Duration is the product: four stories this week about how long stored energy lasts
Victoria Shinder2 min readEnergy storage is usually reported in quantities: barrels, cubic feet, megawatt-hours. Four items from the past few days show that the number which decides value is often a different one — how long the stored energy can be delivered, and how fast it can be called on.
Oil: a reserve that lends rather than sells. The U.S. Department of Energy authorised an emergency exchange of up to 4 million barrels from the Strategic Petroleum Reserve to ExxonMobil and BP after storm disruption in the Gulf. Against U.S. refinery demand, that is a few hours of national crude runs, not a supply cushion. Its value is location and timing: oil already sitting on the Gulf Coast, available within days, returned in 2027 with premium barrels on top. The reserve here acts as a short bridge, priced as a loan.
Gas: fast storage is the thin layer. EIA's weekly report put U.S. working gas at 3,500 Bcf, 68 Bcf above the five-year average. The national surplus is real, but it sits mostly in slow reservoirs in the East, Midwest and West. The fast-cycling salt caverns of the South Central region — the storage that can be drawn hard within days — hold 227 Bcf, 14% below their five-year average and 23% below last year. A system can be long on gas and short on gas it can reach quickly.
Batteries: a market rule sets the hours. In Western Australia, Mint Renewables won approval for a 100 MW / 800 MWh battery at Kojonup — eight hours, double the four-hour designs common in eastern Australia. The reason is a rule: the state's Reserve Capacity Mechanism pays batteries only if they can discharge for at least six hours. The same megawatts with fewer hours would earn no capacity income. Duration here is not an engineering preference; it is what the market buys.
Pumped hydro: the cable is the storage project. Marinus Link, the 1.5 GW HVDC cable between Tasmania and Victoria, started expanded construction. It is a transmission project, but its purpose is storage: it gives the mainland access to Tasmania's planned 1.5–3.5 GWh of new pumped hydro under the "Battery of the Nation" plan. Long-duration storage in one place is worth only what the wire to the demand can carry.
The common thread. In each case the headline quantity — barrels, Bcf, MWh, GW — understates or overstates what is available when it is needed. Policy is increasingly writing duration into the rules directly, as Western Australia has; elsewhere, the market discovers it in a storm or a cold snap. For anyone reading storage announcements, the useful questions are the second and third ones: how many hours, and how fast can it be called.
Sources: DOE SPR exchange — https://www.energy.gov/articles/energy-department-authorizes-strategic-petroleum-reserve-exchange-address-supply ; EIA Weekly Natural Gas Storage Report — https://ir.eia.gov/ngs/ngs.html ; Kojonup BESS — https://www.energy-storage.news/mint-renewables-wins-planning-approval-for-800mwh-battery-storage-system-in-western-australia ; Marinus Link — https://www.energy-storage.news/tasmanias-battery-of-the-nation-plan-moves-closer-as-marinus-link-holds-sod-turn-in-australia