Let's assume a set of solar panels on a rooftop. The sun is shining and the panels are working well converting sunlight into electricity. The brighter the sun, the more the voltage; a controller is regulating the voltage from the panel, feeding the batteries with the proper voltage. Up to here, the system is DC. Unfortunately, chances are very high that the appliances you want to power are AC.

You need a device which will be converting your DC power into the AC necessary for your appliances to work and, that is the role of inverter: converting DC into AC.

We also know that if the sun is not available for a string of days, it might happen that your batteries get empty. In such a case you will run out of power. The option for most off grid systems is to install a back up generator. Generators are AC sources. They are compatible with your appliances but they can't directly charge the batteries.

Then, instead of using a conventional inverter, a multifunctional inverter is more advisable: it is an all in one solution combining the conventional role of an inverter with additional battery charging and regulation features for the more performants.

Inverters come in 3 basics output types: square wave; modified square wave and sine wave.

Modified square wave inverters generally have good surge and continuous capability and are usually cheaper than sine wave types. However, some appliances, such as audio equipment, television and fans can suffer because of the output wave shape. Sine wave inverters often provide a better quality power than the grid supply.

when selecting an Inverters

• input voltage should correspond to system voltage
• output voltage should refer to the voltage supported by your appliances you should also consider:
• wave form;
• output power;
• surge capacity;
• stackability.

All those information are found at inverters specification sheets.

All theDC components of an off-grid PV system, meaning the PV array, the controller and the battery bank must must operate at the same voltage, We refer to it as the system voltage. The inverter input voltage is selected to match that voltage.

Some appliances, such as audio equipments, television and fans can suffer because of the output wave shape. It is therefore important to collect information about any possible implication of the wave form on the loads before selecting an inverter.

Additionally, the selected inverter should be capable of supplying continuous power to all AC loads. In that view, you should de-rate the inverter and take into account its efficiency.

I would like also to mention that the inverter you will have selected should be capable of providing sufficient surge capability to start any loads that may surge.

The last point we will touch about inverter is stacking. This option allows multiple inverters to function as a single system working together to charge batteries and provide power to loads. The advantage of stacking inverter is an increased output.