Skyline Doubles Solar Concentration with New CPV Design

Two years after installing a pilot system to test its concentrating photovoltaic (CPV) technology, Skyline Solar is rolling out its next-generation design, bumping up the concentration factor and, interestingly, relying on glass mirrors rather than the metal reflectors it used for its initial offering.

The Mountain View, Calif.-based company announced the launch of its new concentrator Tuesday and dubbed it Skyline X14 System. The X14 refers to the system’s ability to concentrate the sun 14 times, which doubles the concentration of its previous system, said Tim Keating, vice president of marketing and field operations at Skyline. Skyline executives used to say its gen 1 technology could concentrate the sun 10 times, but turned out that figure actually included power that could be generated from using a tracker.

Each Skyline X14 system runs 11.6 meters long; the distance from bottom to the top of the mirrors is 2.6 meters. The system contains 20 solar panels with a total of 3.6 kilowatts of generation capacity.  

Like the previous system, Skyline X14 still uses monocrystalline silicon cells and sits on a single-axis tracker that tilts the mirrors to follow the sun’s movement. It even uses the same metal fin for passive cooling.  Silicon cells lose their efficiencies when they get too hot, and most of the sun’s energy becomes heat that needs to be dissipated (generally, monocrystalline silicon cells run between 18-20 percent efficiency).The cooling fin only needs to be “slightly larger” than the one for the previous system, Keating said. In fact, the fin for the previous design might have been too big for the job, he added.

What is markedly different with Skyline X14 is the use of glass mirrors. These are curved mirrors that look similar to what concentrating solar thermal developers use for their parabolic trough systems, Keating said. Why switch from aluminum reflectors to the glass version? Keating said there are three key reasons: glass has become cheaper; it can generally reflect a slightly higher percentage of light; and it’s a more bankable material.

Glass mirrors still aren’t as cheap as metal reflectors, Keating noted, but they are worth the cost because the system is designed to double its concentrating ability. Project investors would consider glass an older tech because it’s been used in concentrating solar thermal power plants for a few decades now, including the world’s largest: the 354-megawatt SEGS in California. Still, companies such as 3M are working on coatings and other technologies to boost metal reflector’s reflectivity.

Skyline plans to use X14 in three projects. Two of them, at 100 kilowatts each, will be built at the Edward Air Force Base in California and Fort Bliss in Texas under a $1.58 million contract

The third project is a newly announced 500-kilowatt system in the Mexican state of Durango. Skyline will supply the equipment to contractor DelSol Systems. DelSol is building it at a new industrial park for the Durango government, a project that reportedly will cost $28 million pesos. (US $2.3 million) The plan is to start construction within 60 days and complete project by the end of the year, Keating said. Durango has expressed an interest to expand the project to 10 megawatts, he added.

Skyline has steadily increased the sizes of its projects, and the one in Durango is the largest announced to date. It unveiled a pilot sytem with its first-generation technology, a 27-kilowatt system, in Silicon Valley in May 2009. Founded in 2007, the venture-backed company is among a slew of CPV technology developers who set out to provide an alternative to conventional solar panels, which at the time commanded higher prices largely because silicon price was high. The price has fallen more than half since, and that in turn has made solar panels more attractive to project developers and financiers.

This silicon price decline happened during the time when many CPV technology companies were rolling out their first system. As a result, these companies have struggled to compete. As new technology providers, they have to amass large enough sales volumes in order to drive down manufacturing costs quickly.

Skyline claims its X14 can produce electricity at less than $0.10 per kilowatt-hour. But that only happens under certain conditions: the project has to be at least 1 megawatt and take advantage of the federal incentive that covers 30 percent of the project’s cost, Keating said. It also has to land in places with a super sunny climate that can provide a DNI (direct normal irradiance) of more than 6.0 kilowatt hour/m²/day.

“There has been a continuing interest in this space and projects are getting built,” Keating said. “We are mostly an alternative to the flat-plate system. For the same amount of money, you can buy a Skyline system with 20-30 percent more capacity.”