SolFocus is a Mountain View, California startup that develops and makes concentrating solar energy systems.  Last month SolFocus secured $47.5 million in C round funding that the company will use to commercialize its technology (see the greentechmedia story here).

The funding is primarily from Apex Venture Partners and some other sources, including New Enterprise Associates and NGEN Partners.

SolFocus’s concentrating photovoltaic (CPV) technology combines the company’s proprietary reflective optic system with high efficiency solar cells purchased from advanced photovoltaics (PV) makers such as Spectrolab and Emcore. 

CPV systems reflect and concentrate natural sunlight onto solar cells.  One advantage of CPV is that it requires only small solar cells for power generation because of the high concentration of sunlight, which in the SolFocus system is boosted by a factor of 500.

SolFocus’s optic system is covered by three patent applications filed on May 5, 2006 (probably filed on the same day to avoid any one becoming prior art to the others).

U.S. Patent Applications Pub. Nos. 2007/0256724 (‘724 application), 2007/0256725 and 2007/0256726 describe CPV systems wherein the reflector and lens can be manufactured together as self-forming and self-aligning components, resulting in reduced assembly and maintenance costs. 

The patent pending system also reduces heat damage to the reflector and the solar cells by evenly distributing heat and transferring it to an aperture though which it can escape the CPV assembly.

The ‘724 application is directed to the basic CPV device (100), which includes an optical element (110), a PV cell (120), a primary mirror (130), a secondary mirror (140) and a heat spreader (150).  The optical element (110) has a large convex surface (112) and an upper layer (111) with an aperture surface (115).  The PV cell (120) is located in a cavity region (113) at the center of the convex surface (112).

The reflective or refractive surfaces of the mirrors are designed so that sunlight enters the optical element (110), travels through a specific region of the aperture surface (115) and bounces off corresponding regions of the mirrors, from the primary mirror (130) to the secondary mirror (140) and from the secondary mirror (140) onto the PV cell (120) (see Fig. 2, below).

The central portion (151) of the heat spreader (150) is disposed over the cavity (113), and the curved peripheral portion (152) is formed on or secured to the back surface of the primary mirror (130). 

The heat spreader (150) is made of a high thermal conductivity material, and because of differences in thermal resistance between the heat spreader (150) and the optical element (110), the heat collected by the CPV device is transferred from the heat spreader (150) to the front aperture surface (115).  This results in more than 30% of the generated heat radiating out from the CPV device.

SolFocus’s CPV technology seems to impress customers in the U.S. and abroad:  the company’s solar energy systems have already been installed in Spain and San Francisco (with more to come in Spain), and a division of the Samaras Group has partnered with SolFocus to build a new 1.6MW facility in Greece. 

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