Engineering tool · 01

A year in the life of a seasonal store.

Wind blows hardest in winter, the sun shines in summer, and demand peaks when it is cold and dark. This model runs a simplified Swedish year day by day, sends the surplus through electrolysis into rock caverns, and draws it back out when the system is short. It is a teaching model, not a market model — the point is to make the shape of the problem visible.

System build-out

Wind capacity32 GW

Solar capacity12 GW

Firm power (hydro + nuclear)10 GW

Dispatchable, follows demand up to its capacity.

Average demand16 GW

Winter peak is ~25 % above the average.

Storage

Number of caverns20

200 000 m³ each at 50 bar ≈ 27 GWh of hydrogen.

Electrolyzer capacity6 GW

Re-electrification capacity4 GW

Fuel cells or hydrogen turbines returning power to the grid.

Industrial hydrogen offtake1.0 GW

Steady draw for steel, ammonia and fuels.

Surplus captured

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of available surplus

Still curtailed

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TWh thrown away per year

Unserved demand

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TWh short per year

Hydrogen produced

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tonnes per year

Storage state of charge through the year

Green area = hydrogen in the caverns. A working seasonal store fills through spring and summer and draws down through winter.

stored hydrogen surplus power deficit

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Surplus and deficit, day by day

Above the line the system has more power than it can use; below the line it is short. Storage moves the gold into the ochre.

Annual balance

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