Fibreglass Panel Construction
The solar panels are constructed on top of composite fibreglass/divinycel foam panels, which have the advantage of being strong, lightweight, and non-conductive.
The completed fibreglass base panel is a sheet of divinycel foam with fibreglass laminated onto both sides.
The divinycel foam is a closed cell foam that is commonly used constructing canoes. Because the bubbles that make up the foam are sealed it is buoyant and therefore the canoe can't sink even if it has a hole in it. Because it is light it makes a good stiff foam to use in a composite sheet.
You need a stiff flat surface to make your panel against. The flatter this surface, the better the finish on the flat side of your panel when complete. To prepare the panel, it is easiest to buy something already flat like a large thick piece of MDF.
Coat the flat surface in a few coats of Shellac if necessary to seal it. The Shellac can be sanded flat after it has dried to get the surface flat again.
Wax the surface. We use Easywax which is a wax designed for moulds. The wax gives you a good slippery smooth surface to work with. If you do your waxing job good enough you don't need to use a release agent.
We want to use the mould many many times so we use a release agent anyway. It is called PVA release agent. The PVA stands for Poly Vinyl Alcohol. It is a liquid that evaporates and leaves behind a sheet of plastic. You get a piece of kitchen sponge and apply it all over the mould. It doesn't have to be particularly thick, it just has to be there. A hair dryer or heater can speed up the drying process.
To improve the quality of the finish you should use a vacuum bag. You will need a vacuum pump. Simple venturi vacuum pumps are available and all you need to run them is compressed air. Get some plastic. Large sheets of polyethylene can be bought by the metre from some hardware stores. I buy the clear sheets because you can see what's happening inside. Black polyetheylene is kind of like a very thick garbage bag plastic. You will also need what they call Dum Dum. It is like super BluTack. It comes in a roll. You will need to be ready to seal your panel inside your bag. The bag is made and sealed by putting a sheet of plastic on the table, your mould on the sheet, dum dum around the outside of your mould, your fibreglass job (which we are about to talk about) onto the mould and then attach the top sheet of plastic with a big ring of dum dum around the mould.
Assuming your resin cures slowly there is no real rush to seal the work piece into the vacuum bag. Don't put the dum dum out until you need it because it will stick to everything you put anywhere near it. If you are careful opening the bag you can probably reuse the bag a few times before the number of small holes and tears gets to the point where repairs aren't worth it.
Cut a sheet of peel ply large enough to cover your divinycel sheet. The peel ply is a layer that you can pull off to remove any excess resin. It leaves a nice finish on the bottom side of the panel.
Cut a sheet of perforated film large enough to cover your sheet. The perforated film allows any resin that soaks through the peel ply to be squeezed out away from the job.
Cut a piece of bleeder cloth large enough to cover your sheet. The bleeder cloth allows the vacuum to spread entirely over the job and absorbs any resin that escapes from through the bleeder cloth.
Cut a piece of divinycel the correct dimensions allowing enough of a margin for cutting afterwards. If there are going to be defects and anomolies in the finished sheet, they will probably be at the edge so you want to allow at least about 20mm margin. The finished sheet is supposed to be 512x614 so you need to cut a sheet of 6mm divinycel that is at least 550 x 650mm in size. The laminating process bonds the sheets rigidly so you can use offcuts that make up a sheet the right size.
Take a small piece of wire and in a nice even pattern poke holes through the divinycel. These holes will allow any air bubbles on the bottom to escape when the vacuum is applied. The holes can be about 5-8cm apart in a regular square pattern.
Mix up your resin. I am mixing up approximately 350grams to do a sheet.
If you have a preference for one side being the surface that the cells are applied to start with that side facing you. Mix up your resin and liberally brush it onto the divinycel. You can put plenty on here and it makes the next bit a little bit easier. As you paint it onto the panel, it will run into the exposed cells that were cut when the sheet was made the right thickness. The surface should appear wet before you put the fibreglass onto the panel.
Lay the first sheet of fibreglass onto the panel. Spread it out so that it is smooth. If you get some creases or pulls in the fabric don't worry too much. The other layer will cover them up. We are currently using 60GSM surfboard fibreglass because it is extremely cheap. Two layers gives us approximately 120GSM of glass per side. It is possible to go and buy some fibreglass that was the right thickness and do this in one step.
Take your brush and dip it into the resin to get a bit on the end of the brush. Dab it onto the fibreglass to work the resin into the cloth. This step is complete when the cloth all looks wet.
Lay the next piece of fibreglass cloth onto the one you've just worked the resin into and repeat the wetting process.
Carefully pick up the sheet and fibreglass and flip into over into the centre of your mould.
Repeat the fibreglassing process for the other side. If you work the resin into the pieces of fibreglass that overhang your divinycel sheet the finished product will be a bit easier to handle because there won't be loose fibreglass strands floating around. It is best to do this with whatever resin is left at the end.
Place the peel ply onto the top of the fibreglass and spread it smooth.
Cover the peel ply with the perforated film.
Cover the perforated film with the bleeder cloth. The bleeder cloth allows the vacuum to spread entirely over the job and absorbs any resin that escapes from through the bleeder cloth.
Seal your vacuum bag and wait. The resin and conditions seem to imply that at least 12 hours is required for the resin to completely set. The vacuum needs to be applied for about 8 hours to get a good finish on the panel. Turning it off too early will result in air bubbles getting into the job and the fibreglass not necessarily bonding to the sheet properly, particularly around the edges.
If you get a good seal on your vacuum bag you should be able to leave the job without the vacuum on it if you get a quick release fitting for the vacuum attachment. This allows you to remove the vacuum source and leave the job sealed.
To remove the job from the mould, pry up a corner and lift. The job should separate from the mould relatively easily. If not, you probably didn't put the release agent all over the mould.
Cutting the edges should be done with a large set square. I am using a large piece of aluminium as a ruler to run the jigsaw along when making cuts. It is good because it is heavy and doesn't move while you are clamping it onto the sheets.
The panel cuts relatively easy using a jigsaw with a hacksaw blade. The jigsaw should be set on fast with as little forward angle as possible on the cutting strokes (if you can adjust that on your jigsaw). Make the cut slowly to reduce the number of fibreglass strands left dangling on the edge of the finished panel.
Make a cut along one side and then use that side to make two other cuts at right angles and the right distance apart for the panel. Then measure the relevant distance down both sides and cut the panel to length.