Aalto’s new community-built sauna floats on repurposed wind turbine blades
Aalto-born Reverlast is transforming old wind turbine blades into durable floating structures designed to withstand even harsh marine conditions
On the go: A new life for an old blade
Startup Reverlast repurposes discarded wind turbine blades into durable floating docks, the first of which supports a beloved community sauna on the university’s shoreline.
At first glance, Siipisauna – wing sauna, in English – looks like any other modest, barrel-shaped sauna on a floating dock. But under the edge of the pier, something white and curved peeks out. ‘That’s the tip of a wind turbine blade. It helps stabilise the dock, and it’s also a great spot to jump into the water from,’ says Johannes Peace, CEO of Reverlast, as he tends the sauna’s heater.
Founded by three Aalto alumni, Reverlast is a startup created to solve a growing global problem: what to do with wind turbine blades that have reached the end of their lifecycle. Once a blade – typically weighing around 15 tonnes and worth €200,000 – is brought down, it becomes difficult and expensive to recycle.
The EU’s waste policy has a five-tier hierarchy: prevention, reuse, recycling, energy recovery and, as a last resort, disposal. The higher the method on the hierarchy, the better it is for the environment.
In the US, used blades are buried. In Europe, where landfilling is banned, they’re incinerated for energy or, at best, shredded for use in concrete. Either way, the valuable material properties and engineering of the blade are lost.
In 2022, Johannes Peace had an idea that could move wind blade recycling up the hierarchy.
Strong and affordable
Peace, who studied bio- and chemical engineering and international design business management at Aalto, had long been exploring how to build large, floating marine structures – like seaweed farms – but couldn’t find a material strong enough and cheap enough to work.
Then he came across a photo of a blade graveyard. Wind turbine blades are made of fiberglass, a material familiar to him as a passionate sailor. It’s tough and long-lasting, even in harsh marine conditions. That sparked an idea, and he contacted another boat enthusiast, Aalto University Business School alum Ossi Heiskala. Would he be interested in turning the idea into a business?
‘The combination of positive environmental impact and a solid business case – of course I was in,’ says Heiskala.
After careful research, the team joined the Kiuas accelerator programme and founded Reverlast in August 2024. The third member of the team is Henrik Jansson, a design student at Aalto. Their mission: to turn used turbine blades into floating docks. Their first prototype is already in place – and the sauna floating on it is warmed up and ready to go.
Decades of extra life
Siipisauna, floating just off the Aalto campus shoreline, was completed in early 2025 with the help of a €10,000 Sustainability Action Booster grant from the university. The sauna itself is a classic Finnish barrel model, stained dark and assembled from a kit. The deck is made from Siberian larch, a naturally durable wood rich in resins and minerals. But the real innovation lies beneath: the dock floats on four pontoons made from wind turbine blades.
Each pontoon is filled with polystyrene and weighs over 300 kilograms. The blade segments have a fibreglass shell up to six centimetres thick – compared to around one centimetre in a typical sailboat hull – making them incredibly strong. Siipisauna even survived a full winter in the ice without damage.
A wind turbine blade typically lasts 20 years in its original use. In water, it can last more than twice that long. With painting and surface treatments, its longevity improves further. This approach also reduces the need for traditional dock materials like concrete and polyethylene, lowering the environmental footprint even more.
A dock like Siipisauna prevents an estimated 2.6 tonnes of carbon emissions – and the bigger the dock, the greater the impact.
At a recent boat fair, Reverlast quickly sold out its stock. The team has already outgrown its workshop in Otaniemi, the Aalto University campus area. New premises await in Naantali, a coastal town in southwestern Finland. And globally, there’s no shortage of used blades to work with.
Breakwaters and floating villages
Most Finnish wind turbines are still relatively young. In contrast, over a third of turbines in Germany are already more than 15 years old. WindEurope estimates that starting in 2030, over 52,000 tonnes – or more than 3,000 blades – will be decommissioned annually in Europe alone.
As a result, reuse concepts are being developed around the world: Denmark has made bike shelters from blades, Germany uses them for outdoor furniture, and in the US, researchers are exploring their use in bridge structures.
Reverlast is now launching a partnership with VG-Port Oy, a circular economy–focused port operator in Naantali. The plan is to ship cargo to Western Europe and return with loads of turbine blades.
‘We’ve calculated that transporting 600 metres of blades at a time would make the system financially viable,’ says Heiskala.
The company started with floating docks because of the team’s expertise. Currently, most pontoons are filled with foam glass made from recycled glass, which makes them unsinkable.
A new method is on the drawing board to make the pontoons float without any internal filling at all.
Reverlast’s dock concept is the first of its kind, but the technology is adaptable to many other floating structures, like breakwaters. Looking even further ahead, the team imagines floating villages made from wind turbine blades.
‘Climate change is raising sea levels and intensifying storms, increasing the need for temporary housing in many areas,’ says Peace. ‘And people are naturally drawn to water. It’s calming. When you sit on that sauna bench, feel the gentle sway, and see the tip of the wind blade through the window – you’re literally sauna bathing on a turbine wing.’
A cherished sauna
‘Siipisauna opened to the public in April 2025, and people have absolutely loved it. It’s charming and accessible: anyone can book a slot, and a one-hour sauna session costs just five euros – basically the price of firewood.
Volunteers from Aalto Sustainability Club helped build the sauna, and now we run it together with the Polytechnic Sauna Society. The opening party was packed; at one point there were 17 people in the sauna at once. We played games, swam and saunaed for hours – it was the perfect start to the summer.
Aalto is such an international community, and for many of our international students, experiencing sauna culture is a key part of their time in Finland. There’s no better place for it: the sea view is beautiful, and after a hot steam, it’s amazing to plunge into the cool water. My international friends have been totally enchanted, and I believe this sauna has brought a lot of joy É«É«À²â€™s student community.’
Anna Hakola
Economics student and board member, Aalto Sustainability Club
This article has been published in the (issuu.com), September 2025.
Read more about Siipisauna
See the Reverlast dock and rent the student-maintained floating sauna at Otaranta 9, Espoo.
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