The Solar Panels
Solar Panels: Rod has been interested in PVs (Photo-Voltaics) for many years as plasma processing is used in amorphous solar cells for the deposition of alpha-SiH. The advantage with the amorphous cells is that they can be produced using thin film technology quite cheaply whereas the crystal and poly-crystaline cells have expensive substrates. Also, following discussions with Alan Bonney, a Kiwi now living in the SanFrancisco Bay area, Rod had worked out a method of depositing the films upside down which has considerable advantages in the thermal budget for depositing the various layers. Imagine his chagrin on being informed by a French colleague that a very similar system had been patented by the University of Delft a short 6 months previous. Then to top it all, a quick troll of the web threw up UNISOLAR, a US company which makes flexible amorphous panels by deposition onto steel drums and then peeling the film off and covering it with plastic; oh well, at least the idea was not silly. A 32 Watt UNISOLAR panel was purchased from an Australian web site along with a Plasmatronics 20 Amp regulator (around $400) which allows safe simultaneous charging and load as well as giving the current in, current out, total Amp Hours in and out, battery voltage etc. The panel worked quite well and as with all amorphous cells gives up to 20% more power for a couple of months until the weakly attached hydrogen diffuses out resulting in an efficiency decrease from 12 to around 8%. This is the main difference between crystal and amorphous: crystal has very good stable doped junctions but need about 50 micro-metres to absorb the sunlight whereas the amorphous has a poorly connected network and the many dangling bonds are picked up by the hydrogen and sort of neutralized. This lowers the efficiency and the lifetime but makes for cheap and easy manufacture on a production line as the films scatter the light which help in them being able to operate with thichnesses about 10 times less. Both technologies seem to be heading for the middle ground of poly-crystaline which combines the advantages of both. Whilst looking for some software for the GPS Rod came across an Australian web page wich, incidentally had a small add for a couple of Solarex 53 Watt poly panels with regulator for $800. A quick e-mail and some haggling and they were his for $700 (without the regulator). Apparently he had bought a number for his mates but one of them had piked leaving him with the two panels. By one of those strange quirks of fate, the panel sitted exactly on each side of the mast so they were attached to the Universal Receiver of the sailing kit with a couple of hinges and pop rivets. Tested at vertical sun, the beasts were providing 3.5 Amps each. Allowing horizontal placement this would mean around 6 hours equivalent vertical sun and 42 AH available per day. If the sun were shining. Which it does not all the time. Even in sunny Australia.
Battery. This turned out to be an easy choice as there is really nothing around which can handle the high current loads except lead acid or variants such as a Gel Cell which we quickly settled on. It was a Sonnenschine (?) and could operate in any position and even underwater. Capacity seemed linearly proportional to weight so we bought a 24 AH weighing 9 kilos. Clearly the power would have to be effectively used during the day as more was coming in than could be stored. The regulator was secured on top with plastic binders along with two cigatette lighter inputs for the solar panels and two similar outputs for the various loads. This system was attached to the mast foot with a clip belt which could be easily removed for portage. For the trolling motor the higher currents required a direct connection to the regulator and 3 mm. Twin copper cable leading to the rear of the boat and a connector box requiring a screw driver.