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Build A Solar Panel

The solar panel, is relatively easy to construct. The panel can be constructed using a hacksaw, wood saw, drill, hammer, screwdriver, nails, screws, paintbrush, file and a tape measure. The materials needed are, 10 mm annealed copper tube, 16 swg aluminium sheet, timber for making a frame, glass fibre wool, marine-ply sheet, and 4 mm glass.

Solar panels usually have an efficiency rating somewhere between 40% and 60%. This panel should give approximately 50% of the energy it collects, making it comparable with most commercially available units.

You can construct a panel for about 1/3 rd of the price of a purchased panel. The longer the panel can provide useful energy the more attractive is the case for installing a solar water heating system. If carefully constructed, the panel should have a useful life expectancy of 20 years or more. The materials used will not deteriorate rapidly and as there are no moving parts there is nothing to wear out. There is virtually no maintenance required.

The panel uses copper tubing to carry the domestic water through its collector area. Copper is universally acceptable for plumbing and water systems. It does not corrode in oxygenated water, and so long as a suitable inhibitor is used it will not corrode in water/ethylene and glycol mixtures either. Copper has high thermal conductivity properties, essential to provide efficient transfer of collected solar heat to the water supply. The existing plumbing in your home will almost certainly be copper and the new solar heating system should be copper also to avoid the corrosion problem associated with mixed metal systems.

The copper tubing will be attached to the blackened absorber plate. This plate will collect the sun's radiant energy and transfer it to the water filled copper tubing. The plate should be made from aluminium or copper to achieve the best results. Aluminium, being cheaper than copper and more readily available in most areas, is a good proposition. A thickness of 16 swg is preferable as thinner gauges tend to warp under intense heat conditions and thicker gauges give reduced efficiency. The absorber plate will be painted with black paint and primer and so will the copper tube, so there will be little risk of galvanic corrosion.

The absorber plate will be housed in a wooden tray. The tray is made from a hardwood frame with a marine-ply backing sheet. A good preservative coating should be applied to the tray to ensure minimum maintenance during its exposed life.

The panel should be covered with a transparent sheet to prevent heat loss in cool weather. Glass is preferred because it is readily available and has a high light transmission value. It will 'trap' long wave radiation, thus improving the efficiency of the panel. 4 mm float glass should be used. Acrylic sheeting can be used, and this will result in a lighter panel. Acrylic is usually much cheaper than float glass, but bear in mind that glass does not scratch or discolour. The transparent cover can be placed in the tray and sealed with wood beading and a suitable gum or resin.

Other items you will need are: glass fibre wool (the type used for loft insulation), a few sheets of aluminium foil or highly reflective 'lunar' foil or Mylar Aluminised Film, black paint and primer and a collection of wood screws, nails, wire etc.

CONSTRUCTION

These construction details allow you to build a solar panel 1500 mm by 900 mm, giving just under 13500 mm2 collector area. Two or three panels will be sufficient for the average household (4 people) and you should refer to the following chart in order to ascertain how many panels you will require.

Domestic Heating Installations

No. of panels required Cylinder or tank capacity

  • 1 = 15 gallons
  • 2 = 30 - 35
  • 3 = 35 - 50
  • 4 = 50 - 70

Construction can be broken down into 5 main parts:

  • 1) Panel tray and frame
  • 2) Absorber plate
  • 3) Copper tubing
  • 4) Insulation
  • 5) Glazing

PANEL TRAY AND FRAME

The panel frame should be 1500 mm x 900 mm x 80 mm. A good hardwood should be used such as teak or cedar. Most timber merchants will cut the wood to length, and machine it if desired. The 80 mm x 50 mm section is advised. Good corner joints are essential to achieve good weather-proofing. After the frame has been constructed two holes of 11mm (7/16") diameter should be drilled in the sides of the frame to accommodate the copper tube inlet and outlet. They should be drilled 2" from the top or bottom of the frame as required. Inlet and outlet will be at opposite bottom corners to facilitate draining the panels in cold weather. The frame can now receive its backing sheet. This should be of marine ply quality for best results, but 4mm (5/16") exterior grade plywood can be used. Measure the frame exactly and cut the backing sheet accordingly. Place the sheet in position and nail to bottom side of frame. An alternative method is to machine a rebate in the frame roughly 1/4" from the bottom and slide in the backing sheet before putting the fourth side of the frame in place. The whole frame and backing sheet should now be coated with a wood preservative to ensure a lasting finish.

ABSORBER PLATE

Purchase enough aluminium sheets of about 4'8" x 2'8" x 16swg for your needs (or an appropriate size to fit into the constructed tray). Prices from stockists can vary considerably. Aluminium type H9 or similar is suitable.

Clean the aluminium on both sides and remove any trace of oil that may be present. Turn up the shiny side of the sheet and use some emery paper to etch the surface. This will remove small traces of oil and allow the paint to adhere to the surface better. Apply a primer such as zinc chromate or red oxide. It is best to obtain the paint and primer in aerosol form to achieve the flatest possible coating on the absorber plate. A matt black is a very good choice and has quite a high radiation absorption rate.

COPPER TUBING

Copper Tubeing

You will need about 30' to 35' (10 meters) of copper tubing. The more copper tube the better, up to a point. Two type of copper tubing can be used, either 10mm annealed which comes in soft coils of varying lengths or standard straight lengths of tube with corner connector (see image). The finished ‘snake’ shaped copper should then be sprayed matt black

When the paint is dry, place the formed copper tube on top of the aluminium absorber plate (black side). Drill hole I the aluminium back plate and secure the copper structure to the plate with wire. Copper tube can also be soldered to the aluminium sheet using special solder and flux.

INSULATION

The absorber plate is now ready for insertion into the panel tray, but first the insulation must be in place. 3" glass fibre wool should be laid in the tray. This will compress when the absorber plate is lowered on top of it . A layer of aluminium baking foil can be sandwiched between the glass fibre wool and the plate with the shiny side to the plate. This will help stop heat loss by reflecting heat back to the plate.

The plate can be held in place by strips of wood beading screwed to the sides of the inner frame. A final spray of matt black paint is needed to mask any scratches on the paintwork caused by the wire and to cover the inside wall of the wooden frame.

GLAZING

Finished Panel

The panel is now ready for glazing. 4mm (320z) float glass is the recommended quality for this size panel. 3mm float glass can be used in panels up to 10 sq.ft. but is too fragile for larger areas. The light transmittancy of 4mm glass is approximately 88% to 90% with a reflectance of 8%. Thicker glass will have slightly lower transmittance. There should be a gap of 15mm (1/2") between the top of the copper piping and the cover. A larger gap will result in lower efficiency. After placing the glass in the tray, secure with wood beading and seal with a good sealant to keep out moisture.