Sebastian D.’s solar handbikes

/ Handbike_ / By 
(Source of the article in German, courtesy of the author)

Introduction

How did I come up with the idea of ​​building a solar-powered bike to cross Europe?

Thanks to advances in recent years, there are now electric-assist bicycles that assist the cyclist up to 25 km/h with a maximum continuous power of 250 W. However, 250 W represents a manageable electrical power thanks to photovoltaics: a solar cell with a maximum power of around 200 W occupies an area of ​​approximately one square meter. How can one integrate one square meter of solar energy onto a bicycle? It’s a good idea, but without a trailer or a roof, it will undoubtedly be complex…

Because of my ankylosing spondylitis, which has stiffened my spine and hips, I can’t ride a conventional bicycle. For this, I use a handbike, on which you pedal with your arms rather than your legs. It has three wheels and practically begs the question of building a roof with a solar panel. No sooner said than done! I bought a used handbike from my fellow para-climber Markus Pösendorfer, from the Austrian national para-climbing team, and embarked on the project. I first converted the handbike to electric assistance using an e-bike conversion kit and, as mentioned at the beginning, I made the battery myself from recycled laptop batteries.

This page presents a summary of all the components and tools I have tested and found satisfactory (and sometimes recommended by experienced solar cyclists). Parts that I have not successfully tested or that I deem inadequate are not included in this list.

Technical Description

The bike

I used two used Schmicking handbikes (Kabelbinderexpress and Racer). I don’t know the exact model series or year of manufacture, but Schmicking customizes its bikes to the user’s needs.

The two handbikes are of different designs, but both are equipped with 26-inch wheels. For optimal performance, they are both equipped with racing tires on the rear and a slightly wider, softer tire on the front (drive wheel, high brake load, single wheel). This configuration is ideal for asphalt, but not recommended for off-road use:

  • Front wheel: Schwalbe Green Marathon 32×559
  • Rear wheel: Continental Gatorskin 650×23c or 23×571
  • 26×1-inch inner tube: https://amzn.to/3YBH65P
  • Jante avant : DT-Swiss 535, 26 pouces
  • Boîte de vitesses : Cassette 9 vitesses

    • La motorisation

    Dans mes différents prototypes, j’ai utilisé différents moteurs montés dans la roue avant:

      • Moteur BAFANG 36 Volts, 250 Watts (kit complet avec câbles, console d’affichage 500C, capteur de vitesse…)

      • Moteur GRIN TECHNOLOGIES direct drive, pour axe plein (en 2025).

    Moteur roue BAFANG

    Moteur roue GMAC 10T

    The GMAC 10T motor is equipped with a reduction gear, which gives it good torque and efficiency at low rpm. Thanks to a welded clutch, it also has regenerative capability. This is a rare combination, as most other e-bike motors are either equipped with a gearbox and freewheel (meaning they cannot regenerate energy) or a direct drive (without a gearbox, but with energy recovery). The GMAC 10T seemed like the perfect compromise between the two worlds, but even this comes at a price: the freewheel isn’t “free,” and the gearbox is constantly spinning.

    Display and Control Console // Controller

    The Cycle Analyst CA3 paired with a Grin Technologies BaseRunner controller is the ideal system for any type of electric motor. Regardless of voltage, power, speed, or additional electronics required, the Cycle Analyst supports countless options. Additionally, thanks to what’s called “virtual coasting,” the Cycle Analyst can apply a base current to the engine at idle, allowing the engine to run with virtually no resistance.

    The Battery

    All the batteries I’ve made so far are made from recycled Li-ion batteries made from 18650 Li-ion cells. All cells undergo extensive testing and require specific tools:


      • LiitoKala Lii-500 Li-ion Capacity Tester and Charger (to measure the actual capacity of each cell): https://amzn.to/3CcNSra

      • IMAX-B6 Universal Charger (Li/NiMH, NiCd, Pb 1s to 6s battery charger with balancer for charging all types of batteries): https://amzn.to/48N6471

      • JK-BD6A17S6P BMS (Battery Management System for battery protection and balancing of series-connected blocks): https://amzn.to/3NUWxRQ

    Solar Equipment

    Solar Panels

    Be careful, many ultra-light, glass-free panels for campervans and converted vans lack robustness and overestimate the power output. Here are some brands tested and recommended by other solar bike enthusiasts:

    Note:
    Manufacturers modify constantly expanding their ranges, new sizes and power levels are appearing on the market, while older models are no longer produced. The user must constantly look for new variants and designs. However, reputable manufacturers and their manufacturing technologies should be (more) reliable.

    Solar Charge Controllers

      • Victron MPPT 100/20 48V charge controller (configurable to 36V via the app, for series connection of solar panels; a minimum solar voltage of 45V is required for a 36V battery!).

      • SUNYIMA MPPT 300W Boost Charge Controller (adjustable for battery voltages of 24V, 36V, 48V, 60V, and 72V). The panel output voltage must be lower than the battery voltage.

      • Voltmeter/Wattmeter up to 60V/100A max.

    Feedback and Developments

    After my first major solar bike trip from Mallorca to Germany, I gathered a wealth of data and insights, as well as countless suggestions for improving my prototype. My list was as follows:

      • Improved aerodynamics

      • Larger battery capacity

      • Engine with regeneration

      • More solar energy

      • Better luggage strategy

    It quickly became clear that to implement all these points, I would need to dedicate sufficient time to building a brand new solar bike. Added to this was the fact that my girlfriend wanted to accompany me on the trip.

    It was therefore obvious that it was best to fine-tune the first prototype to make it road-ready, and then start building a second solar bike. I quickly selected a used handbike frame from the classifieds, and a new base model was ready to be converted in Germany. In Spain, I soldered on a new battery and tried to implement all the points on my previous list. The choice fell on a 52V battery system of approximately 2 kWh (previously 36V, 1.6 kWh) and the GMAC 10T motor (formerly Bafang G.020) with the Cycle Analyst CA3 as the control unit (formerly Bafang). Obtaining the Cycle Analyst from Grin Technologies in Canada required a long and expensive process; There are now distributors in the EU, but not for the motor itself.

    The new solar bike features an extremely lightweight roof and no additional underbody; the additional aluminum structure therefore weighs only 5 kg. The total weight of the two finished solar bikes also shows a significant difference:

    Prototype 1: 65 kg
    Prototype 2: 42 kg

    Main difference:
    This lies in the design of the roof and the underbody. Prototype 1 features an additional underbody and a roof supported by 8mm plywood, while Prototype 2 has no additional underbody and relies on an aluminum roof frame.