In Search of Skyline Solar – Part 2

[San Jose, California USA]

Pilot High Gain Solar (HGS) Project at the Cerone Division of the Santa Clara Valley Transportation Authority (VTA).
Project and electricity free to VTA!
HGS concentrating issue at the open end of the trough?

From Skyline Solar’s HGS Pilot Project at VTA Cerone Division

My In Search of Skyline Solar post provided a preview of last Monday’s “Skyline Solar Emerges from Stealth after Achieving Key Customer, Development and Financing Milestones” press release. This was the first I heard of the 24-30 kW (kilowatt) Demonstration Project at the VTA.

Even my machinations about remote prototype locations didn’t anticipate this system being hidden in plain sight. I noticed the installation driving west on Route 237 twice the week before Skyline’s supposed emergence from stealth mode. While I planned to check it out, I thought it was a small CSP (Concentrating Solar Power) plant and didn’t make the connection to Skyline Solar. In my defense, I hadn’t seen more than a few dual trough concentrating solar photovoltaic modules strung together before, and I do need to remain attentive to my driving and not gawk at solar installations.

View Skyline Solar’s HGS Pilot Project at VTA Cerone Division in a larger map

Regarding the Skyline Solar pilot project, the Agenda for the Committee for Transit Accessibility meeting on Wednesday, April 8, 2009 said:

Solar Installation

The installation of solar panels is currently underway at the Cerone Operating Division. This pilot project is a result of a partnership with Skyline Solar of Mountain View. The contractor has experienced delays due to rain and installation is now approximately 50% complete. Barring further rain delays we anticipate the installation will be completed the first week of April.

This project has the potential to bring to market a new type of solar collector that collects more energy per square foot and is less expensive to procure than traditional solar flat panels. Skyline Solar is building this at no cost to VTA. In turn VTA will receive $15,000 to $20,000 in free electricity.

From VTA Media Relations, I learned the prototype Solar Installation is planned to last 12 to 18 months and was already generating a small amount of power. Also, a project press event is scheduled for later this week. I heard elsewhere San Jose Major Chuck Reed will be on hand for the Pilot Solar Project inauguration. Since this is California, you never know who else might show up.

Chatting with a VTA employee, I understand the project did not require usage or building permits since VTA is exempt from those regulations. Fire and I assume electrical inspections were required though.

The four (4) Skyline Solar HGS array columns are oriented in a north to south direction with the open end of the troughs facing south. Each column consists of six (6) HDS arrays in this installation. From the Skyline Solar provided 24 to 30 kW system capacity, each column is rated at 6 to 7.5 kW, and each HDS array at 1 to 1.25 kW.

As can be seen above and in the following Picasa slideshows, I noticed “dark” silicon solar cells towards the open end of the troughs. Is this an optical illusion? This effect was less pronounced looking down the trough from the open end. I never observed dark solar cells at the closed end of the troughs.

On the Demonstration Project webpage, Skyline Solar said:

Bright line running along HGS panels shows where light is being converted to electricity.

During two visits, I observed the effect was most pronounced at noon and 50% (percent) improved by afternoon at 3PM. Skyline Solar’s “Four columns of Skyline HGS arrays” photo only displays a trace of this trough edge effect later in the day at almost maximum single-axis tracking to the west. Did Skyline Solar make a conscious decision to maximize late day power generation?

Skyline Solar was mum to a loaded question I sent them on this; my question was not even acknowledged.

Has Skyline Solar added a parallel bypass diode per silicon solar cell at the trough edge to handle this issue? Is a latitude tilt or installation adjustment needed?

If that wasn’t enough, it also seems as though the concentration resulted in nonuniform solar cell illumination and was most intense at and just above the horizontal center of the solar cells raising concerns about the efficient use of the material and the concentration alignment.

In the second Picasa slideshow, four (4) KACO Solar inverters are used per column. The smallest KACO Solar blueplanet 1501xi inverter sold in the United States is rated for 1.8 kW maximum DC, and four could be sufficient to handle a 6 kW column but not the 7.5 kW upper end. While I don’t know the exact inverter ratings, why were fewer larger units not used instead? Has this been done to capture better granular performance data on the HDS arrays within each column?

In last month’s Agenda for the VTA BOARD OF DIRECTORS MEETING, a review of VTA’s SUSTAINABILITY PROGRAM ACCOMPLISHMENTS included a photovoltaic study for a 1.5 MegaWatt system:

In September 2008, completed a solar assessment of the Guadalupe Division and North Yard. Identified that these sites could accommodate a 1.5 MW system at a cost of $12.5 million with a 13 year payback period. VTA is currently evaluating funding options.

Now, at about $8.33 per Watt ($12.5 million / 1.5 MW), this seems quite expensive for a small utility scale photovoltaic power plant. Perhaps this includes additional land preparation and mitigation costs? Sounds like a great candidate project for economic stimulus funds.

VTA’s Sustainability Fact Sheet details the Santa Clara Valley Transportation Authority’s commitment to green activities including solar powered bus stops. I was an occasional rider of the Rapid 522 and Local Line 22 VTA services last summer and fall during my recovery. I learned to wait for the 522 since it would always overtake an earlier 22 bus.

The prototype solar project has not been the leading attraction for San Jose citizens at the VTA Cerone Division. The sheep and goats grazing project has generated more public interest thus far.


  1. Doug Caldwell says:

    The dark cells at the (south) end of the receiver lines is just geometry. The array is pointed “up” at noon, but the sun isn’t overhead. Later in the day, the sun moves from south to north and removes some of the effect. At sunset on the equinox (and other times when the sun is due west or east), there would be no dark cells. In the early mornings and late afternoons between spring and autumnal equinox, you would see the dark cells at the north ends of the receiver lines. The corollary is that there is light spilling off the ends opposite the dark cells.

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