Hot tub solar heating

[Stew]

I am making the jump into solar and my first project is to heat the outside spa (I run a B&B, its not for me) containing approx 500 gallons of water by solar. I intend on running a very long length of black piping,100ft, attached to a black board circulating water using a solar powered pump. My question is what size solar panel would i need to run
1. A 24v 800mA water pump.
2. A 12v 400mA water pump.

i intend to hook the solar panel directly to the pump as i figure the only time i will want the pump running is when their is sun.

thank you for you answers and if anyone has done anything like this i would love to hear from you.

[Wy_White_Wolf]

Are you going to run the solar panel on a tracker? If yes then the panel IMP just needs to exceed the amperage requirement of the pump.

If no, then sizing the panel IMP at 150% of the pumps Amperage rating should allow it to run for +- 3 hours of solar noon, given that you orient the panel for solar noon.

Pumps also need to be able run under the full voltage range of the panel.

WWW

[russ]

For the black plastic pipe part http://rimstar.org/renewnrg/solar_po...ter_diy_fp.htm

[J.P.M.]

I am making the jump into solar and my first project is to heat the outside spa (I run a B&B, its not for me) containing approx 500 gallons of water by solar. I intend on running a very long length of black piping,100ft, attached to a black board circulating water using a solar powered pump. My question is what size solar panel would i need to run
1. A 24v 800mA water pump.
2. A 12v 400mA water pump.

i intend to hook the solar panel directly to the pump as i figure the only time i will want the pump running is when their is sun.

thank you for you answers and if anyone has done anything like this i would love to hear from you.

I'd suggest it may be more efficient and cost effective to simply buy a pool heating panel or two. They usually have no problem handling 100-105 deg. F. water temps, easier to plumb, and very likely more efficient.
500 gal. seems a bit small ~= 8' x 8' X 1 ft. deep or so.
After initial warm up, the collector need only be sized to make up the heat loss to the ambient. Keeping a cover on the spa when not in use will reduce that loss.
I don't think 100' of plastic pipe will give you the area you need to provide any meaningful heat to a spa.

Fool around with DIY as you like but such efforts are usually much better as teaching tools than workable systems. FWIW, I've done both. Buy the pool panel(s).

[thastinger]

My solar pool heater was 2K and I did the install myself. It is a 9x30 array for a 15K gal pool and it raises the temp 6-7 degrees on a sunny day. I think you're going to have happier customers by running the hot tub off your house electric. The solar water pump won't produce enough pressure for the jets to do anything and you'll never heat the water to 104 and be able to keep it there with solar alone. I'd expect the hot tub to be used at night mostly, so solar is a poor fit unless you want to change the name to coldstagnant tub.

[russ]

so solar is a poor fit unless you want to change the same to coldstagnant tub.

Rather an excellent point! To heat a spa you would have to go to the evacuated tube type solar thermal collectors.