Monday, 20 February 2012

More Solar Thoughts

Solar panels are a great way to make some "free" power for the boat. The initial solar installation is expensive and the peak wattage produced is not guaranteed. Fluctuations in the amount of direct sunlight cause by cloud or other forms of shading can reduce the output. The output of a solar panel is given in watts. So a 100 watt solar panel rated at 12 volts should give us 8.3A output. However, solar panels often give more voltage output that the nominal 12v that we are looking for. Lets say that the solar panel can reach an output of 18 volts. The maximum ampage would be 5.5 A. That calculation is also in perfect conditions with the maximum amount of unobstructed sunlight falling on to the panel. You need to read the documentation for the solar panel to see what figures are being used for calculating the output wattage.

It also helps if you can track the sun's direction and the angle of the sun to improve the wattage output. The angle of the sun can vary over the course of the year but the adjustments would be infrequent. The suns direction can be estimated from nearby shadows (don't look directly at the sun). However, if you can increase the amount of sunlight falling onto a solar panel this should improve the output on hazy days when the panel is working but not as efficiently as it could be. There are two ways to do this. One is by using a lens system to concentrate light (impractical on a boat). The other is by reflecting sunlight onto the solar panel. My thoughts had been based on using a mirror or other device to reflect sunlight onto the panel.

© Geo-Dome

In the above illustration, the mirror is laid on the floor. My idea had been to lay the solar panel flat on the narrowboat roof and then to angle the reflective device above the solar panel. The reflector would also fold flat onto the panel when the boat was moving.

Whilst I was pondering on how to achieve the enhanced output I came across a website (Geo Dome) where someone had already done some basic experimentation using a mirror.
Quote "Most of the time a solar panel is working well below peak power, on hazy days and when the sun is lower in the sky, early morning, late afternoon for example. The light levels are just not high enough, so to boost the light level I tried aligning a mirror to reflect more light onto my solar panel. It worked really well and after a bit of experimentation I found that placing a mirror at least twice the size of the solar panel on the ground in front of the panel could boost the output by as much as 75%."

There are a few caveats to using a mirror and that is when on a hot sunny day the solar device can overheat if the reflective mirror is concentrating too much sunlight of the solar panel. I came across another site (CleanInventors.Org) with a variation on the solar panel and reflector idea. Which I think may be a bit more practical for a narrowboat system. Because the panel and reflector needs to be folded down when moving.

© SolarRib

I now have three 80 watt solar panels for the boat. Including a good quality regulator.  The theoretical maximum will be around 20amps output. I hope to be able to get between 5 and 10 amps under average conditions.


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