Inverter Basics

Every watt of solar electricity passes through an inverter before reaching the grid. Solar panels produce DC. The grid runs on AC. The inverter is the bridge, and its performance determines how much of the panel's output actually becomes usable electricity.

An inverter converts DC to AC by rapidly switching transistors on and off to create a pulsing output that approximates a sine wave. The technique is called pulse-width modulation (PWM): by varying the width and timing of thousands of on/off pulses per second, the inverter constructs an AC waveform that matches the grid's frequency (60 Hz in North America) and voltage. Modern inverters achieve 96-99% conversion efficiency, meaning only 1-4% of DC input is lost as heat in the switching process.

Understand the switching. A simple inverter alternates DC polarity using four transistors arranged in an H-bridge. By switching pairs on and off at 60 Hz, the output alternates between positive and negative voltage. PWM smooths the crude square wave into a near-sine wave.

Size the loss. A 6 kW residential solar array with a 98% efficient inverter delivers 5.88 kW AC. Over a year at 18% capacity factor: loss = 6 x 0.18 x 8,760 x 0.02 = 189 kWh lost to inverter inefficiency every year.

Why do "smart" inverters matter for grids with high solar penetration?

Grid support functions. Modern "smart" inverters can adjust reactive power output, ride through voltage dips, and limit power ramp rates. These grid-forming capabilities are increasingly required by interconnection standards as solar displaces the synchronous generators that traditionally provided these services.

As solar and battery penetration grows, inverters become the grid's primary interface with generation, making inverter standards a policy priority.

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