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Holographic film points light in the right direction

01 Jun 2007

Flick through the technology press and you could be fooled into thinking that solar energy is now all about ultrathin films and flexible photovoltaics. Rick Lewandowski, CEO of Prism Solar Technologies, US, tells James Tyrrell that silicon is definitely still in the frame thanks to a clever holographic film that can squeeze more power out of traditional solar cells.

Prism Solar Technologies, US, has captured the attention of the investment community with its holographic film that extracts more power from traditional solar modules. In February, the company secured an additional $1,150,000 (€848,500) from venture capitalists and individual investors on top of its previous $900,000 funding to develop the technology.

According to the firm, its patented holographic elements can reduce the amount of silicon required to produce a solar panel by up to 75%. This corresponds to a significant reduction in the cost of the device and could help to put solar technology within striking distance of conventional energy sources.

Hitting the right price point is key to conquering the market. "I think that the magic number is still about a $1/W, which translates to just under $3/W installed. At that point you are competitive with traditional electric prices in most parts of the country," Rick Lewandowski, Prism Solar's CEO told OLE. "We are able to reach grid parity in areas that are subsidized already and we'll come to market at just under $3/W either at the end of this year or at the beginning of 2008."

Technology basics
Prism Solar's expertise centres on a volume hologram that is imaged onto a transparent layer and then sealed between two pieces of glass (see diagram). "The hologram is structured so that it spectrally selects the wavelengths we want and then redirects the rest to produce a cooler, more efficient solar cell," said Lewandowski. "Technically, we can work with any solar cell."

The technology originally came out of the University of Arizona and was developed and funded by Apogee, a large speciality glass manufacturer. "Apogee spent about $10 m over a six-year period developing the technology," revealed Lewandowski. "At the time I had a company called Direct Global Power and we were referred to Apogee as a consultant for market development and business planning by the US Department of Energy."

It turns out that Apogee was looking at divesting the technology to focus on its core glass business, and Lewandowski, a 25-year veteran of the solar industry, took the opportunity to become more involved with the project. "We picked up the intellectual property and acquired a worldwide licence for power modules and speciality modules," he explained.

In July 2005, Direct Global Power formed a subsidiary dubbed Prism Solar Technologies and work began on a second generation of prototypes. "Technically, the module might be slightly less efficient than leading high-efficiency solar cells, but we can create more kilowatt hours over a day," said Lewandowski. "We are redirecting light from lower angles, which means that we can send more power to the cells in the morning and the late afternoon – it's a kind of passive or intelligent tracking mechanism without any moving parts."

PV partner
The film's ability to redirect light to where it is needed most has won Prism Solar some important fans. Late last year, the company announced that it will be working with Hitachi America, a developer of bifacial photovoltaic cells. "We have signed a contract to build solar modules with Hitachi in the US," explained Lewandowski. "The long-term goal is to see how our holographic material can get sunlight onto the backside of its cell."

Hitachi's double-sided approach to extracting more power is great in theory, but practically there are hurdles to overcome. "The problem is that no one has really found an elegant way of actually getting sunlight to the backside of the module," commented Lewandowski. "At the moment, it's difficult for manufacturers to guarantee the corresponding increase in power without knowing where the module is going to be located and how it is going to be installed."

Lewandowski thinks that Prism Solar's optical film could be perfect for the task. Its holographic properties can be optimized to predictably redirect sunlight onto both of the bifacial cell's surfaces. This would go a long way to reducing the need for natural reflection off water, snow or sand. Critically, it would put Hitachi in a position to offer the market a more attractive performance guarantee for its bifacial products.

Infrastructure issues
When Prism Solar's devices hit the market, it is important that the service sector is prepared. "The technology needs to be plug and play, but only to a certain point. The more fundamental issue is that we have a qualified infrastructure in place. If this stuff was available at 10 cents per watt, could you get it installed?" remarked Lewandowski. "In the 1980s when we had the solar–thermal subsidies you had a lot of people jumping into the industry who were not qualified to install solar–thermal systems and didn't get trained properly."

The ease of installation, the management of bill collecting and the issue of interconnecting with the grid will all play their respective parts in the success of the technology. "You need to have skilled installers that understand the technical issues and you need to have the co-operation of the utilities board that manages those activities," said Lewandowski. "It needs to happen while the technology is getting to the right price point otherwise you are going to see a bottleneck, and nobody wants to see that."

Main markets
Leaving infrastructure issues aside, Prism Solar's business model has worldwide appeal. "We will build solar modules that use our holographic optics in four versions to be sold in the US," explained Lewandowski. "We will also create holographic film that can be integrated with modules made by developers in Europe, Asia and other parts of the world." In other words, although Prism Solar will be competing with standard plate manufacturers, its main customers will also be module manufacturers. Lewandowski thinks that the arrangement will work and that the firm will be able to tap into existing distribution networks and channels to market.

More than just power
Electricity generation tends to be top of the agenda, but the firm's holographic film has other uses, such as daylighting in architectural applications. "You could have an optical panel inside and an optical panel outside, which are linked with fibre-optic cables," said Lewandowski. "Light from the outside will then brighten the room on the inside."

These are certainly bright times for solar technology. "There are many unique technologies coming onto the market that show great promise," said Lewandowski. "A lot of money is coming in with venture capitalists getting involved in clean energy, and that can be a positive thing, but as we saw with the dot-com period it can also have a downside. You can create a little more hype than is warranted in the segment and it can heighten milestone expectations."

• This article originally appeared in the May 2007 issue of Optics & Laser Europe magazine.

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