Building-Scale Gravity Energy Storage for Off-Grid Homes: A First-Principles Design and Cost Test

Design and first-principles cost test of gravity energy storage (a rubble-concrete mass raised in a tower, building shaft, or hillside rail) for off-grid homes. SIMULATED, NOT MEASURED; nothing was built or hardware-tested. Delivering 5 kWh overnight from a 10 m tower requires 235.8 tonnes and costs about $1.96 per delivered kWh over 30 years, versus $0.11 for lithium iron phosphate and $0.46 for lead-acid. Round-trip efficiency is 60.6 percent and self-discharge is zero. The design beats lead-acid only when shared at village scale on a hillside (about 25 kWh per night or more at 50 m) and does not beat lithium at any scale computed.