Solar Power Backup Systems

Solar power backup systems provide a safe and reliable alternative when a blackout occurs. Depending on your needs, an appropriately size reserve system can meet your electrical load and up-time requirement. If you have critical energy needs for computers, communication equipment or electric heaters, such a system may be right for you.

Backup power is usually provided by gas or diesel generators to create electricity. However, they cannot provide immediate power since they need to be primed and started before delivering power. In addition, regular maintenance is also required to ensure the motors are in good working order and the fuel is not contaminated with moisture.

A backup solar power system, on the other hand, works quietly and efficiently in the background during the day, ensuring the battery banks are continuously charged. A non-interruptible power supply can be created for critical applications, like computer and communication systems, so important data or functions will not be suspended when the main power goes out. The following 5 components make up a complete system:

1. Solar Panels

The number of solar panels depends on the load and the up-time duration. First, determine how much energy your electrical equipment requires. All equipment will state the amount of power in Watts that are needed for peak operation. Once you know the total power requirement, use this number to determine how many of solar panels needed for your application. [See: How many solar panels does it take to make one kilowatt?]

2. Charge Controller

A charge controller is necessary to maximize the amount of current generated from the solar panels. Ensure that the controller has an auto-disconnect feature that will disengage the batteries from the solar panels once they're fully charged. This will prevent damage to the batteries that can be caused by overcharging and will also prevent any charge leakage from the batteries when the solar panels are dormant.

3. Battery Bank

The number of batteries you'll use again depends on the load and up-time requirements. Once you determine your energy requirements and estimate how long a blackout may last in your area, you can then determine how many batteries you need. For example, if your equipment requires 300 W of power, then the battery requirement will be as follows:

One 20 AH battery operating at 12 V will be able to supply 240 WH:
     20 AH x 12 V = 240 WH

Five 20 AH batteries operating at 12 V will be able to supply 1200 WH:
     (5 * 20 AH) x 12 V = 1200 WH

A battery bank with 5 batteries will be able to supply:
     1200 W for 1 hour or
     600 W for 2 hours or
     400 W for 3 hours.

Batteries should be checked regularly for fluid levels and leaks. They can be placed outdoors but should be kept out of the cold and have proper ventilation (small amounts of hydrogen gas will be expelled during the recharging phase).

4. Inverter

An inverter is necessary for converting DC power from the batteries into AC power for your equipment. There is a small energy loss in the circuitry but is usually about 95% efficient.

Using the above calculation, five 20 AH batteries will supply 1200 WH of power. If the inverter is 95% efficient, then the usage will be as follows:

     1200 WH x 95% efficiency = 1140 WH

     1140 WH for 1 hour or
     570 WH for 2 hours or
     380 WH for 3 hours.

5. Transfer Switch

A transfer switch is a circuit that can quickly switch the input power from the grid to the battery backup. The operation should be instantaneous to provide an uninterruptable power supply to your load. Look for a unit that mechanically separates the two supplies with a relay so current will not leak from the batteries out to the grid and vice-versa.

Solar power backup is a reliable system for critical equipment. It is more costly than having the batteries recharge directly from the grid but will continuously top up the reserve whenever the sun is shining.