Tuesday, April 05, 2005

Turning Hybrids into Plugins

From the NY Times:

Ron Gremban and Felix Kramer have modified a Toyota Prius so it can be plugged into a wall outlet. EnergyCS, a small company that has collaborated with CalCars, has modified another Prius with more sophisticated batteries; they claim their Prius gets up to 180 m.p.g. and can travel more than 30 miles on battery power.

As it stands, though, modifying a hybrid like the Prius to enable it to plug in would add perhaps $2,000 to $3,000 to the cost of a car that is already roughly $3,000 more expensive than conventional gas cars.
More stats from CalCars (.pdf)
Heavy lead-acid batteries add approx. 300 lb total, reducing mileage by approx. 5 mpg in standard HEV operation on city streets (because of acceleration losses), but by little or nothing at highway speeds (where wind resistance is the main factor)
Under 10-mile all-electric propulsion (at under 35 mph), infinite mpg (i.e., no gasoline use) plus 262 grid Watt-hours/mile vs. 50-60 mpg as a normal HEV.
All-electric miles: power cost approx. 1.25 cents/mile (assumption of 250 Wh/mi and 5 cents/kWh on California off-peak EV "E-9" (PG&E) rate, and not amortizing battery cost), vs. approx. 4.5 cents/gasoline mile ($2/gallon, 45 mpg)
I think the hydrogen economy (and cars) are just a bunch of hype. Because you can't drill for hydrogen, hydrogen is really just a battery, a way of transporting energy and not a particularly good one at that. We should be focusing on trying to make our energy use environmentally friendly and renewable and using hydrogen cars only if it is the best way to produce these two goals. If other technology like biodiesel, hybrids or electric cars are better (and I think there is lots of evidence that they are) then we should go with them.

So I am intrigued by this idea of adding extra batteries to hybrid cars and allowing them to run on either electricity for short trips or gasoline for long trips. This gives the user a lot of flexibility without requiring any expensive infrastructure changes to create new hydrogen fueling stations. But the downside to this flexibility is that you have to pay for both a gas burning engine and an electric motor which means such hybrid cars will always be more expensive than single use cars. Will the extra cost be worth it? I'm not sure. The stats from CalCars are interesting, you add 300lbs of batteries and recharge the battery of the grid at night. Seems economic in terms of electricity vs. gasoline, but the amortization of the batteries is not a trivial expense.

I still don't get how the recharging works. In a normal Prius, the gasoline engine is used to recharge the battery. In these new Priuses, in order to use electricity from the grid, your battery has to be empty when you get home. Not sure how you get the Prius not to recharge the battery, and if you do that doesn't it reduce your fuel efficiency? But this is definitely an idea to keep your eye on.

1 comment:

Anonymous said...

I think the "$3000 more" is some kind of projection ... if I read it correctly, the prototype "PRIUS+" actually uses $15000 worth of additional batteries. That's quite a lot, to hold just $1 of electricity downloaded each night.

FWIW, I think the thing to do is get people into the existing high-mileage cars.

We can kick up our national mileage by 50% just by making (slightly) different choices.

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