Life-cycle nitrogen trifluoride emissions from photovoltaics

Area of Science:

• Materials Science
• Environmental Science
• Chemical Engineering

Background:

• Amorphous and nanocrystalline silicon thin-film photovoltaic (PV) manufacturing requires reactor cleaning.
• Nitrogen trifluoride (NF₃), a potent greenhouse gas, is used for reactor cleaning, raising environmental concerns due to rising atmospheric concentrations.

Purpose of the Study:

• To quantify the life-cycle greenhouse gas (GHG) emissions associated with NF₃ use in PV manufacturing.
• To identify best practices and technologies for minimizing NF₃ emissions in PV production.

Main Methods:

• Life-cycle assessment of NF₃ emissions.
• Measurements conducted at facilities of an NF₃ producer and a PV manufacturer.
• Analysis of GHG emissions per kilowatt-hour (kWh) of PV energy generated.

Main Results:

• GHG emissions from NF₃ in current PV manufacturing (a-Si and tandem a-Si/nc-Si) are 2 and 7 g CO₂(eq)/kWh, respectively.
• These emissions can be offset by the energy produced by the PV system within the first 1-4 months of operation.
• Best practices and technologies were identified to maintain low radiative forcing levels.

Conclusions:

• The environmental impact of NF₃ emissions in silicon thin-film PV manufacturing is relatively small and short-lived.
• PV systems utilizing NF₃ for manufacturing can achieve environmental neutrality within a few months of operation.
• Implementing defined best practices can further mitigate the atmospheric impact of NF₃.