Dear Stan,
As I disagree with your fundamental point when you say: 'my long-
standing recommendation for using power for the energy related
comparisons' I will outline the reasons for my disagreement by
interspersing some remarks in red.
On 2009/05/28, at 9:36 AM, Stan Jakuba wrote:
Thanks for writing Pat. I appreciate your sharing the impression of
MacKay's book and agree, with you except where I think MacKay has a
point in claiming that:
Energy consumption is power.
Energy production is power.
No, you are wrong here unless you add in some time factor such as 'per
second'.
To use another analogy, where you would you say:
Car distance is speed
I would say car distance is car distance as no time unit has been
mentioned or implied.
That is correct. This is why:
Energy, as the AMOUNT of it, is energy producED and it is indeed in J.
Agreed.
But energy producTION is power because it implies a continuous
process that involves time. In other words, energy produCED in 2007
is in joules but the energy producTION in 2007 is in watts.
Let's use solar energy as an example. The solar energy collector
collects as much sunlight as it can and converts a fraction of this
energy into electrical energy. It does this whether it is cloudy or
bright. At the end of the day, we can assess how much energy has been
converted from light energy to electrical energy but, at no time did
the solar panel need to be described as having a nominal power rating.
As the conditions vary continuously so does the power rating second by
second. That said, however, it is in the interests of the solar energy
panel supply company to specify their product according to the maximum
amount of energy that the panel can produce under ideal conditions
(very probably in an enclosed laboratory using artificial light).
Similarly, others who are selling coal fired or nuclear energy
converters tend to apply these idealised power ratings to their
products yet fail to mention that there is down time for cleaning and
maintenance, variations in fuel qualities, etc.
In short when it comes to power ratings on energy conversion plants,
what you see is not what you get. A better more truthful way would be
to specify the likely amount of energy you will be able to deliver for
sale to the real world. The specification of the design capacity of an
energy converter is quite irrelevant when it comes to selling the
energy. It is always sold in energy units (sadly not usually the
joule) and not power units.
You cannot but a watt of power anywhere in the world — the concept of
producing power or selling power is just not possible.
In yet another words, 100 EJ and 3200 GW both represent energy
usage in the U.S. The 100 EJ is the energy consumed in the U.S. in
2007, the 3200 GW is the (average) energy consumption in the U.S.in
2007. The wording of the leading sentence determines if J or W is
appropriate.
Surely it is much easier to decide if you are talking about energy or
power and then use the appropriate SI unit — joule for energy and watt
for power. Any other approach leads to a muddle. And this is not an
academic debate type muddle. This is a muddle that prevents our
politicians understanding a single word about climate change — for
example.
Now there are two points here:
It is better to write: The (average) power consumption thru 2007 was
3200 GW. I would word it that way, but the esteemed Prof. is not
wrong saying it his way. Obviously, his way may cause confusion. And
his kWh per day is silly as a base for comparison and the reasoning
for it is medieval.
To understand your sentence, The (average) power consumption thru 2007
was 3200 GW. is quite complex. I have to know what you might mean by
(average) before I can even begin to think about how much energy might
have been used. To find the energy used, and paid for, do I simply
multiply 3200 by the number of days in a year and then by the number
of seconds in a day?
The second point brings forth what I wrote earlier: Most of the
climate and energy debates are about POWER because they deal with
the amount of some kind of energy PER year, per day, per hour, etc.
For conversions between the two common ways to express power
consider that
1 GJ/y = 31.7 MW and 1 W = 31.5 MJ/y. His silly 1 kWh per day = 42 W
Most of the climate and energy discussions revert to power discussions
because the word, power, is itself totally corrupted by sales people
(as mentioned earlier) and by linguists. Consider these common words
and phrases:
Power station
This does not exist as power cannot be produced. Energy can be
converted at a particular rate but power is not produced for sale.
Power outage
Not possible. The supply of electrical energy might cease for some
reason but no power was supplied in the first place.
Power bill
Ridiculous, how do you charge for something that cannot be supplied.
I will not list all the many other misuses of the word, power, there
are too many.
In summary, the Prof. adheres to my long-standing recommendation
for using power for the energy related comparisons but he should
have worded his sentences better and stick with W. The joule per
time times time is ..... (I don't want to repeat myself).
The best approach in my view is to compare amounts of energy in joules
with other amounts of energy in joules. All else is completely
unnecessary obfuscation.
Look again at how I compared the energy consumpTION of the years
1997 and 2007 in the U.S. in the tables on the last page of the
attachment Ar-Energy-full.doc sent a few weeks ago.
Stan Jakuba
Your tables worked only because you had gone to the trouble of
comparing average production for a year in the same unit, gigawatt
(GW) but your heading for these tables, U.S. Energy Consumption, is
quite inaccurate as from the title we could reasonably expect the data
to be presented in energy units. To my mind, these tables should have
told us how much energy was used in these two years and not some
construction about average power ratings that I have to deconstruct to
find your meaning.
I think the rule is called 'Occam's Razor' where given two choices
between ways to analyse or to present scientific findings, it is
always best to choose the simplest of the two.
Cheers,
Pat Naughtin
Author of the forthcoming book, Metrication Leaders Guide.
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
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