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Robin T – Cost effective solar

image rt03image014.jpg*from Robin T* Here is a simple adaptation of a typical 1500 litre (300 Imp gal 400 US gal) stainless steel storage tank that can turn out hot water for your shower. Remember don’t buy the cheapest because the seams fails (see Dozer article).

The tank is enclosed in 1 meter square box which has the sides splayed out 45 degrees. It’s about 2 meters high. The interior should be given a very slight rendering to make the paint job easier. Paint is matt which inside and paint the tank matt black. The front of the box must face due south with an unobstructed view of the sun for most of the day (say 0900 to 1600 hrs)

Cover the roof with translucent corrugated roof sheeting. A 10 foot by 2 foot length should suffice. Use three more sheets to enclose the front as shown

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Front sheets fitted.

As you can see the idea is a bit like a green house. The sheets allow solar heat through and the box holds the heat inside. Temperature of 60C plus are possible (think what your car is like when left in the noonday sun). In theory the maximum enclosed (black body) temperature you can get on the hottest part of the earth is 80C so you really can fry an egg.

###Construction details

You can use standard cinder blocks, or as Dozer recommends, high quality blocks at 5.5 baht each. As there is no load, the outside doesn’t need to be rendered.

At the back of the box I would use a piece of grc sheeting with temporary support to make formwork so as the gap can be cemented in. I would use a couple of lengths of 2 hun rebar or even chicken wire for reinforcement.

To fix the sheeting so it doesn’t blow away, I would embed short lengths of 3mm galvanised wire into the concrete for the block work. I would also put a couple of lengths of 8mm rebar lengthwise to help support the roofing sheets (heat will tend to soften them). Remember to put a slight upwards bend so as to promote drainage of the sheets. Small holes can be made in the apex of the sheets and the wire can be inserted through, fitted with a small aluminum washer and bend over. One every 2 pitches should suffice.

You can apply a similar technique to the front sheets or go mad and make a door frame (but I am a cheap Charlie).

Note that the edges where the corrugated sheets meet the wall must be caulked. You could fill with cement, Kapok, polystyrene, plastic foam, polyurethane, whatever. The idea is to keep wind out and retain the heat.

Here are some simulations of sunshine in Thailand showing where the shadows fall. Generally you can expect solar gain from around 10 am to 3 pm.

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June 1200 is much the same shadow cast as January 1200 but the sun is stronger

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As you can see, almost no wall shadows are cast on the tank.

Don’t forget to provide decent foundations blocks to support the tank which will weigh at least 1.5 tonnes. I would put a simple cement skirting around the splayed sides where the roof drains so as to take away the rainwater at least 0.5 meters (just so the wall foundations don’t soften .

###The Corner model

This will only work fully with a properly facing aspect say on the top of an apartment block. Mine is similar and produces a surprising amount of hot water even though it is far from ideally placed (only catches the midday to afternoon sun and its not fully enclosed)

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Corner model shown with one panel removed; replace one of the sidewalls with clear sheeting if you can’t get this type of aspect. It will all work more or less.


If you want to make a decent power shower you need a head of water of at least 12 foot above your own head level using a standard shower head attachment. (my tank is on the apartment roof so its not an issue for me). There are small pumps that can do this job for 1500 baht (don’t use a standard recip pump as they are not designed for hot water and the seals and rubber valves may fail quickly). Remember that you cannot use a header tank to pressurise a standard stainless steel storage tank. One solution is to put your tank on a tower or incorporate it in your roof structure. In this case you may want to reduce weight and make your walls from wood with suitable insulation. It’s not advisable to use standard blue PVC plumbing fittings for hot water. Galvanised steel tube is ok but copper seems to be expensive. I would have a go with polythene irrigation tubing. Remember to draw your hot water from the top of the tank and replenish from the bottom.

If you can only get your tank mounted on the first floor say (giving about 6 foot head) then one trick I used comprised a 1″ draw off pipe (I took a chance with PVC because the water never reached more than hand hot (40C). I used the rose from a farmers watering can – big galvanized thing 150mm dia. I fixed up a simple 1″ PVC ball valve and it worked very well – like a warm monsoon rain, luxury – but used up water quite quickly. I could only get 3 showers a day (so I locked the hong nam door against playful kids.)

###How to do this?

Well think of your draw off pipe as an over flow. Use one of those reciprocating Chinese pumps to push cold fresh water in at the bottom. Also take a tee off so that you have cold water to mix with your hot water in case it’s too hot (just like a shower with a conventional hot and cold mixer tap. I would also have a colder water draw off from the bottom of the tank after all the raised storage tank is a reservoir and can feed the house with both hot and cold water even when the electricity fails (you can even have a floating draw off – real rocket science)

With a little forethought you can have free hot water for ever.

I shall be building one on my farm in the future when the electricity comes.

I shall try and keep a log of temperatures, water usage, costs etc.

Plumbing hot water for a shower and other uses can get complex. If anyone gets stuck then mail Dozer. Its too big to discuss here. The important thing to remember is that the hot and cold water feeds must be virtually the same pressure i.e. 25 foot head +/- 10%, otherwise you will never control the mixing satisfactorily.

>editor: great concept, low cost installation and then free hot water forever.

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One Comment

  1. thank you so much. what about this installation in nothern thailand like around chiang mai and during january and february? will it be enought hot?

    Sustainable yours.

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