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Chapter 3: Crystalline vs. Thin-film Solar Modules

Earlier generations of photovoltaic solar modules almost universally utilized crystalline silicon cells, also called wafer or bulk cells. These cells can be considered the gold standard for energy efficiency, operating at approximately 15%. However, the cost of manufacturing crystalline cells is severely crippled by their dependence on silicon. Supply and demand for the precious element, which is also used in computer manufacture, has been the major factor leading to prohibitive costs of solar energy systems since their inception. The price of silicon-dependent solar panels decreased slowly but steadily until 2004, until a dramatic increase in demand led to a skyrocketing in silicon prices.

An alternative to crystalline silicon cells is the use of thin-film solar cells, which use very little to no silicon (1% or less). Several types of thin-film panels are currently available and in development.

  1. Amorphous silicon solar cells: these cells use a very thin layer of silicon in combination with plasma-enhanced chemical vapor deposition (PECVD), a technology that promises lower cost per watt and higher energy conversion with a lower silicon requirement.
  2. Copper-indium-gallium-diselenide (CIGD) is an efficient alloy that is less expensive than silicon.
  3. Cadmium telluride solar cells cost about half as much to manufacture as silicon cells, but depend on the use of cadmium, which is a highly toxic heavy metal and known to be a human carcinogen.
  4. Dye-sensitized solar cells (DSSC) can be generated in a do-it-yourself fashion from inexpensive materials. The main drawback to this technology is that the cells are far less energy efficient than their more expensive counterparts.
  5. Polymer or organic solar cells: Several companies in the business of generating more efficient, environmentally friendly and cost-effective solar panels are seeking to identify or generate additional materials that can replace silicon and other less desirable materials for solar power.

In general, thin-film solar technologies hold promise but today are still less energy efficient than crystalline silicon technologies. Most thin-film solar products are only about half as efficient as their silicon counterparts. Because of this, thin-film solar panels must be larger and heavier in order to capture a comparable amount of solar energy. This results in increased weight on the roof of a home or business, increases in shipping costs, and increases in labor costs.

Grid parity is the point at which photovoltaic electricity is equal to or cheaper than grid power achieved by traditional, exhaustible resources. The Bush administration set a goal of achieving grid parity in the United States by the year 2015. This phenomenon will first be reasonably achieved in sunnier regions, such as the southwest, but as technologies become more efficient, it is hoped that solar power can achieve grid parity even in regions with considerably fewer sunny or daylight hours. As thin-film promises come to fruition and the demand for silicon is reduced among solar cell manufacturers, it is hypothesized that efficiency will increase and cost will decrease by as much as forty percent over the next five years alone.