Home DIY Solar Panel System
- If your goal is to save money, then you need to know how much you will be spending. The key figure with solar energy is the cost per watt. You can figure out the number of watts by multiplying the number of amps produced by a solar cell (the current) by the number of volts. Multiplying the number of watts per cell and the number of cells will give you the total wattage. For example, if you have 36 cells of 0.5 volts and 3.6 amps (36 x 0.5 x 3.6), then your panel will produce 64.8 watts. If the cells cost $65, then you will be spending close to $1 per watt for the cells.
To calculate the amount of money that you will be spending for the panel, you must add the associated costs. In addition to the cells, you will need to buy:
Bus wire to connect the cells to each other and to a junction box
Framing material, either wood or aluminum
Plywood for backing
Primer
Paint
Caulk sealant (Dow PV 804)
A blocking diode
Clear Plexiglass to cover the panel
Soldering iron with silver solder and flux.
Adding the cost of these items to the cost of the cells will give you the total cost of the panel. Divide the total cost of the panel by the number of watts and you will obtain the total cost per watt. Compare this to the cost per watt of commercial panels for a good understanding of the economics of buying vs. building your panel. Some eBay sellers and websites such as sunelec.com will advertise the cost per watt, making the comparison much simpler. - Individual solar cells can be found online, particularly on eBay. Check the rating of the seller to make sure that the person or company is experienced in selling this type of item. Solar cells are available with or without tabs. Many strongly recommend that you invest in tabbed cells, as it will save you a lot of time. While cells with chips on them are generally okay, avoid those who will sell you a bag of broken cells. It isn't worth the effort.
- Solar cells and their connections are fragile and need to be protected. The backing should be made of plywood that is at least 3/8 of an inch thick. If the backing is any thinner, the resulting flex may break or loosen the cells. The frame around the plywood should be made of clear 1-inch-by-2 inch lumber. This should be glued and screwed into place around the plywood, and the assembly needs to be primed and painted with weatherproof outdoor paint.
- Lay the cells face-down for soldering. You will be soldering them in series, which means that the tabs from the front of one cell will be soldered to the solder points on the back of the next. Use a low power setting on the soldering iron and don't press too hard, or you will break the cells. Solder a line of cells long enough to fit the frame, then start the next row. For the 36 cell panels in this case, you may want to use three rows of 12 cells or six rows of six cells, depending on the size of the frame.
Glue the cells to the plywood backing by placing a dot of Dow PV 804 silicon caulk on the back of each cell. Turn the entire row of cells over at once onto the plywood. Press gently to ensure that the caulk makes good contact with the plywood.
Use the bus wire to connect the rows. The end of one row should connect to the back of the next row. Glue the wire down so that there is no strain on the connections, and so that the wire does not cover any cells. - A blocking diode may be thought of as a "one-way" sign for electricity. Without it, your batteries can discharge during the night when the sun goes down. You can find a blocking diode in the range of three to five amps on eBay for a couple of bucks. Get the Schottky type of diode, as these are a bit more efficient. Solder it in line with the positive lead from your cells.
- Plexiglas or polycarbonate (lexan) can be used to cover the panel and protect it from the weather. Tempered glass could be used as well, but it is expensive and hard to work with. Run the wires out of a hole in the frame, then seal with caulk. Make sure all the silicon is cured before adding the cover to let all the solvent escape. Draw a bead of caulk around the frame and then screw the cover down onto the frame for strength.
- You have now completed a panel that can provide power for decades. A solar array that is 25 years old should still work flawlessly. Do you ever wonder how much electricity will cost 25 years from now? If you have your own solar panels, it will be nothing.
Now that you have built one panel, you may be tempted to build a dozen more. Please be aware that with great power comes great responsibility. The amount of current put out by a large number of panels is not for an amateur to handle. When you are ready to cover your roof with panels, it is time to call in a trained professional.