JLC Extra: Solar Cargo Trailer

Here’s a basic outline of how this mobile photovoltaic system works. Four 24-volt solar modules – wired in parallel – send DC power to a combiner box. Inside the box the negatives connect to a negative terminal bus bar and the positives connect to individual circuit breakers – which will trip if there is a problem with the module or wiring.

The combiner box is connected to a charge controller, which is in turn connected to the inverter and four 6-volt deep-cycle batteries that are designed for use in photovoltaic systems. Wired in series, they produce 24 volts. The charge controller monitors the batteries and prevents them from overcharging or discharging beyond 50 percent.

When there are loads on the system, DC power flows to the inverter from the batteries or from the batteries and modules. The inverter converts the 24-volt DC power into 110-volt AC, which passes through breakers on its way to electrical receptacles in the trailer. All components are bonded to the trailer chassis. The system can be connected to a generator or to the grid via a transfer switch. When the system is connected to the grid, the bonding wires become grounding wires.