Aquifer thermal energy storage (ATES) uses naturally occurring underground water to store energy that can be used to heat and cool buildings. When paired with wind and solar energy, ATES becomes a zero-carbon option for temperature regulation. These illustrations show how the water is moved upward for heating in the hot months, then pumped back down and stored until winter, when the (still) warm water is brought back up to heat buildings. The same process occurs in winter, leading to stored cold water to use in summer months.