Once the total amount of power to be generated is known, the solar array size can be determined. But the calculation is not always simple.  As solar panels’ ratings are usually dependent on the best power output, the power generated by the panels is stated for the time when the sun shines at its brightest; giving about 15 to 22 volts. But the related components, like inverters and controllers, are not able to take such high voltages. Cutting down the voltage to within capacity brings down the wattage respectively.Therefore, the energy captured is only about 75 percent of the amount that is collected by the solar array. However, there is a fix to this challenge. There are solar inverters and charge controllers that take into account Maximum Power Point Tracking (MPPT). MPPT optimizes the solar array’s collected power to distribute the right voltage needed by the batteries or inverter so that energy efficiency can be enhanced.

MPPT has proven to be 90 percent efficient. Inverters and controllers working on MPPT cost more than the cheap, common ones. This cost difference should be carefully taken into consideration as you plan for your solar electric system purchase. In general, using an MPPT controller is cost-effective when there is a need for 120 watts of power or more, whereas an MPPT inverter is a better choice for power higher than 300 watts. An MPPT inverter is usually adopted if there are plans to have the inverter linked directly to the solar panel, as in a grid tie solar system. However, an inverter linked to a 12V battery does not need an MPPT inverter.

The solar array power point efficiencies can be computed by dividing the MPPT inverter or controller calculation by 0.9, or by 0.75 for a non-MPPT controller:

Non-MPPT controller calculation example:

402 watts ÷ 0.75 = 536 watts

MPPT controller calculation example:

402 watts ÷ 0.9 = 447 watts