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Home > Nanotechnology Columns > Bo Varga > Nanotechnology Impact on Solar Power

Bo Varga
Managing Director
Silicon Valley Nano Ventures

Abstract:
Solar Markets, Nano & PV Technologies Overview including c-silicon, a-silicon, CIGS, CdTe, GaAs, polymer/DSSC, tandem, and nano-materials based PV.

August 31st, 2006

Nanotechnology Impact on Solar Power

This column will run run monthly in 2007 and focus on nanotechnology conferences, commercialization, companies, fundings, issues, research and other areas of interest to solar power. Later columns will focus on California as both an innovation center and the world's third largest market for solar photo voltaic (PV) and emerging technology centers such as China and Korea. All quotations are referenced and all opinions are the opinions of the columnist and not of Nanotechnology-Now.

We are especially interested in comments whether the information presented is at the right level of detail or if more detail would be useful to our readers.

Readers are invited to send their feedback, ideas, and suggestions to Bo Varga via bvarga at nanotech-now.com. Bo has 27 years experience working with start-up and early stage companies in Silicon Valley & globally and six years experience with the commercialization of nanotechnology.

The primary focus of this column will be photovoltaic (PV) and the table attached gives a good reference point for current product/market trends.

The data source is provided by PV News, Volume 25, Number 3, March 2006, published by the Prometheus Institute for Sustainable Development, www.prometheus.org, one of a handful of high quality web portals that provide top quality news on real technical breakthroughs and major commercial announcements

The left column shows cost in cents per Kilowatt/Hour and the blue trend line shows that the current dominant technology - crystalline silicon - has matured after rapid price declines from 1990 to 1996.

The right column shows total Megawatts shipped annual. Subsidies in Japan and Germany result in these two countries having the major share of installed base, with California number three in the world for 2005 installations.

For readers who can get to California in October, Solar Power 2006, which will focus on new and innovative developments in the solar industry, is ramping up, with pre-registration at seven times more than last year's show, and twice the number of exhibitors to take up more than three times the space at the San Jose Convention Center from October 16 to 19 per the current press release at: www.solarpowerconference.com

The balance of this column will cover the various technologies for PV and give some insight into the potential for nanotechnology to drive costs down below the 10 cents per Kilowatt Hour and eventually to 5 cents per Kilowatt Hour. These costs will make PV very competitive with gas, hydroelectric, and coal based electricity, initially during peak loads and eventually on a regular daytime basis.

A later column will cover various ways of storing solar electricity for use when the sun is not shining.

Major cost elements for current PV includes the silicon material, manufacturing solar cells, assembly & packaging of modules, and installation cost. Current information is available from: www.solarbuzz.com/moduleprices.htm

"The module cost represents around 50 - 60% of the total installed cost of a Solar Energy System. Therefore the solar module price is the key element in the total price of an installed solar system. All prices are exclusive of sales taxes, which depending on the country or region can add 8-20% to the prices, with generally highest sales tax rates in Europe.

The prices are based on the purchase of a single module and take into account prices across all solar module power bands (i.e. 3 Watts to 300 Watts). This approach is taken to ensure a consistent, but broadly based, index.

Therefore, while the US Index currently shows average retail prices around $5 per Watt Peak, prices as low as $4.05 Watt for crystalline silicon and $3.94 per Watt for thin film, are included in the survey database for the retail price of a single solar panel."

A residential retail installation of 1 Kilowatt Peak (assuming 50% installation cost in California) would cost $10,000 before sales taxes or tax subsidies.

The "holy grail" promoted by every PV nanotechnology company is $1 per Watt Peak, which would reduce the installed cost of a 1 Kilowatt Peak system to $2,000.

Crystalline Silicon (C-silicon) PV is 90%+ of the installed base today and currently uses semiconductor silicon (mono or poly) as well as semi-conductor processes. Major vendors include Sharp, Kyocera, Sanyo BP, Siemens, Q-Cells, SunPower (in Silicon Valley, partnered with Cypress Semiconductor), and SunTech in China.

Cell efficiency is in the 15%-20% range and module efficiency is in the 9%-12% range. Module prices range from $4 to $6/Watt Peak and payback is on the order of 10 years at current electricity prices (exclusive of tax subsidies).

Current shortages of semiconductor grade silicon have resulted in price increases over the past two years. As 50%-60% of the cost is stated by various sources to be the initial silicon wafer, pricing for c-silicon PV is closely tied the price of c-silicon.

Amorphous Silicon (a-silicon) PV is the rapidly growing alternative technology. The use of lower cost materials and thin film technology results in modules in the $4/Watt Peak range and also offers the ability to integrated with standard building materials - roofing, windows, etc. Building integrated photo voltaics (BIPV) will be covered in a later column. The focus here is reducing the 50% installation cost by integrating PV into the building materials that will be used in construction. Major vendors include Sharp, Sanyo, Fuji Electric, United Solar, and Schott Solar (BIPV in Glass).

Cell efficiency is in the 8%-10% range and module efficiency is in the 5%-6% range. Two technical issues are the need for 3 layers (triple junction cell) to harvest the major solar energy band gaps and the loss of efficiency over time (we have seen up to 30% quoted by some sources).

CIGS uses copper, indium, gallium, selenide nano structured materials in place of silicon and the players in this field are mainly focused on thin films and "roll to roll" manufacturing to enable downstream cost and price reductions. The potential cost reduction enables an initial target of $3/Watt Peak range with the long term goal of $1/Watt Peak. Initial cell efficiencies are higher than a-silicon and are in the 10%-15% at the cell level but only at the 5%-10% at the system level due to difficulties of controlling the thin film manufacturing process. Given the push by major Japanese vendors to ramp up a-silicon manufacturing using display technology formats - up to 1 meter x 1.5 meter panels on glass or plastic substrates, CIGS vendors will most likely find their market penetration is a lot slower than projected.

Major CIGS startups include Nanosolar, Miasole, and Heliovolt as well as a division of Honda that will be in volume production by the Fall of 2007. Wurth Solar in Germany is an established company selling a CIS module with 11% efficiency.

CdTe solar companies manufacture Cadmium Telluride thin films and have the potential advantage of higher efficiency, lower complexity, and lower cost than CIGS. First Solar is an established vendor that will sell over 100MW of 9.3% efficiency solar modules in 2007. Startups include AVA Technologies, Primestar Solar,& Solar Fields.

GaAS solar companies manufacture Gallium Arsenide solar cells because they have better absorption of sunlight than c-Si and higher efficiencies. This technology is far more expensive & usable only for military applications OR as target cells for solar concentrators. A concentrator that provides 100 suns concentration, for example, could need only 1/100 or less of the density of solar cells to get a power output equivalent to a c-Si module. Boeing/Spectrolab and Emcore Photovoltaics are the major producers.

Polymers / Dye Sensitized Solar Cells (DSSC) have short lifetimes due to instability of materials in prolonged sunlight and absorb a narrow band of the solar spectrum. Efficiencies are in the 5%-10% range at the cell level and 3%-6% range at the system level. Costs are currently below $3/Peak Watt but the short lifetime looks likely to limit this technology to portable or "throwaway" applications - warning signs, tapes, etc.

Konarka is the most well known company in the Polymer space while STMicroelectronics is making a major push to commercialize DSSC with the goal of achieving cost of 40 cents/Watt Peak (not price) in large installations and with 10% efficiency with minimal deterioration.

STM in an October 10, 2005 press release at www.electronicsweekly.com stated that deterioration in a 1,000 hour sun test was from 8% to 7.4% cell efficiency. When or whether STM will achieve their 10% system efficiency goal remains to be seen.

Tandem cells achieve up to 40% efficiency today at the cell level and 30% at the system level but at a cost of $100/Watt Peak, limiting them to mission critical applications. Cyrium in Toronto is a start up targeting satellite power applications where the $20,000 per Kilo cost to place PV systems in orbit makes mass rather than cost the key gating factor.

Nano-materials start-ups are an emerging category. These companies generally focus on quantum dots, carbon nano tubes, or other nano-structured materials with the goal of delivering high efficiency by matching solar spectrum bands with materials that have maximum absorption at those bands and of developing low cost manufacturing methods. There are several companies in Silicon Valley and a number across the US working in this area. They all seem to target the $1/Peak Watt "holy grail".

Business models include selling nano structured materials or coating services to thin film PV manufacturers, buying thin film solar cells and applying coatings and selling a higher efficiency higher value product, or developing new types of solar cells using new manufacturing processes.

IR Harvesting can deliver a major boost to the efficiency of PV. About 40% of total insolation is in the form of infrared photons that are harvested in a limited fashion by c-silicon and not harvested by a-silicon. Work on infra red emitter / absorber materials by Ted Sargent's group at the University of Toronto and Stephen Forrest's group at Princeton indicates that this is an area where nano structured materials can play an important role.

Where can nanotechnology have a commercial impact?

In general efficiencies can be impacted by nano structured materials that (i) target major solar spectrum bands including IR and maximize photon absorption and exciton generation, (ii) improve efficiency of carrier separation by keeping the electrons generated by excitons from merging with the holes before electricity is removed, (iii) enable multi-exciton generation from one photon - current research indicates that 3 electrons could result from one photon.

In general costs can be impacted by nano structured materials that are (i) lower in cost than silicon and (ii) can be manufactured using wet chemistry processes, especially with "one pot synthesis" claimed by Nanosy, University of Manchester, and other research groups.

The quantum dots conference October 4-6 in San Francisco should be of interest to companies, entrepreneurs, and investors focused on the impact of nano-structured materials on the future of global PV.

In summary there are at least 20 nanotechnology-based companies targeting PV for market entry products. Based on current deveopments and trends nanotechnology will have major impact on the efficiency and prices of PV starting in the second decade of this century.

Readers are invited to send their feedback, ideas, and suggestions to Bo Varga via bvarga at nanotech-now.com

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