Why we need Solar Panel Shunt Regulator?
A recurring problem with energy generating systems consisting of solar panels and batteries is that sometimes there is too much sunshine. At those times it is essential to limit the charging current to an already full charged battery or batteries. These will not only use a lot of water (which in itself is no problem), but their life-span will be shortened.
Voltage regulators are normally series types, that is, the regulator is in series with the load. One of the drawbacks of this is that there is always an additional loss when the battery is being charged. Since the electronic circuits used with solar panel systems already contain a Schottky diode, and solar panels may remain fully loaded even when there is little sun, it is better to use a shunt regulator. These regulators cause losses only when no charging takes place. Apart from this, any unwanted energy is then dissipated in a common resistor rather than in power semiconductors on vast heat sinks.
Solar Panel Shunt Regulator Circuit Diagram:
In the shunt regulator for solar panel circuit diagram, above , T1 switches the external load completely ON or OFF. Therefore, the dissipation in this FET is (in theory) nil since the current through, or the voltage across, it is nil. Nevertheless, it is advisable to mount it on a small heat sink (about 5 K W). When T1 is OFF, the solar panel feeds all its energy into the battery. When the battery voltage becomes too high, the FET switches ON. Provided that R is suitably rated, it will dissipate all the energy delivered by the solar panel, whereupon the panel voltage drops and the battery is no longer being charged. The Schottky diode prevents the battery discharging through the shunt resistor. The solar panel can cope well with this load. It is, however, advisable to use a resistor: short-circuiting the panel is not good practice.
Specifications for the Solar Panel Shunt Regulator circuit:
The voltages at which the shunt is switched in and out are preset with P1 and P2 respectively. Recommended voltages are 14.1 V and 12 V. Since potential divider R1-R2 has a ratio of near enough 1:4, these voltages can be set with the aid of a digital voltmeter at the wipers of P1 and P2 respectively (3 V at P1 and 3.53 V at P2). The circuit itself draws a current of not more than 4 mA.
The BUZ10 can switch up to 20 A. The value of R is calculated with Ohm’ s law and the data of the solar panel. These data should indicate the output rating of the panel, for instance, 14.4 V at 8 A. In that case, the shunt register should be 1.8Ω, 115 W. For security’s sake, take the value a little lower, say, 1.5Ω and double the rating, say. 230 W, otherwise the resistor gets very hot indeed.