Renewable energy has many benefits. First, it can combat climate change because it creates no direct greenhouse gas emissions. The only emissions that they produce are indirect, meaning those that result from manufacturing parts, installation, operation, and maintenance. But even those are minimal. Second, renewable energy can decrease pollution, and therefore reduce threats to our health. Wind, solar, and hydroelectric systems create no air pollution emissions, and geothermal and biomass energy systems emissions are much lower than non-renewable energy sources. Third, renewable energy is a reliable source of power. Because renewable energy sources are, well, renewable, they will never run out. Once built, renewable facilities cost very little to operate, and the fuel is often free as a result renewable energy prices tend to be stable over time. While renewable energy has many advantages, it is not without downsides. It is difficult for renewable energy sources to generate power on the same large scale as fossil fuels. Building wind farms and dams can disrupt wildlife and migration patterns and lead to ecological destruction. Both solar and wind energy are intermittent. They only generate power while the sun is shining or while the wind is blowing. Batteries can store excess energy for later use; however, they are often costly.