Inverters: Converting DC to AC Power

Inverters convert the DC power generated by solar modules to AC power usable in the home. Residential grid-tied inverters supply power to the home – and the grid – through a circuit breaker that also acts as the AC disconnect. All grid-tied inverters are required to quickly shut down when power supplied by the grid fails, to avoid injury to anyone who may be working on the grid, so unless you have a battery system – or a new batteryless backup system from SMA – you will lose power when your neighbors do.

There are two types of inverters; "string," and "micro." String inverters convert the DC power generated by a "string" of photovoltaic modules connected in series; the positive lead of each module is connected to the negative lead of an adjacent module. Voltage in any series-connected DC power source is additive, so the voltages a string inverter sees can be up to 600 volts – the limit imposed by the National Electric Code – or 1000 volts for ground-mounted systems. We currently use only SMA or PowerOne string inverters; both are recognized for their high quality and competitive price.

Microinverters are physically small and are attached directly to a solar module or to the rack that supports it, and see only the voltage produced by that module. 240 volt AC power is output from each micro inverter. Because microinverters are installed on the roof where temperatures may exceed 150º they may have a shorter service life than string inverters. When they do fail they are more difficult to replace, as they require panel removal.

Utah Applied Solar Energy, LLC  2015