A new process developed at the USA’s National Renewable Energy Laboratory (NREL) could possibly remove one of the greatest costs associated with manufacturing silicon solar panels and help bring the cost of solar power generally even closer to that of coal or gas sooner.
The NREL’s Oak Ridge National Lab has led collaborative research with solar start-up Ampulse Corporation into making silicon wafers using a chemical deposition process onto cheap metal foil that with the aim of dramatically cutting the cost of producing wafer-based solar cells.
The production of the silicon used in solar wafers accounts for around half the cost of a finished solar panel.
According to the NREL, while silicon is a relatively abundant element and current crystalline silicon technology creates high efficiency cells, it involves processes that are complex, wasteful, and energy intensive.*
Before silicon can be used to convert sunlight to energy, it must be converted into pure trichlorosilane (SiCl3) or silane (SiH4) gas. This purified gas is then converted to create a silicon feedstock at 1,000 degrees Celsius. The feedstock is melted at 1,414°C and recrystallized into crystal ingots that are finally sawed into wafers.
Sometimes half of the silicon can be lost in the wafer-sawing process, which drives solar costs higher. The NREL estimates a typical 2-metre bale of silicon loses as many as 6,000 potential wafers during sawing. Also, the wafers produced are much thicker than necessary. To efficiently convert sunlight into electricity, they need be only one-tenth as thick.
NREL developed a method for growing silicon on inexpensive foil, while the Oak Ridge Lab came up with the foil substrate itself. Ampulse Corp. is responsible for building a pilot manufacturing plant at the NREL’s Process Development and Integration Laboratory – where solar companies test new equipment – to test whether the process will be successful on a commercial scale.
The Ampulse process “goes straight from pure silicon-containing gas to high-quality crystal silicon film,” said Brent Nelson, who runs the PDIL at NREL. “The advantage is you can make the wafer just as thin as you need it — 10 microns or less.”
*Some solar cell and panel manufacturers have more refined processes than others. For example, REC solar panels have a 1 year energy payback time; i.e., the time it takes a module to generate the same amount of electricity that went into its production.