Enphase Energy reportedly has raised $22.57 million, according to Private Equity Hub, which cited Enphase's filing with the U.S. Securities and Exchange Commission.

Petaluma, Calif.-based Enphase develops micro-inverters for converting direct current produced by solar panels into alternating current for feeding the grid. Each micro-inverter is attached to a solar panel, a different approach than the more common use of a centralized inverter for the entire system.

The startup, founded in 2006, said its micro-inverters could do a better job of harvesting power from poor-performing solar panels, such as those covered by debris or in the shade. There are competing technologies that also claim to improve energy output, such as National Semiconductor's Solar Magic device.

Enphase announced last September that it had raised $15 million from the then new investor RockPort Capital and existing investors Third Point Ventures and Applied Ventures (the investment arm of chip and solar factory equipment maker Applied Materials). In January last year, Enphase announced a $6.5 million investment from Third Point Ventures.

Enphase declined to discuss the reported new financing.

The startup began shipping its products last summer. Its customers include distributors and installers such as AEE Solar and Akeena Solar. Enphase also has a deal with solar panel maker Suntech Power, which helps to market the micro-inverters to its network of dealers in the United States.