What are Inverter ratings?

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When purchasing an inverter, important considerations are the unit's electrical rating and the option of a "sine wave" or "modified square wave" model.

Here's what to check when selecting an inverter:

Output Voltage

Most North American houses are grid-connected to service loads at 120V or 240V. Small electrical appliances using wall plugs are usually at 120V with heavier electrical loads at 240V (electric stoves, clothes dryers, furnaces, central air conditioning and so on).

Most inverters' voltage rating is 120V which caters for most household appliances from a renewable energy system. If the renewable energy source rating is increased beyond the inverter's capacity, an additional inverter is needed. In general, systems with a generating capacity exceeding 4kW need two inverters. The second inverter is stacked on top of the first to increase the voltage to 240V.

The most reliable connection for a 240V essential load is the domestic water pump. Most 240V loads tend to be appliances that use up a lot of electrical energy like cooking stoves, central air conditioning, clothes dryers, hot tubs and swimming pools. Battery capacity to support these massive loads is limited, although you may have plenty of inverter capacity.

If you only need a 120V inverter for all your applications with a 240V supply for the water pump, then install an auxiliary step-up transformer which costs less.

Many businesses and large homes need three-phase electrical power. This requires at least three inverters. Few off-grid applications use this configuration as it is very expensive: only very large energy consumers need it.