FAQ: How do lifecycle emissions of different generation sources compare?
Examples include wind, solar, hydropower, geothermal, and fossil fuels (like coal and natural gas), and nuclear energy. These sources differ in both how emissions are generated and how reliably they supply power.
Readers should regularly check sites like NREL (National Renewable Energy Laboratory) for GHG emissions associated with various sources. But we provide generalizations on how these major generation sources compare, based on the geography of the US.
Wind and solar emit just a fraction of what fossil fuels do. Most of their emissions occur during manufacturing, installation, and construction; once operational, they produce very little emissions. But their output depends on weather and time of day. Wind typically peaks at night or in winter, while solar peaks during the day and in summer. When combined, they can help balance each other, but they often require complementary technologies to ensure grid reliability.
Other renewable sources like hydropower and geothermal emit slightly more than wind and solar on average, but still far less than fossil fuels. They can often provide continuous power, depending on multiple factors. For example, hydropower’s efficacy depends on geography and dam design. Geothermal provides consistent baseload power in regions with accessible underground heat.
Fossil fuels generate far more emissions than any other electricity source. On top of high operational emissions, the need for a continuous supply of mined, processed, and transported fuels lead to high pre-use emissions. Their historical dominance in electricity generation stems from their energy density, cost, and ability to provide round-the-clock power that can quickly respond to demand fluctuations.
Nuclear energy, while controversial, tends to have a relatively lower carbon footprint when compared to fossil fuels. It is also capable of delivering continuous baseload power. However, nuclear plants take far longer to build than solar or wind. Typical GHG accounting methods do not capture the Time Value of Carbon, the idea that near-term emissions reductions may be more beneficial than those achieved decades later.
