In Search of Skyline Solar

logo_skyline[Mountain View, California USA]

Finding the concentrating photovoltaic (PV) solar collector.
Skyline Solar CEO Bob MacDonald presenting at Dow Jones Alternative Energy Innovations Spring 2009 next week.

Since posting Skyline Solar Dawn, I’ve been keen on learning more about Skyline Solar’s High Gain Silicon PV solution. Some PV insiders may have followed my cryptic closing comment, The Truth is Out There. As I understand it, the slide below showing the Skyline Solar solution was presented by Doug Rose with SunPower Corporation (NASDAQ:SPWRA, NASDAQ:SPWRB) at the Solar Power International 2008 State-of-the-Art CPV session in violation of an NDA (Non-Disclosure Agreement). [There was no NDA in place, see GP Correction note below.] This slide pegs the Skyline Solar trough concentration at 13x (thirteen times).

From State-of-the-Art CPV by SunPower at Solar Power International 2008

A quick search revealed the headquarters of Skyline Solar, Inc. is not far from downtown Mountain View. The first time I drove past the office building, I didn’t notice anything special. Months later, I decided to pedal by during a bike ride. This was when I first noticed a metal structure in the back lot behind the building. Could it be this easy? I had imagined their prototypes would be on sun at a remote site near Skyline Blvd., on the campus of Skyline College, or perhaps following in the footsteps of SolFocus at PARC (Palo Alto Research Center).

Unobtrusive from the road, the dual trough concentrating solar photovoltaic modules are nestled behind a fence covered with an opaque film and circled with medium sized trees. On my first field trip, I photographed the backside of the PV modules. It was a sunny day, and the units were tracking the sun away from my view point. Later in March, I captured part of the inside trough and the silicon solar cell receivers when the sky was overcast with my Blackberry mobile.

At almost the same instant, four (4) Skyline Solar patent applications were published at both the United States Patent and Trademark Office (USPTO) and WIPO:

USPTO Patent Application 20090056787 March 5, 2009
Concentrating solar collector

USPTO Patent Application 20090056786 March 5, 2009
Photovoltaic receiver

USPTO Patent Application 20090056785 March 5, 2009
DUAL TROUGH CONCENTRATING SOLAR PHOTOVOLTAIC MODULE

USPTO Patent Application 20090056698 March 5, 2009
Solar collector framework

I have not had a chance to review these patents in depth, but here are a few quick observations. Keying on the DUAL TROUGH CONCENTRATING SOLAR PHOTOVOLTAIC MODULE patent, I believe the dual trough arrangement concentrates light from a reflector panel (two per trough) to the opposite photovoltaic receiver. There are four (4) PV receivers per dual trough module. Each dual trough module is mounted on a single-axis tracker.

ALANOD Aluminium-Veredlung GmbH & Co. KG is mentioned as one source for the aluminum strip on the reflector panels using MIRO-SUN® PV for Photovoltaic Applications reflection material. An interesting option provides multiple, redundant layers on the reflector panels which can be removed as they are worn over the presumable twenty (20) plus year product life.

[0044]In one embodiment, each reflector panel 106 may be made of Miro-Sun.RTM. KKSP, made by Alanod of Ennepatal, Germany. The Miro-Sun.RTM. KKSP is a 0.5 mm thick aluminum strip that may have a specialty surface providing over 90% specular reflection over the band in which silicon photovoltaic cells operate. A protective lacquer coating may be applied to the top of the reflector panels 106 to increase abrasion and weather resistance. In another embodiment, the reflector panels 106 may be made of any high reflection material, produced by Alanod or a plurality of other vendors. In still another embodiment, the reflector panel 106 may have a silver coated polymer-based laminate over the aluminum strip. Once the reflective properties of the silver coated laminate are degraded from weather and/or the sunlight, the silver coated laminate may be removed to thereby expose a new reflective layer. This allows the collector 100 to be used for longer periods of time without having to be replaced, easily maintained, and less costly. A reflector panel may have between about 1-5 layers of silver coated laminate.

The design appears to favor about 78mm (3.07 inch) square monocrystalline silicon solar cells while almost every alternative crystalline silicon solar cell technology, process, and shape is claimed possible.

[0070]Each of the plurality of PV or solar cells 406 may be connected electrically in series to form a solar cell string 410. The solar cell string 410 may be formed by any known means such as soldering each solar cell together via interconnect wires 414. Each solar cell 406 may have a cell size of about 78.times.78 mm and may be a square wafer manufactured from a monocrystalline silicon boule. Alternatively, the solar cell may be any type of known solar cell such as multi-crystalline, single-crystalline, rear contact, emitter wrap-through, LGBC (laser grooved buried contact), PERL (passivated emitter with rear laterally diffused cell), multi-junction, silicon ribbon, thin film PV cells, and the like. Although each solar cell 406 is illustrated as a square, the shape of the solar cell 406 is not intended to be limiting as any shape may be used such as a rectangle, square with one or more rounded or truncated comers, hexagon, and the like.

With series cell resistance a concern in the concentration application, Day4 Energy Inc. solar cells with the Day4 Electrode inter-connection are one potential source. For back contact monocrystalline cells, SunPower would rank as a favored supplier if the smaller cell size is manufacturable, and they elect to service a cell customer.

[0071]The plurality of solar cells may be modified such that they have a lower series resistance when electrically connected. In one embodiment, the back surface field strength of the solar cell may be increased and the top-surface conductive grid may be thickened or increased in number to reduce the series resistance in traditional non rear-contact solar cells. In another embodiment, for rear contact PV cells, the back metallization of the solar cells may be thickened.

Each photovoltaic receiver has twenty-four (24) series connected silicon solar cells.

[0072]Each solar cell 406 may be positioned with a small gap between each other to allow room for electrical connections, differential thermal expansion, and mechanical tolerances. A single solar receiver 400 may have any number of solar cells 406 to form a cell string. In one embodiment, one solar receiver 400 may have about twenty four solar cells 406 and may be electrically connected in series, parallel, or any combination. Each solar cell 406 when illuminated may generate approximately 1/2 volt. Thus, if all cells are connected in series the single solar receiver 400 may generate a total of 12 volts.

In addition to the above, the intricate heatsink design and simplified tracking arrangement appear novel.

The City of San Jose mentioned Skyline Solar as a possible contender for solar demonstration projects in “San Jose explores solar energy farms” by Lisa Sibley for the Silicon Valley / San Jose Business Journal.

Skyline Solar is among the Presenting Companies at the Dow Jones Alternative Energy Innovations Spring 2009 event from April 21-22, 2009, in Redwood City, California USA. It would appear Skyline Solar CEO Bob MacDonald is prepared to tell =all= regarding development schedules, business plans, and funding requirements to prospective investors next week.

Curious that Skyline Solar opted out of commenting on this post.

I don’t think today’s press release by GreenVolts, “GreenVolts Appoints Executive Chairman” elevating Bob Cart to Executive Chairman invalidates my post, “GreenVolts Jolts Concentrating PhotoVoltaic (CPV) Business Plans”. How actual events unfold over the next few months will tell the tale. Please see “GreenVolts Replaces CEO Bob Cart” at Greentech Media for their take.

GP Correction: Neither SunPower Corporation nor Doug Rose was under NDA with Skyline Solar at the time of the presentation. The Skyline Solar slide had been presented in public before, and the dual trough concentrator module photo was later removed upon Skyline Solar’s request.

4 comments

  1. Anonymous says:

    This design looks similar to Entech’s dual trouph, low-concentrating design.

    Agree?

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