

I have followed some threads on this in the past and think there are a few 'questions' you might need to answer first.
1) Do you intend to stay at that place for a good few years (if you are interested in clawing the installation cost back via energy savings? That time will depend on the cost of the install (may be improved by your diy input) and the cost of 'buying in' energy (going up fast at the moment).
2) From a global point of view, how long would it take to recoupe the energy expended making the items you use for the cheating the project (along the lines where electrical solar panels used (?) to take more energy to make than they ever gave back in their lifespans)?
The above is compared with locations where you actually have a choice of course (like a gas / electric supply .. ie you aren't in the middle of nowhere ...) ;-)
Given all positive answers to the above and that you have a favorable outlook (South facing etc) and you make the system 'big / concise enough' then I believe it's possible to provide much of your hot water most of the year .. even in the UK ;-)
All the best .. and good luck if you go for it .. ;-)
T i m
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wrote:

Being in the middle of nowhere makes solar energy more necessary and appealing.

Depending on how it is done (panels looking ugly on the roof right at the front, etc) and positive proof of savings, a solar system can be a selling point, and may add some value.
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On Sat, 4 Mar 2006 08:10:33 -0000, "ashnook"
Yes

No. It was an interesting experiment but never paid for itself and contributed little in terms of energy saved, nothing at all when you considered manufacturing costs. You are far better off looking at improving insulation and ventilation.
--
Peter Parry.
http://www.wpp.ltd.uk/
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wrote:

Mr Parry does have a point. The first stage should be thicker insulation and making the house air tight. But a well designed DIYed solar system can pay for itself, and may even add value to the house as energy costs increase.
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ashnook wrote:

A 2500 system to heat your hot water won't pay for itself. There just isnt enough HW spend for that to be possible in most houses. This is the simple mistake made by most solar DHW designs, commercial systems being among the worst in this respect.
You could save more energy with less setup cost if you implemented solar space heating. If your aim is to cut costs or reduce energy use, this is a more logical choice.
Concentration improves efficiency and extends the heating season.
Solar systems dont add house value. They arent taken very seriously, and most buyers have way bigger concerns, so the solar system is pretty much ignored when valuing a house. Of course there may be exceptions, but thats usually the way.
Dont attempt to solar heat a thermal store / heat bank, as DHW panels run this way will have very low efficiency, and contribute close to zilch. Preheat cylinders are used because they are the one way to get good efficiency from unconcentrated panels. Concentration is the other way to up efficiency.

They can be, and very cheaply. These systems arent robust enough to put on the rooftop, but theyre ok for ground use. Polythene is much cheaper than sashes. Spacing the pipe turns out increases their efficiency. Using several parallel circuits dramatically reduces pumping power requirement. These panels aren't freeze proof. They wont boil if stagnant.
Dont forget a drain heat exchanger, the payback on those is good.
NT
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You xclearly know little of thermal stores/solar to come with such a crass comment.

The pre-heat cylinder can be the bottom half of a thermal store, not heated by anything but solar panels. The DHW drawoff can take off water from the solar section and when too cool start to use the cooler solar heated water for mixing, instead of much colder mains water. An depletion of hot water in the upper section heated by a boiler, will be replaced by warmer water from the lower section, not very cold mains water, hence keeping the burner off for longer. Not difficult or expensive to do, using only a 3-way blending valve with a remote temperature.
Also any solar generated heat can be used for CH too.
Preheat cylinders are notorious for being inefficient to all one cylinder thermals storage.
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Doctor Drivel wrote:

In principle its a good idea. To work the panels efficiently though you need a lot of stratification, as panel efficiency drops rapidly as the water they heat gets hotter. I'm not sure how much temp diff in the tank one would get in practice.

not really hot enough. CH runs at close to flat panel stagnation temp, making efficiency close to zero. Evacuated tubes would contribute, but are high cost and lower output.
I suppose in principle one might try circulating the CH system via the solar panel, with boiler off, when the room stat is already satisfied. The lower heat output could then extend the time it takes before the boiler refires due to the stat calling for more heat.
On 2nd thoughts a comfort zone would be the thing, let the solar heat run when the stat is satisfied, but only as far as 1-2C above stat setting.
This is only going to fly when the boiler off periods are long enough for rad water to cool to below solar panel output temp, at peak heat times the panels would contribute nothing.
Really quite a lot could be done with solar HW once you have a flexible and capable multivalve controller panel. These are unheard of today, but if they become low cost they could control the flow from multiple inputs to multiple outputs, working out how to maximise return at all times. For example the inputs might be: - minimum cost solar collector, eg black radiator or hose panel - medium cost flat panels - high cost evacuated tube collectors - boiler
and the outputs would be several layers in the HW heat store, each at different temperature. The controller would monitor all the temps and work out what to route where when to maximise output.
The controller would also automatically drain down collectors when frost damage risk arose. This means an all direct system, with its lower install cost, higher efficiency, and more routing flexibility.

They extract heat from the panels efficiently, which is why they get used, then they use that heated water inefficiently.
NT
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You are only guessing here.

The solar section is at the bottom with the DHW top, CH middle and solar bottom. No CH return to the solar section, only the middl;e CH section. Using a plate heat exchanger the return from the DHW can be directly into the bottom of the cylidner in the solar section. That is because the efficiencies of the plate is phenominal. There can be 80C into the plate and the temp of the pipe coming out is so low you can grab the pipe infefinately. So, cold/very cool water enters the solar section. A tall thin cylinder helps in stratification.

http://www.navitron.org.uk
No. Just heat the solar section. Any heat extracted from the centre CH section (cool return water) will be replaced by hotter solar water in the lower section (hot water rises).

May as well fit the optimum cost/perfoanmnce panel rather than inefficient black rads.

Mixing and prioritising water use is the problem. A preheat may have very useful hot water at the top, yet this only enters the run cylinder when it draws-off hot water. Then this hot ware mixes with the run cylinders cooler water cooling the water overall. Not what you want. An all one thermal store can prioritise the use of solar water very easily with one blending valve and mix the solar water with hotter DHW boiler heated water.
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Doctor Drivel wrote:

no, as explained here:

DHW is usually not as hot as CH, 65 versus anything upto 82, so an unusual choice. Why choose to heat dhw to above its use temp, to extend heat capacity?

return from DHW? whats that? where does the plate exchanger connect in your scheme (it has 4 connections)

hard to know what to think until you explain your setup clearly.

yes
20" of panel for 220 is steep (10x 2" tubes). Evacuated tubes also dont perform well in winter in Britain, flat plate works better. Tubes are good with direct sun only, plates work ok on diffuse IR too.
BTW when are people going to start cutting fl tubes and putting copper or plastic pipe thru them? 10 tubes for a tenner that way.

But its not cool return water, CH return is still not that far from panel stagnation temps. Except of course with vac tubes, but those are just too expensive to pay their way.
You still need to change the thermostat setup to make use of the solar heat, otherwise the pump only comes on when heat is needed, and the solar part wont supply high enough water temp to avoid the boiler firing. IOW the system would not heat the rads between boiler firings.

The point is that each type of panel has its own advantages, and is the best choice for some and only some of the work.
Tubes are best for the highest temp water input, theyre the only ones that will heat water thats nearly hot enough with any efficiency. But their cost is excessive for any other task, and they dont collect well in winter.
Flat plates are the middle ground, mid price, mid efficiency, no use at higher temps, and unnecessarily costly for heating cold water. But the best option for a fair range of water heating temps.
Black rads will preheat cold incoming water effectively, and do so at less cost than the others, but are not for medium or high temps. Their inbuilt water storage means no need to allocate more tank capacity for the lowest temp water layer, that temperature layer is effectively done in the rads. Adding 15-20C to the tank's incoming water temp means more piping hot water out the other end, and at minimal cost. That means savings can be made elsewhere in the system for the same overall system performance, giving better energy/ ratio.
Most simply, rads can be connected between header tank and water tank, though thats not what I'm suggesting doing here.
The whole point of a mixed panel system is to get the highest output with the least cost - which is the only way solar dhw will ever pay. Using vac tubes to heat cold incoming water is sheer folly - yet its often done.

Yes... if you can maintain enough stratification.
Also a separate preheat cylinder means more surface area per volume stored, meaning more heat loss or more insulation expense, or both.
NT
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no, as explained here:

DHW is usually not as hot as CH, 65 versus anything upto 82, so an unusual choice. Why choose to heat dhw to above its use temp, to extend heat capacity? <<<
It is clear you don't understand the principle of heat banks.thermal stores. the DHW stored water is between 70-85C to instantly heat the incoming water.

return from DHW? whats that? where does the plate exchanger connect in your scheme (it has 4 connections) <<<
It is clear you need to understand how they work. See http://www.heatweb.com That gives good explanations. No se sens ein continuing until you understand, you think about it and then form questions.
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Doctor Drivel wrote:

What is clear is you didnt fully describe your proposed system. Now we know which body of water is in the tank. And we also know that this approach makes solar collection less efficient, which is why I had initially guessed you had the DHW in the tank, being drawn off at the top for the taps. This would be more efficient.

Either describe your setup or dont.
NT
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wrote in message

I said thermal stopre and heat abnk. I can't get any clearer. If don't understand the principle then....

You keep saying that without knowing what a thermal store is. Again, is is not less efficient is it more efficient and controls that prioritise the use of solar gained heat are in place.

Understand what I am describing. Draw it out and think it through.

I did, re-read. Read again, draw it out and come back to clarify.
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ashnook wrote:

http://www.sustainable-girton.org.uk/pv/ gives a few figures on a new PV installation, which in *February* produced 2/3 of the owner's consumption. On good days it made 3.3Kw.
If you contact me privately I could get more details for you but you should be able to work out the installer's website from the pictures.
Douglas de Lacey
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We've just done it and it's a joy! We weren't thinking about pay-back but it will be worthwhile in that respect, especially given fuel price rises.

We bought a panel and pv pump from www.Solartwin.com and they've been extremely helpful and friendly. It's probably been the best company we've ever dealt with for anything. We installed it ourselves, it didn't save much because it meant that we weren't eligible for a grant but it was far more satisfying than having someone else do it.
We're getting a large tank full of water at over 40C even on recent days when everything outside has been frozen.
Several of our friends and family have been so impressed that they're looking into it.
Mary
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wrote:

"The total cost was large,...If the predictions are correct, these costs will be paid back in around 24 years"
Solar water heating may be marginal but solar pv is a wonderful way of wasting money.
--
Peter Parry.
http://www.wpp.ltd.uk/
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We were somewhere around Barstow, on the edge of the desert, when the
saying something like:

I don't see how. Sure, if you buy factory-made panels and all the necessary pro stuff and pay for the installation.
This is a DIY group. Building panels from base materials and feeding a pre-heat cylinder works out at less than a couple of hundred quid if you DIY the whole thing from salvaged materials.
In my own situation, I have several suitable sized radiators and double-glazing units which will be pressed into a different role from their intended one. I have a few used-but-good hot cylinders and the perfect position upstairs for a gravity solar system fed by 3 or 4 panels at ground level.
I don't expect it to work miracles, but I do expect it to work a bit - enough to cut the cost of electrically heating water by at least a third and probably half.
--

Dave

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On Mon, 06 Mar 2006 22:53:09 +0000, Grimly Curmudgeon

I'm not sure DIY construction of solar photovoltaic panels is really going to catch on :-).

I've helped build such a system for warming a swimming pool and it works quite adequately - it's also very large and pretty hideous. Where we built it it was possible to hide it behind a large hedge but not many people have a farm to play with.
--
Peter Parry.
http://www.wpp.ltd.uk/
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