Inverters for Off Grid Systems

All Inverters convert Direct Current (DC) from solar panels or from batteries to 115 Volt 60 Hertz Alternating Current (AC), similar to power from the electrical grid.

There are two major types of inverters: off-grid (for cottages, trailers, RVs and boats) and grid-tie (for revenue-generating systems such as microFIT and FIT). Off-grid inverters are further divided into two types: modified sine wave and pure sine wave, and grid-tie inverters are further divided into two types: central inverters and microinverters.

Off Grid Inverters
Modified-sine-wave (MSW) inverters produce power at the same frequency as electrical utility power, but the waveshape is more like a square wave. They may not be suitable for running some types of electric motors or sensitive electronic equipment. The only advantage of MSW inverters is that they are less expensive than PSW inverters, particularly in small systems.

Pure-sine-wave(PSW) inverters produce power that is identical with power from the electrical utility in frequency and wave shape, and are available in a wide range of capacities.

Grid Tie Inverters
Grid-tie inverters are pure-sine-wave inverters that track the voltage, frequency and phase of electrical utility power so that they can feed power into the electrical grid. They automatically shut down if utility power is lost, so that they do not pose a shock hazard to utility workers.
 
Central inverters accept direct current power from a string or several strings of solar panels, and are normally mounted in an electrical room or near the main electrical panel. Several central inverters can be connected together at their outputs to handle power from large systems.

Microinverters accept direct current power from one (or two) solar panels and produce 115 Volt 60 Hertz alternating current. Microinverters are normally mounted directly on solar panels or on mounting rails and their outputs are tied together in parallel before the output meter.

Microinverters have several advantages over central inverters: they require no mounting space in the electrical room, they work better in partial shade conditions, they provide better energy capture at low light levels, and failure of one inverter does not cause shutdown of the entire system. Their only disadvantage is that they are slightly more expensive in large systems.