How to hook up solar panels to RV batteries in 4 easy steps

An RV usually has two batteries. The automotive or starting battery is there to start the engine. The second one is a so-called house battery, which feeds electrical appliances in your RV.

In theory, a house battery isn't necessary for an RV, but certainly comes in handy to keep, for example, a fridge on 24/7. Usually it's a 12V deep-cycle battery, either lead-acid or more modern lithium-ion. A house battery can be charged via several methods:

• RV hookups in trailer parks. Basically, it's a charging station.
  
• Generators which use gasoline, diesel, or propane.
  
• Alternator, which is built into the engine of an EV and charges the battery while you are driving.
  
• Solar panels. They are a great addition to an alternator, as they supply you with energy when you stop along the way. They became a solid alternative to RV hookups and generators since they produce no sound or smell, require almost no maintenance and pay for themselves over time.

To charge an RV battery with solar panels, first you have to hook them up. The whole procedure is rather simple. While you can call for professional help to perform the installation, it's a fairly easy task to do yourself. We'll break down this process in four steps.

There are two ways to install solar panels for an RV. You can use a portable kit and install them on the ground each time you park somewhere, or simply put panels on the roof and generate energy round the clock. To attach panels to the roof, you can use the following tools:

• Mounting Z brackets for solar panels come with nuts and bolts, but can be attached to the roof with strong adhesives.
• Aluminium tiltable mounting brackets allow you to adjust the angle of panels, but require drilling. Panels on these brackets or frames can be also safely put on the ground.
• Light flexible or amorphous (thin film) solar panels can be just glued to the roof or fixed with velcro tape. However, they tend to overheat, which lowers their already below-average efficiency

It is best when there is some space between panels and roof. That way the air helps to cool down panels. When solar modules overheat, they degrade faster and produce less energy as their voltage drops.

Think about positioning and angle of solar panels before installing. In the USA, solar panels should be facing south — this way they'll generate the maximum amount of energy. Of course, RV is made to move around, but keep it in mind when parking your trailer in a new place. The angle of solar panels on the RV roof can be equal to your latitude. Generally, a tilt between 30-45 degrees works fine in the USA.

Whenever there is a battery in your solar panel system, a charge controller is a must. Its role is to protect the battery from high voltage of panels, as well as from overcharging and deep discharge. If you simply hook up a battery to panels, it will overheat and might explode.

There are two types of charge controllers:

• PWM-regulators are cheap, but they are suitable only when the voltage of panels is slightly higher than the voltage of a battery. They simply cut down the voltage to the level of the battery.
  
• MPPT-controllers are more sophisticated and expensive. They convert extra voltage to electricity, so you barely lose any of the generated energy.
  

The size of a controller is measured in amps. To figure out the power level of a regulator that you need, divide the combined power of your array by the voltage of the battery. For example, if you have two 300 W solar panels and a 12 V battery, then the size of your charge controller should be bigger than 300W * 2 ÷ 12 V = 50 A.

It is necessary to first connect the controller to the battery and make sure it works. Follow the instructions for your model of charge controller. For this task you would need a stranded copper core wire. Don't mix up the positive and negative current: connect the negative terminals of your battery and charge controller with the black wire, and the positive terminals using red wire. Screw the wires tightly into the charge controller and check the battery connections.

Once you've connected the controller, turn it on and make sure it's working. Read the manual for more info on your particular model.

Charge controller is a good tool for monitoring your solar panel system. On the display of the most basic charge controller you can see the current state of your battery, its charge and the voltage of panels. More advanced models measure the temperature and can be programmed to manage the charging process. At this point all that is left is to connect the charge controller to solar panels.

To connect your solar panels and the charge controller you might need two cables with standard MC4 connectors for solar panels.

Out of the junction box of a solar panel comes a positive cable with a "male" MC4 connector and a negative one with a "female" connector. Add another pair of connectors with wires on the other ends to connect to your charge controller.

Then plug wires into the charge controller and screw tightly. The job is done.

Once solar panels are connected, the charge controller should be able to recognize them and measure their voltage. Keep in mind that you can't manually turn solar panels on and off. They generate electricity as long as they are exposed to the sun.