Posts

New New Solar PV

/0 Comments/in , /by

There are a number of fascinating new developments in the world of solar photovoltaic cells, which represent major shifts from the usual crystalline silicon cell based on semiconductor technology, which supplies as much as 80% of the market today (referring to wafers sliced from large single crystal or polycrystalline ingots). Here is a quick overview. Much more information exists on most of these topics.

Evergreen Solar
Evergreen has one of most mature of the new approaches, and is now a growing public company (symbol ESLR), ramping up production of its unique string ribbon Silicon cell. The Evergreen cell is fully equivalent on a functional basis, but is considerably than the ingot slice method. Evergreen anticipates sales of $6-9 million in 2003. The website does a good job explaining the whole story. http://www.evergreensolar.com/

Solar Grade Silicon
In March, Solar Grade Silicon LLC announced full production of polycrystalline silicon at its new plant in Washington, the first ever plant dedicated wholly to producing feedstock for the solar industry. They supply the purified silicon that is then melted and made into single crystals, i.e. in large ingots, or Evergreen’s ribbon. In the past, solar cell makers relied on scraps from the semiconductor industry, which won’t be sufficient to handle the growth in the PV industry.
http://www.newsdata.com/enernet/conweb/conweb85.html#cw85-5

Spheral (ATS Automation)
In one of the stranger sagas of solar, you may recall that in 1995, Texas Instruments finally gave up on a major development program to develop “Spheral” solar cells, an effort they’d devoted many years and many dollars to (with considerable support from DOE). Spheral technology comprises thousands of tiny silicon spheres, bonded between thin flexible aluminum foil substrates to form solar cells, which are then assembled into lightweight flexible modules. TI’s goal was to develop a manufacturing process that would drive PV costs to $2/watt. Ontario Hydro Technologies acquired the technology, set up manufacturing in Toronto, and sold some systems, but in 1997, reorganizations and a return to basics led them to sell it off. Apparently dormant since then, in July 2002 ATS Automation announced it had acquired the technology, set up a subsidiary, and was scaling up production with plans to be in commercial production this year. The Canadian government put in nearly $30 Million. The jury is out on this one. For the story, go to: http://www.spheralsolar.com/

Thin Film-CIGS
Commercially produced thin film PV falls into 3 general categories, Cadium Telluride, Amorphous Silicon, and CIGS (Cu(In,Ga)Se2). The first two technologies are struggling, with BP’s notable exit last November from both. CIGS is having instances of some apparent success and continuing development efforts, and enjoys strong support at NREL, a true believer. There are production facilities doing CIGS as well as innumerable development efforts around the world to make it cheaper and more efficient. CIGS has the unique feature of becoming more efficient as it ages.

Global Solar**
Global, partly owned Unisource, the parent of Tucson Electric, is selling thin film CIGS modules to the military, commercial and recreational markets. One product is a blanket a soldier can unfold on the ground. Current production capacity is 2.3 MW per year, and they’re fundraising to expand to 7.5 MW. http://www.globalsolar.com

Raycom**
Among the new entrants, Raycom is a startup in Silicon Valley, led by veterans of thin film coating for disk drives and optical filters. They believe their experience (and existing equipment) will enable them to avoid the long and painful development cycles that have traditionally characterized the solar PV industry, and be in production in less than 2 years. Their secret is “dual-rotary magnetron sputtering” a patented process that has already proven effective in high volume manufacturing. Cost targets are under $1 per watt. They also have brought a fresh eye to the formulation of CIGS, and see ways to make it without cadmium, which is highly toxic. Raycom produced their first working cells in a matter of months. They are in the midst of fundraising. One might observe that this is a rare instance where someone comes to PV from manufacturing instead of science. Normally, people develop PV technology in the lab and then endeavor to become manufacturers. This time it’s the other way around. [To see the magetron sputtering technology, go to:
http://www.precisdesign.com/solutions/technologies.html]
Contact David Pearce 408-456-5706, dpearce@rcomtech.com

Konarka
Konarka has attracted a great deal of attention and sizable VC participation (funding round Oct 02) with promises of a way to commercialize the “Gratzel” cell, which Dr. Michael Grätzel developed and subsequently patented in the 1990’s. The core of the technology consists of nanometer-scale crystals of TiO2 semiconductor coated with light-absorbing dye and embedded in an electrolyte between the front and back electrical contacts. Photons are absorbed by the dye, liberating an electron which escapes via the TiO2 to the external circuit. The electron returns on the other side of the cell, and is restores another dye molecule. The jury is out on this one, whether it’ll happen quickly as the company and its investors hope, or will there be a long road ahead. One of the biggest issues since this idea was first tried has been the stability of the organic dyes. http://www.konarkatech.com/

For a good discussion of dye-sensitized cells, see this pdf:
http://www.polymers.dk/research/posters/Dye-sensitisedKW.pdf

Nanosys
This Palo Alto based company has a long list of goals for its nanotechnology, ranging from chemical/biological sensors, to electronics and photovoltaics, based on formulations of nanowires, nanotubes, and nanoparticles. Their idea for PV is reportedly to embed nanorods of photosensitive material in a polymer electrolyte, on a principle not unlike Konarka’s. On April 24, they announced an amazing $30 Million VC funding. You have to wonder about this one, i.e. if the nano-hype has taken over, and how successful they’ll be about solar as compared with the other areas.
http://www.nanosysinc.com

The technology was originally developed at Lawrence Berkeley Lab:
http://www.lbl.gov/Tech-Transfer/collaboration/techs/lbnl1810.html
http://www.lbl.gov/msd/PIs/Alivisatos/02/02_1alivisatos.html

NanoSolar
Also Palo Alto based, this one is in stealth mode. The basic idea is similar to Nanosys, but they are focused only on solar. They also incorporate technology licensed from Sandia for nano-self-assembly to align the nanorods perpendicular to the surface, which is supposed to make a big difference in the efficiency. (Nanosys’s nanorods are said to be randomly oriented in clumps.) NanoSolar has some very famous investors, who are maintaining an extremely low profile.

Solaicx**
Solaicx is a new spinout from SRI International, and has a way to make polycrystalline silicon cell material in a continuous process atmospheric-pressure furnace. Their presentations and materials tell very little about what they have, making it pretty hard to judge.

Solaria
This is a very unusual concentrator story involving the use of variable “graded” index glass optics. The work started in the mid 80’s. Solaria Corporation was formed in 1998 by the founders and former management from LightPath Technologies, Inc., Albuquerque, New Mexico. Solaria holds the exclusive license from LightPath to use its proprietary GRADIUM® optics in the field of solar energy. http://www.solaria.com/

** These companies presented at the Cleantech Venture Forum in San Francisco, April 30.

Photolytic Hydrogen from Sunlight

/0 Comments/in , /by

Researchers have been working on a process that uses sunlight to produce hydrogen by splitting water directly. To understand photoelectrolysis, think of a PV cell underwater, where the electrochemical energy produced is immediately used to electrolyze water, instead of creating an external current. The light hits the cell, and hydrogen bubbles appear on one side of the cell, while oxygen appears on the other side, just as in electrolysis. (Of course one could use a PV cell to power an electrolyzer, but the idea here is to make a simpler and more economical system.)

The interface between the water (electrolyte) and certain semiconductor materials forms a diode junction that generates power–and thus does the electrolysis. The presence of catalysts at the surface can also help with the energetics and kinetics of the reactions that form the hydrogen and oxygen, respectively.

One of the problems is that the minimum voltage for splitting water (1.3 volts) is higher than a photocell can easily produce, and high-bandgap materials capable of generating enough voltage can utilize only ultraviolet light, which is a small fraction of the solar spectrum.

Work at NREL and the University of Hawaii has focused on developing multijunction cells which use more of the solar spectrum. These additional layers are sandwiched inside the basic cell that does the photolysis, and provide a boost to the electro potential available to do the water splitting. The electrochemistry and solid state physics of these devices are very complex. One of the main challenges has been to come up with materials and configurations that will be less susceptible to corrosion from the electrolyte and which will last long enough to be practical. Efficencies above 12% have been seen (i.e., the energy value of the hydrogen produced vs. the amount of incident sunlight. (See the 2002 H2 DOE Program Reviews–ref. below. Also, the 2003 meeting in May will have new updates.)

Researchers at the University of Duquesne published an important development in Science Magazine last September. Titanium dioxide is known to be a cheap and stable photocatalyst for splitting water, but hydrogen yields were always less than 1% (due to the high band gap of the material). The new development involved preparing the material in a flame, introducing carbon into its structure. Cells using this new material saw a factor of 10 increase in hydrogen production. The University is actively seeking licensees or partners to pursue this technology. (Contact me for details).

The design goal at NREL and Hawaii is to come up with a monolithic device that needs no external electrical connections. The simple version of the Duquesne cell requires an external bias power source (which could be powered by a fuel cell using some of the hydrogen produced), but which would still be a net producer of power. Net yields are already at 8.5%, and are expected to improve.

Though commercial devices are a ways off, photosplitting of water is another process that could supply hydrogen by purely renewable means.

References:

2002 Hydrogen Program Review Meeting – Renewable Production Electrolytic Processes
http://www.eere.energy.gov/hydrogenandfuelcells/hydrogen/annual_review2002.html#Renewable

Science…27 Sept 02
“Efficient Photochemical Water Splitting by a Chemically Modified n-TiO2”

Science 17 April 98
“A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production via Water Splitting”

( I can provide pdf copies of the Science articles).