solar bicycle

I'm a physics teacher building a solar bicycle at my high school. I don't know what size battery/solar panel or what kind of regulator to use. Any suggestions? (I have a 3-wheeled recumbent bike that goes very fast when pedaled.)

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    Re: solar bicycle

    I guess it all depends what you are trying to do...

    If you are entering a solar powered vehicle for a race across America or Australia, there would be one type of answer.

    If you are trying to demo solar power on a sunny day in the parking lot at school, it would be another.

    If you are trying to create a reliable commute vehicle, the answer would be a 3rd option.

    And, depending on your skills, how much money you wish to spend, who will be riding it, where you life (sun, wind, and hills) and how far, all will modify the top three questions.

    You probably are looking at a 300 to 600 watt motor (isn't a typical human capable of about 0.1-0.2 hp on a bike or 0.2*746watts=149watts)... Assuming that you cruise at 0.1 hp for 1 hour, then that would be 149 Watt*Hours. A typical car size storage battery would contain about 1kWh or 1,000 Watt*Hours of energy... If you use about 1/2 (for long battery life), a car size battery would send you about 500Wh/149W=3.3 hours (at whatever a good cruise speed for conditions would be).

    If you wished to use a solar panel at high noon mounted to the bike... A full size panel of ~175 watts (~$900+tax list price) would be capable of driving the motor... Of course, high noon, panel pointed (and tracking) towards sun, and that the wind blocking effects of such a panel (63" by 31") don't slow you down or allow the wind to blow you off of the road.

    To make a commute bike, your best bet would be a good motor and battery back that you can charge from a solar panel charging station... The most efficient charging station (energy and money) would be to attach a couple panels to a Grid Tied Solar Inverter that could "spin" your meter backwards (if your utility company allows net metering) during the day (say at work), and when you come home at night just plug the bike into a charger... You can even get Time of Use metering where you pay less for power during the night and morning, and pay more during the day (noon-6pm Mon-Fri for my utility in California).

    An alternative would be to have a charging station where you park the bike during the day--and use the bike for morning/evening commute. Not as handy, but would work OK and be a more obvious solar demonstration project.

    There are many variants that you can play with... For example a charging station with several storage batteries to store power during the day, and use to charge the bike at night. How much you use the bike, how much sun you get, the number of solar panels you can afford, the type, size and number of storage batteries, etc. are all parameters you can play with based on your needs and ability.

    If you keep your power needs small (smaller battery and solar panel(s)), then you can go with a cheaper, non MPPT type controller. Those are more expensive and don't help recover extra solar power in a small system.

    If some of this is beyond your comfort zone, you talk with the electrical/automotive/engineering tech teacher(s) in your school and make a joint project out of it... Could be a very cool collaboration (as cool as engineering types can ever be--In my schools, the Physics Instructors were always way more cool than anyone in Engineering :wink: ).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: solar bicycle

    Thanks for good advice and good forum.

    I have 16" weel bike-electrical with litium battery 36v ?10a with hub motor and can go 35km/h with speed 22km/h.

    I am plannig to charge battery with solar panel.

    In Toronto in canadian tire there is panel-folding for back-pack 800ma 12v.

    Please,
    1.advice me with that panel or any how to make
    2.must I need controler and which
    3.where to buy (in toronto, world or europa)?

    Thanks Vlada
  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    Re: solar bicycle

    Short answer, there are several reasons that you should not do this...

    1. Lithium (Ion?) batteries are very difficult to charge and design a charger for... If you do something wrong (over/under charge the battery), it will catch fire--or worse. Do not try to make your own charger or "convert" their charger to solar panel use.

    2. Small solar panels do not output much power. I am not quite sure what size battery you have but assume that is:

    36volt*10amps*1hour=360Watt*Hour

    Assuming you can figure out how to convert an 800 mA 12 volt panel to put energy into your battery pack (see reason #1)--then:

    360 WH / (0.8A*12v) = 37.5 hours... Or 8+ full 5 hour days of sun to recharge (actually about 16 days because of other inefficiencies)...

    If you are set on doing this--there are two reasonable ways to approach this...

    First would be to go with Grid tied charger at home.

    Second would be to convert the battery to a Lead Acid or NiMH or other easier, and safer, battery technology that could build a charger for (including a much larger solar panel--several hundred watts would recharge in about a summer's day).

    Lastly, would be to create a hybrid charging station... Use a large solar panel (array) with a lead acid battery bank to charge during the day. And at night (or during the day too) use a 120 VAC inverter to power the bike's AC battery charger... Because of the losses, you would probably need somewhat larger panels than the previous several options.

    Buying panels--if you can get them in the US and pack them back in the car across the boarder--you can probably save some money.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,582 ✭✭✭✭✭
    Re: solar bicycle
    vlada3 wrote: »
    I am plannig to charge battery with solar panel.

    In Toronto in canadian tire there is panel-folding for back-pack 800ma 12v.

    Look at your existing charger, we need the #'s off that. It might say 1800mA 45V

    LiIo batteries REQUIRE a specific charge controller, and when you alter the charge parameters, it makes the newspaper (laptop battery burns house down, cellphone battery burns mans leg)

    You may find that your charge conditions require 2 panels in the sun for 9 hours. That's tough in the winter.

    You could convert to Lead Acid batteries (like a conventional Deep Cycle) and hope you never crash and spill the acid. You then could use nearly any charger.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • SolarJohnSolarJohn Solar Expert Posts: 202 ✭✭✭✭✭
    Re: solar bicycle
    mike90045 wrote: »
    Look at your existing charger, we need the #'s off that. It might say 1800mA 45V

    You could convert to Lead Acid batteries (like a conventional Deep Cycle) and hope you never crash and spill the acid. You then could use nearly any charger.

    To avoid the acid spill danger, you could use as many gel-cell batteries as you need. This will work as long as you don't plan to go long distances. Typically they're rated at about 5ah, so you might need quite a few. These batteries are used in computer UPS units, toy autos, alarm systems, and other applications. They're typically 12-volt batteries, so they could be charged via a simple off-grid PV system consisting of PV panel(s) and a charge controller. You don't even need to buy a charger, so you'll save money there. The charge controller will prevent overcharging, so it's a safer solution than most other options.

    Since this is a school project, I'm sure you'll appreciate the safety of this approach.
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: solar bicycle
    vlada3 wrote: »
    Thanks for good advice and good forum.

    I have 16" weel bike-electrical with litium battery 36v ?10a with hub motor and can go 35km/h with speed 22km/h.

    I am plannig to charge battery with solar panel.

    In Toronto in canadian tire there is panel-folding for back-pack 800ma 12v.

    Please,
    1.advice me with that panel or any how to make
    2.must I need controler and which
    3.where to buy (in toronto, world or europa)?

    Thanks Vlada

    Since the charger is only incidental to the project, perhaps you could hook a number of panels in parallel, use the 12 volts to power a car inverter, and plug the existing charger that came with your electric bike into that. It would be horribly inefficient, but would demonstrate the principle. Take a look at the existing charger, and see what it needs in terms of power. I suspect you would need panels on the order of double that power for this scheme to work. I suspect the cheap folding panel from the tire store would not be enough, unless you had 10 or 20 of them in parallel.

    If you have an Electrical Engineering hacker friend, they might be able to open up your existing charger and modify it to run straight off the solar panels. Most likely, inside the charger, there is a switching power supply generating (say) 60 volts DC. The friend would remove the switching power supply part, and patch in the solar panel connection, instead. And again, the panels would still be costly, possibly rivaling the price of the bike, itself.
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