A country needs electricity on a winter evening as well as enough over the year. Switzerland can export more than it imports over a year and still buy electricity from abroad in winter.
That is why our proposal keeps productive reactors, develops their successors and secures supply in between. Power, energy and storage explain what each part of the plan can do.
Winter supply and our proposed pathPower is how fast. Energy is how much.
Power tells you how quickly a plant supplies electricity or a device uses it. Energy is the amount supplied or used over time.
Power
Measured in watts. Large plants use megawatts (MW) or gigawatts (GW).
Energy
Measured in watt-hours. Your bill uses kilowatt-hours (kWh). National totals often use terawatt-hours (TWh).
One TWh is one billion kWh. Winter electricity production depends on both the plant’s power and its output over the season.
EIA: power and energy unitsUnit conversions and capacity factor
One GW is 1,000 MW. One TWh is 1,000 GWh, and one GWh is 1,000 MWh.
Capacity factor compares actual generation with the energy a plant would produce at its rated power throughout the same period.
Both hours of operation and output below full power affect the result.
Calculate actual MWh ÷ (capacity in MW × hours in the period). Keep the measurement boundary consistent.
Capacity-factor method and Swiss reactor examplesA yearly surplus can hide a winter deficit.
Switzerland exported more electricity than it imported over the year from October 2024 to September 2025. In winter, the balance went the other way.
Observed physical electricity trade, in terawatt-hours (TWh).
Winter
October 2024–March 2025
0.73 TWh
net imports
Summer
April–September 2025
4.61 TWh
net exports
Full year
October 2024–September 2025
3.88 TWh
net exports
Net imports mean imports exceed exports over the period. Net exports mean the reverse.
BFE: seasonal electricity balances, table 5Compare five winters and check the calculation
| Winter | Net imports (TWh) | Direction of balance |
|---|---|---|
| 2020/2021 | 1.82 | Net imports |
| 2021/2022 | 7.82 | Net imports |
| 2022/2023 | 3.64 | Net imports |
| 2023/2024 | -2.04 | Net exports |
| 2024/2025 | 0.73 | Net imports |
Subtract physical exports from physical imports to get net imports. Divide GWh by 1,000 to get TWh.
The full-year export balance equals summer net exports minus winter net imports. Use the unrounded data for exact calculations.
These flows show recorded cross-border trade. Assessing how much was essential requires hourly conditions and the available alternatives.
Download all seasonal balances (CSV) · Definitions and data (JSON)
Calculation, original data and definitionsImports supply electricity from abroad. They can cover a domestic shortfall when foreign generation and border capacity are available.
The winter balance changes between years: Switzerland had net exports in winter 2023–24.
BFE: five winter trade balances, table 5Our plan therefore secures winter delivery separately from the annual energy total. Stored energy, other generators and trade carry hours when solar output is low.
Hydro and nuclear supply much of the winter electricity.
See the measured winter generation mix →
The winter chapter shows the measured mix. It also includes solar, wind and other thermal plants. Solar contributes in winter, with lower generation than in summer.
What the measured winter mix includes
BFE records electricity used to pump water uphill separately. Subtract that input before calculating the national net electricity balance.
Electricity lost in the grid must also be allowed for when comparing supply with the amount delivered to customers.
“Other thermal” is BFE’s thermal generation category excluding nuclear. These totals describe domestic production. Household electricity labels describe the origin of purchased electricity.
Seasonal solar totals reflect both changing weather and additions to the installed fleet.
All generation, pumping, trade, loss and consumption fieldsThe nuclear operating record shows the production that a replacement plan must address. Future availability and new construction costs need project-specific evidence.
See ten years of reactor output, safety conditions and the case for nuclear →
Storage moves energy to a different time.
A battery must first be charged. Pumped storage uses electricity to lift water, then releases it through turbines. Both return less electricity than charging consumes.
EIA: storage, charging and energy lossesA simple example
An imaginary store holds 4 GWh of usable energy and supplies 1 GW continuously. It lasts 4 hours.
Hypothetical example: a full store with constant output, zero recharge, and zero further discharge losses or reserve.
Duration equals usable energy divided by power. The same unit rule applies to a battery or a water reservoir.
Example inputs, formula and limitationsHydro needs an extra distinction. Rivers supply flowing water. Reservoirs can hold natural inflows for later use. Pumping uses electricity to move water uphill.
EIA: river, reservoir and pumped-storage hydroWe give batteries a short-duration role and develop viable hydro for longer shifts. Generation and fuel-backed reserves cover prolonged gaps. Storage and hydro owners need payment for the services they provide.
Storage roles in our proposalReplacing fuel changes electricity demand.
Electrification means using electricity for a task previously powered by another energy source. Replacing an oil boiler with an electric heat pump is one example.
A heat pump uses electricity to move heat from air, ground or water into a building. Part of the delivered heat comes from the environment.
SwissEnergy: how a heat pump worksThat can reduce the energy a household buys while increasing its electricity use. Electric transport has a similar effect on the national energy balance.
We therefore pair efficient electrification with more electricity supply. The demand chapter gives our chosen planning reference and a worked household example.
Demand model: inputs, efficiency and scopeWhat this means for the plan
- Keep useful production: pursue safe, viable Gösgen and Leibstadt extensions because losing their output adds to the supply we must replace. Develop two successors.
- Secure the earlier bridge: arrange replacement electricity before Beznau’s announced retirement, which comes before new reactors in our schedules.
- Use each technology for its useful service: solar and wind generate; hydro and batteries help with timing and need energy available to deliver; efficient heating and transport reduce fuel use.
Our strategy links those choices to quantities, dates and remaining risks. The next chapter starts with how much electricity an electrified Switzerland could use.