Gravity Is a One-Way Street: Pumped-Storage Hydro
🌊 Gravity & tides
Question
How do engineers store electricity - and what does that say about gravity?
You cannot store electricity directly at grid scale, so we store it as gravity: pump surplus water (from wind, solar, or off-peak power) up to a high reservoir, then let it fall back through turbines to make power when it is needed. The energy is stored in the water's height - and it can only be recovered by letting the water fall. Things fall down, never up. Gravity is the one-way street that makes the storage work.
The math
The energy stored is E = m·g·h (mass × gravity × height). Pumping 1 m³ of water (1,000 kg) up 100 m stores 1,000 × 9.81 × 100 = 981,000 J ≈ 0.27 kWh. Round-trip efficiency is 70-80% - you get back 70-80% of the energy you used to pump.
Why it matters
Pumped storage is the world's largest form of grid-scale energy storage. It works because gravity is reliable and directional: water always falls the same way, every time, forever. An engineer who thought gravity was optional would not build a pumped-storage plant. Gravity is one of the things engineers take for granted - and it is never wrong.