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Scientists have quantified the impact of wildfires on the availability of direct normal irradiance and global horizontal irradiance at the state, regional, and national levels in the United States. They found that direct irradiance is more sensitive to smoke than the global horizontal irradiance relevant to photovoltaics.
A research team led by Colorado State University in the United States has analyzed the impact of wildfire smoke on solar resource availability, specifically direct normal irradiance (DNI) and global horizontal irradiance (GHI). Using satellite observations of smoke, aerosols, and clouds, the team was able to measure the impact at state, regional, and national levels across the United States at different time scales.
“Solar resources are assessed by the amount of DNI and GHI shortwave radiation a site receives,” they explained. “Concentrated solar power is based on DNI, while photovoltaics is primarily based on GHI. However, combined, GHI and DNI indicate the amount of diffuse radiation, which affects PV panel technologies differently.”
The researchers used clear-sky and all-sky DNI and GHI data from the National Renewable Energy Laboratorys National Solar Radiation Database (NSRDB) at 4-km spatial and 30-minute temporal resolution across the continental United States. All-sky measurements include the impacts of both clouds and aerosols, while clear-sky values ??include aerosols but exclude clouds.
"We calculated daily means for each variable using times when the solar zenith angle (SZA) is less than 75°, cloud-driven changes by subtracting clear-sky (i.e. cloud-free) and all-sky values, and smoke-driven changes by subtracting clear-sky values ??on smoke-affected days and on reference smoke-free days," the scientists explain.
At the finest scale of their investigation, the team examined two days of California’s 2020 wildfire season and compared them to analogous smoke-free conditions on the same days in 2019. At larger monthly and annual scales, the team compared regional and national solar resources under the high-smoke conditions of 2020 and the low-smoke conditions of 2019. At an even larger scale, the analysis was extended to 2006–2021 to characterize longer-term regional smoke-irradiance interactions.
“We found considerable losses in model-based daily mean DNI (32-42%) and GHI (11-17%) in California due to local smoke,” the group explained. “Local smoke can also significantly reduce monthly mean DNI (max: 61%) and GHI (max: 25%), with the impact on DNI persisting downwind of fires. However, the impact of transported smoke on GHI is relatively minimal (<5%) on average across the contiguous United States (CONUS), even during an extreme wildfire season.”
In conclusion, the academics stated that the scale of the GHI reductions implies that the average impact of smoke plumes on PV resources is relatively minimal across the US, which they described as “encouraging” as more and more utility-scale battery storage capacity becomes available, when local smoke causes potentially large changes in irradiance on finer time scales.
Their findings are presented in “ Solar energy resource availability under extreme and historical wildfire smoke conditions,” published in Nature Communications . Scientists from Colorado State University, Springfield College, and NASA Langley Research Center conducted the research. |
