The rapid growth of solar energy requires storage innovation to make sure that the clean energy is available 24/7. In Sweden, a team of scientists is developing a liquid energy storage medium that can not only release energy from the Sun on demand but is also transportable. Meanwhile, in China and the U.S., scientists are capturing carbon-dioxide pollution to use in an energy-storage system that can back up clean sources like solar and wind. The captured CO2 is compressed and stored in a deep reservoir. When there’s no wind or the sky is dark, the compressed CO2 can be can be used on demand to spin a turbine that produces electricity. The technique kills two birds with one stone by removing pollution from the air while storing renewable energy.