Solar Power at Half the Cost

A new roof-mounted system that concentrates sunlight could cut the price of photovoltaics.
A new mechanism for focusing light on small areas of photovoltaic material could make solar power in residential and commercial applications cheaper than electricity from the grid in most markets in the next few years. Initial systems, which can be made at half the cost of conventional solar panels, are set to start shipping later this year, says Brad Hines, CTO and founder of Soliant Energy, a startup based in Pasadena, CA, that has developed the new modules.

Concentrating sunlight with mirrors or lenses on a small area cuts the costs of solar power in part by reducing the amount of expensive photovoltaic material needed. But while concentrated solar photovoltaic systems are attractive for large-scale, ground-based solar farms for utilities, conventional designs are difficult to mount on rooftops, where most residential and commercial customers have space for solar panels. The systems are typically large and heavy, and they're mounted on posts so that they can move to track the sun, which makes them more vulnerable to gusts of wind than ordinary flat solar panels are.

Soliant has designed a solar concentrator that tracks the sun throughout the day but is lighter and not pole-mounted. The system fits in a rectangular frame and is mounted to the roof with the same hardware that's used for conventional flat solar panels. Yet the devices will likely cost half as much as a conventional solar panel, says Hines. A second-generation design, which concentrates light more and uses better photovoltaics, could cost a quarter as much. He says that a more advanced design should be ready by 2010.

The Soliant design combines both lenses and mirrors to create a more compact system. Each module is made of rows of aluminum troughs, each about the width and depth of a gutter. These troughs are mounted inside a rectangular frame and can tilt in unison from side to side to follow the sun. Each trough is enclosed on top with a clear acrylic lid. Inside each trough, a strip of silicon photovoltaic material runs along the bottom. As light enters, some of it reflects off the inside surface of the trough and reaches the strip of silicon. The rest of the incoming light is focused on the strip by a lens incorporated into the acrylic lid.

As a solar concentrating system, this design has a few drawbacks. Because the troughs are mounted close together, they shade each other during parts of the day, decreasing the total amount of electricity produced. They can also only track from side to side, which makes it impossible for them to follow exactly the arc of the sun across the sky. This second problem will be addressed in the second-generation design, in which each trough will be divided into sections, each of which can pivot from side to side and also up and down.


But the ease of installation could help convince solar installers to use the technology, says Craig Cornelius, the technology manager for the Department of Energy's (DOE) solar-energy technology program. DOE recently announced $168 million in funding for 13 solar projects, under which Soliant will receive up to $4 million. Cornelius says that the lower installation costs will help reduce the overall costs of solar power from the modules.

Cornelius thinks that some customers, such as those with plenty of roof space, will opt for cheaper, thin-film solar panels, which in some cases can double as shingles, but are less efficient than conventional solar panels. But for those who need more power for the space they have, Cornelius says that Soliant's approach may prove the best option. Its modules produce as much power as conventional flat panels but are less expensive, using 88 percent less silicon. The company's next-generation system would be even better, producing three times as much power per area.

To test the panels, Soliant is working with DOE and Sun Edison, an established solar-system installer and operator based in Beltsville, MD. The second-generation system will be even more challenging to develop because light will be focused on a smaller area, requiring better tracking of the sun. Soliant will also be working with Emanuel Sachs, professor of mechanical engineering at MIT, to improve manufacturing techniques and the system for aiming the concentrators.

"In some ways, what's interesting about [Soliant's] approach is [that] the engineering issues they have to solve are relatively mundane," Cornelius says. "This is one of the projects that I'm most excited about in our whole portfolio."

Supplying the World's Energy Needs with Light and Water

A leading chemist says that a better understanding of photosynthesis could lead to cheap ways to store solar energy as chemical fuel.
While researchers and technologists around the world scramble to find cleaner sources of energy, some chemists are turning to nature's own elegant solution: photosynthesis. In photosynthesis, green plants use the energy in sunlight to break down water and carbon dioxide. By manipulating electrons and hydrogen, oxygen, and carbon atoms in a series of complex chemical reactions, the process ultimately produces the cellulose and lignin that form the structure of the plant, as well as stored energy in the form of sugar. Understanding how this process works, thinks Daniel Nocera, professor of chemistry at MIT, could lead to ways to produce and store solar energy in forms that are practical for powering cars and providing electricity even when the sun isn't shining.

What's needed are breakthroughs in our understanding of the fundamental chemical processes that make photosynthesis possible, according to Nocera, a recognized photosynthesis expert. He is studying the principles behind photosynthesis and applying what he learns to making catalysts that use solar energy to create hydrogen gas for fuel cells. Nocera's goal: a world powered by light and water.

Technology Review: What's the biggest challenge related to energy right now?

Daniel Nocera: The real challenge with energy is the scaling problem. We're going to have this huge energy need, and when you start looking at all the numbers, there's only one supply that has scale, and it's the sun. But it's still a research problem. Technologies all follow lines; then there's a discovery and a new line that's better. We're on a very predictable line now in solar. Most things you hear about are incremental advances.

TR: You're studying photosynthesis to get ideas for how to convert sunlight into a chemical fuel--hydrogen--for use when the sun isn't shining or in powering fuel-cell vehicles.

DN: You can use the electricity directly when the sun is out, in places that have sun. [But] you need storage. There's absolutely no way around it. I am distilling the essence of photosynthesis down to be able to use it.

TR: Why is photosynthesis attractive in finding a source of clean energy?

DN: [Photosynthesis] does three things. It captures sunlight, and [second,] it converts it into a wireless current--leaves are buzzing with electricity. And third, it does storage. It stores the converted light energy in chemical energy. And it uses that chemical energy for its life process, and then it stores a little.

It turns out [that] photosynthesis is one of the most efficient machines in the world for energy conversion. But it's not great for storing energy because that's not what [a plant] was built to do. It was built to live and grow and reproduce.

And so that's the approach we take. Can we now do what the leaf is doing artificially, which is the capture, conversion, and storage in chemical bonds? But my device doesn't have to live: it can take a lot more of that energy and put it into chemical bonds.

Your Coffee Table as a Computer

Microsoft has announced a touch-screen table that interacts with gadgets placed on its surface.
Today Microsoft unveiled a new addition to computing: a coffee table that doubles as a computer for viewing photos, videos, maps, or Web pages, for instance. The electronic furniture, called Microsoft Surface, lets users manipulating these objects directly with their fingers--to resize a picture or rotate it so that someone across the table can look at it.

The table's surface is a multitouch screen, which means that it can accommodate the input from a number of different points of contact at once, not unlike Apple's forthcoming iPhone.

Surface is also similar to technology created by a startup called Perceptive Pixel, founded by Jeff Han, a researcher at New York University. (See "Touch Screens for Many Fingers.")

Microsoft's technology distinguishes itself from that of other touch screens by wirelessly interacting with gadgets on the tabletop. The table is optimized to accommodate up to 52 points of contact, which could mean, for example, all the fingers on 4 people's hands and 12 devices sitting on the surface. A user can set her camera on the tabletop, and cameras inside the table's thick base will detect its presence (as well as the presence of other objects and fingers). Then software that leverages Bluetooth short-range wireless signals uploads the pictures from the user's camera to the tabletop screen. The user can flip, crop, resize, and organize the pictures using her fingers. To transfer a picture to another device on the table, such as a cell phone, she simply flicks the photos toward the gadget. This Popular Mechanics video offers a nice demonstration of the table in action.

The tables are expected to appear in hotels, casinos, and retail stores by the end of this year.