Enphase Energy, a pioneer in solar microinverters, has hit the 500,000-units-shipped-to-date milestone. The firm expects to triple its capacity in 2011 to support between 300 megawatts to 500 megawatts of annual production to meet rising demand.

"We are shipping more inverters than any other company in the world," according to Paul Nahi, the CEO of the VC-funded growth-stage firm.  Of course, it's not exactly an apples-to-apples comparison. Each Enphase microinverter is a 200-watt unit, installed one per panel, so a number of units are required per roof and that gives Enphase a bit of a unit count advantage compared to a one-per-home central inverter. In any case, 500,000 is a big number.

Relying on contract manufacturer Flextronics has allowed Enphase to ramp production at this speedy rate. “Enphase is one of our fastest-growing customers,” said EC Sykes, president of Flextronics Industrial.  

Enphase reached a 13 percent market share in 2010 in residential installations (up to ten kilowatts) in California -- up from 5.3 percent in 2009 out of a total of 74,000 solar project applications recorded in the California Solar Initiative (CSI) database (see chart below).  Enphase has also grown in commercial systems (ranging from 10 kilowatts to 100 kilowatts), capturing 9.3 percent CSI market share in 2010, up from 3 percent in 2009.

The U.S. is still the source of almost all of Enphase's business but that will change in 2011 and 2012, according to Nahi, as European approval has been achieved and EU business starts to grow.

When it comes to microinverters, Enphase and Petra Solar look to be the only vendors shipping product in volume quantity. A search of the CSI database lists only one microinverter firm -- Enphase. Other PV distributed electronics vendors, notably SolarEdge and Tigo, are shipping their chosen approach, the power optimizer, in convincing volume as well.

Enphase's recent product developments include an integrated microinverter meant for AC modules (ACM) and an in-home thermostat that integrates with the Enphase software and solar energy monitoring system.   

Greentech Media's Networked Solar Event explores the convergence of solar power, inverter electronics and the smart grid. More details here.