What is MPPT solar controller?

Solar panels have photovoltaic cells which convert solar light energy to electrical energy. For off grid solar energy systems, the electrical energy produced has to be stored in storage batteries for use when sunlight is not available. Maximum power point tracking (MPPT) is a technique used with variable power sources like a solar panel, to maximize energy extraction. Similar system can also be used with wind turbines which also have variable energy availability. Efficiency of solar panel depends on the amount of sunlight available, shading, temperature of the solar panel and characteristics of the load to which it is connected. The load could include rechargeable battery, inverters, electrical grid and other electrical loads. MPPT controller matches the load impedance for maximum power transfer. This optimum point is known as maximum power point. The process of adjusting load impedance is done by the MPPT.

MPPT circuit can be built inside a solar inverter which converts the direct current from the solar panel to alternating current for various purposes. MPPT can analyze the non-linear relationship between temperature and total resistance based on current-voltage and power-voltage curves. In case of off-grid systems, battery discharges at night leading to lower voltage at sunrise. At that time battery voltage is below the maximum power point of the solar panel. This mismatch is corrected by an MPPT controller. When the battery is fully charged, production from the solar panel will not have a load to match. In some situations, a resistive load is used to keep the solar panels operating at MPP. This will ensure that the panels remain as cool as possible. Solar energy systems in spacecrafts may use this method.