How to Build a 3500 Watt Solar Generator

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A large solar installation mounted on a roof can contribute substantially to the power used by a residence.
A large solar installation mounted on a roof can contribute substantially to the power used by a residence. (Image: solarenergie anlage image by Otmar Smit from Fotolia.com)

Solar panels of 3,500W generate a substantial amount of power which, on a sunny day, will supply a large part of the average house's consumption. Building the panels is not complicated but rather time consuming. A large number of solar cells must be assembled into panels covering about 300 square feet. The power generated is large enough that a connection to the grid via an inverter would be desirable. Depending on the local cost of power, such an installation could easily generate electricity worth $500 per year.

Things You'll Need

  • 2,100 solar cells, 3 inches by 6 inches, 1.75W, tabbed with long tabs
  • Extra tabs and solder
  • 28 pieces of 3/4-inch plywood, 32inches by 48 inches
  • 400 feet of pine board, 1 inch by 2 inches nominal, 3/4 inches by 1 1/2 inches actual, or similar
  • 20 pieces of plexiglass, 33.5 inches by 49.5 inches
  • 200 feet solar (UV resistant) cable rated 1,000V
  • 66 DC connectors

Build the panels. Each panel consists of a piece of 3/4-inch plywood, 32 inches by 48 inches, which is a 4-foot by 8-foot standard piece cut into thirds. Cut the 2-inch by 1-inch pine into 33.5-inch and 48-inch lengths to fit around the outside of each piece of plywood, and screw into the edge of the plywood. The plywood is 3/4-inch thick because solar cells are very delicate and need a backing which is rigid. The pine goes around the edge of the plywood rather than on top so that the edge of the plywood is protected from the weather. Paint the back and sides of the panel to weatherproof it.

Mount the solar cells in a 5 by 15 arrangement in each panel with the five cells horizontal along a 32-inch side. Draw pencil lines to show the location of each cell. Place a solar cell face down on a soft cloth with the tabs pointing up. Solder tabs onto the solder points on the back of the cell and let the excess length point down. Place the cell at the top left corner of a panel with the front tabs pointing down. Fold the right back tab over to meet the left back tab and solder together. Drill a hole in the plywood at the top of the panel. Insert 6 inches of solar wire with a negative connector and solder the wire to the tab. Secure the wire with a wire clamp. Attach the cell with a single bead of silicone sealant at the center of the back of the cell.

Place a soft cloth over the cell and place a second cell face down over the first cell. Bend the front tabs of the first cell over the back solder points of the second cell and solder into place. Rotate the second cell down into place below the first cell. Repeat until the end of the column. Fold the left front tab of the last cell over the right front tab and solder together.

Repeat the process with the second column, starting at the bottom. Fold and solder the back tabs of the bottom cell of the second row to meet the front tabs of the last cell of the first row. Repeat with the third column, starting at the top. Repeat with the fourth column, starting at the bottom. Repeat with the fifth column, starting at the top. Drill a hole in the plywood at the bottom right of the panel. Insert the end of 5 feet of solar wire with a positive connector and solder the wire to the tab of the last cell. All the cells of the panel are now connected in series to generate 37.5V and they are ready to be plugged together.

Install the plexiglass. Each sheet of plexiglass, 33.5 inches by 49.5 inches, should just fit over each panel. The plexiglass should be thick enough so that it will not bend to touch the solar cells at the center of the panel. Drill holes in the plexiglass at the corners, halfway between the corners and again halfway between the holes. Countersink the holes for the screws to be used. Run a bead of silicone sealant around the edge of the panel on top of the pine. Screw the plexiglass into place.

Put the panels in place and wire them up. Use the connectors because the panels will be live and generate dangerous voltages. The insulated connectors allow wiring of the panels without touching live parts.

Arrange the panels in a 4-foot by 7-foot grid on a roof or on a slanted structure. Raise the panels slightly off the roof or structure to allow the wiring to go behind the panels, and for drainage under the panels. Plug the positive plug from the bottom of the first top left panel into the negative plug at the top of the second panel in the top row. Continue plugging the panels together until the end of the row. Repeat with the other three rows. Each row will have all the panels connected in series and generate 262.5V.

Connect the positive plugs of the first panels of each row together using branch connectors. Connect the negative plugs of the last panel of each row together. Bring the wire from the positive plugs and from the negative plugs to a junction box at the bottom right of the solar generator and terminate there. Run conduit from the junction box down to the inverter. The solar generator will be rated to produce 3,675W, which will be 3500W after the losses of the inverter.

Tips & Warnings

  • In some climates the panels may get too hot or show condensation. In that case, ventilation holes in the plywood backs may be required.

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