Typical Solar Panel System Schematic

Solar Panel With LoadMost solar DIY enthusiasts start out by building a solar panel and hooking it directly to a load just to see how it works. Most likely they will try a 12V light bulb. The panel may have 36 cells producing a maximum voltage output of 18V. The bulb will glow extremely brightly in full sunlight but will fail to illuminate at nighttime. Check the diagram to the right to see how that simple circuit would look.

Having power available only when the Sun shines is not always practical. Most often the power is needed at nighttime or on overcast days. To solve this problem a battery is attached to the output of the solar panel and is continually charged during daylight hours when there is sufficient Sun. The load is attached to the battery output and may be operated any time there is energy available in the battery. A Schottky diode is placed between the panel and the battery as a safety precaution to prevent the battery from discharging into the panel in lowlight conditions, especially at night, when the panel voltage drops below battery voltage.

Solar Panel Battery and Load

While the previous arrangement may be OK for limited use, where the panel is erected only when needed, it is not an ideal arrangement. Exposing the battery to the full 18V output of the panel for extended periods will shorten battery life and quite possibly result in a major rupture as the battery overheats.

To prevent early battery failure a regulator referred to as a Charge Controller is placed between the panel and the battery. The Charge Controller has two primary functions, (1) to control the power input to the battery, in particular limit the maximum charging voltage, and (2) to prevent the battery from backfeeding into the panel in low-light conditions when the panel voltage drops below battery voltage.

Solar Panel Charge Controller Battery and Load

The previous arrangement will work great for 12V DC loads. This might be fine at the fishing cabin but won’t be very practical at home where all the appliances run on 110V AC.

An Inverter is required to convert the stored energy in the batteries (12V DC) to 110V AC. This is installed between the battery and the load. Now the entire system will not only capture the energy from the Sun, but it will store it for later use and convert it into a form that will run regular household appliances.

Solar Panel, Charge Controller, Battery, Inverter and Load