Bouncing Ideas on Reflection

There are many features in our solar node which are designed to conserve every millivolt and milliampere from the solar panel. This is something which Julian Ilett, designer of our solar charge controller, has incorporated into the PWM5. For example the diode he uses to ensure current is not going towards the solar panel is a Schottky diode. As I understand this diode is not pure semi-conductor but also has some metal incorporated somehow. The purpose of this is to have a lower forward voltage than a normal diode. The Schottky diode has a forward voltage of approximately 0.3 V. Not the usual 0.7-0.8 V. This means at peak solar panel output of 5 A we only lose 1.5 W, not 3.75 W. Great!

Somethings we have done to minimise power loss is have our measuring circuits only engage upon pushing a push switch and having enough control to turn on and off the loads even if all they do, when not used, is power a single LED.

Recently we have had another idea which may be of benefit to our maximization of solar output. We know quite well now that the angle of the solar panel towards the sun makes a large difference. We had an entire less about this with the youth center. If you have the panel perpendicular to the sun's rays then you will have maximum current from the panel and the more angled the more that output drops off. (Of course, due to the photoelectric effect, the impact of angle on the voltage of the panel is not really observable.)

Now we cannot pivot the panel multiple times throughout the day. A mechanism which would be strong enough to do this and still be secure from theft seems very ambitious especially on a thin tin roof. But we are thinking of doing something else. Instead of moving the solar panel we could move some lighter mirror in the morning and afternoon which would reflect light onto the panel. In the morning you raise one mirror to capture and direct the sunlight when it is quite low. Around 11 am you would lower this mirror, wait until 2 pm and then raise another mirror on the opposite side. This would require moving 2 ropes to be moved per day and since there are people always at the center this is a very minor piece of work.

We tested what a single mirror would give us if perfectly directed for the solar panel at around 4:30 pm.

Junior sets up.

Junior focuses the mirror to be exactly on the solar panel.

Checking the current output increase.

From this testing we got a rough 800 mA increase from that mirror. The mirror is not the full width of the panel and it is a bit dirty but this was a notable increase. The main issue to a flat mirror however is that it is perfect for only a very short time during the day. After that time the mirror's reflected light will spread over the panel unless redirected.

We are thinking of creating a very light curved mirror from aluminimum foil. This will not be as reflective as a mirror but with a large surface area and curved surface we may get up to an amp. Luckily we have a way to easily test curved shapes.

We have not done the actual mathematical derivation yet but we have tested arbitrary curves so far using a piece of software called GeoGebra. This is a terrible name for a piece of software and it is essentially a more annoying version of Geometer's Sketchpad, but its free! So this software allows you to define lines which are tangent to surfaces or points which are the reflection of other points about lines etc.

We take the sun's rays to be parallel to each other and not radiating from a point since the sun is so far away and then we just construct all the necessary lines from first principles. We can then move certain points, still keeping the integrity of all of the lines, so that we can test different mirror angles, sun positions etc.

Screen shot from our GeoGebra model. The curve through B represents the reflective surface  and the sun is opposite.

We still have plenty of practical and theoretical testing to do before we begin even thinking of constructing a real mechanism. Hopefully this will be worth the effort.