Most solar panel arrays are designed for 12 VDC. Combinations in series could produce 24 or 36 VDC. But the better approach is to stay with a 12 volt system and charge a 12 volt battery system. a dozen 12 volt car battery array could run your refrigerator for up to a week, depending on the size and efficiency of the refrigerator and how often you open the door.
If you are performing a small experiment you can collect a small solar panel to a car battery. When you connect multiple arrays to multiple batteries to is time to use a solar charge controller.
Benefits of a charge controller
- Prevent over charging
- Condition batteries
- Prevent discharge at night
- Manage discharge
- Pretty blinking LED lights
When selecting a charge controller, the most important thing to match is the size of the solar array to the rating of the controller.
A good rule of thumb is that on a 12 volt solar array, for every 15 watts of solar array we need an amp of solar charging controller.
As we write this article, $38.00 gets you a 4.5 amp solar charge controller, which would then well serve 70 watts of solar panels. They also happen to sell a 70 watt solar panel for $225.00
If you have run an array of one dozen car batteries, a 70 watt solar panel would charge that over time, measured in hours. a 70 watt system with no losses would provide 70 watt/hours per hour. Large car batteries might store 700 watt/hours. Each battery that is 50% discharged will need 4-6 hours of direct sunlight to charge.
By the way, one final thought, a 1500 watt inverter, to provide a 120 volt outlet for a refrigerator or freezer will cost around $200.00, so not including batteries we are spending around $500 on the panel, controller and inverter. Now go find a dozen batteries and a sunny spot.