DIY Drain Back Solar Thermal

[www.GymRatZ.co.uk]

As ever, I have a wave of ideas rattling around in my head (that will probabaly never be actioned as too many other jobs to do first!).

Following on from last years very successful new system only gas boiler, thermal store, and wood-burner/boiler installation I still have the un-connected solar thermal coil tails poking out at the bottom of the thermal store taunting me daily.

Has anyone successfully added a DIY Solar Thermal system to a thermal store? I'm presuming a drainback would be simplest but when I start adding pitfalls such as thermal siphoning and flow temperature monitoring/regulation, added to the fact I now only have a W-N-W facing roof left for collector AND through the summer I find even a "cold" shower is perfectly acceptable now I've reduced the shower flow by 50% with a small washer in the shower hose, the actual benefit of adding solar-thermal to the tank is rapidly diminishing to the point of not being a viable project worthy of further consideration.

Our neighbour has 2 tube type thermal panels on their roof and they say they switch off the gas boiler completely for six months of the year but how much is 2 x warm showers a day going to cost, the standing charge for gas will still make up the biggest part of the monthly charge.

No doubt others have looked into this and done juggled the numbers?

Cheers Pete

[Theo]

...

Indeed, although 365 quid a year is not nothing. So it depends whether you can make it with pipecleaners and sticky backed plastic - if you start investing in a 'system' your payback starts to decline.

The main cost here is access: if you need scaffolding or cherrypickers that gets expensive, whereas if you can do it with ladders then the cost is much lower.

The other way is to look at PV - a 400Wp PV panel is a bit over 100 quid, and you get to use the electricity for other things (displacing 35p elec rather than 16p gas). The PV panels are cheaper to install (no pipework, no glycol, no pumps). See, for example:

I suppose you could even do a hybrid system - PV panels as collectors driving a small immersion in a loop that uses the solar thermal coil in the cylinder. While it's not taking advantage of the ability to use electricity for other things (which is mostly the whole point of PV), it simplifies matters because you're just doing DC and you don't need to invert to AC. Although you probably want at least an MPPT to get the best output from the panels.

PV is much less efficient per panel area, but you may make that back in savings in installation and maintenance.

Theo

[www.GymRatZ.co.uk]

Thanks Theo.

The roof is the easiest access roof ever. No scaffold required.

The Thermal store also has 2 x 3KW immersion heaters fitted, one at the bottom and one somewhere between 1/3rd and 1/2 the way up the tank, neither are wired up as I have a 4.6KWp PV array and all excess generated power "winds the clock back" to be used at night or on rainy days so no point dumping it to the store as nothing gets wasted.

A P.V. to DC heater is an interesting idea I hadn't thought of.

I guess there might come a time in my lifetime when an air-cource heat pump or alternative technology becomes an economically justifiable "investment" which presumably could be hooked up to the solar coil in the tank and give a more useful heating season.

Claimed output of the solar coil is "SOLAR COIL OUTPUT 20KW (0.75m2)"

Perhaps I'd better complete some of the hundreds of other jobs before starting a new project. :)

Thanks for your input as always.

Cheers Pete

[www.GymRats.uk]

There could potentially be a header tank in the ridge slightly higher than the the collector/panel, I hadn't thought of that as another variation to rattle around in by head. :)

Another benefit of a drain-back system is simplicity of over-heat prevention, pump could be shut of by the solar t/stat on tank when upper temp. limit is reached. It sort of looks after it's self.

Cheers Pete