As a child, I was often in charge of preparing the mayonnaise. I remember pouring with care (and faith) olive oil, raw egg, and lemon juice, hoping to have come up with the right amount of each so that the sauce would set – it did most of the time!  In a bit more complex way, the energy transition seems to require some sort of cosmic alignment as well — every ingredient needs to fall into place: governance, technology, policy.

When it comes to solar power adoption, sun hours are not necessarily among these determining factors. At least not yet, as shown by the fact that Germany – not exactly your typical beach holiday spot –  is leading the way in Europe. Germans are getting so good at optimizing every inch of the built environment for renewables that they’re experiencing, since 2022, a real boom in balcony solar panels,  Balkonkraftwerk. This plug-and-play solar power system is transforming access to renewables in the city. In 2024 alone, 435,000 new plug-in balcony systems were registered in Germany, contributing 2.4% of the country’s newly installed solar capacity. A Balkonkraftwerk set consists of a couple of lightweight panels, often mounted on balcony railings or facades, connected directly to a power socket. They can produce up to 800 watts—enough to power essentials like a fridge or a few devices. For renters or apartment dwellers without access to rooftops, it’s a game-changer. With prices ranging from 200 to 800 euros (including inverter and cables), the systems are easy to install and affordable – rooftop installations average 10.000 euros.

These tiny power plants may not cover an entire household’s needs, but they help reduce bills and make urban energy systems more resilient and self-sufficient, key elements for cities’ energy transitions. Balcony systems indeed bypass obstacles of other forms of solar — they’re versatile, easy to install, and recent legal changes in Germany now protect renters’ right to have them. No roof? No problem. Moving house? Take it with you. And balcony solar is also well suited to a grassroots and community approach, further contributing to the decentralization and democratic governance of the energy systems. In Hamburg, for example, the non-profit association SoliSolar drives a bottom-up energy transition through solidarity-based self-build communities for solar power systems, including Balkonkraftwerke. Founded in 2022, it organizes collective orders to reduce costs for residents (renters in their majority), offers support with official registrations and interactions with landlords, and facilitates community-based installation teams that emphasize financial mutual aid and shared learning.

Similar grassroots solar initiatives across Germany are helping to build a broader citizen-led energy movement, promoting ecological and socially responsible practices alongside accessible energy education. Or in other words, helping the mayonnaise set : )