About Thin Film Potovoltaic Solar Power

Thin film photovoltaic solar cells represent the most promising technology for significantly reducing the cost of solar electrical systems.  This technology has the potential to provide low cost solar power by using non-silicon solar cells, low cost plastic substrates and  through currently available, high volume and inexpensive manufacturing techniques.  Traditional silicon cell manufacturers have been constrained by the shortage of silicon (previous post), high prices of silicon and the difficulty of processing it.

DayStar commercially sells non-silicon thin film Copper Indium Gallium diSelenide (CIGS) cells that are deposited, rather than printed, on a stainless foil.  See this post for a discussion of CIGS cells deposited on a stainless stainless foil.  Thin film amorphous (not crystalline) silicon cells made with a roll to roll process on a stainless substrate are available commercially from Iowa Thin Film Technologies and Ovonics.  This post is not concerned with these cells, but rather the silicon-free thin cells printed on plastic substrates that are currently under development.

The next generation thin-film cells are based on non-silicon semiconductors, which can absorb the same amount of sunlight as crystalline Silicon but in layers that are at least two orders of magnitude thinner.  These thin film photovoltaic cells consist of layers of a semiconductor material such as CIGS, Copper Indium diSelenide (CIS) or Cadmium Telluride (CdTe), and applied to a low-cost substrate, such as plastic. The economic benefit of thin film PV cells is that they use much less semiconductor material than the crystalline silicon cells, a lower cost substrate and can use much less costly manufacturing methods.

The cost of solar electricity is not simply determined by obtaining the maximum efficiency of converting sunlight to power.  The lowest cost is obtained by optimizing the watts obtained per square foot, the product cost per square foot, the lifetime, and the installation costs.  This means that the manufacturing cost and the cost of raw materials become very important.

Thin film cell manufacturers do not talk about price of their products as the products are generally not available to the consumer market, except in some specialized applications. The Konarka web site  states "that its cells are cost-effective (1/3 of traditional solar)". (I would interpret that as being between $2.00 and $3.00 per watt)  By comparison DayStar is planning on having lower cost, higher volume continuous production facilities operating by the end of 2006 which should reduce their costs to about $2.00 per watt.  They also project that in full scale production they can reduce costs to $1.00 per watt.  Based on sales of $18 million for 5.6 MW of panels for the quarter ending June, 30, 2005 Ovonics amorphous silicone panels cost about $3.25 per watt.

Photovoltaic cells have traditionally been built using crystalline silicon, which requires expensive processing and results in ridged, bulky, inflexible solar panels.  The ability to "print" (solution-coat) the most expensive layers of a solar cell onto a low-cost, lightweight, flexible plastic substrates is what makes it possible to reduce manufacturing costs.  Printing processes are simple and robust in comparison with other thin-film deposition techniques and enable unprecedented process throughput with roll-to-roll production methods.  This process makes it possible to produce solar cells that can deliver as much energy and lifetime as conventional silicon cells and achieve unprecedented cost and production volume scalability advantages. This results in very price competitive photovoltaic cells even though the efficiency of thin film cells may be less than for crystalline silicone cells. 

DARPA in conjunction with the U.S. Department of Energy's National Renewable Energy (NREL) held a competition to select contractors to conduct further development of thin film PV cells.  More than 100 leading technology companies competed under this procurement process, with four of them making the final cut and contracts being awarded to: Nanosolar ($10.3 million), Konarka ($6.1 million), Nanosys ($2.3 million), and NREL.

The following material has, with some editing, been taken from the respective companies websites:

Nanosolar is collaborating with Stanford University, the University of California at Berkeley/Lawrence Berkeley National Laboratories, and Sandia National Laboratories on the development of next-generation solar cells that match and exceed the efficiency and lifetime of conventional solar cells but are far less expensive, less heavy, and less fragile.

Nanosys, Inc. is a leader in the development of nanotechnology based products utilizing high performance inorganic nanostructures.  By coating or printing photoactive materials onto a flexible plastic substrate, energy can be absorbed from both the sun and indoor light.  In particular, this technology has the potential to provide low cost solar power through currently available, high volume and inexpensive manufacturing techniques based on conventional film based processes such as roll to roll manufacturing. To develop their nanotechnology-enabled solar cells they are collaborating with Matsushita and several United States government agencies.

Konarka develops and produces light-activated power plastic (thin film solar cells) that are inexpensive, lightweight, flexible and versatile. This material makes it possible for devices, systems and structures to have their own low-cost embedded sources of renewable power. By integrating energy generation functionality into everyday devices, Konarka allows manufacturers to offer truly wireless applications.

Konarka's material is cost-effective (1/3 of traditional solar), lightweight (1 to 2 oz. per square foot), aesthetically appealing (can be colored and patterned), integrate-able (can be cut to fit), flexible and versatile so as not to increase or otherwise impede the application's form factor.  Konarka's polymer photovoltaic materials are manufactured in a continuous roll-to-roll process that is significantly less expensive and capital intensive than the multi-step assembly of traditional solar cells. This proven process, similar to photographic film, is simple, energy efficient, environmentally friendly, replicable to multiple plants and scalable to high volumes. 

Konarka and KURZ, a global manufacturer of printed polymer electronics technology, have formed a partnership to take Konarka's organic photovoltaic technology out of the lab.  Howard Berke, chairman and chief executive officer of Konarka, said, "KURZ is a world leader in innovative printed materials, and this relationship enhances Konarka's ability to take its organic photovoltaic program beyond the laboratory and into development for manufacturing and production scale-up.

Konarka' polymer based thin film technology working with Evident technologies "quantum dot" technology to make their film sensitive to a wider rage of the light spectrum and higher efficiencies.

Konarka has signed a $1.6 million contract with the United States Army. As part of this new program, their light-activated power plastic will provide critical power supply to soldier systems and Army support including portable AA battery chargers, solar powered tents and solar powered sensors.  (Iowa Thin Film Technologies also has contracts to supply battery chargers and tents)

This technology seems to be moving in the right direction and unless there are unexpected glitches (there always are in R & D) we should have some substantial reductions in the price of solar cells in the next few years.  With at least four US companies competing (there be some I am unaware of) the chances of at least one of them coming through is high.  One of the four is DayStar who is claiming their CIGS cells on a stainless steel substrate can be produced for $1.00 per watt. (The only reason that I have given so much space to Konarka is that they have much more information available on the web.)

References:

Iowa Thin Film Technologies, Inc.,  Ames, IA, http://www.iowathinfilm.com/index.php
ECD Ovonics, Rochester Hills, Michigan, http://www.ovonic.com/sol_srv/3_1_solar_sol/solar_solutions.htm
"United Solar Ovonic, Achieves Record Product Sales and Production", Ovonic's press release
"As solar gets smaller, it future gets brighter, Nanotechnology could turn rooftops into a sea of power-generating stations" SDGate.com, 7/11/05
Konarka Technologies, Inc., Lowell, MA, http://www.konarka.com/
"For Tech's Sake: Lightweight Solar Power for Mobile Users", Washington Technologies, 2/8/05
Nanosolar, Inc, Palo Alto, CA, http://www.nanosolar.com/index.html
Nanosys, Palo Alto, CA, http://www.nanosysinc.com/index.html
Technology hones the efficiency of sun-powered energy systems. NREL
EERE Solar Energy Technologies Program - Thin Films

Technocrati tags: solar power, renewable energy, solar cells, thin film

Comments

[dan]

Traditional photo-cells uses silicon in a crystalline state which is expensive to make, but the new technologies, such as from IowaThinFilm, claim to use amorphous silicon.

[Ben Kenney]

In my last podcast at theWatt.com I spoke to the CEO of ICP Solar, a company in Canada that makes thin-film PV. He was saying that there's a growing problem in the industry with companies overstating their wattage...so for example, it would say 12W on the box and actually only produce 6W. This has especially been a big problem in Kenya, which has a thriving solar market (at least in growth). There are now rules for importing soalr technology in Kenya because of these scandals, although the same problem exists in North America.

[JesseJenkins]

Thanks for a very comprehensive post on this topic. I am very excited about the prospects of thin-film solar technologies. I have researched these companies myself and while they are making some wild claims, I think the likelyhood of their ventures paying off is high. This technology could dramatically lower the cost of PVs and make the dream of solar panels on every rooftop an achievable possibility.

Solar has a long way to go to reach to competitive pricing that wind power has been able to offer lately. Wind has thus been getting the most attention in industrial-scale applications but these technologies could also move solar power into competitive price ranges and see a boom in large-scale solar development as well although I still prefer a distributed solution: there's so much roofspace that could be utilitzed, no sense clearing more space for PV farms, plus you get the added bonus of making the power where its used which avoids transmission losses and transmission infrastructure costs. All in all a great deal.

JesseJenkins aka WattHead (watthead.blogspot.com)

[Alan]

Nice overview of thin-film PV. I particularly welcome your pointing out that the cost of electricity is not a simple function of manufacturing cost or efficiency, as that is a point that is often missed by folks accustomed to comparing silicon with silicon. I should point out, though, that crystalline silicon is a moving target that still has plenty of room for cost improvement. While I am still a firm believer that it will someday be supplanted, any technology that hopes to dethrone it must first prove that it is manufacturable and scalable with high production yields. So far, nothing -- not even amorphous silicon, in my opinion -- has passed that test, and regardless of the success or failure of the companies you mention I fully expect silicon to continue dominating the PV market for at least another decade.

[ann]

Live in New England, by the shore -
Very cold in winter, and, windy.
Summer is O.K. , but lots of wind.
Always wondered if wind power on top of roofs, couldn't be harnessed.

[Joe]

I am looking for a clear or nearly clear, flexible thin film PV material to put on windows. I have read a lot about this material online but I cannot find any place to buy it. Does anyone know if this material is available for sale and if so where?

Thanks.

Joe

[Sunil Abhyankar]

Excellent Article.
Is there any one to Know more about organic PV.Looking for more information
Thanks and Regards
Sunil
India