It’s one thing to lower your carbon footprint by installing a solar PV system. But for the most environmentally conscious, a nagging question might remain in the back of one’s mind: What about the greenhouse gas emissions emitted in the production of the system itself? Could it be that another form of electricity generation treads more lightly on the earth over its entire lifetime?
To answer that question, researchers have taken pains to trace the carbon footprint of all the raw material inputs (its “cradle”) used to build and maintain electricity generation technology. They also calculate the emissions produced during the manufacturing of the systems’ components, as well as during the consumer service phase. Finally, they add on the environmental impact of the post-consumer (“grave”) period.
Using this information—and by taking into consideration the number of years the system will be in service—they can conduct a lifecycle assessment (LCA) for its carbon footprint and determine the total amount of greenhouse gases emitted over its lifetime.
But because researchers have used different methods and made varying assumptions to calculate their LCAs, their results have been very different—which makes them fairly impossible to compare. So what’s a decisionmaker to do?
Enter the National Renewable Energy Laboratory (NREL). Researchers at the Department of Energy’s lab in Colorado have conducted the most comprehensive analysis to date of LCAs focused on the greenhouse gas emissions of energy system technology, including those powered by renewables (such as solar PV, wind, concentrated solar power), nuclear energy and fossil fuels (coal-fired power plants and plants fueled by natural gas, for example).
Funded by the DOE, the study was a gigantic task that took several years. First, the team examined 3,000 published studies, then whittled that number down to 400 after reviewing for quality, relevance and the complete reporting of results. Next, they “harmonized” the remaining studies’ data so that the results could be compared in an apples-to-apples format.
NREL’s results were clear: The systems powered by renewable energy beat out the fossil fuel-powered systems used to create electricity.
“[Our research] shows that they have quite a bit lower and a characteristically different lifecycle analysis of greenhouse gas emissions than those technologies powered by fossil non-renewable resources such as natural gas and coal,” said Garvin Heath, a NREL senior scientist who led the research.
While coal-powered technology used up 1050 g of carbon dioxide per kwH of electricity over its lifetime (a median estimate measured in CO2 eq/kwH), solar PV consumed 55 g CO2 eq/kWh. Nuclear power used 12 CO2 eq/kwH.
“All renewables have their median estimate at or below 50 g,” he said. “The LCA of solar PV looks similar to other renewables—even nuclear power.”
Though Heath characterized nuclear power in the same ballpark of PV (by saying that a difference of 40 g CO2 eq/kwH does not have a “large climate consequence”), he emphasized that unlike solar PV, the inputs to nuclear power are nonrenewable, and take more energy to harness into the appropriate type of fuel to use in a nuclear facility.
“This tends to push up the LCA greenhouse gas emissions,” Heath said. “But for PV solar, the sun is not changing—we’re actually having a downward trend in the LCA because the technology is improving.”
Because solar PV’s technology is changing so quickly, he advised that the R&D departments of solar companies should pay close attention to the most updated LCA data when designing their systems.
“LCA is something that can feed into the R&D process,” Heath said. “[One should] think about where do I want to get to as a goal—and if I’m trying to drive costs down, what impact does it have on GHG emissions? If you’re doing a future assessment for PV, think about what it’s going to look like in the future, not today.”