Hi all, I'm currently building a very small, off-grid house (
http://jaystinyhouse.com a similar commercial design can be seen at
http://www.tumbleweedhouses.com/houses/fencl/) and looking at water heating options. Originally I was going to just go with a small propane on-demand water heater with water supplied via a pump from a rainwater storage tank, as in the first diagram below. This was simple, relatively cheap and lightweight.
I was then given a 20 tube evacuated tube panel by a very kind member on here, Ecogeorge, which has had me rethinking things a bit. My next thought was to simply mount the panel on a frame on the floor outside and put a domestic hot water tank above it to create a thermosyphon, then pipe the water from the tank into the house ahead of the water heater. This is less tidy, but uses no additional power and can be modified at will while on the ground. It also doesn't need to have a tank inside which saves on space which, in a house of 8x16 feet, is at a premium.
However, it's not very neat and I like things to be neat and tidy. The roof on the house will be at 45º which is close to ideal for england, so I figured that if I put the panel on the roof, and used a smaller than normal tank fitted under the work surface in the corner of the sink, I could perhaps get away without the gas heater completely. I know there would be days when I'd be short of hot water but I only need it for a shower and washing up.
Now, the problems that instantly come to mind are that I'd need a 12v pump which might be running quite a lot. My power supply is limited to a 220ah battery pack and two 85w solar panels. The 12v DC pumps I've seen are expensive but reasonably efficient, although I have no idea how often a pump would be running on a solar hot water system. I might be able to get hold of an unused 240v central heating pump for free so perhaps running that through a small inverter might be a cheaper option with only a small additional loss for the inverter.
Controllers seem to be very expensive (to me at least) and I'd need one that runs on 12v. I'd be grateful of any suggestions for simple options, perhaps second-hand, that I could look for on ebay etc.
I know I'd need to put in a pressure relief valve and expansion tank, can this be any expansion tank from a central heating system, again I'd probably hunt on ebay, obviously smaller is better.
I already have a thermostatic valve on my shower, would I need to fit one to the cylinder as well. There would be only me living in the tiny house, and I thought perhaps I could put the temperature controller unit where I could see it in the kitchen to keep an eye on water temps.
Looking round a reclamation yard yesterday at old hot water tanks, they seem to basically have a single coil plus an immersion heater. I think this would be perfect for my setup, I could run the panel into the coil and take water from the tank. When I finish building my first wind turbine (treadmill motor type) I could get a 12v immersion heater and use it as a dump load. My only problem is finding a small tank, ideally I'd like to fit it under a kitchen worktop but I haven't found one small enough, so may just have to raise the worktop in that corner of the kitchen.
OK, that's quite enough questions to be throwing out in one post, I'd be very grateful for any advice and suggestions for what is a very small system that I'm putting together on a minimal budget.
Cheers,
Justin.
