[coldandwindy]

Has anyone got solar water heating? I don't mean from solar electricity, I mean where you circulate cold water through a black panel that absorbs heat.
I'm just at the looking into it stage. I'd want to put it on a vertical wall in a very hot south-facing porch. Can I do that - do they work vertically or is the roof angle essential to the flow?
Do I circulate antifreeze in a closed system that then heats my water or is it cheaper to just circulate my water? Sounds preferable but am I missing something? Why do some people prefer the other way?
Is it worth buying an off the peg system or is it just as effective to use radiators painted black?
How do I combine using it with my existing system , do I need two separate hot water storage tanks in the loft or is there a way of switching which supply we use ?
That's all the questions I have swirling round my head just now but if you can think of any unknown unknowns...

thanks, Windy.
 

[John]

What are you proposing to do with the hot water?
Radiators painted black in a box with insulation behind and glass over will work well. They will work on the vertical but there are optimum angles for absorbing light.
Preheating water in a tank further heated by whatever makes sense - but it is a broad subject
The financials of buying a system don't make much sense - too expensive with too low a return.
This book is pretty good: https://store.cat.org.uk/collections/books/products/solar-hot-water-choosing-fitting-using-a-system

[coldandwindy]

Thank you. I was looking at that book - I'll buy it!
The hot water will be to use in the house. We come in needing a shower and then wash up etc. Most of our hot water use is in the evening. The plan (very vague just now ) is that solar does its best & then the back-up is timed to turn on half an hour or so before we come in.
I was wondering if the porch itself could act as the insulation and glass.
What's the hottest it could get & what happens about the water boiling in the pipes on a hot day? As kids we had a fire with a back boiler & when it started banging someone had to volunteer to have a bath!

[John]

What's the hottest it could get & what happens about the water boiling in the pipes on a hot day?

Over-heat protection will depend on the type of system I suppose. Hopefully the book will cover it although I don't expect it's a common problem in the UK!

[comfreykid]

We had solar water panels on the south facing slope of our roof in our first house  nearly forty years ago .
It was a fitted system ( Sunray   I seem to remember) and it was basically black painted radiators in aluminium framed glass fronted boxes. The water was lovely and hot on sunny and not so sunny days but never got scalding hot or boiled on hot days . 

[Swing Swang]

If this topic is still 'live'
The OP also asked how solar thermal would integrate with their existing system. If the OP means that they already have photovoltaics then if they are overproducing during the day then energy divert, whereby energy that wiuld be otherwise sent to the grid is 'dumped' into a hot water tank, might be a simpler/cheaper option. It's what we do and we reduced our heating oil consumption by about 800-1000l per annum.

[Subversive_plot]

I'm re-opening a fairly old thread here, but just noticed the topic.

During my consulting days, I worked a fair bit in Puerto Rico.  The common way to get hot water was to have a water line (mains pressure, or regulated down from that) that went to a tank on the roof (most single-family homes in Puerto Rico are made of concrete, with a flat horizontal concrete roof).  The tank was painted black. 

Turning a hot water line on inside the house delivered water from the tank to (the laundry, shower or whatever).  It worked and was low-tech, but don't try taking a shower in the morning after a dark night!  Or after everyone else had taken a long shower.

In northern climates, your peak water temperature will of course not be as high as in Puerto Rico.  The whole system would need to be drained during a northern winter.

[coldandwindy]

Thanks for your input S.P.
I still haven't done this but it is mulling around in the back of my mind while my subconscious self thinks of a solution! The general idea is that I'd have a black radiator inside the house somewhere (probably my very hot porch) so it would be out of the wind and frost.
My hate for doing plumbing and the need for a new hot water tank are stopping me so far!