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 thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA . Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada , the UK , and the USA . See http://www.metricationmatters.com for more metrication information, contact Pat at [email protected] or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
