How to Store Solar Energy With Car Batteries

Solar photovoltaic panel

The electricity produced by a solar photovoltaic (PV) panel can be stored in any kind of battery that stores electricity. Car batteries can easily do this job. However, a small device called a charge controller or charge regulator is needed to ensure that the batteries are not overcharged by the solar panel when the panel is generating electricity and the batteries are fully charged.

Things You'll Need

• Solar panel
• Charge controller
• Tape measure
• Battery interconnect cables
• Electric cables

Instructions

Preparation

1. Check the information regarding your solar panels and make sure they are designed to power a 12-volt system. Some solar panels can be wired up for 24 volts. In this case, the panels would generate a voltage that would seriously damage a 12-volt battery.

2. Place the batteries inside your building in a well-ventilated space. The 12-volt batteries must be connected in parallel. This means that the positive terminals of the car batteries will be connected together. Then, the negative terminals will be connected together. Count how many battery interconnect cables you need to hook up the batteries in parallel.

3. Trace the path of the cables linking the batteries and the solar panels and measure this distance as accurately as you can. Multiply this distance by two. This is the length of cable you will need. The gauge or thickness of the cable is important. The higher the current produced by the solar panels, the thicker the cable should be. Consult one of the many websites that show you how to chose the correct AWG number for the cables that run between the solar panels and the batteries.

4. Use a charge controller to control the charging current from the solar panels to the batteries. Charge controllers are sized for the maximum current generated by the solar panels in full sunshine. Go to a store that sells solar energy equipment and supplies, or check out one of the many websites on the Internet. Buy the charge controller, the battery interconnects, and the length of cable required.

Installation

1. Install the charge controller on a wall close to the batteries. Connect the battery interconnects so that the batteries are connected in parallel.

2. Connect the solar panels and the batteries to the charge controller. A charge controller will have three sets of terminal connections each marked plus and minus: two terminals for the batteries, two terminals for the panels and two for the load. The manual that comes with the charge controller will show you how to connect up the batteries and the panels.

3. Check to make sure your solar PV system now delivers 12 volts direct current (DC) from the batteries. There are many small appliances that run on 12-volts DC, but more often the charge controller is connected to an inverter that will produce 110 volts alternating current (AC) from the 12-volt DC batteries. The AC current from the inverter can then be used to power any typical household appliance-- always assuming that the inverter can handle the load.

Tips & Warnings

• Set the angle of the solar PV panels so that they get the maximum amount of sunshine. A rule of thumb is to set the angle equal to the latitude of the location where the panels are installed. Assuming you are in North America, incline the panels towards the south. Remember to check that no trees, walls, or other tall objects cast a shadow on the panels during the day. Check the batteries at least once a month, and top them up with distilled water. Do this in the evening when the sun is down and the batteries are not charging.

• Lead acid batteries give off gases that are explosive. Keep the batteries in a well-ventilated area and away from children. Wear protective eyewear when topping the batteries up with water as acid can sometimes spit up from the battery cells.

References

• Energy Savers: Stand Alone PV Systems