Renewable Energy Information

 

All About Regulators for Solar PanelsSolar regulator

The purpose of a solar regulator is to prevent batteries being overcharged. How the device goes about doing this is to limit the current as the battery voltage starts to rise. (see moreon our "batteries" page). Battery charging is not an exact science but we are pretty close to knowing the best way to go about it! What has changed most in the solar industry over the last decade is the trend towards building more and more grid feeding solar panels and less and less of the (once common) battery charging variety.

Once upon a time there was no such thing as a grid connected solar system and the vast majority of solar panels sold to us motals were designed to charge batteries. Most were 12 volt, meaning they were designed to charge a 12 volt battery, there was the odd 24 volt model for 24 volt battery banks and the odd rare 48 volt solar panel was sometimes offered.

Times have changed, the most common solar panels on the market now have no relationship to battery voltage, seemingly the designers have chosen an ad hoc voltage somewhere between 22 and 55 volts. Welcome to the new breed of solar panel, the grid feed unit, designed for the household roofs of suburbia. But never fear, if it is battery charging that you want, grid feed panels coupled with the correct regulator will perform better than the battery charging panels of old.

With a battery charging panel, you could simply connect it to your battery and then disconnect it when the battery was full. This simple switching arrangement was the basis of the first solar regulator, it simply switched the solar array on and off according to the battery voltage. You could do the same with a grid feed solar panel, and assuming the panel voltage was higher than the battery voltage, current would flow to the battery.

The problem with connecting a grid feed solar panel with a rated power voltage of say 35 volts to a 12 volt battery is not actually the mismatched voltage. The panel will indeed charge the 12 volt battery ok and this is what you would do if your solar regulator failed. The real problem is that a 35 volt panel is not designed to operate at 12 volts and there will be a substantial loss of rated power. Your 185 watt solar panel suddenly becomes a 120 watt panel.

Maximising Regulators

The solution to using grid feed panels efficiently to charge batteries lies in a device called a maximising regulator. These devices and take a high voltage (often up to 150 volts or higher) and convert it to a battery charging voltage. This is useful for several reasons besides making it efficient to se grid feed panels for battery charging. Running the solar array at a higher voltage than battery voltage allows the power to be moved over longer distances with thinner wire. This saves money. A good solar maximiser will also track the difference between Pmax and Vmax as it varies throughout the day. (Vmax and Pmax are explained on the "solar panels" page.

The device pictured on this page is an "Outback Power" maximising regulator and is one of several brands that will take the current from a high voltage solar array and convert it to a current and voltage suitable for battery charging.