Not sure if you are not confusing a file name for the table title. Should you
be looking for HHV, typically, it is 10 % more for hydrocarbons.
Concerning the ethanol numbers, ball park figures, that table was written at
the time Dr. Wang was probably still in higschool. His paper and the plethora
of others prove only one thing - there is a disagreement. Listening to both
sides, I interpret it to mean that any energy gain/loss from using ethanol in
cars is going to be tiny (probably not worth it - Sisyphus' work). But the
increase in food prices will not be tiny. The net monetary loss is assured. The
world has been thru similar ethanol dreams on and off for 100 years.
As you hint, I also say that if everybody wrote their papers in SI, the ethanol
(or any other energy topic) would be far less "debated." Conclusions could
actually be reached even during public forums attended today mostly by people
using various units to their advantage including interchanging the terms energy
and power as seen fit or ignoring the difference altogether.
Stan Jakuba
----- Original Message -----
From: John M. Steele
To: U.S. Metric Association
Sent: 09 Apr 03, Friday 15:44
Subject: [USMA:44295] RE: Efficiency, was Energy and power units
I agree with your points about the joule and no other unit to measure
energy. Also I found your table of fuel LHV values very useful (Note: I only
found LHV, I did not find the HHV values as indicated in title).
However, I would like to take issue with the footnoted efficiency
values in note (3).
If it took 60 MJ of electricity to generate 1 kg of H2, having an LHV
value of 120 MJ, this would be a perpetual motion machine of the first kind. I
would simply connect to a 100% efficient fuel cell, and generate 120 MJ of
electricity, paying back the 60 MJ to make the H2, and using the other 60 MJ to
make extra H2 or light light bulbs.
A couple of links describing the theoretically reversable reaction at
the activation potential of 1.229 V and Gibbs free energy of 237.13 kJ/mol.
http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/electrol.html
http://en.wikipedia.org/wiki/Electrolysis_of_water
To drive the reaction at an acceptable rate (not the infinitesimal rate
of reversible reactions) you probably need 60 MJ of excess energy on top of the
the 120 needed at reversible conditions (180 MJ total electrical input)
Secondly, I would like to take issue with the energy stated as required
to make hydrogen by steam reformation. Take a look at Table 6 on pdf page 21,
document page 13 of this NREL report:
http://www.nrel.gov/docs/fy01osti/27637.pdf
It reports total process requirements per kilogram H2 (120 MJ, LHV) of
159.6 MJ natural gas, and 23.6 MJ of other energy for a total of 183.2 MJ input
for 120 MJ output. (they then go on to claim a higher efficiency based of HHV
of hydrogen). Again if I could produce hydrogen totally 120 MJ of energy with
only 20 MJ of energy input, that would again be a perpetual motion machine of
the first kind.
--- On Fri, 4/3/09, Stan Jakuba <[email protected]> wrote:
From: Stan Jakuba <[email protected]>
Subject: [USMA:44288] RE: Energy and power units
To: "U.S. Metric Association" <[email protected]>
Date: Friday, April 3, 2009, 8:49 AM
I agree with Pat. The SI unit of energy (any kind) is the joule and
that of power (any kind) is the watt, as we all know. Using SI units "create a
level playing field," indeed. It is obvious to anyone who works in several
fields or professions concurrently that using SI (a coherent set of units)
enables one to switch among values without conversions. Among the many
engineering professions, only the electrical people insist on Wh; everybody
else goes with Btu, cal, ft-lb, quad, etc. The joule only is hopefully in the
future for all. Can you imagine the attached table in Wh?
To illustrate the stupidity of unifying on kWh, I had a manuscript
rejected recently because the editor did not distinguish between W and Wh and
consequently thought that my numbers were incorrect. Fortunately, he informed
me of the rejection and pointed to the "wrong" numbers. Being a considerate
person, he did listen to my defense and accepted that there is a difference
between kW and kWh. How many such occurrences are happening daily? How many
editors would bather with checking themselves?
Accepting J and W is a way to avoid such mistakes. Unfortunately, it
requires a bit of education many are unaware is needed. It is so much easier to
say - "nobody uses the joule." How would the newton or pascal caught on if
everybody were waiting for it to catch on without anyone ever using it. The
author of the book I recommended (withouthotair) is guilty of the anti-joule
attitude also
Fortunately, I see the new graduates publish papers in SI. So there
is a hope. Soon we'll be celebrating 50 years of SI existence.
Stan Jakuba
----- Original Message -----
From: Martin Vlietstra
To: U.S. Metric Association
Sent: 09 Apr 02, Thursday 17:21
Subject: [USMA:44281] RE: Energy and power units
Pat,
While you might be correct, I was stating the actual position in the
UK .
I checked some recent statements and the cost of my gas is 2.26p/kWh,
while the cost of my electricity is 9.02 p/unit [sic].
As long as I am aware that a “unit” of electricity is one kWh, I can
see that the cost of electrical energy is four time the cost of gas energy.
Thus, heating using electricity is much more expensive than heating using gas.
If I am interested in the cost of the energy to the planet, then yes, I will
take into account the cost of production and transmission. In the UK (where
there are a number of gas-fired power stations), I believe that there are
considerable losses in the generation of electricity, so gas heating does less
harm to the planet that electrical heating. When I was living in South Africa
, the inverse was true.
Regards
Martin
----------------------------------------------------------------------
From: [email protected] [mailto:[email protected]] On
Behalf Of Pat Naughtin
Sent: 02 April 2009 07:50
To: U.S. Metric Association
Subject: [USMA:44279] Energy and power units
On 2009/04/01, at 4:17 PM, Martin Vlietstra wrote:
“What is the rationale for billing in kilowatt-hours?”
To create a level playing field with the electrical industry.
Dear Martin,
With respect, using kilowatt-hours to bill people for electricity and
for gas does not, In my opinion, create a level playing field. I think that
many people have difficulty distinguishing between kW and kWh and between their
related physical quantities power and energy. It seems to me that power and
energy are more clearly identified when power is measured in kW and energy is
measured in kJ (rather than power measured in kW and energy measured in kW.h).
Consider an example where natural gas is supplied directly to your
home with an energy content of (say) 53 MJ/kg compared to the same gas supplied
to an electricity turbine to produce electrical energy that is then transmitted
through the grid to your home. The gas that is supplied to you directly should
not be compared to the energy supplied as electrical energy because of the
production and the transmission losses via this pathway.
Cheers,
Pat Naughtin
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the modern
metric system smoothly, quickly, and so economically that they now save
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