Video of my first DIY Solar Collector Box using 300' Pex Coil
 

YOUTUBE VIDEO : ‪DIY Solar Collector using Pex Coil tubing‬‏ - YouTube


The project consisted of building a Solar Box/Oven for 300' of 3/4" Pex-B Tubing to sit inside of and was built using 2x12's with a finished size of 36"x36" . 1/2" plywood was used for the backing with 1" Polyiso Board sitting on top of that with a thick piece of sheetmetal plate on top of that --- everything inside the Box was painted a flat black including the aborber plate, inner / outer box walls , and Krylon Fusion Paint for the Pex Coil . The top of the Box recieved a double pane argon-filled Low E window in vinyl sash which has good light transmittance with ability to retain heat in the Box. Collector Box is on a 30 degree angle from vertical. Piped in parallel to the water heater so the house hot water supply is either fed by 100% Collector water or from the standby electric Water Heater (accomplished via bypass valves) .

Results after 5 hours of recharging :




90 f. totally sunny day :
Temp. inside Box : 161 f.
Exiting water Temp : 158 f.





84 f. totally cloudy day with mostly rain :
Temp. inside Box : 105 f.
Exiting water Temp : 100 f.
















(The Pex Coil holds about 6 gallons, but since i live alone ... it is more than enough hot water for my limited water useage for 100 f. showers and occasional Dishwasher ; in fact on a sunny day I have to cool it down alot with cold water at the Shower Head so Im using less than the 6 gallons of Collector Water. I have the Collector Water bypassing the Water Heater and going directly into the hot water line to the house . The Pex I used has a rating of 200 f. at 100 psi and the CPVC leading from the Collector Box to the house is rated at 180 f. at 100 psi. Total material cost : $400).

I'm curious on how you painted the pex.

I set in exact position the Pex Coil within the Box , angled the Box at the desired 30 degrees from vertical ... then painted the coils on the top and sides (and the bottom as much as i could by slightly moving the coils around) : I waited for the paint to dry then did it 2 more times until i had good coverage . I used Krylon Fusion plastic paint which the Mfg'r told me is good for 200 f. The paint finish hasnt dulled in the least after a few days of operation with the outdoor temp. being 95 f. in full sun.

Great compilation video shows all you need to know. Thanks!

you should paint the sash too
 

more absorbtion the better you know!

I rekon if you want to regulate, you could drill a few holes in teh top and the bottom, problem with that is you lose allot of heat on cloudy days. best solution would be to build yourself a little microcontroller (not hard) and trip a relay everytime temp gets above your set point to turn on a cpu fan or something that blows in outside air.

Daox, Thank you...its working very well for me.

Xymox , Ive found it amazing how much absorption i can get from using hi temp. plastic Pex in such a compact collector box as this ; obviously this installation isnt going to work for most people but its great for one person who has minimal daily hot water requirements . If it doesnt work well enough in the winter months when it only gets up to 55 f. during the day, I might add another 300' Pex coil to the box by building the existing Box higher . Right now, during a 90 f . sunny day, I can usually get roughly 140 f. water with the Box on a steep 30 degree angle....and with the Box laying horizontal on the ground I have reached 165 f. After a 10 min. shower, i still have some hot water left over since im diluting it so much with the cold faucet to end up with about 100 f. at the showerhead. This is one installation where Collector stagnation is working out superb .

I was going to hang that piece of shiny sheetmetal on the face of the Collector Box to restrict the amount of suns rays...but as i mentioned on the video, I didnt find it necessary. Had the stagnation water temp. reached 180 f., I would have...but lately on the present 30 degree angle, ive been getting between 135-145 f. on fairly sunny days with the outside temp. in the 90's . Going the CPU fan route sounds interesting but it would have to have an automatic damper so the heat stays in the box when i want it to.

How long does the collector hold heat? If you take a shower at night, do you have hot water or are you manually adjusting the valves so that the water heater takes over at night?

I havent used the water heater since i installed the Solar Collector 3 weeks ago. Right now in Northern Florida, its been 93 F. + every day and normally sunny --- at 4 pm I start to loose the sun on the Collector and at that time of day the water is between 145-160 f. depending if its a totally sunny day or partial . Ive taken a shower as late as 9 pm , and the water is still so hot that I have to cool it down alot at the shower faucets. I dont adjust the manual bypass valves at the water heater...i leave them alone. The Box holds the heat pretty well with it being 2x12's as well as the double pane glass . Im expecting it to work quite well in the winter months when we only reach 55-60 f. for a daytime high , because all i need for my shower is 90-95 f. water (anything hotter than that and i have to cool it down with cold water at the faucet) .

After the sun beating down on the wood for 8.5 hours which is painted flat black, the surface is so hot you cant keep your hand on it. And this is at a 30 degree angle from vertical. So, it has exceeded my expectations by far.