Tribute to a Pragmatic Swiss Solar Pioneer – Who Called to Action in 1989

He is called a pragmatic doer, knowing his physics and engineering, devoid of ideology. This is how Josef Jenni is introduced in the preface to his document called How can we achieve the energy transition (Wie erreichen wir die Energiewende). It’s a manifesto and a technical overview – by the pioneer whose company had built the first fully solar powered home in Europe in 1989.

Jenni emphasizes that there are no easy hacks. You cannot fool physics. And we need to stop marketing unnecessary stuff that’s detrimental to the environment.

We need to sell what we consider good, instead of considering good what we sell.
(Wir müssen verkaufen, was wir als gut betrachten, und nicht als gut
betrachten, was wir verkaufen.)

His philosophy is not cherry-picking life-style minimalism. He has been walking the talk since decades. He is also not advocating for utopian politics. Jenni believes that a healthy, successful business is the best foundation to achieve the energy transition. He is against governmental subsidies. There has to be a real market for good solutions to the energy problems. Jenni’s company has been growing organically since its foundation in the 1970s.

He nails it – in a section called Useless Work (section 2.13 of the PDF). As Jenni stresses often, being popular isn’t his goal!


In our society, and in renewable energy in particular, more and more people are wasting time with developing impossible strategies and scenarios, with writing grant applications or reviewing them, with creating or enforcing useless regulations and laws – rules that are restricting personal autonomy and taking the joy out of creative, effective, technical work.

The major part of publicly subsidized research belongs to that category. You feel that nothing is foolish enough to be ‘investigated’ with unreasonable efforts – while some simple, down-to-earth rules-of-thumb grounded in physics would be enough to settle the issue.

And the worst part is that the most brilliant and creative minds get sucked into this: they are paid well for useless work. I credit this to an unfortunate educational system; its goal is ‘higher’ education for as many students as possible. Having earned their degrees and diplomas they need to work in adequate jobs – not working manually for sure, while we lack skilled craftspeople on our construction sites and in our workshops.

In energy politics, there are too many lawyers, economists, and politicians without physics knowledge. If the energy transition would be solved with computers, by attending conferences – we would be done already. The solution is to do something and hold yourself accountable, and to do the hard, detailed, nitty-gritty, mundane work.

When Jenni built his first solar house in 1989, it was accepted ‘wisdom’ that it is simply not possible to live off solar energy for a whole season (in Switzerland). A remarkable error: You can for sure discuss if a solar house is commercially feasible or accepted as a product by buyers, but you cannot argue with the physics of heat transport and storage. Jenni wanted to prove the ‘experts’ wrong.

On the company websites, two videos document the solar house – the Oberburger Sonnenhaus.

Video documenting the construction:

Video by Jenni Energietechnik, click image to view on Youtube. Construction of the Oberburger Sonnenhaus,

Heat was stored in three large water tanks – 118 cubic meters in total, about 100 times the size of a typical 1000 liters hot water tank used with solar thermal collectors. Jenni used 84 square meters of solar thermal collectors, about 9 times a typical solar thermal installation for auxiliary heating.

The house used traditional wood construction. The tanks were stored in one large basement+ground floor – that’s why the house looked as if it was built on a small mound or as if the ground floor was buried in the earth. The insulation was one meter thick, and tanks are heated up to 90°C in summer. The temperature decreased by considerably less than a degree °C per day.

Electricity was generated with 43 square meters of photovoltaic cells (48kW), so also a factor 5-10 more than a typical installation today. The visualization shown in the video looks quite modern. Note that Jenni is a trained electrical engineer and started his business with programming control units for solar systems. You see that this was a research project – the systems is generously equipped with temperature sensors.

Jenni installed batteries! The exact specifications aren’t given, but they look like series of connected standard lead-acid batteries. The batteries powered one 24V DC circuit and one 220V AC circuit.

In the interview, he is asked about his motivations: “Interested in the technology”, “joy of building”, “showing what solar energy can do”. A pragmatic, modest maker. “As the sun does hardly shine in winter, we have to store the heat harvested in summer.” Data obtained for this house were the foundation for building solar apartment houses – which Jenni successfully did in 2005!

This video documented the legendary launch event – a mid-winter pool party:

Video by Jenni Energietechnik, click image to view on Youtube. Oberburger Sonnenhaus – house warming party,

You see people living in the house heated to 22°C room temperature (“It’s nearly a bit too warm…”), and they did not have to make trade-off re “standard of living”. Also electricity consumption is typical – they say that dish washers and toy trains etc. never emptied the batteries completely. They were operating in island-mode: “The advantage is you still have power if your neighbors’ home goes black.”

The 25000 liters outdoor pool was heated to 37°C on January 31, 1990. In this winter, one third of the stored heat energy had been used so far. Interview asks: “Other solar engineers call you a tinkerer and a nerd – what’s the idea behind today’s event?”. Jenni: “We are happy our system works, but we also want to call to action. The water is literally up to our necks [dives into the water] – we need to stop talking and do something about environmental protection.”

He said that – more than 30 years ago.

We watch it today while we agonize about our dependency on fossil fuel from Russia.


If you want to know that I/we did – check out the posts in the Energy section of this blog, dated 2014 to about 2019. We have also turned our house into a research lab, simulated, planned, and built a heat pump system, later added PV panels (and recently switched to an electrical car), went fully remote long before the pandemic. I am only mentioning it as a post like that might trigger a “And what have you done??!??” response, but – more importantly – I want to add my usual silly Donate for Ukraine button: From feedback and backlinks I have concluded that our freely available detailed content was helpful for other self-builders. If it was/is for you, please consider donating to organizations or individuals that support Ukraine and Ukrainian refugees!

Edit: I recommend donating to the Austrian project (registered NGO) Cards for Ukraine.


And I fear it has to be said in times of Influencers (What might Jenni say about that type of job?): No, this is not a sponsored post. I only ‘know’ Jenni from the sources I am quoting. His project and his attitude have been an inspiration to me in the early stages of our project, more than 10 years ago.

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