Increasing Solar Yield: Reflection!

One of the first things we noticed with our panel was that the trajectory of the sun and the orientation of the roof leaves a lot to be desired when it comes to intensity and duration of sun exposure.  We lose a fair amount of energy between 8 A.M. and 11 A.M. and then between 3 P.M. and 5 P.M.  These are hours that should be high yield but lots of rays are lost in the poor angles. Hence, our reflection project!  Working on the ground with the panel we experimented with a mirror and with foil, trying to focus the reflection from the sun off of the foil/mirror onto the solar panel.  The ultimate idea was that we would install reflective wings, one on each side of the solar panel, to be raised and lowered depending on the time of day, so in early morning the wing facing just about east would be raised, reflecting early morning rays that would overshoot the panel back onto the panel.  At midday that panel would be lowered, and in the early afternoon the opposite wing would be raised.

Here, I've only drawn the rays that get reflected by the wing so the picture isn't too cluttered.  This diagram shows the panel on the roof, with a wing on either side, one raised and one lowered.  (Note: when a wing is "lowered" it's still not completely lowered because the force that it takes to raise a wing from completely flush with the roof is too much.)

Our on the ground test suggested that close to 900 mA increase in yield follows from using the mirror, and a 600 mA increase in yield follows from using foil (when we were testing, it was a little after 10 A.M.).  For a system that can power 6 additional lights or power 2 additional phones with the margin of increase from foil, we decided that this is worthwhile energy to try and capture.  To buy a mirror the right size would cost between 50,000 and 100,000 UGX and would have to be bought in Kampala, whereas a roll of foil that could make significantly more than 2 wings costs 14,000 UGX at a supermarket in Masaka (those convert to $20 USD, $40 USD, and $5.60 USD respectively).  So we opted for foil on a plywood frame as the cheapest and most easily acquirable option.

The construction and installation of the reflective wings has 3 main challenges: stability, lifting it, and maintaining the reflective surface.

First, to build the reflective surface we used plywood on a mounted wooden frame (our frame wood was incredibly hard and straight, good for our goal of having a totally flat face to spread the foil on, bad for having to saw and nail it).  Before nailing the plywood to the frame, we carefully spread foil over the top of the plywood and then nailed it to the frame, nailing the top of the foil and clamping the folded bit to hold it in place in between the frame and the plywood.  The flatter the frame and the less crinkled the foil, the more rays of sunlight will be reflected onto the panel and not reflected in random directions.

Laying out the frame for the wings.

Folding the foil under the sides of the plywood, so it would clamp in between the plywood and the frame.

After realizing that the nails wouldn't be enough to hold all 3 long strips of foil tight to the wing, we decided to glue the long edges of the foil down to the wood.  Before this, wind easily could have fit into the cracks between the long overlaps, either ballooning the foil out so it got crinkled/was no longer a flat surface, or even ripping the piece.

The finished wing! 

Installation Part #1:

We used the same basic installation plan for the reflective wings that we have been using on solar panels.  The twist here is that instead of bolting the piece of wood that goes on top of the roof to the wing, we attach it via a hinge likeso:

Imagine the purple bit is a hinge.

The panel itself is tall, maybe seven feet (see above, where it dwarfs Obama and myself), so stability on the roof, i.e.: the solidity of the mounting system and its ability to hold the wing there is very important.  Holding the wing upright when wind is blowing is similar to holding a sail in the wind because it has such a large area, and if it falls it might smash the solar panel (this is the one that traveled with me from RDU to Boston, was rechecked and then traveled on to Amsterdam, Kigali, Entebbe, Kampala, Masaka, Kalisizo, and Lwemodde before being mounted on this roof).  So stability is something that I've been incredibly nervous about and that we focused on.

Originally, we nailed the hinges to the panel (after we had already put the foil on, rookie mistake).  It was difficult to prevent the foil from crinkling while we were nailing.  However, with the wing on the roof, it was very clear that nails wouldn't be sufficient.  They were too loose and seemed to be close to being pulled out of the wood from the weight of the panel.  We ended up installing as is the first day, but tied multiple safety ropes and decided not to use the mechanism until we could replace the nails with screws.

The hinges.  Notice nails are driven in halfway then bent to hold the hinge in place.  Ultimately, not a great idea. 

Winching up the foil wing very, very carefully!

Obama works his sealant magic on bolt holes.

What a great looking group!

Screwing in the bolts.

Raising the wing for the first time!  A little shaky at the hinges, but all in all not bad!  Just very very heavy.

I'm sure you've noticed that putting a wing on a roof is all good and fine but doesn't really do anything for you if there's no mechanism for raising/lowering it.  This first bit of the process was completed in the last days Julian was here and the next week, we have since upgraded to screws (see post: Foiled Again!), and are in the process of working towards a raising/lowering system.

With a variety of other irons in the fire, we've been kind of distracted from the reflection project, and for whatever reason the Lwemodde Youth Group members themselves have been dragging their feet about it.  They don't seem to be excited about the project (definitely doesn't have the glamor of circuit-building or internet cafes), and so as a result it's been getting pushed back and back.  I think another element of this might be concern about the safety of the panel, although with our safety rope mechanism, even when it's raised and lowered the wing should have no way it could break free and fall on the panel.  This project will probably be one that we continue through the end of my time here as priorities shift.