Letter Re: Backup Electric Power Design Considerations


As a full time user of off-grid power I’ve a few quibbles with this article. One is the casual reference to rooftop solar panels. Solar panels get dirty-fast. Solar panels in general are not all that wonderful in generating concentrated energy and dirty panels generate far less than optimal. They need to be cleaned with a soft brush and hose often. In northern parts snow sticks to panels real well and then generate nothing. Unless you have a widows walk installed below the panels, don’t even think about installing them on high roofs. Anything that gets in the way of the sun will have a totally unreasonable negative effect on solar panels. Even that tiny bare twig way up in the top of a tree, so make sure you have a clear path especially in winter when the sun is low in the south (for northern hemisphere).

The author mentions “installing an inverter at the panels and sending an AC current down the line to the battery bank”. Obviously you cannot charge batteries directly with AC power. Any inverter has to be installed after the battery bank. As the author says, hook several panels up in series to boost the voltage to higher values and minimize current loss. The author also mentions using welding cables for the battery to inverter run. No reputable solar company or installer does this. Short runs of dedicated 0000 swaged cables are the best option for any reasonably sized system. These can be bought online or a local installer can make them up for you. Regards, – Expat