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Hewlett-Packard, tapping into its IP back catalog, recently announced that it would license its thin film transparent transistor technology to Livermore, Calif.-based Xtreme Energetics (XE) to develop advanced concentrating photovoltaic (CPV) solar arrays for rooftops and utilities.

HP’s thin, flat transistors, which are made of cheap, plentiful zinc and tin, will create a tracking system that directly focuses sunlight on XE’s proprietary solar concentrators. These will allow XE’s concentrators to achieve double the conversion efficiency of conventional silicon solar panels. XE’s solar trackers could also be adapted for concentrated solar thermal applications, opening the door to other potentially lucrative deals.

The transparent electronics, in addition to preventing light from being blocked as with conventional systems, allows for a greater degree of aesthetic appeal by enabling the placement of artistic patterns on the arrays — which means they could eventually be incorporated into a variety of building materials and in facades.

Furthermore, the use of HP’s transistors avoids the need for mechanical tracking devices, which incur high maintenance costs and are one of the biggest obstacles to installing CPV systems — often casting shadows onto themselves. XE CEO Colin Williams told CNET that its final design would call for a multilayered solar panel with HP’s transparent transistor technology, a high-efficiency solar cell and a plastic internal reflection concentrator. In an industry where space and efficiency come at a premium, XE could grab a large slice of the rooftop solar market with its flat, compact systems. The ease of use and adaptability its transparent electronics offer means XE could break into other, more specialized markets — especially given their aesthetic value.

Though the company has yet to develop an actual prototype, it expects to have its first-generation array model for utilities available next year. Williams said his firm’s array would be able to convert up to 43 percent of sunlight into energy at a cost of $1.50 per watt once it reaches a 100 megawatt production capacity.

It is currently in the process of raising a $5 million first round of funding and plans on raising another $35 million round within the coming months. It will use these funds to continue its product development and to build national and international manufacturing, marketing and sales operations.

The field of high-profile CPV startups has grown by leaps and bounds over the past year. Silicon Valley Solar, which develops internal concentrator modules, Cool Earth Solar, which received funding a few months ago to develop plastic balloon concentrators, and Sunrgi, which has claimed 5 - 7 cents per kilowatt prices from its solar concentrator design, are just a few of the companies we’ve covered.

According to the San Francisco Business Times, HP is considering 150 licensing deals with applications in solar and energy efficiency. Other tech firms that have parlayed their expertise into energy efficiency technologies include IBM and Intel. IBM unveiled a new line of small, modular data centers and green financing software as part of its Project Big Green initiative this week while Intel, which showcased 70 research projects at its recent Research@Intel event, is developing energy efficient platforms and environmental sensing systems, among others

Writing on Nanosolar’s blog, CEO Martin Roscheisen has unveiled the next prong in his firm’s business plan — a focus on municipal solar power plants of 2 - 10 megawatts in size. The idea is to build 10 acre lots on the outskirts of small cities that could feed into the municipal power grid directly.

Each lot, consisting of several rows of solar panels mounted on rails above ground, could provide up to 2 megawatts, enough to serve 1,000 homes. The panels would be mounted on rails to prevent them from affecting the surrounding wildlife and vegetation.

Nanosolar’s scheme could be scaled up to supply the needs of larger cities — for instance, 5 lots, which would generate 10 megawatts of electricity, could serve 5,000 homes. Unlike coal-fired plants, which typically take 10 - 15 years to build, solar power plants can be done in as little as 12 months — and much more cheaply.

Though Rosencheisen acknowledged the appeal of rooftop arrays, which solar installers like SolarCity, Sun Run and Sungevity focus on, he also criticized them as a business “that’s difficult to scale rapidly in a truly meaningful way,” and “a somewhat more expensive proposition.” Imagine having to hire a contractor to crawl around your roof to install an expensive array or — worse yet — having to set it up yourself, he noted irreverentially.

This small plant approach, though new to the U.S., has already been widely implemented throughout Europe and Asia in what Rosencheisen called a “silent revolution” that has yet to be picked up on by the mainstream press, and that is too often criticized by utility executives as being too costly or unrealistic. “It works, it is economic, and it is possible now,” he said.

Nanosolar has gotten plenty of attention for its claim that it can sell its cells for as low as 99 cents per watt, low enough to be competitive with non-renewable energy sources, as well as recently raising over $50 million more from EDF Energies Nouvelles. However, there are a number of other, less-sung companies that have either implied or outright stated that they have a similar game plan for small-scale power plants.

SolFocus, for example, makes large solar concentrator panels, which use mirrors to focus more light onto highly efficient solar photovoltaics. Its initial product isn’t designed for rooftop installation, but would work perfectly on open spaces near facilities that need modest amounts of power — such as universities or off-grid villages. It raised $63.6 million last year to build its panels in the U.S. and, through its new subsidiary SolFocus Europe, across the Atlantic.

In fact, the move to build small has swept most categories of solar power, as companies have come to realize that they can thus avoid most of the bureaucratic snags involved in building plants that produce over 50 megawatts. Furthermore, by grouping their panels into small lots, they’ve been able to grab small tracts of land on the edges of cities and towns, or on land that can be dual-purposed like farms. A secondary advantage is the ability to hook into the existing power grid without the modifications required to channel power from a large plant.

Another example is Cool Earth Solar, a startup based in Livermore, Calif. that hews to the “cheaper is better” model, using inexpensive reflective balloons to concentrate light on cells. It plans to suspend its balloons on cable-bound arrays 12-14 feet above active farmland, letting sunlight strike both the solar cells and crops beneath. The firm claims that it can produce electricity for 18 cents a watt, and hopes to ramp up its production of balloon concentrators to 50 megawatts by next year.

And there’s Infinia, a company that just raised its second round to $57 million, which specializes in the production of 3 kilowatt dishes that, lumped into groups, will generate 1-10 megawatts in small-scale projects. Finally, in the solar thermal category, there’s eSolar, which just snagged $130 million from Google, Oak Investment and Idealab to pursue a similar approach — building a number of small plants that produce up to 33 megawatts each.

The only category to have mostly stayed away from this trend is expensive silicon-based solar, which is generally relegated to rooftop installations. Yet even there a few exceptions are already starting to appear. OptiSolar, for example, a Hayward, Calif., based startup, makes somewhat less expensive thin-film solar cells. It last year announced plans to build a 40 megawatt solar power installation near Sarnia, in Ontario, Canada, and has since announced several more of a similar size.

If solar power is expensive in part because the materials come dearly, then use cheaper materials. That’s the design principle behind thin film solar cells, and now also behind a form of concentrated solar using plastic balloons, designed by a firm called Cool Earth Solar.

Concentrated solar uses mirrors to shine more light onto regular solar photovoltaic cells, in order to get more energy, and thus more profit, out of a single cell. However, the mirrors themselves and machinery needed to keep them precisely aimed usually drive the cost per watt back up.

Cool Earth’s idea is to use a reflective inflatable made out of mylar, a cheap plastic often used for food packaging, to reflect light onto cells. The company claims that its scheme produces energy at a lower cost than natural gas plants.

The balloons, which are about eight feet across, are hung on cabling arrays that keep them turned toward the sun. The top layer of plastic is clear, while the underside is coated in a reflective material, directing sunlight back onto a solar cell in the center.

Because of their design, the arrays can’t be use on a rooftop, and their size means they’re an unlikely candidate for urban installation. Cool Earth is planning instead to install them on farmland, suspended 12 to 14 feet above the crops.

The company will be handling deployment of the arrays itself, and will profit from selling electricity back into the grid at about 10 cents per kilowatt, according to CEO Rob Lampkin. The funding, Cool Earth’s first, will be used to ramp up production of its concentrators to about 50 megawatts per year by 2009.

An unnamed private equity fund provided $20 million of the $21 million total funding; Lampkin says he made pitches to a half dozen top Valley firms, but “amazingly enough, [the PE firm] had the best deal and moved the quickest.” Cool Earth is based in Livermore, Calif.