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Listen to part of a lecture in an environmental science class. Professor: We often think of renewable energy sources like solar and wind as perfect solutions to our energy needs. However, they have a major drawback: intermittency. The sun doesn't always shine, and the wind doesn't always blow. This means that when demand peaks in the evening, solar panels may not generate enough power. To solve this, engineers are developing large-scale battery storage systems. But batteries have their own challenges, including cost and the need for rare materials like lithium. Another approach is pumped hydro storage, where excess energy is used to pump water uphill into a reservoir. When energy is needed, the water is released to spin turbines and generate electricity. While this method is efficient and has been used for decades, it requires specific geography—hills and water sources—which limits where it can be built. So, the key is to combine multiple storage methods and diversify the energy grid. That way, we can ensure a steady supply even when conditions are not ideal.