About 12 Volt Solar Power Systems

12 Volt solar power systems are used most mainly for small-scale projects. They are easy to install for applications needing less than 600 W such as boats & RVs, and where the individual components are relatively close together (less than 50 feet). If the batteries are located too far from the solar panels, then more of the current will be lot as heat instead of being used to recharge the batteries.

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Solar panels supply 12 V power to recharge 12 V deep cycle batteries. Components can be readily purchased online or at local hardware stores and are easy to assemble. Other parts, including the charge controller and inverter, are relatively inexpensive since 12 V equipment is so common.

When the components are close together (less than 50 feet), then 4-gauge wire can be used to safely handle the DC current. This common copper wire can be used to transport up to 60 amps without too much voltage loss. However, the longer the wire, the more resistance there will be and more energy will be lost. This means that the precious current will be lost as heat instead of going to recharge the batteries. The goal of a good solar power system is to minimize this resistance by using wires that are short as possible.

Advantages of 12 V Systems

Parts are readily available online or from local hardware stores and are relatively easy to setup.
When the components are close together, these systems are very efficient and lose little energy as heat.
These systems are easily scalable. Adding solar panels and batteries is straight-forward.

24 V Solar Power Systems

Sometimes the layout of the landscape causes the system to be larger than expected. For instance, if the best location for the solar panels is on the roof of a three-story house, the batteries may be located more than 50 feet below. When wires are going to greater than 50 feet in length, consider installing a 24 V system instead.

Background - Electrical Basics

Power is measured in Watts and is calculated as follows:

Power = Voltage * Current

To get the same amount of power, you can vary the voltage and current. For instance:

300 W = 12 V * 25 A
300 W = 24 V * 12.5 A

Increasing the voltage means:

Reducing the current to provide the same amount of power.
Requires thinner and lighter wire (higher gauge).
Wires can be longer since there will be a lower voltage loss along the length.

If your installation is going to be spread out, then consider a 24 V system. The components are made up of the same 12 V solar panels and batteries but are arranged in a different configuration. To create a 24 V solar panel, simply place two 12 V panels in series (connected back-to-back). The supply voltage from each unit will add up (12 V + 12 V = 24 V) and this will have more drive to overcome the increased distance of the cable. There will still be a voltage drop across the wire but not as significant as before.

To create a 24V battery bank, simply connect two 12 V batteries in series (connected back-to-back). The voltage from each battery will add up to create 12V + 12 V = 24 V. With an increase in the system voltage, the current does not need to be as high to get the same amount of power. Just ensure that the charge controller and inverter are rated for 24 V.

Advantages of 24 V Systems

Longer wires can be used so components can be distributed further to take advantage of the landscape.
Can easily be constructed out of 12 V parts.

The parts of 12 volt solar power systems are readily available and easy to assemble into a system. However, if the system needs to be spread out, then consider reconfiguring the system into a 24 V system. You'll be able to reduce the energy loss and have more usable power.