ELECTRIC TRACTORS

Enlarge Image Image Gallery Designer Steve Heckeroth using his versatile solar-powered tractor.The adjustable shade canopy is made of PV panels that charge the tractor's batteries. PHOTO BY Steve Heckeroth (2)

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ENERGY & ENVIRONMENT

The case for solar-powered.

The world is clearly running out of oil and gas, yet most people ignore the coming crisis. Food production and distribution in the industrialized world have become so dependent on petroleum use, it's hard to imagine how agriculture will function without this fuel.

The most promising option is solar-powered electric tractors, which offer several advantages over gas diesel-powered tractors. Electric motors can operate at more than 90 percent efficiency, while combustion engines are less than 15 percent efficient. Electric propulsion is ideally suited to high torque, slow-speed agricultural operations. Electric motors have only one moving part and require little maintenance. Internal combustion engines, on the other hand, have hundreds of moving parts and require a lot of maintenance.

Electric motors don't idle, which saves energy. Plus. while the vehicle is going downhill or braking, an electric motor can become a generator and return energy to the battery. This process, called regenerative braking, further increases the efficiency of electric propulsion and cannot be duplicated using other technologies. Electric-wheel motors eliminate the need for an internal combustion engine, transmission and differential. allowing new options in the design of tractors. Mounting an electric motor in the hub creates a self-propelled wheel that can provide new levels of versatility and visibility.

If an electric tractor is combined with photovoltaic (PV) charging, whether on the tractor itself in the form of a solar panel shade canopy or on the roof of a building, no other fuel source is necessary N . Unbreakable PV panels and PV roofing that can turn any sunny surface into a power station are now available with a 20-year warranty. Photovoltaics provide an ideal energy source for agriculture because the growing season coincides with the availability of solar energy.

The biggest obstacle to the performance of most electric automobiles is battery weight. Unlike automobiles, tractors depend on weight for traction, thus heavy, deep-cycle, lead-acid batteries that are inex pensive, recyclable and long-lived can be used to great advantage in an electric tractor.

In addition to an onboard battery pack between the traction wheels, auxiliary battery packs can be loaded on the tractor's three-point hitches to balance implement weight and extend operating time. Electric linear actuators (no-maintenance screwjacks that push and pull) replace less efficient hydraulics for steering and for positioning the three-point hitches. The electric tractor can include a separate power take-off (PTO) motor that can be sized for specific needs and operate independent of ground speed.

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