A dam wall is not supposed to do anything except hold back water and get checked for cracks every few years. The Muttsee dam in the Glarus Alps has been doing exactly that since 2016, sitting at 8,200 feet, higher than any other dam in Europe. Since the end of August 2022 it has also been a power plant.<\/p>\n
There are 4,872 solar modules bolted to its south face, rated at 2.184 megawatts, running close to 3,000 feet along the wall. The interesting part is not that somebody built it. It is that a team from Switzerland’s EPFL spent a full year measuring what came out, then published the numbers.<\/p>\n
From October 2022 to September 2023 the plant returned 1,434 kilowatt-hours per kilowatt of installed capacity. Of that, 43 percent landed in the winter half of the year, the stretch when Swiss solar normally goes quiet and the country starts importing power.<\/p>\n
Meanwhile, the law Switzerland wrote to get dozens more high-altitude plants built has stopped taking applications. Of the 54 projects on the record, 26 are dead and none is finished.<\/p>\n
Muttsee is the upper reservoir of the Limmern pumped-storage complex, which is why the site had a 16-kilovolt grid connection sitting there before anyone drew a solar panel on it. Axpo initiated the project and built it with Basel utility IWB, which holds 49 percent. Discount grocery chain Denner signed a 20-year power purchase agreement for the entire output.<\/p>\n
The wall faces south and it is steep, which matters more than it sounds. Snow slides off a steep panel instead of sitting on it and turning the array into a very expensive white rectangle for four months.<\/p>\n
Getting the hardware up there was the hard part. There is no road to the dam, so all 730 metric tons of steel, aluminum and glass went in by helicopter from the valley floor at Tierfehd over about four months. The lifting crane was taken apart down in the valley, flown up in pieces, and rebuilt on the crest.<\/p>\n
The modules are Megasol glass-glass units in two sizes, 460 watts and 385 watts, pre-wired into tables 47 feet wide before they went on the wall. Frames are 1.6 inches thick, sized for snow load, and the design allows for drifts up to 16 feet.<\/p>\n
The bottom 16 feet of wall was left bare on purpose, so the snow has somewhere to land.<\/p>\n
Tilt is 51 degrees across most of the array and 65 degrees in places, against the 30 or so you would use down in a valley. Total cost was 8 million Swiss francs, roughly $10 million.<\/p>\n
Christian Heierli, Axpo’s project manager on AlpinSolar, has since told the company’s own magazine that they did not pick the dam because it was cheap. They picked it because they knew it would get approved. The project drew no formal objections at all, which turned out to be a luxury nobody else in this story enjoyed.<\/p>\n
The study came out of EPFL’s Laboratory of Cryospheric Sciences with ZHAW and the consultancy SUNWELL, and ran in Frontiers in Energy Research<\/a> in June 2024. It measured the dam against a conventional 6-megawatt ground-mounted plant at Payerne, 1,476 feet up on the Swiss plateau and a fair stand-in for the national solar fleet.<\/p>\n Across the same 12 months, the dam produced 168 percent of what Payerne managed. Across the winter half, it produced 380 percent.<\/p>\n Winter here is a legal definition, not a vibe. Swiss energy law splits the year at October 1 and March 31, and that split is what the subsidy rules are written against.<\/p>\n The dam put 616 kWh\/kWp into that window, 43 percent of its year. Payerne managed 26 percent of its own, smaller year. Capacity factor at Muttsee came in around 16 percent, performance ratio at 0.89, thermal capture losses at 0.3 percent, which is what happens when your power plant spends most of the year cold.<\/p>\n The authors flag one caveat themselves. This is a single year of data, and that particular January through May ran well below the multi-year average at the reference sites, which flatters the 380 percent figure.<\/p>\n Here is the part that gets reported wrong nearly every time this plant comes up in English. The modules are bifacial, meaning both faces generate, and the standard explanation is that the back side harvests sunlight bouncing off the snow.<\/p>\n At Muttsee, it barely does. EPFL measured the annual optical bifacial gain at the dam at about 1.5 percent.<\/p>\n The reason is structural rather than optical. The modules hang roughly five feet off the concrete, and that gap exists so technicians can still walk the wall and map its cracks, which they are required to do at least every five years. Five feet of shaded concrete is not an albedo source.<\/p>\n What the dam actually runs on is altitude. It sits above the fog layer that parks over the Swiss plateau from October onward, the silicon stays cold, and the steep tilt meets a low winter sun almost head-on.<\/p>\n The snow-bounce effect is real, it just needs room to work. At EPFL’s open test rig near Davos, at a similar altitude, the same comparison came out at 19 percent for panels tilted at 60 degrees and 28 percent at 90 degrees. The best setup up there returned 1,853 kWh\/kWp, well clear of the 1,434 the actual power plant delivered.<\/p>\n That gap is the study’s real finding, and it applies to every alpine project still on a drawing board. A test rig gets one perfect orientation. A full-size plant gets whatever the terrain allows, which at Muttsee means azimuths smeared from southeast to southwest, two tilt angles, and surrounding slopes throwing shade at inconvenient hours.<\/p>\n Some bottom-row modules also got buried in snow that first winter, costing an estimated 1 percent of annual output.<\/p>\n It is the same lesson coming out of every unconventional mounting scheme, from Austria’s vertical solar crosses at a glacier ski resort<\/a> to the panels standing edge-on in a Bavarian lake<\/a>. The physics works. The site decides how much of it you collect.<\/p>\n Switzerland passed its emergency solar package on September 30, 2022, six weeks after the dam went fully live. Known as the Solar Express, it stripped back permitting for large high-altitude plants and offered up to 60 percent of investment costs back as a one-off payment.<\/p>\n To collect, the Federal Office of Energy requires<\/a> a plant to produce at least 10 gigawatt-hours a year and at least 500 kWh per installed kilowatt across the winter half. The scheme is capped at 2 terawatt-hours of new production nationwide.<\/p>\n Muttsee clears the winter test without breathing hard, at 616 kWh\/kWp. It misses the other one by a mile. The plant was announced at 3.3 million kilowatt-hours a year, and Axpo’s own project page now describes it<\/a> as producing around 3 million. Either figure is a third of the legal minimum.<\/p>\n So the flagship that spent two years being photographed as proof the concept works could not have collected a franc under the law it was built to argue for. It also predates that law, which makes the point twice.<\/p>\n Axpo was blunt about the economics from the start. Announcing the project in January 2021, CEO Christoph Brand said the missing regulatory framework meant “this type of plant is barely economically feasible”<\/a>, and said the company was building it anyway to make a point.<\/p>\n Applications for the Solar Express shut on December 31, 2025. Parliament had already softened the test that March, dropping the requirement to be feeding power into the grid by that date and accepting a publicly filed building application instead. Projects that missed it are out.<\/p>\n An independent tracker run by Oberli Engineering<\/a>, updated July 21, 2026, counts 54 projects. Twenty-six are finished in the sense that they are never happening: seven abandoned during preliminary study, three dropped later, and 14 voted down by the municipalities that would have hosted them.<\/p>\n Of the 28 still alive, exactly zero are complete. Four are partly built and generating. Add up everything either legally approved or already under construction and you get 78.2 megawatts and 115.6 gigawatt-hours a year, which is 5.8 percent of the 2 terawatt-hour target.<\/p>\n Canton Valais, where the idea was born and where the loudest projects were announced, had not built or legally approved a single plant by the end of 2025, according to an analysis by Swiss public broadcaster SRF<\/a> published in January 2026.<\/p>\n Bern keeps adjusting the machinery. On November 26, 2025 the Federal Council dropped a proposed cap on Solar Express funding after 97 consultation responses came back against it, and swapped the old altitude bonus for a winter-power bonus on large plants commissioned from January 1, 2026.<\/p>\n A separate acceleration act took effect on April 1, 2026, handing cantons a single consolidated permitting procedure for solar and wind projects of national interest.<\/p>\n Madrisa Solar, above Klosters at around 6,560 feet, ran roughly 3,600 modules through its first winter, about 20 percent of the finished plant, and produced about 1.5 gigawatt-hours between October and March<\/a>. Output rose around 15 percent after the first snowfall. The full build is a 70 million franc project, about $87 million, with commissioning due by the end of 2027.<\/p>\n Sidenplangg in canton Uri has 13 percent of its array running and reports winter output roughly three times what valley plants managed. The operators declined to give the Keystone-SDA news agency any actual figures, which is its own kind of data point.<\/p>\n The dam, meanwhile, has picked up a second job. Since August 2025 it has been supplying tertiary balancing power to national grid operator Swissgrid under a pilot called PV4Balancing, throttling its output on command when there is too much electricity in the system. Pooled with other solar plants, it is now a grid asset rather than just a generator.<\/p>\n The uncomfortable summary is that the best-performing alpine solar plant Switzerland has measured is the one it built before the subsidy existed, on a wall somebody else had already poured, wired and inspected. Those walls are not being handed out. Neither, on the evidence of the last three years, are the permits.<\/p>\n","protected":false},"excerpt":{"rendered":" A dam wall is not supposed to do anything except hold back water and get checked for cracks every few … <\/p>\nThe panels have two working faces and the wall wastes one of them<\/h2>\n
Muttsee would not qualify for the law it helped argue into existence<\/h2>\n
The window has closed and nobody has finished a plant<\/h2>\n
What the four working plants are reporting so far<\/h2>\n