Maximum Power Point Tracker for Photovoltaic Array
Simply connecting your solar panel directly to a battery is not enough to get the maximum performance out of your expensive PV panel. This simple circuit based on the ubiquitous LM311 voltage comparator is designed for use with solar panels for 12 volt systems. These panels usually have their maximum power output when their terminal voltage is around 16.5-17.5 volts. The aim of this circuit is to keep the PV panel voltage within this range. By using this in combination with a shunt regulator (not shown here), this can be used for battery charging (This was the main intent of this circuit, since the idea was to power a remote electric-fence).
Adjust the MP voltage set potentiometer so that the recommended maximum power is observed at Vin. Adjust the balance such that about 0.5 volts hysteresis is achieved about Vmax (an oscilloscope may be needed to observe this, but a rough no-load measurement can be done using an adjustable voltage supply and a voltmeter to observe when the comparator makes its transitions).
Note that any low-voltage N-channel, enhancement-mode power MOSFET is suitable for this circuit, as long as it can pass the required current. Also, the Schottky diodes should be sized accordingly. All resistors are 1/2 watt and all electrolytic capacitors have signed polarity. The inductor is not critical, but should be about 10mH and the windings should be thick enough to pass the required current (20 turns of 2.5 sq mm copper wire on a 5cm outer diam powdered iron toroid should more than suffice for 10-15A applications).
The measured efficiency (if good electrolytic capacitors and a low on-resistance MOSFET are used) can exceed 90% Note that this circuit (with some modifications) can form the basis of a step-down DC-DC converter.