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.
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 (www.Goldenmotor.com), 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 www.solarsellers.com, 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.
The Trike cost a little over $910 to build
Schwinn Meridian Trike
Q-cell Mono-crystalline Solar panels:
$ 95.00 www.solarseller.com
Electric Hub Motor Kit
$260.00 www.goldenmotor.com- also sells regenerative braking motor speed controllers
$ 60.00 Earl's industrial liquidation, Hawthorne, CA
High pressure tubes $ 15.00 Any bicycle store
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
Second Prize in the
Park Tool Bike Month
First Prize in the
The Instructables Book Contest
Second Prize in the
Discover Green Science Fair for a Better Planet