#

Green Collar Careers - Thin Film Solar Panels

The next generation of solar PV cells may add several new technologies with higher efficiencies and/or lower costs.  Over the last decade there has been a tremendous rise with development of Thin Film Photo Voltaic (TFPV) technology.  TFPV offers several solutions to the limitations of silicon PV cells including lower cost and higher efficiencies. Production methods are very different from silicon PV cells and many of the up & coming producers are still refining manufacturing processes for mass production.

By overcoming some of the band gap restrictions TPFV produces more power under less optimal "filtered" sunlight conditions including cloudy days as well as morning & evening light.  Some systems are being installed with solar tracking as the cost is now offset.

There are a few different key material technologies used in TFPV design, each offering different advantages.  Three of the leading technologies are:

• Cadmium Telluride (CdTe)
• Copper indium gallium selenide (CIGS)
• Thin-film silicon (TF-Si)

CdTe uses a nearly transparent film of Cadmium and Tellurium on sheets of glass eliminating the need for more costly pure silicon.  Under optimal "high noon" conditions these cells are slightly less efficient then silicon, however over the course of a day and in particular under cloudy conditions, these cells produce more power then silicon PV's. 

They are not without some disadvantages.  Cadmium and Tellurium are both toxic materials to handle through manufacturing and disposal.  Once in the finished panel they are considered quite safe.  Although the raw material costs are much lower then silicon, they manufacturing process is somewhat more expensive, typically a vapor deposition method.  As production is ramping economies of scale are beginning to show significant cost reductions and the current cost comparison to silicon per actual production watt is about 70%.

Due to the limited production CdTe is only available to commercial operations that produce over 50 kW per installation, and even then there is an 18-24 month waiting list.

CIGS uses less hazardous and generally more available materials then CdTe however has a more complex manufacturing process to control.  Recent advances in electroplating are likely to reduce the cost over the next five years.  CIGS has demonstrated higher efficiency capability then most commercially available silicon PV reaching close to 20%.  Several key advantages with exploiting a varied range of band gap efficiencies are still in development with some very optimistic theories on substantially higher efficiencies yet available.

A major advantage is this technology can be applied to flexible substrates.  There are a few manufacturers producing solar films that can be applied to windows that both reduce the sunlight and generate electricity.  Flexible substrates open up many new possibilities for architectural solutions.

Disadvantages are primarily a shorter expected operating life.  Materials used have an affinity to absorb moisture that quickly corrodes the films so the layers must remain sealed to the environment.

TF-Si is still silicon based however rather then binning with an expensive pure silicon cast ingot, they rely on thin films of silicon generally applied with chemical deposition or sputtering techniques.  These have a lower efficiency then traditional silicon PV's however also have a lower cost per actual production watt.  There are developments that have produced flexible translucent substrates providing attractive prospects for building integration similar to the CIGS thin films for windows.  There are few companies that are investing much into developing this technology so it may not become a major player in the next generation of solar PV cells.