<%@LANGUAGE="JAVASCRIPT" CODEPAGE="65001"%> Solar Power for RVers
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Course Topic: Solar Power (6/98)

Instructor: Greg Holder, Owner, AM Solar

The topic is really about "photovoltaic modules", rather than "solar panels". A solar panel is really related only to heating water, not to producing electricity. Benefits of solar electricity: clean, quiet, easy to use, maximizes battery life, "electrical independence", low maintenance, safe, and reliable.

To be an informed buyer, there's a need to understand some of the technical terms. A "solar module" captures sunlight, passes through a "charge controller", goes to a "deep cycle battery", then runs either DC loads, or, via an inverter, supports AC loads such as microwaves, TVs, or other appliances. Caution: Solar power is not ordinarily adequate to support heavy appliances such as air conditioners.

"Solar" is really nothing more than a battery charger. Lead and Lead Dioxide plates in a solution of sulfuric acid produces electricity. As battery is used, Selfware in the liquid causes both plates to become lead sulfate, and the solution to become water. This is a fully discharged condition. Recharging moves the Selfware off of the plates and into the water, reforming sulfuric acid.

Equalization: If you don't recharge every week, eventually the battery will form sulfate crystals which will reduce efficiency. Equalization is a planned overcharge, which drives the accumulated crystals back into the solution. This means each of the six cells will be "boiled" to bring them all into equal status.

Batteries are essentially of three different types: Starting batteries are good for short bursts of heavy power, and capable of rapid recharge. They're good for about 15-30 cycles -- i.e., deep discharges and recharges. RV/Marine batteries are a bit of a hybrid -- 300 - 400 cycles. True deep cycle batteries last for 700 - 800 cycles. These are typically much heavier than the other two types. For purposes of designing an RV solar system, "true deep cycle" batteries are by far the best bet. Trojan T 105 golf cart type battery is at the top of the recommended batteries. This is a six volt battery, so one must buy them in pairs. The disadvantage is they are somewhat larger, and often don't fit in RV battery boxes. Trojan SCS 12 Volt battery is a more standard size, and is the next best bet. The benefit of the Trojan, in the instuctor's view, is that they simply last longer. Some of the students noted they had found Trojan batteries through Price/Costco at about $50 per unit. A tip when buying batteries: "H5" stamped on top of lead battery post means battery was manufactured in August (corresponds to "H") of 1995. It's a good idea to check this when buying batteries, to get the more recently manufactured batteries. And if you use more than one tied together, get batteries of same manufacture date.

Solar modules are of three basic types: "Amorphous" (6-10 % efficient); "Single Crystal" (15% efficient) ; and "Polycrystal (14% efficient). Amorphous technology isn' t there yet, so single crystal and polycrystal panels are the most suitable for RVs.

30 cell solar panels (usually 3 x 10) are self regulating panels. 33 cell 15.9 V modules are "cool climate" panels (usually 3 x 11 cells). Forget self-regulating modules for RVs, as they're simply not suitable and will damage batteries. The 33 cell panels are okay for cooler climate, but can be troublesome in warm temperatures. The 36 cell (9 x 4) "warm climate" modules are most suited for RVs.

Voltage Drop: On the back of each module there will be listed a peak power voltage. But there will always be an approximate voltage loss of about .5 V going through the charge controller. The instructor has concluded that if a solar panel is not of the 36 cell type, it simply doesn't belong on the roof of an RV. This, despite the fact, that thousands upon thousands of RV installations have used the 33 cell type units. The reason is that the at the higher temperatures the 36 cell units don't lose voltage. The Solarex 50 watt VLX is the favorite.

Angle of Incidence (i.e., the angle of sun on panel): Surprising to me -- adjusting mounts are not recommended. In practice, most persons who pay extra for them don't really use them. And those who do all too frequently forget to put them down when they leave, and end up losing some expensive equipment. Finally, the adjustable mounts are not as secure as the permanent, flat mounts. His advice is to simply leave them flat-mounted, and, if necessary, add an extra panel to compensate for the loss of efficiency. Examples of efficiency loss was provided by a chart which shows that panels can be 90% efficient while 25 degrees "off", and 64% efficient at 50 degrees off.

Battery charging strategies: There are essentially two types of charge controllers -- "on-off" types versus "pulse width modulation". On-off voltage controllers are usually set at about 14.8 volts. When the voltage reaches that level, the controller then completely cuts off all current. The bottom line effect is that they can be very hard on batteries, reducing battery life. Pulse width modulation is now the state of the art, and are now considered an essential part of a well designed RV solar system.