When there is something that is abundant and highly accessible, instead of saying it is "a dime a dozen," Germans say "This is like sand in the sea." You can find sand everywhere as it covers about 20 percent of the Earth. You might think that silica, a key ingredient of sand and basis material for silicon, could be easily and cheaply extracted from that earthy powder to produce solar cells.

If it were only that easy. Solar cell manufacturers need pure, highly refined silicon to produce solar cells. So far, solar cell producers used mainly the unwanted hand me downs of the semiconductor industry: the silicon scraps.

But now the high demands of the solar industry for solar grade silicon has outgrown the silicon waste and surplus of the semiconductor industry. Since 2003 both industries have been in a fierce competition for silicon. Prices for silicon have roughly doubled in the last three years ¬– and since there aren't enough silicon producing companies, prices will keep on climbing.

This leads to a costly chain reaction: more expensive solar cells, solar modules, and higher costs for consumers despite increasing competition between component producers.

Today most of the solar modules you see on your neighbor’s roof consist of either monocrystalline or polycrystalline cells. Monocrystaline cells are the first generation cells. Their edges are a little rounded, and they are the most expensive cells with the highest efficiency rate and the highest use of silicon. Most homeowners have polycrystalline cells on their rooftops.

So-called amorphous solar cells are much thinner than the other types of solar cells. While two of them are in a rather experimental stage (a-si and CdTe) the most promising technology is CIS.

Those CIS (Copper-Indium-Diselenid) cells are much thinner, flexible, need less material to produce and are suitable for a promising mass production. Instead of casting silicon into blocks and cutting them into wafers, cells and combining them into modules, thin solar cells can be rolled off on film with much less waste.

Germany in the Lead Germany has experienced a solar boom in the last five years: In 2005 alone more photovoltaic systems were installed in Germany than anywhere else in the world. According to DENA (Germany's Energy Agency, 75,000 solar power systems with an output of 600 MW were connected to the grid, increasing the total installed solar power output to 1,500 MW – Germany is the "Weltmeister“ (world champion) in installed PV, leaving Japan and the US with installed 400 MW far behind.

But this is going to change. California's million solar roof law takes effect in January 2007 and should bring an enormous solar boom to California. The goals are ambitious but achievable: By 2017 California wants to have at least one million solar roofs and a total installed PV power of 3000 MW.

Will such a high demand bring down the prices for solar modules? Probably not, as the bottleneck is still the silicon producers. It takes at least two years to expand production of an existing plant, and new "solar silicon"-only factories are still in construction.

This scenario presents an opportunity that non-silicon thin film cells could fill. While there are research and pilot projects underway worldwide, Germany again is at the forefront. Würth Solar's CISfab was the first thin film production facility to go online in October.

In contrast to conventional modules, CIS solar modules do without the scarce raw material silicon. For the first time, CIS solar modules made of Copper-Indium-Diselenid will roll off the line in large-scale production. With around 1000 feeder bands and a continuous process from the raw material to the finished CIS solar module, CISfab produces thin solar cells in 24 individual network steps. Beginning in 2007, Würth Solar plans to produce 200,000 CIS solar modules a year. This corresponds to 14.8 MW.

And there are at least two other European companies following next year: Dutch Scheuten Solar BV is developing mass production capability, and German Johanna Solar Technology is currently building a CIS manufacturing fab that will more than double (30 MW) Würth's planned production.

Thin Film Solar to Rule the Roof

There are many advantages for the usage of thin film cells as the cells are easier, faster and cheaper to manufacture. Also, the solar producers will be less dependent on silicon, and thin film cells can be applied much more creatively in architecture.

The efficiency rate of thin film solar cells is approximately 11 percent. That’s less than the 18-19 percent efficiency rates of polycrystalline cells, so thin film cells require more space to produce the same amount of energy.

However, thin film solar cell's consistent performance at varying temperature may balance the need for more real estate. Polycrystalline solar cells love light but hate heat. The higher the temperature on the roof the less voltage and less power you will get from the cells. For example, a crisp but sunny winter day in Colorado would produce more power than a balmy and sunny day in San Francisco.

Worldwide demand for solar cells is increasing, and the approximately 50 MW of mass produced CIS thin film cells in 2007 clearly won’t be enough to satisfy a solar hungry United States, Germany, Span, Italy and China. Even by 2020 Würth Solar estimates that 7.5 GW (22 percent) of the worldwide produced solar cells will be applied on thin cells.

The market price for the power of solar modules is currently between $4.50 and $5.50 US per watt. In order to be cost competitive without subsidies on a global scale against using fossil fuels for electric power, the price must drop to less than $2 per watt. This would require accelerated growth and increased production efficiency to cut the cost of thin solar cells.

While the thin film solar cell technology is promising, there will be new players and technologies emerging. However, silicon will likely be the most dominant resource for solar modules for many more years.

Sustainable investors should continue to back silicon manufacturers including Hemlock, Wacker Chemie, REC, MEMC, Tokuyma, Mitsubishi and others, and keep an eye on the emerging thin film mass producers. For the immediate future, solar won’t be printed exclusively on thin film solar cells but continue to be found in the sand. But maybe, just maybe, someday people will use the expression: "This is like CIS on the roofs."