GORV - Digital Magazine Issue #40 | Page 41

Right now, we are seeing truly major changes in solar cell technology. Our still mainly siliconbased (commercial) solar cells were about 6% efficient in 1954. The best are now 20%-22% and not expected to exceed that. Amorphous solar panels are flexible panels that can be rolled up or installed on a curved roof. While convenient, they are only about 14% efficient. PURCHASING TRAP There is a trap when buying, in that the claimed output is not of the overall output. It is the most typical output of the 36 or so individual cells that make up a typical 12-volt solar module. All are individually joined endto-end by soldering. There are inevitable losses. All (silicon-based) solar modules lose output when they become hot. Total panel efficiency is measured under standard test conditions based on a cell temperature of 25°C, not ambient temperature. In practice, that cell (in the sun under hot glass) will reach 25°C at only 50°C ambient temperature. An excellent general guide to a solar module’s realistic maximum output is to assume about 71% of what is claimed in the module’s promotional material. This corresponds to the solar industry’s nominal operating cell temperature. INSTALLATION In practice, it is extremely important to ensure at least 50mm of free air space beneath all silicon-based solar modules, and to use adequate cable size to connect them to your solar regulator and batteries. For most RVs, use a minimum of 6.0 square mm cable. HOW MUCH SOLAR? As noted above, the price of solar has substantially fallen in the past eight years. Battery capacity continues to rise. The best thing to do is to maximise solar capacity, using the most efficient solar modules you can find. This will ensure that your battery bank receives some charge even when it is overcast. It also necessitates using AGM or lithium batteries, because deep-cycle lead-acid batteries cannot absorb a high current charge. In essence, use as much solar as feasible. As long as you also use an adequate solar regulator, there is no risk of your battery overcharging. The writer says this is one of the earliest known uses of RV solar. This image shows his wife, Maarit, and his 1974 Westfalia VW Kombi in 1994.