Energy Mechanics · Electricity · Hydroelectric generation

Dispatchable carbon-free
at the mercy of water years

HYDRO · TWh/YR · GW
RELEASE · EIA EPM TABLE 1.1.A · USACE + BPA WATER YEARS
VINTAGE · —
NEXT EPM · —
CONVENTIONAL + PUMPED STORAGE
STATUS · LOADING
U.S. hydroelectric generation is — TWh/year — the only large-scale dispatchable carbon-free source on the grid, but with a swing of ±— TWh between dry and wet water years. Conventional hydro (run-of-river + reservoir) is the headline; the Pacific Northwest is half the country's total. Pumped storage is the grid's only at-scale battery — net negative generation (round-trip losses ~20%) but the only way to store many GWh of energy at grid scale today.
Conventional hydro Pumped storage Unused capacity (low water years) bar length ∝ TWh/year · pumped storage net = generation − pumping draw
TYPE · TWh/YEAR CAPACITY (GW) & CAPACITY FACTOR Conventional hydroelectric DAMS · RUN-OF-RIVER · COLUMBIA · NIAGARA · SIERRA — Capacity — GW CF — · varies with snowpack and reservoir storage Grand Coulee + Chief Joseph alone are ~30 TWh — more than every PV plant in California combined in most years. Pumped storage ~95% OF U.S. GRID STORAGE BY ENERGY · NET CONSUMER — Capacity — GW Net generation negative · round-trip efficiency ~80% Pumps water uphill at low-price hours (overnight, solar-noon), spills back through turbines at peak. Battery storage growing but still <10% of pumped's energy capacity. TOP GENERATING STATES · TWh/YEAR Washington — Columbia Basin · Grand Coulee + Chief Joseph + 13 BPA dams Oregon — Lower Columbia + Willamette · BPA shares Columbia output with WA New York — Niagara + St. Lawrence + Massena · NYPA flagship assets California — Most drought-sensitive · Sierra snowpack drives ±50% swings Montana — Upper Missouri + Clark Fork · NWE + PPL fleet TOP 5 STATES = — OF U.S. HYDRO · PNW (WA+OR) ALONE = —
Conventional hydro
—
vs 5 yrs ago
—
Water-year range
—
drought — ↔ wet —
Total hydro capacity
—
GW · conventional + pumped
Share of U.S. generation
—
largest single dispatchable carbon-free source
SOURCE · U.S. Energy Information Administration, Electric Power Monthly (Table 1.1.A net generation by source; HYC = conventional hydroelectric, HPS = hydroelectric pumped storage). Per-state numbers are EIA EPM Table 1.6.B. Water years run Oct 1–Sep 30; snowpack from Oct–Apr drives reservoir refill, which determines summer hydro output. The Pacific Northwest's Columbia Basin (WA + OR + ID) provides ~40% of U.S. hydro in a normal year; California's Sierra system swings from ~10 TWh in drought to ~40 TWh in wet years. Pumped storage is reported as net negative because the pumps consume more energy than the turbines produce — round-trip efficiency is ~80%. The U.S. has ~22 GW of pumped storage at ~40 sites; the largest (Bath County, VA) holds 24 GWh of usable energy, equivalent to ~12 large battery installations. Lithium-ion battery storage is growing fast but is still <10% of pumped's energy capacity nationally.
SECOND·ORDER·EDGE