A reader recently wrote:
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I need an electric pusher unit like yours that has possibly 30-60 hp for an electric assist on a 25 ft motorhome. It could be set for one cruising speed like 65 mph, I could turn it on when going down hill or up hill with my cruise control on. This should increase my mpg. I could also charge the batteries when going down hill.
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First of all, you're absolutely right. A pusher trailer
would increase your motorhome's MPG.
Unfortunately, beyond that I don't have any more good news for you. It's not really a practical approach, because you'd have to spend a
boatload of money on high tech batteries to make it work.
It's a question of the energy content of the batteries: it takes about 700 lbs. of lead acid batteries to equal the energy content of
one gallon of gasoline. How far would a pusher trailer with 700 lbs of batteries get you at highway speeds?
My electric car -
the ForkenSwift - with its 8 golf cart batteries (520 lbs worth) has as much energy on board as 3/4 of a gallon of gas. (Actually that's when they were new. Half dead as they are now, they probably have half that much power again - so 1/3 of a gallon of gas).
Of course you could use batteries with more energy density: nickel batteries (NIMH or NICAD) are better, and lithium batteries are better still. But you'll have to sell the motorhome to afford an advanced battery pack that's able to push it any distance
You can see why EV technology is used mainly for low power/low speed applications. Or why hybrid gas-electric cars are designed to use electric assist at low speeds in the city, rather than for extended periods on the highway.
It's all about the batteries.