Conventional solar panels contain photovoltaic cells that use materials such as silicon to convert energy from sunlight into electricity. While soda cans can't convert sunlight to electrical power, they can be used to capture solar energy to heat air. A simple soda-can panel relies on natural convection – hot air rises -- to move the air: cold air is drawn in through the bottom of the panel and up through the cans, where the air is heated by the sun. The heated air exits through the top of the panel and is channeled into a duct that delivers the air to the living space.
Determine the size of the solar panel by arranging cans in a single horizontal row and a single vertical column. All of the cans should be touching their neighbors. Measure the length of the row and the height of the column to find the interior dimensions of the panel, adding about 1/8 inch to each measurement to provide a bit of wiggle room.
Add 4 1/2 inches to the width and height of the panel interior to find the overall panel dimensions. These additions account for the thickness of the two-by-four panel frame and the foam insulation board. As an example, if the can array measures 39 inches wide by 78 inches tall, the interior of the panel should be about 39 1/8 by 78 1/8 inches; the overall dimensions will be 43 5/8 by 82 5/8 inches.
Cut 1/2-inch plywood to the overall panel dimensions (not the interior dimensions), using a circular saw; this is the panel back. Cut two pieces of two-by-four lumber to match the width of the plywood; these are the bottom and top of the panel frame. Cut two more pieces to match the length of the plywood minus 3 inches; these are the frame sides. Fasten the top and bottom frame pieces over the ends of the sides with 2-1/2-inch screws. Lay the plywood back over the frame so all outside edges are flush, and secure the plywood to the frame with 1-1/2-inch screws.
Position the panel faceup and line the interior surfaces with ¾-inch-thick foam insulation board, securing the board with dabs of silicone caulk. Note: Use insulation that's rated for 300 F or higher temperature. Paint the insulation with black grill paint.
Drill a 3/4-inch hole through the bottom of each can that will go into the panel, centering the hole on the bottom of the can. Remove the pull tabs from all of the cans.
Assemble each column of cans by stacking the cans vertically and taping them together with foil duct tape. Note: Do not use conventional plastic duct tape, which degrades with heat exposure. Wrap the tape in a continuous horizontal band to create a tight air-seal between cans. Paint the completed can columns with the black spray paint and let it dry.
Lay all of the columns into the panel, then make marks corresponding to the center of each column, marking the edges of the top and bottom pieces of the panel frame. Transfer these marks to the outside faces of the top and bottom pieces. Remove the columns from the panel and set them aside. Drill a 1-inch hole through the top and bottom of the frame at each mark so the hole is centered over a column location. These are the intake and outlet holes that will allow air to flow into and out of the columns.
Apply a bead of caulk to the edge of the can at the top and bottom of each column, and set the column into the panel, centering it over the holes in the top and bottom of the frame. Install all of the columns in the same manner, then let the caulk cure overnight.
Cut a sheet of clear acrylic to fit the panel frame, using a circular saw or other method recommended by the manufacturer. Run a continuous bead of caulk along the top edges of the panel frame and set the acrylic onto the caulk to secure it. Let the caulk dry.
Cut a piece of window screening to cover the bottom of the panel, and staple the screen in place to keep insects out of the can columns. Note: Use screen with a mesh size that is small enough for adequate protection but allows for maximum airflow.
Create a custom hood for the top end of the panel to channel the heated air from the outlet holes and into a duct or other desired means for bringing the air into the living space. One option is to cut and bend pieces of thin sheet metal to form a hood that tapers down to the size of the duct opening. Cut sheet metal with aviation snips or tin snips, and assemble the pieces with foil duct tape, as well with sheet metal screws if desired. Fasten the hood to the top of the panel with screws and seal the joint with foil tape.
Position the panel in a location and at an angle that maximizes daily sun exposure. Connect the panel hood to your living space with a section of rigid or flexible metal duct or other heat-resistant material that promotes rapid airflow.
- ['Aluminum cans, emptied and rinsed clean', 'Tape measure', '1/2-inch plywood', 'Two-by-four lumber', 'Circular saw', '2-1/2-inch screws', '1-1/2-inch screws', 'Drill with 3/4-inch and 1-inch bits', '3/4-inch-thick rigid foam insulation board', 'Silicone caulk', 'Exterior grill paint', 'Foil duct tape', 'Acrylic sheeting', 'Window screening', 'Stapler', 'Sheet metal', 'Aviation snips', '4-inch or larger metal duct (as desired)']
The larger the panel the more heat it will generate. A small panel might measure around 3 by 5 feet overall, while a large version might be close to 4 by 8 feet, based on a standard full sheet of plywood.
An old storm window or patio door makes an inexpensive substitute for acrylic sheeting, which is likely to be the most expensive material in the panel.
Install a small fan, such as a computer fan (preferably solar-powered), in the duct line to increase airflow through the solar panel and deliver the heated air into the living space.
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