How to Use a Solar Panel to Charge Lead-Acid Batteries

Lead-acid batteries are used in boats, travel trailers and recreational vehicles to supply power when the vehicle is not connected to shore or campground power. They also provide power to the brakes in emergencies. In recreational vehicles a common problem is keeping the batteries charged when the vehicle is in storage or being used in remote areas. One solution is to use solar charging panels to recharge the batteries during sunny or partially cloudy days. The design of a solar charging system depends on the power requirements of your battery system.

 

1. Calculate the power required to recharge your vehicle's batteries. If you have a 500 amp-hour (ahr) battery that is 50 percent discharged, you will need to supply 250 ahr of power to it to fully recharge it. Less power is needed for storing batteries, but you should estimate for the power required to recharge batteries. Solar charging is a slow process; it will not quickly recharge depleted batteries.

 

2. Calculate the number of solar panels needed for your batteries. Assume that a 15-watt panel will provide 1 amp per hour in direct sunlight. Since solar panels will only provide power to the batteries in daylight hours, you will need to oversize the solar array if you plan to use the batteries while charging them.

 

3. Install a battery charge controller between the panels and the battery bank. The charge controller monitors battery charge and prevents discharge when the solar panels are not operating. The charge controller should also be designed to reduce power to the batteries as they fully charge. This prevents overcharge and overheating of the batteries.

 

4. Install a battery condition monitor. These devices monitor battery voltage and will show the state of charge of your batteries. If the solar charging system does not keep up with your battery usage, you need to reduce battery demands or add additional solar charging capacity.

 

5. Inspect your batteries regularly. Maintain tight connections on all electrical components. Keep battery acid levels full and remove any corrosion on battery terminals.