The giant Ivanpah solar power plant in the California Mojave Desert recently detailed how much natural gas it burned to generate power when the sun wasn’t sufficient—the equivalent to 46,000 tons of CO2 emissions in its first year, according to reports.
Along with its impacts on wildlife and its receipt of federal incentives, news of the CO2 emissions has renewed criticism of the 377-megawatt facility, which supplies 140,000 California homes during peak hours of the day.
Why is a solar power plant using natural gas, and does the associated CO2 disqualify it as “green”?
The use of natural gas to complement solar in fact highlights a trend toward what I call “speckled green” electricity generation—approaches that are not completely green, but in which natural gas enables more widespread, reliable, and affordable deployments of renewables.
Power Tower
Unlike the solar photovoltaic (PV) panels that are proliferating on rooftops such as my own, Ivanpah generates its power by angling mirrors to gather the intense sunlight of the Mojave Desert to produce heat. The mirrors reflect sunlight onto three power towers, where steam turns turbines to generate electricity.
This “concentrating” solar thermal approach is even more sensitive to clouds and particles than PV panels, since the mirrors can concentrate only the sunlight that arrives in a direct beam from the sun. Clouds and particulate matter scatter the light into directions that can still be utilized by photovoltaic panels but not the precisely angled mirrors.
Ivanpah was designed and built to burn some natural gas to maintain peak power generation during times of intermittent clouds. Without the natural gas, Ivanpah’s steam turbines could trip offline, interrupting power generation. The extra energy from natural gas can enable peak power production to continue until sunny conditions resume or the turbines pause for the night.
