SOLAR-POWERED TRANSPORTATION
SOLAR-POWERED TRANSPORTATION
Yes, folks, it is possible to enjoys olar-powered transportation in an off-grid and off-road system. After several years of studying all the angles, we finally came up with a combination that has survived thorough testing during the summer.
Our site is in McCarthy, Alaska, a remote bush communitywhere my partner, Meg Hunt, and I make our home. For eleven years we've enjoyed the full benefits of solar power.
We wanted to extend our solar usage to include transportation. None of the many vehicle conversions were exactly what we wanted. Then the Bombardier Neighborhood Electric Vehicle (NEV) came on the market. We liked what we saw. But could the NEV, designed for charging from 120 volts AC, be converted to work from solar panels? I am happy to report that the answer is yes.
Performance
This is a neat little car with plenty of power for realwork. It is fun to drive - very quick to turn or accelerate. We have yet to try a hill it won't climb or a trailer it won't pull. Our community is separated from the road system by a river. The farthest we can drive is fivemiles (8 km), climbing about 800 feet (244 m) in the process. With driver and passenger, this takes less than half the NEV's battery charge. The downhill return is practically a free ride. We sized the PV array to allow this ten mile (16 km) round trip every other sunny day. Inpractice, one clear day gets the NEV back up to full charge.
The Numbers
The NEV is 100 inches long, 55 inches wide, and 61 incheshigh (254 by 140 by 155 cm). The curb weight is 1275 pounds(578 kg). The drive motor is a 72 volt, 4 KW, shunt-wound DC motor, geared directly to the rear differential. Power is stored in six GNB Type M83CHP12V27 Champion 12 volt batteries connected in series. These are sealed lead-acid batteries with absorbent glass mat separators between the plates. They are rated at 110 AH at a 20 hour rate and are designed for EV use.
The on-board charger draws 15 amps maximum at 110 volts. When the batteries are discharged to their design maximum, 80% depth of discharge (DOD), it takes eight hours to recharge. A sophisticated sensor and display system reportsstate of charge (SOC) and status of the power system. A separate 12 volt, 24 AH battery supplies power for light sand accessories. The on-board charger recharges this auxiliary battery and the main battery. It uses a complex charge program for the propulsion batteries, finishing witha 2 amp equalizing charge, up to 110% of the previous discharge.
Maximum speed of the NEV is 25 mph (40 kph), limited by the motor controller for safety. The design range is 30 miles (48 km). This assumes level ground on a paved road, non existent here in McCarthy. The NEV is fully equipped with headlights, turn signals, and seat belts. It is street legal where allowed by state slow vehicle laws.
Solar Modifications
We wanted to be able to charge from both the PV array andan AC household outlet. Thanks to extensive and helpful discussions with the design engineers, we can do this. Theon-board charger rectifies the AC power and uses amicro processor-controlled DC to DC converter to recharge the battery. I replaced the AC cooling fan in the chargerwith a DC fan, powered through a full-wave brid gerectifier. So we can charge the Bombardier on either AC orDC.
The PV array design was based on a season of solar power data. We logged our data with a Fluke 87 meter from theout put of a single 48 watt Kyocera PV panel. We designed anarray of seven 75 watt BP panels connected in series fornominal 120 volts DC at about 4 amps in full sun. This was not enough power to run the charger for its full programmed charging regime, but enough to make it work. With our marginal PV charging capacity, it shuts down after two hours. I installed a fused panel on the NEV dash, withjacks giving direct access to the main and auxiliary battery terminals. Parallel pin jacks allowed easy monitoring of the battery voltages.
Switching
At Alaskan latitudes, this is obviously a summer vehicle.Very little sun is available in mid-winter, and sub-zero temperatures degrade battery performance. But no solar enthusiast is going to let all those PV panels sit idle for 6 months of the year, just when they could offer a big boost to our house system. So we've set up a system that allows us to switch from EV battery charging to charging our house battery bank.
The change-over requires switches - lots of them. Each panel connects to a double-pole, double-throw, center-off switch. In one position, all seven panels are connected inseries. In the other position, the panels are connected inparallel to a 12 volt bus bar feeding our house system. This arrangement runs the panel outputs through a lot ofwires. In order to minimize losses, the switch box is located within six feet (1.8 m) of the array.
A separate switch allows us to select the series output from either six or seven panels; six for direct EV battery charging and seven for the on-board charger. When we switch the array to six panels in series, we connect it directly to the main 72 volt battery. This works fine, but it does require manual monitoring and control. A 72 volt charge controller will be the next improvement. My present practice is to charge direct, close to the battery gassing point, then switch over to seven panels and the on-board charger to finish the charge.
The big unknown here is how this modified charging method will affect battery longevity. Good management for alead-acid battery means only withdrawing half of its capacity and then fully recharging it. By retaining the AC charging option, I do have the occasional chance to do a programmed recharge cycle by plugging into a diesel generator.
Downside
The designers of the electrical and propulsion systems ofthe NEV have done a first-rate job. But prospective buyers should be aware of some peculiar deficiencies.
When it comes to servicing, this vehicle is not just user-unfriendly - it is downright user-hostile. The mainand auxiliary batteries and the on-board charger are mounted on a single tray weighing 480 pounds (218 kg). To access these components the NEV must be put up on a rack,and the tray lowered by a fork lift using a special pallet.The main fuses for propulsion, auxiliary batteries, motor controller, and on-board charger can be reached only by removing the battery tray. If you need a forklift to changea fuse, someone was asleep at the design board.
The vehicle is furnished without a spare tire or jack,which is very optimistic for a street vehicle with a 30 mile (48 km) range. Fortunately, a standard four lug, twelve inch (30 cm) trailer wheel serves nicely as a spare and fits in the trunk.
On a dry gravel road, driver and passenger are enveloped in clouds of dust even with the canvas hatch and doorcovers completely closed. Liberal use of duct tape and silicon sealer helps, but dust still boils up through the battery compartment vents.
Success
We racked up an estimated 100 happy miles (161 km) on the NEV this past summer (there's no odometer). It has delivered just what we wanted at this remote site - a way to get around, haul supplies, and have a little fun. Taking visitors for demonstration rides is part of the fun. Freedom from hauling gasoline or diesel oil ove r a long and inconvenient route was a big motive for exploring EVoptions in the first place. But the real reward was the satisfaction of designing the PV-powered system for pollution-free transportation. Compared with noisy, gas-powered ATVs common in this area, the silent running of the NEV continues to astonish onlookers. And if you want to use wheels to sneak up on a moose, go electric!
Written by: Ed LaChapelle
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