BicycleCinema.org
School hall at the Helmholtz-Gymnasium Karlsruhe, January 2026: bicycles on red roller trainers in the foreground, pupils seated before the stage and screen
Photo: Helmholtz-Gymnasium Karlsruhe (helmholtz-karlsruhe.de) — via helmholtz-karlsruhe.de

KLAK / Solare Zukunft e.V.

Germany, Freiburg im Breisgau · School programme

Active last verified 2026-09 The funded KLAK project ended 30 April 2019; the operator, Solare Zukunft e.V., remains active in the school market (Karlsruhe deployment 12 January 2026).
Battery-buffered AC
10 roller trainersDocumented
  • Open manual source

Websitehttps://fahrradkino.org

KLAK (KlimaAktionsKino) was a publicly funded climate-education bicycle cinema run by Solare Zukunft e.V. from Freiburg, 2016–2019. Its technical manual of 20 December 2018 publishes the ten-trainer, LiFePO4-buffered system down to its shutdown logic — the most completely documented system in this corpus.

Key facts

  • Pedalling stations

    10 roller trainers1

    Documented

  • Per-bike average

    50–60 W1

    Documented

  • Projector draw

    340 W1

    Documented

  • Buffer

    LiFePO4 central unit1

    Documented

  • Project funding

    €634,468 (2016–2019)2

    Documented

“Trotz des großen Engagements reichte die selbst erzeugte Energie nicht vollständig aus. Rund 30 % des zusätzlichen Akkus wurden benötigt. Ursachen dafür waren vor allem, dass die Fahrräder gegen Ende nicht mehr dauerhaft besetzt waren.”

Despite the great commitment, the self-generated energy was not fully sufficient. Around 30% of the auxiliary battery was needed. The main cause was that the bikes were no longer continuously occupied toward the end.

Helmholtz-Gymnasium Karlsruhe, report on the Fahrradkino project day of 12 January 20263

KLAK was a project of Solare Zukunft e.V. in Freiburg and UfU e.V., funded under Germany's National Climate Initiative. Its system is battery-buffered: roller trainers with generators feed a central unit holding a LiFePO4 battery and an inverter, which supplies 230 V AC to a fixed set of consumers — projector, sound system and playback laptop. The centrepiece was a sixteen-city Fahrradkino tour in 2018, and complete systems were installed for six months in four youth hostels. Solare Zukunft continues to run school deployments; the Karlsruhe project day of 12 January 2026 is the basis of the active status.

Specifications

What do these labels mean?

FieldValueConfidenceSources
Pedalling stations10 roller trainers with generatorsTen people must pedal simultaneously; the manual asks for a group of at least thirty.Documented1
Generator rating per trainerup to 250 WAverage 50–60 W per bike per the manual's information sheet.Documented1
Per-bike average output50–60 WDocumented1
Generator typenot disclosedThe manual describes the friction roller and screw tensioning but not the generator's construction.Not disclosed1
Buffer chemistryLiFePO4 (lithium iron phosphate)Documented1
Buffer capacitynot disclosedNot disclosed1
Output230 V / 50 Hz, maximum 500 WDocumented1
Projector draw340 WProjector model not disclosed.Documented1
Auto-shutdownafter 10 minutes without pedalling; also at 100% state of chargeWarning below 20% SOC; events should start at 60–70% SOC.Documented1
Field output, Ludwigsburg (November 2024)about 400–500 W from 10 bikesDistrict press release; rotating schoolchildren.Operator-stated4
Battery draw, Karlsruhe (12 January 2026)about 30 % of the auxiliary batterySchool report; bikes were not continuously occupied toward the end.Operator-stated3
Project grant634,468 € (funding code 03KF0034A/B, 1 May 2016 – 30 April 2019)Documented2

History

The National Climate Initiative funded the project from 1 May 2016 to 30 April 2019 2,5. The technical manual is dated 20 December 2018 and remains the current published version 1. After the project closed, several Fahrradkinos covered regional demand across Germany 2 and Solare Zukunft kept the system in use for schools 6. The Zurich collective Vélorution's VéloKino credits "© fahrradkino.org" as its design source 7.

Line diagram redrawn from the KLAK technical manual showing the full power path to projector, sound and laptop
Energy-flow diagram (from the manual): riders → trainers → two Anderson harnesses → Zentraleinheit → inverter 230 V/500 W → beamer + PA + laptop1,3,2,5,6,4 Image: BicycleCinema.org, drawn from the research corpus
Map graphic from the operator's own site: an outline of Germany, hatched, carrying eight location pins
Image: KLAK / Solare Zukunft (fahrradkino.org) — via fahrradkino.org

Technology

Each trainer's generator has a friction roller pressed against the rear tyre by an adjusting screw, and two cable harnesses of five Anderson Powerpole connectors each carry the ten outputs to the central unit 1. The manual fixes the consumers at projector, sound system and playback laptop and warns against adding anything else: the projector alone takes 340 W of the 500 W maximum, while ten riders at the 50–60 W average generate 500–600 W, a margin that keeps the battery roughly neutral as long as every station is occupied 1. Both lids of the control unit stay off during operation for cooling, and the projected image carries a colour-coded bar for each of the ten bikes with a battery indicator showing whether the pack is charging or discharging 1. At the Karlsruhe project day, students rotated every five to fifteen minutes under a live wattage display, and the auxiliary battery covered the shortfall once the bikes were no longer continuously occupied 3.

Data card comparing two documented KLAK deployments, including the Karlsruhe event where about thirty percent of the battery was consumed
Ludwigsburg 400–500 W; Karlsruhe 12 Jan 2026 about 30% of battery needed1,3,2,5,6,4 Image: BicycleCinema.org, drawn from the research corpus
KLAK's illustrated Fahrradkino Tour 2018 banner: a drawn audience and cyclists before a screen bearing the KLAK logo, lettered Klick Klak Film Ab!
Image: KLAK / Solare Zukunft (biorama.eu) — via biorama.eu

People and community

The manual lists Rolf Behringer of Freiburg as its contact, and Behringer explained the system to the students at the Karlsruhe event 1,3. It recommends participants from about age ten and excludes mountain-bike tyres for noise 1.

In their own words

"Um den Akku zu schonen, schaltet die Zentraleinheit automatisch ab, wenn länger als 10 Minuten keiner radelt. Zuvor erfolgen verschiedenen Warnungen, optisch und akustisch." — To protect the battery, the central unit switches off automatically if nobody pedals for more than 10 minutes. Various optical and acoustic warnings come beforehand. 1

"Alle zehn 'menschlichen Kleinkraftwerke' sollten im grünen Bereich fahren. … Der gelbe Bereich bedeutet: Teil dir deine Kräfte ein. Der rote Bereich bedeutet: Da geht noch mehr." — All ten 'human mini power plants' should ride in the green zone. … The yellow zone means: pace yourself. The red zone means: there is more in you. 1

Seeded:Vélorution Zürich VéloKino / velokino.ch / VCS / Pro Velo

Sources

  1. [1]Solare Zukunft e.V., Technisches Manual Fahrradkino, 20.12.2018fahrradkino.org
  2. [2]klimaschutz.de (NKI) — KLAK KlimaAktionsKino project pagewww.klimaschutz.de
  3. [3]Helmholtz-Gymnasium Karlsruhe — Fahrradkino school report (event 12.01.2026)www.helmholtz-karlsruhe.de
  4. [4]Landkreis Ludwigsburg — Fahrradkino press release (2024-11-29)www.landkreis-ludwigsburg.de
  5. [5]UfU e.V. — KLAK KLimaAktionsKinowww.ufu.de
  6. [6]Solare Zukunft e.V.www.solarezukunft.org
  7. [7]Vélorution (Zürich) — VéloKinovelorution.ch

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