World Solar Challenge
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Back in ‘94ish, I participated in the World Solar Challenge as part of a TAFE team. It was a very low cost, low tech entry, basically it was a fiberglass canoe shape body with two wheels at the front and one at the back. A big flat solar panel array above our heads which could tilt.
I was in it more for the experience than as a serious contender, although our TAFE teacher was pretty excited and thought we could win.
It’s held in Australia, from Darwin to Adelaide, 3000km. It’s a really interesting area of the world and well worth going to Darwin to check out the sites and the cars. If you have an opportunity to participate, jump on it. It’s hard but very rewarding.
Here’s a nice video of one of the contenders last year. They came 4th in their class.
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Building On The Ridge or V Trough Solar Concentrator Array
Filed Under Concentrator, Homemade, Solar Panel, Solar Tracking, Sun Tracking | Leave a Comment
A V trough solar concentrator array would look like the below, not shown is the solar tracker.
This particular array has a 60 degree concentrator, with the reflector surface the same length as half the width of a solar panel. The yellow lines represent the sun and show the sun reflecting to the middle of the solar panel.
Ridge or V Trough Solar Concentrator
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A solar concentrator is a shiny surface that reflects sunlight on to a collector.
One type of concentrator is a ridge or V trough
In this diagram, the solar panel is 50mm wide, the angle of the reflector trough is
60 degrees and the reflector trough in 50mm. You can use the solar funnel
calculator to workout the angle. x being the solar panel, y being the reflector.
You can see light hitting the top of the reflector is angled down to the edge of the
solar panel. With this configuration you need a solar tracker, otherwise the
reflector trough will cast a shadow over the solar panel when the sun is angled
60 degrees or more from directly overhead.
Heat is the enemy of solar panels, so reflecting extra infra red light on the the panel
might shorten its life. Sitting the solar panel on a heat sink, perhaps a sheet of
aluminium with plenty of ventilation will extend the life of the panel.
Homemade Solar Oven Solar Funnel Calculator
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There’s a complicated math formula for calculating the angle of a solar funnel for solar ovens, and the like. But fear not, the solar funnel math calculator is here.
Enter the width and height of the funnel, and we’ll tell you the angle.
It’s better to round up a degree or two to allow for tolerances. The problem with being too accurate is you’ll have to be pointed exactly to the sun to avoid the sun being reflected back out the funnel, which might hurt your eyes or alarm planes ;)
See the math formula post for how to apply the answer.
Solar Box Oven - Solar Funnel Maths
Ridge or V Trough Solar Concentrator
Homemade Solar Oven Solar Funnel
Solar Box Cooker Improvements
Solar Box Cooker
Solar Box Oven - Solar Funnel Maths
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The angle and size of solar funnel is interdependent. The idea is you want to reflect the suns energy into your solar box oven, that would have otherwise fallen outside the box.
This is a cross section of the funnel and part of the oven. The solid vertical lines represent the inside of the solar oven, and x is the inside measurement. We will assume the oven is square. The height of the funnel, y, you’ll have to pick based on convenience, really. The larger it is, the more sun it collects, but the harder it is to carry around. So we know x and y, we have to calculate the angle. The angle should be such that sun hitting the top of the funnel is reflected into the oven, if it’s too shallow, reflected sun will hit the reflector on the other side and is just wasted. Too steep and we’re not collecting as much sun as we could.
The formula for working out the angle is:
You’ll want to round up a degree or two just to allow for tolerances.
See the solar funnel calculator post which will calculate the angle for you (aren’t we kind)
One side of your funnel should look like.
Some examples to check if you’re punching the right buttons. If x = y, say they are both 50, cos theta = 0.5, inverse cos 0.5 = 60. So the inside angle on the diagram to the left is 180 - 60, which equals 120 degrees.
If y is twice as large as x, say y = 100, and x = 50. cos theta = 0.366, inverse cos 0.366 = 68.5 degrees. So round up to 69 (or 70) and 180 - 69 = 111 degrees
Homemade Solar Oven Solar Funnel Calculator
Homemade Solar Oven Solar Funnel
Solar Box Cooker Improvements
Solar Box Cooker
Ridge or V Trough Solar Concentrator
Homemade Solar Oven Solar Funnel
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Adding a solar funnel to your solar oven will help it on marginal days. Square solar cookers work best, but if yours isn’t square, you’ll need 2 sides of different sizes. Square solar cookers just need the one size. The funnel fits on the inner box.
Homemade Solar Concentrator Solar Funnel Outline
Cut out four panels, line the insides with foil and tape together with masking tape.
Solar Box Oven - Solar Funnel Maths
Homemade Solar Oven Solar Funnel Calculator
Solar Box Cooker Improvements
Solar Box Cooker
Ridge or V Trough Solar Concentrator
Solar Box Cooker Improvements
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The Homemade Solar Cooker works well on most days, although there are a number of ways to improve it for more marginal days.
The easiest way is to make the reflector as big as the outer box. More reflectors could be made separate to the Homemade Solar Oven. You’ll need a way to hold the position the extra reflectors in place, a few pieces of wire than can be bent to adjust angles might work OK, depending on the wind.
A piece of sheet metal to replace the drip tray, painted black, and lifted off the bottom of the solar oven with cardboard strips will help. The sheet metal will hold more heat.
Making foil covered cardboard pieces the same size as the oven sides placed in the wall spaces will improve the oven, as well
Solar Box Cooker
Filed Under Concentrator, Homemade, Solar Cooker, Solar Oven | 4 Comments
Solar box cookers or solar box ovens are one of the easiest cookers to make, and they are very effective. You’ll need a few cardboard boxes, some foil, non toxic black paint, white glue, and an oven cooking bag. It’s a great way to start experimenting in Homemade Solar Concentrators.
The two cardboard boxes need to fit into each other with at least a two inch gap all round. The inner box needs to be big enough to fit your cooking pot, with at least an inch gap. Unless you’re lucky, it’s probably easier just to cut up and stick together cardboard from a few larger boxes, rather than find two boxes of the perfect size. You’ll also need a cardboard lid, which should be at least a four inches larger than the outer box.
Close the flaps on the larger box and sit the inner box on top and trace an outline. Cut out the outline so the inner box can fit inside the lager box.
So there should be roughly a two inch gap between the walls and floors of the inner and outer box. Cover and glue the insides of the inner and outer box with foil, including the undersides of the outer boxes cut down flaps. Crumple up some newspaper and sit on the bottom of the outer box to provide support for the inner box.
Glue the inner boxes flaps to the outer box and trim excess. Cut out a piece of cardboard a little smaller than the floor of the inner box, glue some foil on it, and paint the foil black. Sit this on the bottom as a drip tray.
Trace the edge of the outer box on your lid, and cut flaps so you can bend the edges down so it fits over the outer box. Glue the flaps together, but don’t glue the lid to the outer box. You need to be able to remove it. Trace out three lines on the lid that correspond to the edges of the inner box, cut the three lines and bend up to form a reflector. Glue foil on the flap. Use coat hanger wire or similar to set the angle of the flap to direct sun into your oven.
Take an oven bag and glue the end shut, then glue the bag to the underside of the lid. This creates a double layer of plastic with some air trapped inside that will slightly expand as the oven heats up, creating two layers of plastic, slightly separated. Now you’re ready to cook with your new solar oven. Let us know how you go.