Solar thermal using solar-powered pump question

[mangocrazy]

The tubes are mounted on the roof and have 15mm copper flow and return pipes back to the DHW cylinder. The 12V DC pump (driven by a small solar panel) is on the return leg right by the collector. The DHW cylinder has two internal indirect coils, one for solar thermal, one for the wood burner (when I finally get it installed). It's as simple a system as I can make it, and their is nothing peculiar about it. The issue I am having is that the solar-powered pump is waking up early and pumping the water in the collector that has cooled down overnight and is cooling (rather than heating) the water in the DHW cylinder. At around midday the tubes start heating the water in the collector and the temperature in the cylinder starts to climb again, but from a lower base than is desirable.

As a very low-tech solution I've made a box to fit over the solar panel once the sun has gone down which will stop all pump activity until such tme as I take it off.

When I fitted the solar panel cover tonight the cylinder temperature was 50 deg C. I'll check in the morning and see what we have then.

 

[mangocrazy]

This morning at around 10 am the cylinder temp was showing as 30 deg C, a 20 degree C loss overnight, which is a little more than I expected. Having said that, some hot water was drawn for washing and the last 3 or 4 metres of 15mm pipework to the cylinder has not been lagged/insulated, so it's probably about par.

 

[Nomad]

Hi. Bumping this in case anyone know where I can get a roof-mounted system plumbed for 2 circuits ?

Are there standard guidelines for sizing the system? I can see tanks from 150L to 300+

I'm wanting to install a fit-and-forget system, if I can find one that has a feed for hot water and another to use for radiators in the house that would be ideal.
(it looks possible to run the radiators from a 12 volt pump fed by a solar panel / car battery but that can get organised at a later date)

Something that looks like ...


All info appreciated, I've seen the systems and used them but never had to look into buying one

 

[Nomad]

I've now got a system - next question does anyone have advice on fitting it onto a toled roof with insulation under the tiles ?

More info & photo https://www.mig-welding.co.uk/forum/threads/today-i-acquired.50192/post-2433327

 

[Onoff]

I've now got a system - next question does anyone have advice on fitting it onto a toled roof with insulation under the tiles ?

More info & photo https://www.mig-welding.co.uk/forum/threads/today-i-acquired.50192/post-2433327

You mean insulation as a continuous layer under the tiles or insulation between the roof joists, as in top of insulation level with top of joists, or insulation set lower for an air gap etc? What's your roof build up?

If you have to go through insulation and it's thick you might want to look at support rails running down the roof slope rather than horizontally as the lever arm on any long fixing screws / spacers will likely be large. Then consider any penetration of the vcl if fitted and cold bridging albeit minimal.

How about attaching it to a roof ladder or two? Great for easy maintenance on the panel

 

[Nomad]

The insulation is a solid layer between the traditional wooden ceiling and the tiles - as far as I know @Onoff

Viewed from below it's beams (4x6 ?) with thinner wood (floorboards? ) on top


Above that, it's a thick (6" ?) polystyrene insulation slab with no joists or battens to frame it, it's free mounted as a layer on top of the floorboards - the blue bit on the left of the photo.
Thinner battens above that hold the tiles in place.


With hindsight a lot of things would have been done differently but moving forward I need to work out how to fit water heater "A" onto roof "B"

All suggestions welcome, I normally do my own work but roofs & installing water systems from scratch are a new thing. Fun times