PDA

View Full Version : Home built solar hot water



roverrescue
19th August 2010, 03:32 PM
Just interested to see if anyone has knocked up their own solar collector for heating water.

I have most of the components but too many ideas, just wanting to get the system close to right first time.

closed loop / open loop / thermosyphon or pumped? Any leads. Obviously in Cooktown I have plenty of 'ol Sol and no freezing pipes issues which should simplify things. The hot water is really only for an outside shower and washup basin that is nice to have at the shed/workshop before heading home after tinkering. Also mates tend to camp at the shed a bit so nice for them too.

My current favourite is thus:

Half a plastic 44 supported on roof, cistern float valve controlling the feed in water level to about 60L. Marine bilge pump circulating water from tank through a copper coil painted black mounted on formply under an old glass window. Power the bilge pump with a 15W solar panel.

Theory being bilge pump will only run when powered by panel, ie sunlight hours. Water will cycle through the collector plenty of times in 8 hours of sunlight, should get pretty hot. I will keep the top open in the tank such that pressure relief wont be necessary, may just float some thick polysterene on top to keep heat in. Tank may need to be insulated to maintain heat.



Steve

bee utey
19th August 2010, 04:51 PM
If you mount the tank above the collector there is no need for pump. Mind you the collector needs to have a number of tubes in parallel to 1 inch collector tubes top and bottom so you flow enough water. Not as easy as whacking up a coil.:)

JDNSW
19th August 2010, 05:00 PM
You will need a pretty big copper coil to give enough area with it not attached to a metal collector. You really need to have a flat sheet metal collector with the copper pipes attached to it to give the area. An alternative is to use a larger quantity of black plastic tubing. In that climate you probably need a collection area of about a square metre, depending on how big your tank is.

You need to have an insulated tank to store the water - if it can be arranged above the collector you can use thermosyphon action, and this also means the collector will not cool the water in the dark!

With no frost problem there is no reason why you should not use an open loop system unless your water supply is corrosive or very hard.

The tank is better closed with a small float valve controlled feeder tank just above it (also acts as an expansion tank) as this will not lose heat to any extent.

Problem with using an old window for the cover on the collector is hail! Also, don't forget to insulate the back of the collector.

John

Bearman
19th August 2010, 05:22 PM
Sounds good Steve. Let me know when you get it all sorted out and I will come up and camp in the shed for a couple of days.:D:D:D

roverrescue
19th August 2010, 08:10 PM
Always welcome to stay Brian! Still havn't bolted that Maxi in... Im waiting on some airsprings which I will do at the same time!!!

Thanks for the hot water system comments. I want to use the junk that I have, this includes about 20m of 8mm copper tube. Too small a diameter to thermosyphon well from what I have read, but will limit flow increasing heating time using a 250GPH bilge. I have the solar panel collecting dust so no biggy to drive the bilge.

I was going to "coil" the copper on some 16mm form ply (insulation) maybe with a thin sheet of Aluminium between all painted pot belly black. The window I have, we dont really get hail and if it lets rip in a cyclone, well not too many people or buildings near by for it to kiss!!!

John, when you say Ill need 1m2 of collector, is that overall tube area if attached to metal bonding... the window I have is 1800x800 so 1.4m2 sound feasible?

Will start construction this weekend and see how it flys.

Thanks for tips and ideas,
Steve