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Re: (ET) Fwd: [EVDL] The Case for the Electric Tractor




On Fri, 24 Aug 2007, Rod Hower wrote:

Much higher efficiencies are just around the corner...
http://www.udel.edu/PR/UDaily/2008/jul/solar072307.html

42.8% !!!!

Keep in mind that these high efficiencies are achieved through the use of multi-layer (multi-junction) semiconductors, to minimize losses of photon energy above the band-gap energy. THe problem is that the cost of making the cells ends up going up roughly at the same rate as the efficiency. So, while you would need less surface area, it wouldn't necessarily cost less to get the same total energy captured. Also, these high efficiency numbers are usually based on lab tests in which the PV is kept fairly cool (being tested in low light and heat conditions in a lab, rather than on a rooftop). As temperature goes up, the effectiveness of the electric field at the N-P junction of the photovoltaic becomes less effective at directing the freed electrons, and efficiency decreases sharply. That's why the PVs in use now achieve efficiencies only in the low teens, while when tested in labs they were hitting 20% and higher.

Mike


--- David Roden <etpost drmm net> wrote:

On 24 Aug 2007 at 15:11, Darryl McMahon wrote:

solar panels are the most efficient way of
converting
radiant sunlight energy into electricity
(approaching 20% vs 1% or
much less for plants).

Where do they get this number?  I think I've read
that mass-produced PV is
around 10% efficient at normal operating
temperatures.

I may have missed it, but they also don't seem to
have figured battery
amortization into the operating costs.  For road
EVs, this is the largest
contribution to per-mile expense, and I'd bet that
this will also be true
for an electric tractor in daily service.

I'm not saying they're wrong or that they shouldn't
explore this option.
Far from it!  It's just that I think we as EV fans
hurt ourselves when we
aren't realistic about the utility and costs of
electric transport.


David Roden - Akron, Ohio, USA

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