I have a roof which faces due south and is pretty much unshaded, so want to build in solar thermal and PV to my renovation project. Need to make a decision soon as the PV installers are becoming choc-a-block with the FIT deadline looming!

I have a space available of approx 3.7m x 8.5m. For aesthetic reasons I want the PV panels to be arranged landscape rather than portrait.

The property is about 250m2 and there will only be two of us living there most of the time, and we are not huge hot water users. Property has mains gas, and will also incorproate a MVHR system. There will also be 2 wood burners, one of which MAY have a back boiler.

I have so far had quotes from two companies for the PV and solar thermal. One has suggested a 15 panel Kioto PV array plus a 2 x IFK 2.1 (not sure exactly what this means!) solar thermal flat panel system. The otehr has suggested a 12 panel LGS array plus 20 Kingspan Thermomax evacuated tubes.

I suppose my main question is how much solar thermal would just 2 people actually need, as if what has been quoted for is too much would we better halving it and upping the PV array a bit?

Thoughts would be much appreciated.

Simmo

No idea concerning how much we use each day but in our existing house we have a crappily lagged copper cylinder that I guess is no more than 150 litres. This has only proved inadequate when we have several guests who have a strange desire to be both warm and clean.

We will be having new everything, and a tank/ thermal store of about 210-250 is probably what we will go for.

John

We are two people with low DHW usage (and a crapily lagged copper cylinder of about 115l). We have 40 47mm vacuum tubes, which is 'oversized' (3l/tube) by the standard rules. 5-8l per tube is normal, lower end 'better' by most people's view. This means one needs a heat dump in summer. If our tank was better insulated we'd need it more often, but it also means we can get 80-90% of our hot water. Those panels take up ~5m2. (1.5x1.7 x2). You shouldn't go below 3m2 IMHO. 58mm tubes are worth approx 1.5 times 47mm tubes in output, so you could have 30x47mm tubes or 20x58mm tubes (3.6m2). Dimensions here: http://www.eco-nomical.co.uk/SolarWaterProduct.htm
(those are particularly good value panels (and happen to be the ones I've been using for 3 years)).

I would strongly favour evac tubes in a UK climate because they work a whole load better when it's cold - i.e at the end of the year when solar thermal is in short supply. And if you shop around there is no price premium over flatties. Nothing wrong with thermomax panels, but last time I looked eco-nomical and Navitron were _much_ cheaper for essentially the same thing. It is possible to get 20-30% more energy per square metre by getting direct flow tubes rather than heat-pipe tubes, however they are significantly more than 30% more expensive (insofar as I could get any direct-flow suppliers to give me prices). But if you are trying to cram max PV and ST onto the roof then HIT PV panels and direct-flow ST panels may be worth the expense.

You can get endless advice on ST sizing over at the Navitron forum. If you go far a 250l tank and use a conventional bottom-coil then you ought to be aiming for more like 50x47mm tubes (or 30x58mm tubes), otherwise you find that you get a warm tank too much of the time, but not a hot one. You can use a large tank with a smaller ST area and still get hot water with a top-loading set-up, but those are never supplied by 'the industry' in my experience.

This is an IFK2.1: http://www.solfex.co.uk/ifk2.1.htm roof-ingrated flat panel. Specs look fine, although I'm not sure what "min output 525kWh/m2a" means. Is 'a' 'annum'? You should expect to get about 900kWh/yr from a basic chinese 2.5m2 20x47mm panel in bottom half of UK (from memory).

Considering PV and ST together is a good idea as you can maximise roof area utilisation. I did ST first and in isolation so have some wasted area: http://www.wookware.org/pics/solar/PV/025-IMG_0639.JPG.html
note that if you shove your ST right to the top of the roofline then you can't easily have a convenient internal bleed valve (I think - maybe something clever can be done).

Hope that helps.