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Solar hot water - advice?

Posted: Sun Aug 15, 2010 5:49 pm
by KathyLauren
I want to install a solar hot water system in our house. I thought about a commercially-installed system with antifreeze in the pipes and a heat exchanger beside the electric water heater. However, my roof gets no sun at all in winter, due to surrounding tall trees, so installing a frost-proof system seems a waste. It will be a summer-only system anyway due to the trees. Given that a Rolls-Royce system is pointless, I am leaning towards a Volkswagen system.

What I have in mind is about 80 feet of 2-inch black pipe on the roof. There will of course, be bleed, drain and bypass valves to empty it in winter. The question is how to connect it to the water heater. I can think of two ways. I am interested in any thoughts anyone might have on them.

1. I could connect in in-line ahead of the electric heater. Cold water would flow through the roof pipe before entering the heater. Pro: Easy, low-tech plumbing job. Con: Collected heat is only used when water actually flows as I draw hot water. When water is not flowing, heat is wasted and could damage plumbing through over-heating.

2. I could connect it in a loop to and from the water heater. This would require a pump, probably solar-powered, to circulate the water, since the heater/tank is in the basement and therefore can't thermo-siphon. The pump would draw water from the bottom of the tank, circulate it up to the roof collector, then back into the top of the tank. Pro: Energy collection is continuous while the sun shines. More energy collected. Less chance of overheating. Con: More elaborate plumbing. Requires differential thermostat (or maybe not?) and pump with solar panel.

Any thoughts? Has anyone tried one of these schemes?

Re: Solar hot water - advice?

Posted: Sun Aug 15, 2010 9:34 pm
by homegrown
Hi keith, the one advantage of a closed loop system with glycol is that it doesn't have to be on your house roof do you have a nearby slope or even a nearby shed or garage roof that gets more sun?
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Re: Solar hot water - advice?

Posted: Tue Aug 17, 2010 2:53 pm
by contadina
We use option 2 Keith. A differential temperature controller will improve efficiency, and shouldn't cost much. There are electronics plans for them available for free on t'internet. The important thing is to pop in a couple of non-return valves to prevent the system going into reverse at night and thermosiphoning away all the heat. Circulating pump recommendation: Ivan System El-Cid 5w

A system that drains down in the autumn would be better than using anti-freeze, I reckon.

Re: Solar hot water - advice?

Posted: Tue Aug 17, 2010 8:48 pm
by KathyLauren
Thanks for the tip on the non-return valves! I might not have thought of that in time.

Re: Solar hot water - advice?

Posted: Mon Sep 13, 2010 6:54 pm
by Muddywheeler
Hi Keith, don't know if you have built your system by now, I built a system earlier this year and so far (We use oil for heating) the heating system has not been on for 112 days out of 114 days, I used vacuum tubes (most efficient) in a pressurised system as increased pressure lets you obtain a higher temperature with A differential temperature controller . I used copper piping well insulated don’t use the common pipe insulation as it can’t stand the high temperature produced by the panel, all joints are compression as solder can’t be used, high temperatures again, I got all my bits from ebay and it cost a fraction of a commercially installed unit, its easy to do and I can’t understand why firms charge so much.

Re: Solar hot water - advice?

Posted: Tue Sep 14, 2010 7:38 am
by boboff
This sounds so excellent.
Being a ludite, where is a "solar for Idiots" site?