Storage helps when electricity is available at a different time from demand. A battery must charge first. Its usable energy and output power determine how long it can help before another charge.
We favour batteries for short gaps, smart charging before vehicle exports, and heat stores where a heating network makes them useful. Hydro and dependable generation remain necessary for prolonged winter supply. Each owner needs income for the service.
Storage roles · Heat storage evidenceA powerful battery can still empty quickly
Power is the rate of delivery. Stored energy determines how long delivery can last before recharging. This difference makes a battery useful for one job and insufficient for another. Refilling a tank many times increases its annual throughput; it does not enlarge the tank. The same distinction applies to batteries and pumped storage.
Storage power, energy and lossesThe full track represents one day.
Usable energy ÷ output = duration. The usable-energy assumption sets recharge, further discharge losses and reserve to zero.
Compare the outputs and check the units
| Output | Duration |
|---|---|
| 0.5 GW | 8 hours |
| 1 GW | 4 hours |
| 2 GW | 2 hours |
This hypothetical store illustrates duration at a fixed output. A Swiss project would also need a charging plan, a price and a delivery commitment.
Energy trading alone falls short in our example
We tested a battery against historical Swiss day-ahead electricity prices. Day-ahead trading is buying and selling electricity for delivery on the following day. The model uses perfect knowledge of prices throughout the test year to calculate a trading benchmark.
Historical-price data, model and assumptionsCHF per year · same scale: 0–250,000
Trading uses perfect knowledge of future prices. Ownership includes assumed capital recovery and upkeep. Additional services and contracts could change a project’s revenue; they are outside this comparison.
Trading and ownership assumptions
Sales minus purchases minus trading fees; 85% round-trip efficiency, 365-cycle limit, fixed 0.95 CHF/EUR and CHF 1/MWh trading fee in each direction.
CHF 1,500,000 × [0.07 × 1.07^15 ÷ (1.07^15 − 1) + 0.04]. Capital assumption: CHF 600/kW × 1,000 kW + CHF 225/kWh × 4,000 kWh.
The ownership example uses a 7% annual financing rate and a 15-year recovery period, plus a 4% annual allowance for operation and battery upkeep. These are scenario inputs.
The ownership calculation spreads the purchase cost over an assumed working life. It includes financing and an allowance for operation and battery upkeep.
Ownership-cost assumptions and calculationUnder these assumptions, the modelled energy-trading margin is below the illustrative annual ownership cost. We would not finance this illustrative battery on energy-trading income alone. It would need a lower complete cost or additional contracted income, such as payment for grid services. Other projects can have different economics; these are an assumed battery and historical prices.
Storage owner economics: historical-price benchmarkBattery stock estimated for the end of 2025
Batteries already in use
The Swiss solar-industry statistics estimate the following battery stock at the end of 2025:
Reported energy capacity within the survey’s scope.
Calculated from sales and retirement assumptions.
This gives an existing deployment base. To count part of it as dependable grid supply, we also need usable energy, power, charge levels and participating owners.
BFE / Swissolar: battery stock, page 11; methods, pages 24–28A car fleet can provide a grid service
Bidirectional charging lets a parked car send electricity back through its charger. The V2X Suisse project tested this with 50 cars in Mobility’s sharing fleet. The fleet met Swissgrid’s technical requirements for frequency-control services, which help keep generation and consumption balanced.
V2X Suisse: demonstrated capabilityPer vehicle per year from grid services, under the study conditions.
The expected income fell short of the additional V2X costs in the studied cases.
The final report is dated August 2024. A current offer must account for charger costs, vehicle availability, battery obligations and the price of the contracted service.
Final report: technical and commercial results, pages 3–5Our choice is smart charging first. In an earlier 2035 model, smart charging achieved most of the shortfall reduction obtained with the tested vehicle services. That comparison uses its own solar and reactor assumptions, before the separate data center allowance. Bidirectional charging adds a smaller national energy benefit and needs extra equipment. Local grid services can still justify it. The matched cases show the difference.
Same-car charging and export comparisonOwners should receive payment that covers their costs and preserves travel needs. Until participation is contracted, our starting supply requirement gives vehicle flexibility no credit.
Heat can stay in a heat store
We recommend thermal storage alongside suitable heat networks and controllable heating. If the customer needs hot water, storing heat can move production away from an expensive or constrained hour. The useful output is heat supplied to buildings. This can complement electricity storage without requiring every heating service to pass through a battery.
Operating heat-network example Applications and site requirementsMeasured heat storage · Denmark, 2024
Store heat when the customer needs heat.
Høje Taastrup's hot-water store serves a district-heating network. It stores about 3.3 GWh of heat and fills and empties repeatedly.
34.04 GWh of heat went in during the year. The balance below shows where it went.
- Heat delivered
- 29.92 GWh heat
- Heat lost
- 3.6 GWh heat
- Extra heat left in store
- 0.53 GWh heat
These are thermal quantities. The installation's electricity saving depends on which heat source it replaces, pumps and other equipment. No Swiss national electricity saving is assigned.
The Danish report lists €1.34 million in grants separately. The total includes the storage, connections and associated works.
Cost, efficiency and Swiss applicability
The 2024 inventory-adjusted heat efficiency is about 89%. The public measurements reproduce this result. The report for 2025 gives 90%, but its public CSV does not reproduce the annual energy totals. Flow gaps could contribute; their role remains unresolved. Both percentages concern heat, not electricity returned to the grid. DTU: 2025 report · Public-data reproduction and limits
The cost is for the Danish project built in 2020–22, reported in 2025, at its implementation-year prices. A Swiss project needs its own land, groundwater, heat-network and owner-cost assessment.
The annual balance is heat in = heat delivered + losses + additional stored heat. The report's efficiency divides delivered heat by input minus the inventory increase. It describes repeated short-term operation; a seasonal store needs a separate holding-time assessment.
The report's annual operating cost is estimated and income is modelled. They do not establish an audited profit. Customers, tariffs, maintenance and replacement costs determine a viable project.
DTU: measured annual heat balance, Table 4 · Danish Energy Agency: full investment, page 35
The owner still needs a durable business. Drake Landing in Canada achieved high solar-heat delivery, but ageing equipment, maintenance and insufficient revenue contributed to its closure. Our proposal is owner-led projects with funded maintenance and viable customer tariffs. Credit reductions in winter electricity only when a site’s measured heating alternative supports them.
Municipal account: operation, costs and closure Heat-storage recommendation and limitsPay for the hydro service
The costs chapter shows how annual use changes storage cost, and why emergency readiness needs a separate payment test.
The hydro chapter compares specific projects and explains the different services they could provide.
We favour viable hydro projects for seasonal shifting and batteries for short-duration services. Reservoirs still depend on water, connections and operating rights. Holding water for a national reserve gives up other sales, so the owner needs a paid agreement.
Water value and owner costsThe cost chapter shows why use frequency changes a battery’s price per discharged MWh.
Cycling-cost exampleThe role we give storage
Our choice
Buy the service, and keep its owner viable.
Support short-duration batteries and vehicle services with credible income. Preserve useful hydro for longer shifts and develop viable heat-network storage. Secure generation and fuel-backed contingency supply for prolonged shortages.
We include no unpriced national battery build-out in the base plan. Its scale would need supplier commitments, grid access and complete project costs.
References
- WattInfo archive-to-model checks: demand, thirteen weather years and heat storage
WattInfo · Additive model evidence review, 18 September 2026 - DTU Høje Taastrup measured 2024 report official repository alternate
Technical University of Denmark · 2025 - Danish Energy Agency thermal storage case study
Danish Energy Agency / PlanEnergi · 2025-10-22 - Town of Okotoks Drake Landing background June 2024
Town of Okotoks · 2024-06 - WattInfo proposed supply path: decisions and supporting calculations
WattInfo · Proposed priorities and fixed-charging supply screen, 18 September 2026 - 2035 day/night supply and vehicle-flexibility model
WattInfo · First 2035 supply package and 12 matched/sensitivity runs - Cost comparisons: inputs, calculations and boundaries
WattInfo · Curated from the cost-metrics research package, 17 September 2026 - Energy storage for electricity generation
U.S. Energy Information Administration (EIA) · Web edition retrieved 2026-09-16 - Visual explanations: seasonal stress, demand and storage
WattInfo · Visual chapter data and explicit teaching assumptions - Storage owner economics: historical-price benchmark
Swiss Energy research project · Frozen research output - Swiss solar and associated storage statistics for 2025
Swissolar for BFE · Reference year 2025; report dated 9 July 2026 - V2X Suisse: cars supplying grid services
Mobility and project partners / BFE · Final report dated 30 August 2024 - Operator battery project pipeline and conditional commissioning dates
BKW · 2026-10-23 - Høje Taastrup 2025 measurement report: full original
DTU · January–December 2025 measurements; exact publication date unavailable - Cost boundaries and heat-storage reproduction
WattInfo · 2026-10-26
Find definitions, calculations and model inputs in the source register.