This article will give our readers an idea of what is needed to build a vehicle that utilizes solar panels, a DC to AC power inverter and a battery bank to enable the use of 120 volt appliances and tools while mobile and away from any power. Our system is mounted on a four wheel drive Chevrolet pickup with a utility commercial shell.
Several solar panels joined together are called a solar array. For our purposes we used a 12 volt array. There are also 24 volt arrays as well as 48 volt arrays which are usually reserved for residential or commercial buildings. We will only deal with 12 volt arrays for this article. Our service truck has four Kyocera 125 watt, 12 volt panels on the roof of our utility shell. The formula for figuring how many amps that relates to is, 125 watts divided by 12 volts = 10.42 amps per panel or 41.68 amps for the set of four. To put things in perspective, a large auto type battery charger puts out 40 amps. This is a very high power system and is enough power to power our personal travel trailer for about two cloudy days.
The next major component of our system is a charge controller. The power from the panels goes to the charge controller which is a Xantrex 40 amp, three stage controller capable of taking the full power to the battery bank when maximum charging is needed. As the battery bank becomes closer to being fully charged, the controller “tapers" off to a lower charging rate until the bank reaches about 14 volts when it then goes into a “float" mode that basically just maintains the batteries charge to 100%.
Batteries used for renewable energy are not the same as starting batteries as used to start a vehicle. Renewable energy batteries have much thicker plates and are built for many cycles of being discharged and recharged than would be a starting battery. They also have much more capacity than a starting battery. We use four Concorde Sun Extender 6 volt batteries which are wired in series and parallel. This wiring configuration gives our battery bank about 440 amp hours of reserve power. These are AGM (absorbed glass mat) batteries which are sealed and are spill resistant and therefore pose no safety hazards as far as acid spills are concerned. Each battery has a 220 amp hour rating. When using a series AND parallel wiring configuration however, you end up with 440 amp hours. To illustrate the power here, remember most new homes have incoming power from the utility company of 200 amps!
Once we have all this power stored in our battery bank we need to convert it to usable ac power. This is accomplished by our 2500 watt inverter. The battery bank and the inverter are connected by very large gauge welding cables. An inverter takes the 12 volt dc power from the battery bank and changes it to 120 volts of ac power so that we can use household appliances such as coffee makers, microwaves for use in our travel trailer and most importantly on our service truck, for all our power tools.
Our system enables us to go out on new construction job sites and work all day even though there is no power to the building yet without the noise or expense of a generator. Of course the battery bank will be drained eventually and is why we built such a large one. A system should not be drained below 50%. The lower the discharge rate, the less life expectancy you will get from your batteries. Most of our equipment was purchased from Back Woods Solar in Idaho, who we found to be very knowledgeable and reasonable in cost. They also went the extra mile for us when we had questions. The cost of our system ran around $4,000.00 with us supplying all the labor.