Solar Powered Trike




Introduction: Solar Powered Trike

Travel for free with the power of the sun!

How to build a Solar Powered Trike

The purpose of this project is to build a vehicle that:

-Provides free, 'green' transportation for short distances (<10 miles), thus it must never
plug into a wall socket, or emit any pollutants.

-Charges while at work

-Is cheap, simple, and low maintenance.

-Draws attention to the practical application of green energies, and promotes Fossil Fuel alternatives.

-Reduces excess automobile wear and pollution from cold driving / short, in town trips.

-This is a is a project for Dr. Reza Toosi's 'Energy and the Environment, a global perspective' class at California State University, Long Beach. We look at the sources, technologies, and impacts of energy on our environment.

Link to other class projects, some of Dr. Toosi's ENG-302i lectures, and other interesting videos.

Short video:

Step 1: Acquire a Vehicle

Find a lightweight vehicle with low rolling resistance. A two, three or four wheeler will do, depending on how much work you want to do, but the concept is the same. Four wheeled vehicles may be regulated under different laws. Of course the best vehicle is one that you already have, if you happen to have a three or four wheeled pedal powered vehicle. In the interest of simplicity, a three wheeler was chosen for my project. This Schwinn Meridian Trike was $250 new, readily available locally, and the basket provides a convenient location for batteries and solar panels with minimal fabrication.

The first thing to be done was completely disassemble the trike and paint it a bright 'fern' green. This step may not be necessary, but I felt that it was in my case since this is a school project that is supposed to grab your attention, and let you know that it is a true green vehicle. It is a vehicle that does not use gas, and does not plug in to a wall socket, which would defeat the purpose since electricity from the grid likely comes from a non-renewable energy source. It runs on pure solar energy.

Before painting the frame, I used this stage as an opportunity to reinforce the frame where the Batteries were going to mount. Lead acid Batteries are heavy, but they are relatively cheap.
One tube was welded in to distribute the load over 4 points on the axle carrier instead of two.
It also ties the rear sub-frame together, which makes the tube the load bearer rather than the weld beads, which may eventually fatigue and fail.

High pressure (65psi) tubes were equipped and the Trike was meticulously assembled in order to minimize rolling resistance.

While the welder was out a battery mount was fabricated, and bolts welded to the basket to be used as battery mount studs making removal easier. 12 volt LED's were put in the reflectors and wired as brake lights through the brake levers that cut the motor when you brake. They are wired through only one of the three 12 volt batteries.

Step 2: Drivetrain / Running Gear

The drivetrain consists of your electrical system and electric motor. The Electric Hub Motor kit was purchased from (, costs $259 and consists of a front wheel with an integrated brushless 36 Volt electric motor as part of the hub, along with the necessary components such as a twist grip throttle, brake levers that are wired to cut power to the motor, battery level indicator, and the motor-speed controller, 36V battery charger and a battery pack connector. Not sure if the kit is still available but they still sell everything needed. The customer service is basically an owners forum, which did prove useful in diagnosing a bent pin in on of the electrical connections.

The motor install requires a simple front wheel change, and routing the wires back to the controller which will be mounted under the rear basket. Slack must be left in the wires around the steering tube / fork juncture so they will not be in tension even at the maximum steering angle. The grips and brake levers are replaced with the new ones, and their wires also routed back to the controller.

Choosing the right battery is a compromise between price, weight, and range vs. charge time. Lots of money can be spent on batteries, but since I was on a budget, I had to take what I could get. I took a multi-meter to a local industrial liquidation warehouse and found 3 batteries for $20 each, and have worked good so far. (3) -12 volt, 20 Amp/hour batteries are run in series to make 36 volts. 20A/hr provides long range, with the trade-off being a longer charge time. Abattery cut of switch was added so the rider does not have to unplug the battery pack to shut the electrical system off.

Step 3: Charging System / Solar Panels

The solar panels need to be as large as possible to maximize the available wattage, but they also must provide the right voltage. Solar panels produce a range of voltages, which peak and drop, but the nominal voltage of the panel is what matters for selecting the right charge controller. I purchased 3 Q-cell brand mono-crystalline solar panels that I found on Ebay for $110 each. They produce 21.8 Volts peak and 17 volts nominal, at about 1.2 amps nominal. With the 3 panels wired in series, this makes around 66 volts peak and 51 Volts nominal, which is plenty over the 42V needed to charge the batteries. a basket was added in the front to accommodate the third solar panel.

From Ohm's law Power (P) is equal to voltage (V) times current (I), (P=V*I), so the panels produce ((17Volts*3)*1.2 Amps)= 61.2 Watts nominal, and over 80 Watts peak. A Maximum power point tracking (MPPT) charge controller tricks the panels by hiding the battery load from them and allowing them to operate at their peak power when conditions allow.

A charge controller was purchased from, where Mr John Drake was very helpful in assisting me and ordering a custom charge controller for my application. The controller basically takes the varying voltage / amperage input from the solar panel array and converts it into a constant voltage (42V) or current, to optimize charging the 36 volt source. Maximum input voltage to the controller is 100 Volts, so the peak of 66 Volts will not harm the controller. The controller is a Maximum power point tracking (MPPT) type, which charges faster as more sun is available, rather than at a set rate as most controllers do.

In order to charge the batteries in a practical amount of time, they need to charge about as fast or faster than the provided 110V wall socket to 36V charger/converter, which charges at a rate of 1.5 amps. At 1.2 amps the panels do not quite achieve this, but with the MPPT Controller it takes right around the same amount of time for a charge. The bike is stored in a location that gets a few hours of sun every day (where I live the sun is pretty reliable), which keeps the batteries topped off and ready to go whenever needed.

And for those of you wondering, the electric motor draws up to 20 Amps, and the 1.2+ Amps added by the solar panels do not make it go faster, since the 1.2 amps are routed through the controller and only serve to charge the batteries. The motor speed controller does not see this extra Amperage, and outputs just the same as without panels, except the batteries will stay charged slightly longer, (extending your range) with the net drain being (20-1.2)A= 18.8A rather than 20A without the panels. The motor only pulls 20 Amps when taking off though, so the draw is much less when at cruising speed. The motor speed controller cuts the voltage off at 32V to keep the batteries from going below 10.5V, but I monitor the voltage and try not to discharge the batteries below 36V.

Step 4: Solar Panel Mounts

Now you have to figure out how your going to mount the panels on your vehicle. Hinges were welded on the baskets to mount the panels and allow them to tilt for access to the basket, with rubber hold-downs on the other side to keep them from opening while riding.

Once your wires are all routed and zip tied, your batteries and panels held securely down, double check every thing and you are ready to go.

This Solar Powered Trike does about 15-18 mph depending on the weight of the rider. The furthest I have gone is a little over 10 miles with small hills and little pedaling, and the battery meter still read full (green) at the end of the trips.

At ten miles, the voltage drops to around 36V, safely above the controller's cut-off voltage. If the batteries are kept from discharging too low the panels take about the same amount of time as the plug in charger, since both the plug in charger and the solar charge controller charge with constant wattage. With constant wattage charging, Power, (P), and Ohm's law again (P=V*I), the charging current goes down as the voltage goes up, as the batteries near their fully charged state.

What this means is if you keep the voltage from dropping too low, the panels provide adequate current to match the charging speed of the plug-in charger, but if it drops below a certain point the panels are slower at charging. This is easily avoided since my typical trip range is around 3 miles or less, semi daily at most, so low voltage not an issue, but on longer trips I bring the multi-meter.

Cost Breakdown:
The Trike cost a little over $910 to build

Schwinn Meridian Trike

Q-cell Mono-crystalline Solar panels:

Charge Controller:
$ 95.00

Electric Hub Motor Kit
$260.00 also sells regenerative braking motor speed controllers

$ 60.00 Earl's industrial liquidation, Hawthorne, CA

High pressure tubes $ 15.00 Any bicycle store

Total $910.00

Other solar trikes / information

The last picture is a scan of a page straight out of Dr Reza Toossi's book,
Energy and the Environment, Sources, Technologies, and Impacts.

Book information / purchase

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Second Prize in the
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    355 Discussions

    would adding on a wind turbine sort of thing work, as you move the air pushes on the turbine great idea not very original though is there a way to collect some energy from the wheels while they spin using magnets to add to more energy gain. 4/5

    13 replies

    As mcpguru said you can't power the bike by a wind generator while it is running. BUT, you could have the wind generator working while the bike is parked to help recharge the batteries. This would work if you are in a windy enough area. But any wind would help. You would have to consider the added weight of the generator, because you would have to move it with the bike, unless you just had it mounted at home, or work to plug into your bike. Kent Secor In Cape Coral, FL USA

    They (the magnets) would slow down the wheels, yes, but you can always use them when you want the wheels to slow down, such as while applying breaks, it will not be a permanent source of energy, but some source. This idea isn.t riginal either though

    it's called regenerative braking. It's used by many electric cars.

     Hey, that could maybe be a good concept- when you hit a wall at 30+, it recharges the batteries! Sure, you'll break every bone in your body, but you'll have added a bit of power to the cells!

    Canno: I think you're on to something with your comment. If the magnets were in counter position on each side of the wheel, wouldn't the steel spokes break the magnetic field and produce electrical current??? Surely someone has thought of this already but what if.....? I get a kick out of these experts who continue to say "there's no free lunch in science" but there are many energy sources that are FREE already, e.g., the sun's heat and light energy for one.

    i think main problem with a generator is that it would be taking energy out of the system. Lets say you are going 30 mph and have a generator going...if you want to get any kinda of useful current out of the generator it's going to cause your setup to slow down therefore converting mechanical energy into electrical energy also take into account resistance in the wire/batteries causing loses due to heat, also any inefficiency in the motor anytime you have heat even small amounts it's all wasted energy. so no, "there's no free lunch in science"

    I cant resist.  There are trade-offs with the suns energy too, likegetting too hot, or the fact that the sun 'digests' materials here onearth (just had to replace the little skylight/vent top in the rv). ;).

    You can't do that, because the magnets would cause more resistance to the spinning wheel because of their attraction to the metal, so you still lose more energy than you generate.

    ha, the wind hitting the turbine would just add more drag to it and use more voltage.

    A better idea to get more power from the existing set-up would be to have a way to pivot the solar panel so that is perpendicular to the sun. This would take a minimum weight and would provide substantially more power to the battery. This would mean faster charging time.

    Sorry - no free lunch on energy, so the magnets would pull more energy out of the system than they put back in (unless you had a perfect system, then it would break even). The wind turbine might work to the the extent the wind is from nature, not the movement of the bike -- again, no free lunch on energy -- but if you were going to do that, just put up a sail and skip the weight and translation of kinetic to chemical to electric to kinetic.

    I am so not mechanically inclined so maybe this is a stupid question. Would it be possible to make this so when pedaling the bike helps to build up the charge in the batteries and would it be possible to use the electric motor as a pedal assist rather than for full power?

    2 replies

    This would make it harder to pedal and you wouldn't get any net gain. You could have a generator that you attach to the wheels to slow down instead of brakes. This is called regenerative braking and is used on many electric cars.

    I ask this because I have a bad ankle and knee. I have an electric bike which I love but a trike would be fabulous for grocery store runs, etc. I pedal my electric bike (good exercise!) and use the pedal assist mode or full electric power on hills and inclines.

    Thanks for alerting me to the Schwinn Meridian. Cool even without solar power.
    As an alternative I might look at the old 80cc 0.01Hp "Chicken Power" two cycle motor from the 1970-80's.
    What really bugs me is the power wheel uses 36V (rather than 12V) and you must use multiple 12V panels and batteries (adding excessive weight).
    Does anyone make lower voltage wheel motors or higher voltage solar panels?

    2 replies

    the only problem is that to get the same amount of watts (energy) at a lower voltage, current (amps) increases, so you need 3 12v batteries in parallel instead of series. You also need wire that is 3 times thicker.

    it's not 3 times thicker, it's 3 times cross-sectional area