PV and other alternative energy sources.

[Digit]

Andy! Basically yes, it is that simple, in theory. A little more complicated in practise but well within most sensible DIYers capabilities.

Roy.

 

[MikeG.]

Spot on Andy............

You didn't have any plans for the weekend did you! Show us the pictures next week.

Oh, and depending on where you are in France, with a decent south facing roof you should be able to comfortably exceed the figures I gave.

Mike

 

[dedee]

Roy,

It's the "A little more complicated in practice" bit that bothers me.
Could you explain further?


Andy

 

[Dibs-h]

Came across this the other day - looking for some other info on heat exchangers,

http://www.bigginhill.co.uk/solar.htm

 

[MikeG.]

No, Andy, there is nothing to worry about. Just make sure that everything is done well, and don't use plastic pipes. The only complication I can think of is that you will need to be able to bleed and drain the system.......and I know nothing at all about how expansion is dealt with (if there is any, with antifreeze).

BTW, I have heard of engine oil being used in place of the anti-freeze solution.

Mike

 

[dedee]

I't will take me a while to get all this together and I am a bit bothered by Roy's remarks - see my earlier post. But I do feel like giving this a try.

Of course sourcing the bits over here is bound to be more complicated than in blighty, but if I can get the planning right (the 6 Ps) I could have this done after Easter when my next supply drop arrives


Andy

 

[Digit]

Any system of hot water heating needs to have the smallest water content possible, you want to warm the domestic hot water, not spend half the day heating the water in the collectors and pipework.
On a poor day let us assume that the water in the collector system is 15 Degrees C, if the water in the tank is at higher temp the collectors will extract heat from the tank, not heat it!
Therefore controls to arrange that the collectors deliver water to the tank's heat exchanger at the right temps is necessary.
Using a small water content usually means small bore pipework in the collectors, therefore a pump is necessary, again with appropriate controls.

Roy.

 

[MikeG.]

Roy,

the solar driven pump overcomes the need for all that complication.

Admittedly, it will have imperfections on intermittently cloudy/sunny days, but it has the huge advantage of being simple. When the sun shines, the pump circulates the fluid through the system. When it doesn't shine, the fluid sits still. You could build delays or thermostats into the system to improve it, but I would go for simple and just have the 12V panel & pump.

Good point about the water content, BTW. Some of the basic DIY collectors are just domestic radiators painted black and put in a box, but they do suffer from having too great a volume of water and are correspondingly inefficient.

Mike

 

[Digit]

the solar driven pump overcomes the need for all that complication.

Absolutely Mike, I was simply trying to explain the principles involved.
The answer to Andy's basic question is yes, it is simple. Just don't fall off the roof!
My place faces south with a roof area of 30 sq mtrs, and once I get rid of the Asbestos cement covering solar panels are going on!

Roy.

 

[CNC Paul]

I reckon that with a few plumbing skills, you could install a decent solar system for around a couple of hundred pounds, and with a typical UK system producing 40 to 50% of the annual household needs, that could pay for itself in very short order.

Mike,

Thank you for some interesting information.

For a decent solar system what wouild you use for collectors ?

Many thanks

 

[MikeG.]

Sorry Paul!!!

I wasn't ignoring you, I just didn't see your post.

I would use small bore copper tubing, available from any plumbers merchants, and roll it into a pattern on a piece of copper sheet scrounged from an old hot water cylinder. I would mount this on a sheet of ply, and "twitch" everything together with some thin wire, laced through holes in the sheet copper & ply. This is no more than fiddly DIY work, no soldering at all in the collector. The important thing is to achieve as much contact as possible between the copper sheet and the copper tube.

Back the whole lot up with some decent insulation, put it in a box with a 4mm glass lid, seal it all up and away you go!

I guess the major complication is getting the whole thing up on the roof, and keeping it there. You'll need some sturdy mounting brackets, and some fiddly lead-work where they protrude through the tiles.

Mike

 

[Steve Maskery]

Mike
Wouldn't his work better with the unit on the ground? I would have thought that the tank needs to be above the sloar panel for it to work without a pump, given that hot water rises. If the panel is on the roof, then won' the hot water of the tank drive the flow, sending all that nice heat out onto the cold nght roof? What am I missing?

S

 

[dedee]

Mike/Roy,

I see no reason why it has to go on the roof. In my head I plan to place the collector on an angled stand in the garden as close as possible to the exiting water heater. Running the necessary water pipes to and from the roof is adding complications especially as I wold need to drill through 2 concrete floors!

As for the likelihood of running heated water back through a cooler collector I'll take that risk just to keep things simple. KISS and the 6 Ps always help me!

Andy

 

[Digit]

You can mount them anywhere. The roof is usual to keep pipe work to a min and avoid shade from trees etc. If your roof faces N/S alternative positions would need to be considered anyway. Solar pumps are after my development work so I only know of them from what I've red, but I believe they would prevent any back flow. Mind, with small bore pipework gravity circulation is most unlikely.

Roy.

 

[CNC Paul]

Thanks Mike, Nice and simple

 

[MikeG.]

Steve,

yep, the collectors can be placed anywhere......so long as they are in the sun! The problem with being low down is that they are more likely to be over-shadowed at some point, but if you have a big clear garden, or say, a first floor flat roof, then it is perfectly feasible to stand them there. Bear in mind the losses from long pipe runs.

As we are suggesting micro-bore pipes and a pump, the vertical relation of the collector to the cylinder is irrelevant.

I can't exactly remember the formula for the angle at which they should be placed, but it is something like "latitude minus 10 degrees", so in the UK that is between 40 and 45 degrees, roughly. It just so happens that this fits in well with the angles of most rooves.

Mike

 

[Steve Maskery]

that is between 40 and 40 degrees, roughly.


Mike

That's rough?


S

 

[MikeG.]

that is between 40 and 40 degrees, roughly.


Mike

That's rough?


S

Ooops! .....now edited!!

 

[wobblycogs]

I always thought you had to have an expension vessel in an indirect solar water heating system? I would have thought the system would just self destruct in the heat otherwise.

 

[Digit]

I'd have thought so too.

Roy.