Switzerland ended the 2024/25 electricity year with net exports, but imported more than it exported in winter. Hydro and nuclear were its two largest domestic sources that winter.
We recommend keeping safe, viable reactors and strengthening hydro’s winter service. Other generation, storage and contracted delivery must cover the hours they cannot supply. A summer surplus needs a way to reach those hours.
Seasonal supply and trade · Our winter prioritiesTwo seasons, different balances
In the 2024/25 electricity year, Switzerland exported more electricity than it imported. During that year’s winter, imports exceeded exports. Winter 2023/24 had net exports. The balance changes between years.
BFE: seasonal balances, table 5TWh · bar length shows the size of each balance · common scale 0–15
2020/2021
2021/2022
2022/2023
2023/2024
2024/2025
Winter: October–March. Summer: April–September. Each value is imports minus exports, or the reverse. The figures record physical cross-border trade. Assessing supply dependence requires hourly conditions and alternative-supply assumptions.
Imports are a working part of Swiss supply. Our sovereignty objective is to keep the country supplied when that access is restricted. That requires domestic production, energy held for later use and a reserve able to deliver during the same difficult period.
Trade and resilience in the proposed pathWhat supplies the winter months?
Hydro and nuclear were the two largest sources of domestic generation in winter 2024/25. Solar also contributed. The chart includes electricity generated from previously pumped water; pumping uses electricity elsewhere in the balance.
BFE: generation categories and pumping, table 5Domestic generation, October 2024–March 2025. TWh.
- Hydro18.45
- Nuclear12.6
- Other thermal1.89
- Solar1.77
- Wind0.09
Generation before subtracting electricity used to pump water uphill. Hydro includes pumped-storage output. The totals cover winter 2024/25.
BFE: generation by technology, table 5We recommend preserving safe, viable nuclear output and improving hydro’s winter capability. Closing a reactor removes electricity that the rest of the system must provide. Adding solar helps when it produces, while reservoirs and other supply carry the hours after sunset. An earlier 2035 model illustrates daytime and night-time demand.
Compare solar costs, summer sales and the supply still needed at night.
A difficult week reveals the remaining job
This future-supply test uses the weather of a historical cold week. It compares demand with an optimistic ceiling: all reservoir turbines and permitted imports at full power. The future heating peak still needs engineering checks.
50 hours exceed that ceiling, requiring at least 159 GWh of additional electricity. Insulation, controlled heating, thermal stores, batteries and dependable generation should compete to cover these hours.
How the ceiling is calculated
Each hour adds the available nuclear, solar, river hydro and other generation to every reservoir turbine, pumped-storage turbine and allowed import running at full power. It ignores reservoirs running out of water, so actual supply can be lower. The shaded gap follows directly from these inputs; it does not rely on where a solver places seasonal shortages.
For historical scale, Swissgrid’s 2024 hourly metered end-user peak was 9.4 GW. That boundary excludes losses and pumping. The future curve adds substantial electric heating and transport; its cold-weather peak remains an engineering assumption to validate.
Hourly inputs and calculation · Observed load and historical holdout checks
The winter package we recommend
- Plant owners: pursue safe, viable Gösgen and Leibstadt extensions while developing successors.
- Hydro owners and electricity buyers: agree winter services in which buyers pay for water held back and sales the owner forgoes.
- Willing customers: shift charging and suitable heating to useful hours through workable contracts.
- Electricity suppliers and reserve providers: secure remaining winter delivery and separate outage cover, including fuel where needed.
Our choice
Prioritise dependable winter delivery.
Expand solar alongside the generation, storage and contracts that cover its gaps. Keep useful existing production until replacement services can carry the load.
The 2035 package gives this direction quantities and dates. The later nuclear programme replaces the bridge as projects enter service.
The official monitoring framework already addresses winter imports, networks and supply security. Our proposed change is to include new nuclear explicitly and tie investment to delivered winter service and viable owner contracts.
BFE: monitoring frameworkThe next chapter explains which hydro projects can contribute.
References
- Import reliance, winter solar inputs and forced shortages
WattInfo · Archived-input calculations, 25 September 2026 - Programme assumptions, dispatch choices and cost scope
WattInfo · Archived-input interpretation, 25 September 2026 - WattInfo proposed supply path: decisions and supporting calculations
WattInfo · Proposed priorities and fixed-charging supply screen, 18 September 2026 - Swiss Electricity Statistics 2025
Swiss Federal Office of Energy (BFE) · 2025 - Swiss seasonal balances and electricity examples
WattInfo · Five hydrological years, 2020/21–2024/25 - Visual explanations: seasonal stress, demand and storage
WattInfo · Visual chapter data and explicit teaching assumptions - Independent demand model v1
Swiss Energy research project · Frozen research output - Storage owner economics: historical-price benchmark
Swiss Energy research project · Frozen research output - Energy Strategy 2050: Monitoring Report 2025, full report
Swiss Federal Office of Energy (BFE) · 2025 report, corrected March 2026 - Winter solar: capacity, seasonal costs and paid storage
WattInfo · Conditional component comparison, 22 September 2026 - Energieperspektiven 2050+: Kurzbericht
Prognos / TEP Energy / INFRAS for BFE · 2020-11 - Energieperspektiven 2050+: Exkurs Winterstrom
Prognos / INFRAS / TEP Energy / Ecoplan for BFE · 2021-10-13 - Supply scale, fuel and nuclear owner-cost sensitivities
WattInfo · 2026-10-02 - Matched electricity, peak-power and trade comparisons
WattInfo · 2026-10-02 - 50 Gigawatt Photovoltaik bis 2050 – welche Anlagen braucht es?
Swissolar · 2022-11-30
Find definitions, calculations and model inputs in the source register.