Hydro can produce electricity and help move it to the hours or seasons when it is needed. Each project has a specific role.
A useful national plan must respect the water available, the physical connections and the owner’s business case.
Three different ways to improve hydro
River plants use flowing water. Reservoirs can retain natural inflows. Pumped storage uses electricity to lift water for later generation. A scheme can combine these functions. Hydro principles · Pumped storage
More room for water
A larger reservoir can retain more inflow for later use. The annual energy gain depends on the project.
More power
A larger turbine can deliver more electricity at once. It does not create more water.
Pumping back uphill
Where a pump and connection exist, electricity can lift water for reuse. The cycle has energy losses.
This diagram explains the functions. Actual lake connections vary by project; pumping requires an installed pump and a physical route uphill.
For every proposed expansion, ask whether it adds annual generation, moves production into winter, or increases output power. Also ask whether it adds pumping power or usable storage. Those quantities describe different benefits.
Project definitions and reviewed distinctionsReal projects, different benefits
The projects below would add different capabilities. Their current development stages show what remains before those benefits can be delivered.
Grimselsee
More stored energy for winter
Additional storage in the proposed enlargement. The building-permit phase comes next.
Additional stored energy. The effect on annual generation is a separate project question.
Stage supported by evidence dated 2026-09-09.
Mattmark
Move production into winter
The operator estimates CHF 83 million. Annual production would stay unchanged.
Potential seasonal transfer. The project status is supported by the dated proposal below.
Stage supported by evidence dated 2025-01-16.
Grimsel 4
More power between existing lakes
Two 84 MW machines; a CHF 300 million investment decision. Works were scheduled to finish in 2032.
Adds power and flexibility. Additional reservoir volume and natural generation are outside the stated contribution.
Stage supported by evidence dated 2026-07-07.
GWh measures stored or generated energy. MW measures power. These project figures describe different services and cannot be added together.
At Mattmark, the proposed raising would retain more existing inflow. Axpo says annual production would remain unchanged while more production moves into winter. Its dated proposal also identifies unresolved concession, environmental and economic conditions.
Operator proposal and conditionsAt Grimsel, enlarging the lake and building Grimsel 4 are separate projects. One adds storage space; the other improves the connection and power transfer between existing lakes. Their milestones must also stay separate. Lake enlargement · Pumped-storage project
Why holding water has a cost
Keeping water for winter can mean giving up an earlier sale. The later electricity must earn enough to justify that choice. Pumped storage also buys charging electricity and loses some energy during the cycle. Hydro seasonal-shift economics · Storage losses
The BFE-commissioned hydro revenue study also accounts for this trade-off: reserving capacity for grid services can reduce income from electricity sales. An owner needs the combined result after those competing uses are reconciled.
Hydro revenue study: reserve capacity and foregone sales, page 6Our position: offer voluntary contracts with clear delivery obligations. State who pays for availability, who pays for delivered electricity, and who carries the risk. Price availability and delivered energy separately in the agreement.
The agreement for a new storage service must cover the required investment, financing, maintenance and future renewal, as well as operating costs.
Capital recovery, operating assumptions and limitationsGet more flexibility from existing plants
The SmallFLEX Goms trials at Mörel demonstrated additional power adjustment of approximately ±3 MW. Controlled use of water already inside the plant’s waterways can provide short-term flexibility. Safe water levels, inflow and the risk of air entering the waterways limit how it can operate.
Mörel trials and hydraulic limitsOur proposal: assess these operating improvements alongside larger construction projects. Buy a defined power response for a stated duration, with maintenance costs and foregone sales included.
What the hydro trial establishes
The reported result concerns short-term power adjustment under tested conditions. A winter-energy contribution needs its own duration and water balance.
The report also models business cases. Its imbalance-cost analysis uses annualised forecast data that are not fully aligned with market-price dates, and describes its stochastic model as unfinished. Realised owner returns require further evidence.
Summary, page 4; trials, pages 128–136; economic limits, page 162
A practical test before counting a project
Measure the right benefit
State power and energy separately. Identify which lakes and machines connect, and how much water is actually available.
Check the next milestone
A study, a concession, a building permit and a construction decision are different stages. Publish the remaining dependencies.
Show how it pays
Include financing, charging costs, upkeep and income lost elsewhere. Make any public support explicit.
Test a less favourable year
Check low inflows, unavailable equipment and delayed work. State what covers the remaining demand.
Our proposal: buy a defined winter service
Our proposed action
Prioritise useful projects and viable contracts.
Compare hydro expansion, continued generation, storage and demand flexibility against the same winter supply need.
Count each project only at its documented stage. Keep a fallback for delayed delivery, and preserve the owner’s incentive to maintain and invest.
Hydro has an important role in our proposed electricity mix. Its role must be supported by a specific physical contribution and a sustainable business case.
References
- Hydropower explained
U.S. Energy Information Administration (EIA) · Web edition retrieved 2026-09-16 - Energy storage for electricity generation
U.S. Energy Information Administration (EIA) · Web edition retrieved 2026-09-16 - Grimselsee enlargement: project design
Kraftwerke Oberhasli AG (KWO) · Undated project page; design includes older milestones - Grimselsee concession and Grimsel 4 construction start
Kraftwerke Oberhasli AG (KWO) · Published 2026-09-09 - Mattmark: proposed dam raising
Axpo · Published 2025-01-16 - Grimsel 4: investment decision and technical specification
Kraftwerke Oberhasli AG (KWO), mirrored by VSE · Published 2026-03-27 - Storage owner economics: historical-price benchmark
Swiss Energy research project · Frozen research output - Visual explanations: seasonal stress, demand and storage
WattInfo · Visual chapter data and explicit teaching assumptions - SmallFLEX Goms: flexibility from existing hydro
HES-SO and project partners / BFE · Final report dated 22 May 2026 - Hydropower revenue opportunities and marketing costs
Swiss Economics / ETH Zürich for BFE · Final report dated 30 September 2023
Find definitions, calculations and model inputs in the source register.