Solar electricity on our motorhome

I asked Kelly for some notes on our solar setup on our motorhome, a 21-foot 1983 Toyota Dolphin, and he wrote:

We enhanced the basic 12 volt DC system for our little motorhome by first adding two extra deep cycle 12 volt batteries (wired in parallel) to give us much more capacity than the just the original single coach battery. This was initially only charged when we were driving, so if we stayed anywhere for very long, we would run the batteries down, although they did last several days with just running the lights, fans, and water pump.

For this current trip we decided to add a couple of 75 watt solar panels to the roof of the RV (lying flat), connected to those same batteries via an inexpensive charge controller. This allows the batteries to gain a charge whether we are driving or not, as long as we are parked where the sun shines on the roof, expanding the time we can stay at any one place without the need to be plugged into "shore power". We have found that this new system keeps the normal coach requirements for DC electricity covered nicely (except for long periods of grey weather). However if we want to have intensive use of our computer system (which is usually the case), then we do need to be plugged in for that usage.

He added that if someone were to buy the componants now, it might run around $800. We had the solar panels already (see Kelly's site about his solar car, sunvee.com) and he says you could get by with one panel. He guesses that something like this might cost about $500. It wouldn't save you that much in electricity for a long time, but sometimes the difference between being able to stay in a great place or not is how your utilities work.