From steam engines to spaceships, humans have been using flywheels for centuries. These simple wheels serve as batteries by stockpiling excess energy as mechanical motion, spinning faster the more energy they store.

Now, WISE researchers suggest this tried-and-true technology could give photovoltaic systems a boost, addressing two of the key challenges involved in tapping the sun’s energy.

Challenge number one is that the sun doesn’t always shine when we need energy, creating a mismatch in…