DIY Solar Pool Panels and Heating Installation
I have to say that I have gotten tired of paying a lot of money for heating my pool with natural gas. My roof is covered with PV solar panels so I didn't have room for solar water heating panels. I decided to create a rack-based system on the ground and put solar panels on this assembly. My pool is about 40x20 so I should need close to 400 square feet of panels. Despite having a large backyard, I have a lot of trees that I don't want to cut down, so the best I could do is 336 square feet. The system will have 7 panels that are 4x12 feet in size. My rack will face south at an angle of 35 degrees.
I only use my pool between May and the beginning of September. I am at 40 lattitude. The sun's elevation from the horizon from the equinox to the solstice is between 50 and 73 degrees. For the rack to squarely face the sun it would have to be between 40 and 17 degrees. The latter figure would be the angle of the rack at the sun's peak elevation. Since my pool will be closed before September 21st the rack angle would probably be between 38 degrees and 17 degrees. I choose an angle that gives me the best exposure towards the end of the summer. This is how I choose 35 degrees for my rack angle. Also, I have a fence and tree to navigate around, as well as working around where there is shadow from some of the trees in the morning. Thirty-five degrees worked out best. Ideally, I probably would have like 30 degrees.
The rack will be 30 feet long by 13 feet wide. The lowest elevation at the bottom of the rack will be 2 feet from the ground; the highest elevation from the ground will be 11 feet. Eight posts will support each end with the accompanying cross-supports. The frame will be covered with plywood flooring. The plywood will get coated with exterior latex paint. Finally, the panels will go on top of the flooring. All of the wood is pressure treated. I got the panels from Bargain Pool Supplies. The hardware was from Home Depot.
First, I had to make the footings. I bought an earth auger and drilled 16 holes in the ground 2 feet deep by 8" in diameter.
Once I had the holes I mixed 16 bags of 80lb concrete in my wheelbarrow. I inserted galvanized fasteners into the concrete and let this set overnight. I used a string to make sure the fasteners were aligned properly.
Once the concrete set I started screwing in the 2 foot 4x4 posts with 3/8" lag screws. The string is level so the tops of the posts are all at the same height of the string despite the sloping of the ground.
Here I am getting ready to raise the 10 foot 4x4 posts. My wife used a dual leveler to align the posts while I screwed them in place.
Here the rack is almost complete.
Now I am starting to add the plywood sheathing. I've already primed and painted them.
Here I have cut and glued a three-way diverter valve into my pool's plumbing. There is nothing like taking a completely working system and taking a saw and cutting it open and hoping it won't leak when you are done. The three-way valve allows me to send the pump's output directly to the heater or to the panels. If it goes to the panels it will come back to the heater through the piping on the left. I put a shut-off valve so I didn't have water leaking while I was working on the piping. The system already has a check-valve so this is one less thing I need to insert.
I decided to get the local gofers to dig a trench for me from the pump to the rack. It is about 100 feet long and a foot deep. This took an entire day to dig through the hard clay and rocks. I am not worried about freezing since I will blow out the water in the fall.
Here is the completed system, front and back. I have a drain valve at the lower side so I can drain the panels. I plan to blow out all water during the fall. All the pipes are painted black.
The first day I used them I recorded the water temperature at 70F. There was a 3.5F degree difference between the water going and coming from the panels. I measured the GPM of my pump by measuring how fast it filled my spa. Based on a flow of about 60 GPM I calculated that the panesl were putting out close to 101 KBTU/hour. (60 gall/min * 60 min/hr * 8 lb/gall * 3.5F) I also measured the temperature rise from my 400,000 BTU/hr heater. It gave an 11F change in temperature. Using this I got 127KBTU/hr (3.5/11 * 400kBTU) So, the panels are putting out somewhere between 100,000 - 127,000 BTU/hr. It is now the second day and the water temperature is starting in the morning a full 6F warmer.