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"I built my first pedelec in 2016, batteries cost a lot of money back then and were quite weak. I think Samsung brought out the 30Q cell the year after. Me being broke (permanent feature...) I bought a Korean spot welder when I decided to migrate from LiPo to LiIon cells, and building your own batteries is quite easy and much cheaper. 270€ for a 14.7 Ah battery made from 21700 cells in 3P12S format, a popular German company will charge you 326€ for a similar Ah capacity so a savings of about 17%.
Batteries last a long time. My LiPo bricks lasted for 4 years - daily use and just over the number of charge cycles advertised by Hobby King. I did calculate at one time the cost per km, electricity, charger(s) and battery combined and was at about 0.04€/km, I can not buy a bus ticket* for that price so for me it was an economically sound investment. I am still using the battery chargers so the price per km is decreasing even today."
Batteries last a long time. My LiPo bricks lasted for 4 years - daily use and just over the number of charge cycles advertised by Hobby King. I did calculate at one time the cost per km, electricity, charger(s) and battery combined and was at about 0.04€/km, I can not buy a bus ticket* for that price so for me it was an economically sound investment. I am still using the battery chargers so the price per km is decreasing even today."
Back to solar cars, I initially though about making a solar trailer with 200W of panels and feeding that directly to the motor. This is of course illegal because it is only interesting technically if you feed the motor permanently and so turn off the speed limit of 25 km/h. In this usage scenario the battery is only used as a backup for night driving and very rainy days.
Now my idea is having 2 x batteries and a single 100W 12v panel on the trailer. The panel feeds the chargers which charge the second set of batteries while I am driving. The advantage is a smaller trailer (shorter by length) and being able to stay within the pedelec limits. At the theoretical maximum efficiency the panel provides 8.33 Amps and I charge at 3 Amps so even with losses there is still enough current for both chargers. A typical long range solar velocar driving scenario is:
- in the morning the human motor provides as much power as it can/wants to
- after lunch lighter pedalling effort so an average speed around 25 km/h
- this allows longer driving days without damaging the human component (now 66 years old...)
- desired range is > 250 km/day
- in theory no need to plug the chargers into a mains socket
I have a budget:
- solar panel from the nautical world 12v and 100W plus bits 150€
- Burley Coho trailer + frame for panel about 450€ - I chose this trailer because it will follow at velocar speeds downhill. When I am not using it for touring I can strap oars and other boat/fishing bits to it.
- battery #2 270€
- approximately 870€
In an imaginary ideal world I imagine 10,000 km/year which is 0.87€/km the first year.
* Going from here to San Sebastian costs about 9.5 euro cents per km with public transport.