Writer George Monbiot's recent Peak Oil article entitled "If Nothing Else, Save Farming" included this comment:
There are no obvious barriers to the mass production of electric tractors and combine harvesters: the weight of the batteries and an electric vehicle's low-end torque are both advantages for tractors.
I read this and immediately tweeted the question "Where are the electric tractors?"
Well, scientist-turned-farmer John Hewson has responded to Monbiot's assertion with an explanation that lacks Monbiot's, shall we say, sanguinary spirit:
[T]o anyone who has worked with farm machinery, especially on smaller and poorer farms, the idea of electric tractors will seem ridiculous. So far, electric traction has been developed only for transport, and most successfully in railway trains. The development of batteries and control systems has been directed at the needs of passenger cars, which do not have to pull heavy loads at low speeds for long periods.
Electric tractors do exist, but are light machines similar to ride-on lawn mowers, with power outputs of around 40kW. Typical farm tractors have outputs of 100kW-200kW, and no currently available batteries could provide anything like this amount of energy, or anything approaching the working life of a diesel engine.
The best lithium-ion electric car batteries and motors work at high voltages (500V for example). As an engineer, I would blench at the idea of maintaining a 100KW, 500V system in a damp and muddy farmyard, let alone carrying out running repairs in the middle of a 50-hectare field, in the rain.
As far as I know, electric traction for farm machines has not yet been even considered as an option. If it ever reaches the stage of production, it will be very expensive indeed -- far beyond the budgets of even large farms.
But here's the good news. Hewson appears to be, to a large extent, wrong!