Roof top range extenders for EVs?

[larryg]

Most of the electric cars that are scheduled to appear in the next 3
years (Aptera, Nissan, iMiev, Th!nk, Tesla S) appear to have
all-electric ranges around 100 to 160 miles.  So I wonder if there
would be a significant market for some time for add-on range extender
kits.  The range limitations appear to be due more to the cost of
batteries than to limits on their size and weight.  It is not clear
how long it will take to reduce the cost for much longer ranges.

Rather than building in a range extender, like the GM volt, where you
own it and have to carry it around with you all the time, an add-on
kit would let you add it for only the %5 to %10 percent of the time
when you might actually need it.  Therefor you would have all the
advantages of a pure electric car %90 to %95 percent of the time.

I see at least two possibilities for these kits:

   (a) A very small trailer.  See:
              http://evnut.com/rav_longranger.htm
       for an example of a 500cc 20 KW motorcycle engine in a
       350 lb extender trailer for an electric RAV4 that gives the
       same fuel economy as the gasoline engine RAV4

   (b) An aerodynamic rooftop car carrier.

Now the trailer would be easy to add, but even a small trailer is
difficult to maneuver and backup, so I am wondering if a range
extender kit for a rooftop carrier would be small and light enough to
provide the necessary range extension?  We do know that aerodynamic
rooftop carriers are very common and accepted by the motoring public
and can hold 18 or more cubic feet for storage, but I don't know if
the weight of such as engine would be acceptable.

The 350 weight of the above trailer seems a lot, but I wonder if this
is mainly due to the fact that it is a variable RPM engine that is not
specifically designed for this operation, and if the wheels, axle, and
hitch might add much more weight that a rooftop carrier?

From my calculations, for a typical 3000 lb car with a Cd of 0.28, it
would only require a gas engine with about 30 HP to provide the
*average* power needed to keep the batteries charged at 75 MPH.  If a
simple fixed RPM engine can be made small and light enough we could
envision this scenario:

   (a) Most of the time you drive your pure EV w/o the range-extender

   (b) If you know you are about to go on a long trip, or suddenly
       find yourself in that situation, you drive to a "service"
       station where they add the range-extender to your roof rack.
       When done, you return to the same franchise and have it removed.

This way you are relived of any maintenance or storage associated with
the range-extender.

Any thoughts on the practicality of this idea would be welcome.

  -- Larry

[kevin gaw]

Larry
I met you at the SEVA August meeting and concurred with the validity of the idea.  Email me at kevingaw2003@yahoo.com and we can discuss the issues you raised further. I see the range extender in a much more frequently utilized function, much greater than the 95% non-utilization you mentioned.