One of the three panels installed. This picture illustrates the construction of the panel rack.

My three 240 watt panels each have 60 cells. As each cell produces approximately half a volt, the panel output voltage is about 30 volts. As this is slightly greater than 24 volts, I want the voltage of the combined panels to remain the same and the current output to be additive. To get this, I wired all three panels in parallel (+ to + and - to -). I then landed the positive wire on the positive termination of the charge controller, and the negative wire on the negative terminal (see the schematic below).  Each panel produces 8 amps of current at 30 volts, so the combined current (from the point where the wires join) is 24 amps.  For most industrial type wire, I needed a minimum of 10 AWG wire for this current level. I was very conservative and went with 6 AWG wire to the charge controller.

Illustrating the termination wires on the bottom of the panels.  The panels came with connectors for wiring in series (additive voltage). Since I was wiring in Parallel, I cut of the connectors and re-lugged them with ring terminals.  I then bolted the lugs together (along with the wire leading to my charge controller) and taped the connection with rubber tape.

Before running the solar panel output wiring into the charge controller, I put a circuit breaker in between the two.  This allows me to isolate the solar panel from the charge controller and battery. The circuit breaker also provides overcurrent protection.

I used a “Morningstar” 30 amp charge controller. It’s purpose is to limit the current going to the battery so it doesn’t get overcharged. A display at the top alternately reads: battery voltage, solar panel output current and load current. My load is fed directly off the batteries and doesn’t go through the charge controller, so the load current display will always read “0” on my installation.

The other breaker shown in this picture provides a disconnect and overcurrent protection for the line that comes from the battery and feeds the inverter.

Charge Controller with a pair of 60 amp, stand-alone breakers that allow me to isolate the high energy loads going to, and coming from the battery. The breaker also act to isolate the battery is there is a short circuit downstream.

When constructing the battery compartment, I had to bear in mind the three primary hazards associated with lead acid batteries:

1. Never allow a short circuit.  Lead acid batteries can release a tremendous amount of short circuit current (around 10,000 amps).  This can burn you, blind you, or actually cause the battery to explode. Not shown in this picture are the pieces of 2x6 that are used to wedge the batteries in place. In addition I will also be covering the metal frame piece at the back of the compartment with rubber.  When working around batteries, it’s always better to use smaller tools that can not accidentally cause a short circuit from positive to negative if they are dropped.

2. When the charging voltage is greater than 2.3 volts per cell, electrolysis of the water will occur and hydrogen gas is generated. Not show in this drawing are the vent holes at the back of the compartment. The cover for the compartment will be sealed with a rubber gasket. This will allow the hydrogen gas to be vented outside.

3. Batteries are full of concentrated sulfuric acid.  When checking the electrolyte level or adding water to the cells, where rubber gloves and eye protection.

My batteries are wired series-parallel to provide a 24 volt DC output. (Reference the schematic and the primer).

Battery compartment - still under construction.

The battery output wiring to the inverter runs through a 60 amp circuit breaker. The inverter is rated for 1500 watts of continuous power.  The circuit breaker should trip at, or just prior to the inverter producing it’s rated power level.  Since 60 amps of power should be ran through a minimum of 2 AWG wire, I ran parallel 6 AWG wire instead.  This is more than sufficient for 60 amps.

Since 24 volt DC to 120 volt AC inverters aren’t available everywhere, I’m carrying a spare one on this trip. The fan is pretty quiet on this inverter, so I’m installing it in the wagon, on the bulkhead leading to the driving compartment.

Schematic Of the Wagon 720 Watt Solar System