HOW DO I DECIDE ON THE BEST SIZE/CAPACITY OF SOLAR CHARGE CONTROLLER FOR MY SOLAR POWER INSTALATION

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Choosing the appropriate size/capacity of solar charge controller will go a long way to ensure the efficiency of your solar power system.

Most customers complain about the poor performance of their solar power system. On close observation we usually find out that while they made the right investment in solar panels and also went for good batteries and very reliable inverter, they did not go for the appropriate size/capacity solar charge controller for their solar power system installation.

Choosing the right size/capacity of solar charge controller is very important. There are so many sizes/capacity of charge controller in the market and so you need to know a few things before selecting one for your use.

Each time you charge deep cycle batteries with solar panels, it’s necessary to use a charge controller in the circuit in order to protect the battery from overcharging or from over discharging.

Choosing the most suitable charge controller size/capacity is simple and only requires two steps.

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Step 1 – Voltage selection

Select a charge controller that is compatible with the system voltage. The standard configurations are 12, 24, and 48 volts, 96 volts, 196 volts. If you are wiring your batteries for 24 volts you need a charge controller that is rated at 24 volts or one that will give 24 volts as output.

Some controllers are voltage specific, meaning that the voltage cannot be changed or substituted. Other more sophisticated controllers include a voltage auto-detect feature, which allows it to be used with different voltage settings.

Step 2 – Current capacity

Select a charge controller that can handle the maximum output current of the solar panel (or solar array). The maximum possible current that a PV panel can generate is the “short circuit current,” indicated as Isc in the panel’s label or specs sheet.

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It’s recommended to include a safety factor for isolated events as well. For example, a solar panel with a LSC of 7.89 amp could potentially produce an extra 25% on a very sunny day. This results in a possible maximum of 9.86 amp (7.89 x 1.25 = 9.86 amp). In this case, a 10 amp charge controller would be recommended.

If you do your calculations well, you will have no problems and your solar power system will definitely work well.

Let us consider another method.
Take the number of panels x watts to get the total watts of the solar array. You then divide it by the voltage of your battery bank to get amps, add 25% to allow for cold temperatures and as always, round up.

Example: 2 units of 140 watt solar panels in series = 280 watts / 12 VDC battery bank + 25% = 29.18 amps. You would choose a 30 amp, 12 VDC charger in this example.

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Another example: 4 units of 250 watt solar panels = 1,000 watts / 24V battery bank = 41.7 amps + 25% = 52.09 rounded up = 60 amp controller.

Please do not forget that solar charge controllers are rated and sized by the solar panel array current and system voltage.

These examples are simple calculations for small systems. If you have a larger system with muliple strings you are considering, you should consult a good solar technician for help.

CHUKWUEMEKA ONWUKA.

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