Re: Fuel Cells and "green" energy

[Rick Tarara <rbtarara@SPRYNET.COM>]

Dan,

These are the numbers I see at the DOE site

1999 figures for the U.S. (DOE numbers converted to kWh by me)

TOTAL Energy resources used:  28,303 x 10^9 kWh
TOTAL Energy DEMAND:           21,063 x 10^9 kWh
Total Electrical energy used:         3,346 x 10^9 kWh
Total Hydro                                     312 x 10^9 kWh
Total solar                                          3 x 10^9 kWh
Total wind                                           4 x 10^9 kWh

Where the difference between the first two numbers IS the thermal efficiency
effect you note.  These numbers have electrical use at 16% of DEMAND and
hydro at the levels I previously quoted.  I concur on the 35-36% TOTAL
energy used to produce electricity.  The Wind and Solar number amply
illustrate how much must be done to make these into major players in our
energy future.

There is a major problem here in that wind and solar are not energy on
demand  resources.  Wind is a little more reliable but the sun sure doesn't
shine at night!  Therefore, to be used directly they both are best used to
supplement current power sources--to provide extra energy at peak times.
However, if you want to project wind and solar as eventually providing
25-50% of the TOTAL energy needs then these must be stand alone sources.
You might try to do that by using the wind and solar to make hydrogen (where
this thread began) and then use the hydrogen to power conventional style
power plants--now very clean burning. The problem with that is that you now
have the thermodynamic efficiency losses plus losses in the hydrogen
production such that you must now produce
4 kWh of wind and solar energy for every 1 kWh you can deliver to consumers.
I don't know what the overall efficiency would be if we used giant fuel cell
complexes running off the hydrogen--maybe that is better.  Anyway, to get
large amounts of solar and wind into the system as 'energy on demand'
sources may require up to 4x the generators and solar collection areas as
would be needed if these were used directly.  Such a system would then
require tens of thousands of square miles of photovoltaics and 10s of
millions of large (megawatt) wind generators.

Rick

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Richard W. Tarara
Associate Professor of Physics
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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----- Original Message -----
From: "Daniel Schroeder" <DSCHROEDER@CC.WEBER.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, June 14, 2001 6:33 PM
Subject: Re: Fuel Cells and "green" energy


> > But today hydro produces only 8.5% of our electricity and electricity is
> > less than 20% of our total energy demand--so about 2% of the total.
> > Improving existing installations by 25% only brings us up to 2.5% total
and
> > less than 11% of the electrical....
> >
> > Rick
>
> Rick, according to the 1999 Annual Energy Review, hydroelectricity
> accounted for 3.2 QBTU in 1999, or a little over 3% of total U.S.
> energy consumption.  As you know, 2/3 of this figure is fictitious
> energy, added in to make the comparison between hydro and thermal
> generation a fair one.  (Thermal plants are only about 1/3 efficient.)
> Electricity *consumption* was actually only about 12% of total U.S.
> energy consumption in 1999, but the fuel used to generate electricity
> was about 35% of total U.S. energy consumption.
>
> Dan