NREL scientists delve into reducing the carbon footprint of photovoltaic technology

In their new Joule paper, “Embodied Energy and Carbon from Cadmium Telluride and Silicon Photovoltaic Production,” National Renewable Energy Laboratory (NREL) researchers Hope Wyckoff, Samantha Reese, and Matthew Reese focus on the two dominant deployed photovoltaic (PV) technologies: silicon (Si) and cadmium telluride (CdTe) PV. These green technologies help reduce carbon emissions and meet global decarbonisation targets – but their production processes can themselves lead to greenhouse gas emissions.

“Green technology is great, but as we work to scale it to incredible magnitude, it makes sense to take a closer look to see what can be done to minimize the impact,” says Samantha Reese, senior engineer and analyst at NREL’s Center for Strategic Energy Analysis.

To understand the overall impact of these green technologies on global decarbonisation goals, the team looked beyond traditional metrics such as cost, performance and reliability. They estimated “embodied” energy and carbon – the energy absorbed and carbon emissions involved in producing a PV module – as well as energy payback time (the time it takes for a PV system to generate the same amount of energy as it takes to produce it). .

“Most advances are driven by cost and efficiency, as these metrics are easy to measure,” said Matthew Reese, a physics researcher at NREL. “But if part of our goal is to decarbonize, then it makes sense to look at the bigger picture. There is certainly value in trying to increase efficiency, but other factors are also influential when it comes to decarbonisation efforts.”

“One of the unique things this paper has done is that the perspectives of industry and science have been brought together,” continues Samantha Reese. “We combined life cycle analysis with materials science to explain the emissions results for each technology and explore the effects of future advances. We want to use these results to identify areas where further research is needed.

Place of production and type of technology have a large impact on carbon and are two key knobs that can be turned to affect decarbonisation. Looking at current grid mixes in solar-producing countries, the authors found that generating with a cleaner energy mix – compared to using a coal-rich mix – could reduce emissions by a factor of two. Furthermore, although Si PV currently dominates the market, thin-film PV technologies such as CdTe and perovskites provide another path to reduce carbon intensity by an additional factor of two.

This insight is important because of the limited carbon budget available to sustain the expected scale of PV production in the coming decades.

“If we are to meet the decarbonisation targets set by the Intergovernmental Panel on Climate Change, one sixth of the remaining carbon budget could be used to produce photovoltaic modules,” adds Matthew Rees. “That’s the scale of the problem – it’s a huge amount of production that needs to be done to replace the energy sources that are used today.”

The authors’ hope is that by illustrating the scale of the problem, their paper will make people look differently at the potential use of thin-film photovoltaic technologies, such as CdTe, and pure grid-blend manufacturing.

Ultimately, accelerating the inclusion of low-carbon energy sources in the electricity grid is paramount.

“One of the great strengths of PV is that it has this positive feedback,” says Nancy Hegel, director of NREL’s Center for Materials Science. “As we clean up the grid — in part by adding more PV to the grid — PV production will become cleaner, which in turn will make PV an even better product.”

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