Can more solar cover Switzerland’s winter?

How large would the solar fleet be?

Solar overbuilding means installing extra panels to obtain more electricity during the weaker part of the year. It also produces more electricity in summer. A BFE-commissioned study explicitly considers this approach.

The result is a seasonal energy balance. Winter nights and prolonged poor weather still need a supply plan. Reservoirs can save water while solar supplies demand, but their stored energy and turbine power are finite. More nuclear, wind or other winter generation reduces the solar quantity in this example.

The 120–140 GWp illustration is neither an official target nor our proposed build programme. Our nuclear-inclusive programme tests 53 GWp alongside existing hydro and two new reactors. It too requires additional winter supply.

The hourly programme uses a different solar profile, with lower winter yield per installed kilowatt in its selected years. The two fleet capacities therefore need common sites and weather before a matched supply comparison.

What would the extra panels cost?

The Swiss roof-price survey provides a starting point. Its prices vary with installation size and combine offers with invoices. Applying each price to all additional panels shows how much the assumed site mix matters.

The cheapest roof price cannot represent every Swiss site. Large, simple roofs are a different opportunity from small roofs, facades and alpine installations. The national potential study includes several such categories. Suitable locations, owners, permits and connections determine how much can actually be built.

The nuclear-inclusive programme also contains substantial solar investment. At the same CHF 1,428/kWp assumption, expanding from 53 to 120–140 GWp adds CHF 95.7–124.2 billion of installation cost. That is a component difference. Each complete portfolio also has its own generation, storage, financing and network costs.

Summer sales can change the comparison

Give summer electricity a realistic value. Assuming it always sells profitably favours overbuilding. Assuming it is always worthless can reject useful projects.

An owner pays for a plant through revenue across the year. The more summer sales contribute, the less winter sales must recover. The following comparison applies this logic equally to solar, wind and nuclear.

The cheap-roof and nuclear examples reach the same seasonal cost at about CHF 45 of net value per potential summer MWh. This uses a 5% required return above inflation and the stated plant costs. Economical roofs can therefore compete on this measure.

“Net value per potential MWh” spreads summer receipts over everything the plant could generate, including output left unsold. For example, selling half at CHF 100/MWh gives CHF 50 per potential MWh before any other deductions. Exports, local use, losses and curtailment—the deliberate reduction of output—determine the actual value. Neither unlimited export income nor zero summer income is established for a national fleet.

Nuclear also needs cost discipline and credible delivery. Raising its construction input to CHF 15,000/kW in 2024 money and its build period to 15 years raises the no-summer-credit result to about CHF 365/winter MWh. That uses the same 5% return. Replacement supply during a delay adds a separate system cost.

Choose winter projects by the service they deliver

Prioritise economical roofs and viable winter wind; require expensive installations to justify their additional service. An alpine plant’s winter share alone does not settle its value. Compare its full cost, timing, connection and likely sales. The finite number of viable wind and solar sites also limits national extrapolation.

Storage has a different job and a separate bill

Generation creates electricity. Storage moves it to another hour or season, using energy that must first be available. The examples below therefore belong beside the generation comparison, with their own service and cost boundaries.

Batteries: pay for usable energy and power. An illustrative 40 GWh four-hour fleet has 10 GW of discharge power. At the assumed CHF 250–500 per usable kWh, initial purchase costs CHF 10–20 billion. Four hours of delivery can cover a short gap if enough charging energy is available. It cannot replace winter generation for weeks without recharging.

Hydro: pay for the winter shift and the sales forgone. Grimselsee’s owner budget is CHF 307 million for about 240 GWh of extra seasonal shifting. Our example requires roughly CHF 108 per shifted MWh: capital recovery, assumed upkeep and CHF 30/MWh of summer sales forgone. It assumes one full shift each year over 60 years at a 5% return. The project moves a finite quantity of water energy into winter; annual natural-water generation does not rise by the shifted amount. Owners need voluntary, viable contracts and respect for their operating obligations.

Network costs also need a fair allocation. Existing-asset renewal and the connections for electrified heating and transport serve several portfolios. Charge each proposed mix for its additional requirements. Assigning the whole national grid programme to solar would overstate its incremental cost.

Continue to the backup and delivery services that keep the country supplied.