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By Robert Rapier on Feb 6, 2012 with 41 responses

Confused about Energy and Power?

Tags: energy, power

When I recently solicited feedback for topics to cover for my upcoming book, several people requested that I discuss the difference between energy and power. Just two weeks ago Congressman Dana Rohrabacher, R-Calif., who is on the House Committee on Science, Space, and Technology, admitted that he’s “not educated enough to know the difference between the terms … energy and power.” You would certainly expect that someone who influences legislation over science and technology would know the difference, but it is true that people commonly get confused between the two.

So this weekend I wrote up a sidebar for Power Plays discussing the differences, which I share below. If you believe that a point could be clearer, or if anything about my explanation is confusing, I would be happy to hear reader feedback.

Energy, Power, and Units of Measurement

There are a number of potentially confusing units of measurement for energy and power. The first thing to understand, however, is the difference between energy and power. Technically speaking, energy refers to the capacity of a system to do work. In this definition, “a system” could be a gallon of gasoline that contains 115,000 British Thermal Units (BTUs) – a unit of energy. In addition to the BTU, some other units of energy are the joule (J), the calorie (cal), and the watt hour (Wh). Multiples of these units have abbreviations like kilo (one thousand) or mega (one million), so one kilowatt hour (kWh) is one thousand watt hours. Each of these units can be converted into the other. One BTU is equal to 1,055 joules, 252 calories, or 0.29 watt hours.

Power is the rate at which energy is consumed or generated. One BTU of gasoline refers to the energy content, but gasoline consumption over time could be measured in BTUs/hour, a unit of power. Other units of power are joules/second, calories/day, or watts.

A 100 megawatt (MW) power plant is capable of generating energy at the rate of 100 megawatt hours (MWh) per hour. People frequently confuse the energy unit of watt hours with the power unit of watts. This is probably because other measures of power are defined per unit of time (e.g., calories/hr), and therefore it would seem logical that a kilowatt hour would be a unit of power. Alas, it is not. However, it should be clear that a joule/second is a unit of power (energy consumed over time), and that’s what a watt actually is: 1 watt = 1 joule/s. Someone thought it would be a good idea to call it a watt instead of a joule/s, and many people have been confused ever since.

Link to Original Article: Confused about Energy and Power?

By Robert Rapier

  1. By Bob Armantrout on February 6, 2012 at 8:44 am

    What throws me is that a kilowatt hour is a measure of energy, yet a watt is a measure of power. If power is a rate (energy over time), how does this make sense?

    It’s like driving on a parkway, and parking in a driveway. :)

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  2. By robert on February 6, 2012 at 9:45 am

    A nautical mile is one knot hour. Energy expenditure depends on how hard you pedal times how long you pedal. A kilowatt is how hard you are pedalling. An hour is for how long.

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  3. By tom-g on February 6, 2012 at 10:33 am

    This is a very informative posting.  For 20 years my daily work took me to a nuclear power plant which was a challenging and fun job.  Thinking back I can remember hundreds of times kW was used instead of kWh but for the average American does it really matter?  Outside of the engineering or scientific community, how important should it really be?
    I get a kick out of J. Leno’s man on the street routine.  The routine where he asks seemingly simple questions about our country and some of the people in prominent leadership positions like our President, Vice President and Secretary of State.  I was shocked in the beginning to learn the number of people who couldn’t even identify these individuals yet they said they voted for them, LOL.  That was until I remembered what my life was like when I was their age.  I was so busy going to school and raising a family that there never seemed to be enough time in a day to learn everything.  If I had chosen a career as say a plumber instead of an engineer, I might still not know the difference between a kW and a kWh.
    So is the difference between kW and kWh important?  Well in the engineering or scientific community it certainly can be. Should everyone know the difference maybe – maybe not.  I would LIKE everyone to know the difference but that expectation might not be very realistic  That might be like asking an Iron Worker who builds 30 story tall buildings to give a 10 minute talk on global warming.
    Very good posting RR.

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  4. By paul on February 6, 2012 at 11:37 am

    I’m in a rush but “Other units of power are joules/second, calories/day, or watts.” seems to make the error you are trying to fix. Watts/some time period would get you power. An analogy/illustration you might try: the same gasoline (energy) can go in to a 500 HP hot rod or a 45 HP gas sipper or a moped. but they have very different powers. Keep after it.

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  5. By rrapier on February 6, 2012 at 12:07 pm

    paul said:

    I’m in a rush but “Other units of power are joules/second, calories/day, or watts.” seems to make the error you are trying to fix. Watts/some time period would get you power. An analogy/illustration you might try: the same gasoline (energy) can go in to a 500 HP hot rod or a 45 HP gas sipper or a moped. but they have very different powers. Keep after it.


     

    It is explained in the post. A watt is the same as one joule per second. So a watt is per unit of time, they just shortened the definition into something that doesn’t have time explicitly shown. It is there, you just don’t see it.

    RR

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  6. By Rufus on February 6, 2012 at 1:19 pm

    So, a kilowatt is a thousand joules per second?

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  7. By rrapier on February 6, 2012 at 1:21 pm

    Rufus said:

    So, a kilowatt is a thousand joules per second?


     

    Correct.

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  8. By John L Palmer on February 6, 2012 at 1:26 pm

    The confusion, which I had to, is you write joule/second but not kilowatt*hour.

    Plus when you say joule second, you often drop the ‘per’ and when you say kilowatt hour, you never say the ‘times’.

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  9. By mac on February 6, 2012 at 4:44 pm

    Joules measure the quantity of electrical energy flowing:

    1 ampere through 1 ohm of resistance for 1 second. = 1 joule.

    Amperage or “amps” are the volume of electrons flowing through a conductor, Voltage is the EMF or electromotive force that “pushes” the electrons (amps) through a conductor, usually a copper wire.

    Electric appliances such as light bulbs and toasters are actually semi-conductors. like rge nichrome wire in toasters and when you try to fire electrons (amps) through it with 115 vac the electrons, they are transformed into heat and light because of the resistance of the wire. The same is true of tungsten light bulb filaments. The excess energy (electrons) must go through the resistance of the tungsten filament but they can’t and the resultant excess electrical energy is thereby transformed into useful light and heat.

    All those Joules up in smoke !!!
    (just kidding)

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  10. By mac on February 6, 2012 at 5:11 pm

    Joules describe the flow of electrons over time through a conductor. How many watts a certain appliance requires to operate describes how much load it brings to the electrical system, When the watt drain overcomes the joule supply, then look out ! Your friendly telephone pole transformer is about to go POP !!

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  11. By paul-n on February 6, 2012 at 5:39 pm

    This whole debate would be a lot easier if it wasn’t confused by America continuing to use Stone Age units instead of SI (System Internationale) units and the metric system.  

    Even though, as an Australian, I can;t stand the French, I will gladly acknowledge that the metric system is a brilliant invention of theirs.

     

    There is further confusion in that energy can be of different types – kinetic, thermal and electric (and nuclear), and these have had their own units of measure (ergs, btu’s etc) but they can all be equated to each other.

    Regardless of what unit of energy you are using, power is *always* energy/time.

    The Joule was chosen as the name of a convenient *unit*, derived from kinetic (mechanical) energy – one Newton of force x one metre of distance.

    The Watt, is one Joule per second, kilowatt is one thousand of them

    A kiloWatt-hour is one kiloWatt for one hr-3,600kJ

    A kiloWatt per hour is actually a rate of change of power (e.g an engine increased its power(load) by one kilowatt each hour )

     

    Plus when you say joule second, you often drop the ‘per’ and when you say kilowatt hour, you never say the ‘times’.

    But this is a standard convention, just like a “manhour”.

     

    In contrast to what Tom says, I think that since every household pays for electricity by the kilowatt-hour, they should indeed understand what the difference between kW and kWh is.  Everyone knows what a gallon of gasoline is (energy) and they know (or should know) their mpg (rate of use of energy), this isn;t that much different.  IF we have kids in school for ten years, they should at least come out understanding this, amongst many other things…

     

    My physics teacher had the best analogy – ever – to make people understand this.  Energy is like money – $ are the same as Joules, and the cash flow – your hourly wage, or monthly mortgage payment etc – is like power.  

    And, no matter how you slice it , when you run out of either – energy or $ – you are in trouble!

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  12. By Optimist on February 6, 2012 at 6:34 pm

    So is the difference between kW and kWh important? Well in the engineering or scientific community it certainly can be.

    Tom, confusion never is a good thing. A few years ago I discovered by change that one of the USEPA high-ups, in charge of developing a mpg rating for electric cars, didn’t understand the difference between kW and kWh. Better if even the plumbers understand the difference.

    Joules describe the flow of electrons over time through a conductor…

    That is one way to use the unit. Joule (like kWh) is a universal measure of energy that can be used for food, fuel, electricity, etc.

    This whole debate would be a lot easier if it wasn’t confused by America continuing to use Stone Age units instead of SI (System Internationale) units and the metric system.

    Amen to that. Vested interests, or in this case, vested laziness is going to hurt the US of A. The longer this goes on, the more damage will be done. It must cost the country $ billions a year in lost productivity and confusion to keep using the units of King George.

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  13. By Optimist on February 6, 2012 at 6:36 pm

    Other units of power are joules/second, calories/day, or watts.

    You have to add horsepower to that list!

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  14. By mac on February 6, 2012 at 8:11 pm

    Optimist said @Mac

     

    Joules describe the flow of electrons over time through a conductor…

    That is one way to use the unit. Joule (like kWh) is a universal measure of energy that can be used for food, fuel, electricity, etc.

    ————————————————————————————————————————————————————

     

    I agree, it’s just one way to look at it.  I guess I look at it that way because I’ve been involved in the electronics  and radio biz for a large part of my life.

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  15. By rrapier on February 6, 2012 at 8:56 pm

    Optimist said:

    Other units of power are joules/second, calories/day, or watts.

    You have to add horsepower to that list!


     

    Done. Smile

    RR

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  16. By Rob Ryan on February 6, 2012 at 9:17 pm

    This is a portion of a post on my blog from a couple years back.

    So I’m watching “G Word ” (“G” is for green, I suppose) on Planet Green (a Discovery Channel) and the host, Summer Rayne (think Johnny Rivers – “taps at my window”), is in Abilene, TX interviewing someone from AES Energy Systems at their Buffalo Gap wind energy facility. It’s not really bad until Ned Hall, their President, says “this machine is 1.5 megawatts.” Summer asks “and what does that mean?” Hall says “it’s enough electricity for your home for the whole year.” Ummm, an analogous inanity would be me saying “my car goes 125 miles per hour. That’s enough to go from here to San Francisco.” And this, let me repeat, is the President of an energy company.

    Now this guy should have known the difference.

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  17. By tom-g on February 6, 2012 at 10:22 pm

     

    Anyone want to conduct a survey?  Call up your son or daughter and ask them three questions.  If you don’t have a son or daughter, call a neighbor, a friend, brother, sister or anyone else you know.  Try to get at least two 2 men and 2 women to respond.  

     

    1. Ask them to define the difference between a kW and kWh.  

    2. Have them state how many kW hours they used last month, and;  

    3. Ask them how much their last electric bill was +/- 10%  

     

    I would like to know how many people we interact with can correctly answer these questions.    

     

    Thank you

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  18. By tom-g on February 6, 2012 at 10:31 pm

    Optimist said:

     Tom, confusion never is a good thing. A few years ago I discovered by change that one of the USEPA high-ups, in charge of developing a mpg rating for electric cars, didn’t understand the difference between kW and kWh. Better if even the plumbers understand the difference.

     

    You are correct – confused individual don’t usually perform well.  That EPA example is truly sad.  I wonder; are they still working at the EPA?   

     

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  19. By paul-n on February 6, 2012 at 11:16 pm

    “it’s enough electricity for your home for the whole year.”

    Yes, we have seen this unofficial unit of power, called the “home”, creep into use for describing most renewable energy facilities (especially subsidised ones), though it is usually phrased like this;

    The purchase of 60 megawatt hours per year from the Crystal Lake Wind Energy Center is enough to power roughly 6,000 homes.

    Now, this article actually has all the units correct, but many reports and (especially) politicians say it like this;

    “this wind farm is enough to power 6,000 homes annually” which is actually kinda meaningless.

     

    The “home” appears to be 10,000kWh/year, which actually is 15% less than average for a US house, according to the EIA;

    In 2010, the average annual electricity consumption for a U.S. residential utility customer was 11,496 kWh, an average of 958 kilowatthours (kWh) per month. Tennessee had the highest annual consumption at 16,716 kWh and Maine the lowest at 6,252 kWh.

    10,000 could be the median, but I think it has been chosen as a nice round number…

    Incidentally, that amount of energy is a constant power of just 1.1kW – less than most kettles and microwaves.

     

    Oddly enough, the “home”  is *never* used to describe the output of a gas, coal or nuke station.

     

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  20. By Ben on February 7, 2012 at 2:28 pm

    RR

    Conservation is our biggest potential source of new energy “production.”
    On that note, I’d welcome discussion about the practical merits of CHP/micro-CHP and how feedstock costs and non-economic factors impact consumer (residential and commercial) preference for these systems. Notwithstanding the absence of more enlightened energy policies (including incentives) to promote cogeneration’s advantages, isn’t broader application nearly inevitable given equally inevitable increases in the cost of fossil fuels?

    Thanks for the insights.

    Ben

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  21. By robert on February 7, 2012 at 2:59 pm

    I had my dog micro-CHPed so if he runs away they can scan him and return him. Works great.

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  22. By art on February 8, 2012 at 3:17 am

    Thanks RR,

    for the attempt to explain difference between energy and power. let’s check if we understand it better after your definitions and examples;

    just a typical news item that seem to be at the proper place in this discussion.

    http://www.english.rfi.fr/fran…..new-record

    (he 100 Giga watt electrical power was consumed in one night because the French heat their homes with electric heaters)

    I think the term power is used properly in this article according the definitions given in RR’s blog… is it ?

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  23. By robert on February 8, 2012 at 10:37 am

    Peak demand is 100GW. Electricity consumption is energy and should be in GWhs. If the electric company can meet the peak demand, they are golden. They don’t really care what the demand is during off-hours.

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  24. By rrapier on February 8, 2012 at 12:17 pm

    art said:

    I think the term power is used properly in this article according the definitions given in RR’s blog… is it ?


     

    The article says:

    Power warnings have been issued in Brittany and the Var and Alpes
    Maritimes region as electricity consumption is set rise to 100.200
    megawatts compared to the previous record of 96.710 megawatts recorded
    on 15 December 2010.

    If they are referring to peak demand — as other Robert notes above — then this is correct. This would refer to the power output required by the plant. It would be like saying that the plant must produce X BTUs/hour at that time.

    But the amount of energy that they use on a particular date would be measured in megawatt hours.

    RR

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  25. By John L Palmer on February 8, 2012 at 2:14 pm

    The re-write is much clearer. “megawatt hours (MWh) per hour” points me toward the thinking required to do the conversions.

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  26. By mac on February 8, 2012 at 4:23 pm

    The watt is the voltage times the amperage. If you have an appliance in your home that draws10 amps at 115 vac, then that appliance is rated at 1,150 watts,

    To run that appliance for an hour at 10 cents a Kwh amounts to $ 1;15.

    Utilities denominate in Kwh for billing purposes.

    If you have a multi-socket power strip for your computer, it is not rated in Kwh, rather in Joules, since surge protection is a function of the excess supply from power-line surges, lightning strikes etc,

    Joules basically describes the supply side, whereas watts consumed is reflected in our electric bill,

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  27. By Tom G. on February 8, 2012 at 10:30 pm

    Good example mac but don’t forget to tell your audience that when doing calculations in AC circuits, they should also understand that it is just an approximation. Most AC circuits have some reactive inductance and capacitance and those also need to be taken into consideration if you are trying to design something. However for most examples like yours I X E works just fine.

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  28. By tom-g on February 8, 2012 at 11:06 pm

    Today I was fiddling around the house doing some painting like old retired people do and happen to think about this topic.  I wondered – is there more to this story than just some acronyms, terms and definitions?  I think there might be.  

    Did you know that last year [2011] T. Boone Pickens calculated that the U.S. spent $453,000,000,000 [billion] on oil.  I don’t care if we get the oil from Mexico or Canada or OPEC or some other country, that is one heck of a big chunk of money.  If we had all of that money back, what do you think we could have done with it?  Some new roads, new schools, free college tuition, better health care for all and lots and lots of jobs.  Wait a minute; did I say JOBS!  

     

    I wondered how many jobs we could create with $453 billion dollars.  if we took $453 billion and divided it by lets say $40,000 which is pretty close to what the Bureau of Labor Statistics [BLS] says the average America wage is; how many jobs is that?  Must be quite a few.  O.K. so grab your calculators and do the math because I am not going to tell you. BUT you might also find it interesting that according to the BLS there were between 12.7 and 13.9 million people unemployed in the U.S during 2011.  So if we are really sincere and WANT our friends and neighbors to have jobs, maybe we shouldn’t be spending quite so much on oil.  

     

    And remind me again, how much was the stimulus.  Wasn’t that about twice that amount of money.  Gee it seems to me we could have keep millions of our fellow Americans working but instead we decided to … oh forget it.  Besides this is not really what this topic is all about is it.  It has nothing to do with energy and power does it?    

     

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  29. By Ben on February 9, 2012 at 8:48 am

    At the risk of being uncharitable, the simple math described above doesn’t begin to accurately reflect the real world effects resulting from adjusting a trade deficit of $453B from the importation of oil. If such a re-balancing was magically achieved, this level of financial resources hardly becomes available for the job creation or the list of notional public investments cited by Tom. Most of this money simply pays for the ovehead associated with the (current and future) production of this depleting resource and would remain unavailable to support a significant expansion of jobs let alone support additional public expenditures. There would presumably be some measure of profitability associated with this economic activity that becomes available for reinvestment that results in economic (job) growth and some measure of tax revenue for the public treasury (thought these funds might best be spent reducing exisiting deficits rather than promoting additional expenditures). In brief, a shift to domestic energy production may be a worthy objective (I have argued that very point in this space on several occasions), but it does not pose a windfall that readily translates into the magnitude of increases in job creation envisioned by a calculation of simple math from investments made by either the private sector or demand management (“stimulus”) investments of the government. I wish it were otherwise, but as RR is quick to observe, “there’s no free lunch” or, I might add, quick fixes either.

    Ben

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  30. By perry1961 on February 9, 2012 at 10:33 am

    “If such a re-balancing was magically achieved, this level of financial resources hardly becomes available for the job creation or the list of notional public investments cited by Tom.”

    I beg to differ Ben. That $453 billion transferred overseas each year subtracts 3% from economic growth. Had we magically solved the problem a year ago, growth would be 4% right now, instead of an anemic 1%. The economy would be booming and jobs would be added at a rapid clip. Tax revenues would be markably higher and the deficit would be trimmed accordingly. If not for oil imports over the last 10 years, our GDP would be closer to $20 trillion, rather than $15 trillion or so. That’s a LOT of jobs mon frere.

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  31. By Mark Perry on February 9, 2012 at 12:48 pm

    Like Congressman Dana Rohrabacher, I’m still confused.

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  32. By tom-g on February 9, 2012 at 2:42 pm

    And Ben said [in part]: “At the risk of being uncharitable, the simple math described above doesn’t begin

    to accurately reflect the real world effects…”.

     

    I certainly wouldn’t consider any well though out response uncharitable. I really do enjoy posting on this website but realize we are probably not going to solve the worlds energy problems or world hunger. But just maybe someday someone we will hit upon an idea, concept or strategy that is revolutionary enough to bring forth a new vision for our country.

     

    And perry1961 said [in part]: “That $453 billion transferred overseas each year subtracts 3% from economic growth.”. I also believe that this comment adds value to our discussion and last;

     

    Mark Perry who said: “Like Congressman Dana Rohrabacher, I’m still confused”. His comment put

    a big smile on my face and a chuckle I really enjoyed.

     

    I thank you one and all.  

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  33. By Ben on February 9, 2012 at 7:58 pm

    “That $453 billion transferred overseas each year subtracts 3% from economic growth. Had we magically solved the problem a year ago, growth would be 4% right now instead of 1%. How I wish it were so, Joe.

    Regrettably, $453B expenditures on energy imports–a good deal of which gets recycled in the form of petrodollar financing of US Treasuries or in the form of foreign direct investment in the US–doesn’t translate into 3% opportunity costs (lost growth) to the economy. There’s no panacea here; stop US balance of payments deficits and, eureka, we revisit go-go 80′s growth again. The current damper, or shall we call it the kink in the hose, principally results from a systemic deleveraging that the US/World economy has been suffering these past 4 years. Until such time imbalances between debt-service requirements and languishing asset valuations recovers courtesy of healthier levels of current income to debt, the economy will muddle along while high(er) energy costs (both foreign and domestic in origin) simply contribute to an anemic pace of recovery.

    Much like that young lad of ’19 who gushed to to Shoeless Joe Jackson, “just say it isn’t so, Joe!” I’m afraid the sad truth is that reducing oil imports may make for sound (and more secure) public policy and, on-balance, better economics, it won’t offer very much for new job creation anytime soon. That, of course, doesn’t mean that we shouldn’t move in this direction. If I’m not mistaken, I believe that’s the point RR’s been making on in this space for some time now. Fot that we remain grateful.

    Ben

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  34. By paul-n on February 9, 2012 at 10:44 pm

    Well, the “good” news, on this score, is that of the US was using as much oil as it was four years ago, the number would have been *much* higher.

     

    For 2006, total imports were about 12.5 mbd, and for 2011 it will be about 8.5mbd.  using the 2011 the yearly  average import price (Brent) of $111 , the actual import spend  is “only” $344m, but if imports were at the 12.5mbd it would have been $506m.

     

    So, one way or another, the spend on oil imports *is* decreasing.

     

    In fact, IF that current trend continues linearly, the oil imports will reach zero in 2023.  

    Though, personally, I think that is unlikely.

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  35. By Ben on February 11, 2012 at 8:54 am

    Thnks for pointing out the good news, Paul. We need to accentuate the positive–there isn’t an awful lot out worth cheering especially during an election year filled with shrill candidates who focus on everything but what thoughtful voters actually care about. I recall the “It’s the economy, stupid” line from the 90′s and wonder how we manage to get so side-tracked on issues that are trivial by comparison. Then, I’m reminded that wedge politics is the essence of contemporary politics and superficial clowns like the Karl Rove-types continue to ply their wares for self-promotion/financial gain at the expense of the commonwealth. Until rank and file Americans chase such money-changers from our sacred public trusts, the pox will remain at our seats of government and susbtantive reform will elude our grasp.

    Ben

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  36. By russ-finley on February 11, 2012 at 1:55 pm

    Might want to define work.

     

    The Wikipedia article on Kilowatt hours is pretty good:

    Examples

     A heater rated at 1000 watts (1 kilowatt), operating for one hour uses one kilowatt hour (equivalent to 3.6 megajoules) of energy.

     Using a 60 watt light bulb for one hour consumes 0.06 kilowatt hours of electricity. Using a 60 watt light bulb for 1 thousand hours consumes 60 kilowatt hours of electricity.

    RR said:

    A 100 megawatt (MW) power plant is capable of generating energy at the rate of 100 megawatt hours (MWh) per hour.

    To me, the key phrase here is “capable of.” This is where the term MW gets abused. It represents a potential. For example, the lay press may compare a ten MW nuclear power plant to a ten MW solar power plant. However, the nuclear plant will produce far more energy annually (roughly an order of magnitude depending on location of solar plant) than the solar plant of the same rating because the solar plant will only produce energy for a fraction of each day and not every day. Same rating, vastly different amount of energy produced annually.

     

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  37. By paul-n on February 11, 2012 at 3:18 pm

    Well said Russ.

     

    The best way to compare these different plants is not the MW,  but the annual MWh produced.

    Of course, when that is done, solar and wind suddenly become 1/3 to 1/10 of what they were, but that’s reality.

    It would be good if, to at least start down this path,  all the gov agencies would start using this metric.

     

    Consumers don’t think in terms of power, they think in terms of consumption, so these things should be measured in terms of production.  Annual is the best way to do that, and for renewables with seasonal variations, is the only sensible way.

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  38. By russ-finley on February 11, 2012 at 6:42 pm

    Paul N said:

    Yes, we have seen this unofficial unit of power, called the “home”, creep into use for describing most renewable energy facilities

    Good point …a unit that most people might understand except it can easily be abused as well.

     

    “A solar power plant capable of powering 5,000 homes.”*

     

    *Assuming the sun shines 24 hours a day 365 days a year.

     

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  39. By Optimist on February 13, 2012 at 8:54 pm

    You are correct – confused individual don’t usually perform well.  That EPA example is truly sad.  I wonder; are they still working at the EPA?

    Still there, as far as I can tell. Must be nearing retirement.

    Maybe I caught him on a bad day. Still…

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  40. By Mike W on February 15, 2012 at 11:54 pm

    People know the difference between speed and distance right?
    speed = distance / timespeed * time = distance
    just like
    power = energy / timepower * time = energy
    The concept is simple. People never say “the speed limit is 65 miles”, so they ought to be able to keep kilowatts vs kilowatt hours straight.

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    • By Mike W on February 15, 2012 at 11:56 pm

      argh, my comment got mangled
      People know the difference between speed and distance right?
      speed = distance / time and speed * time = distance just like
      power = energy / timeand power * time = energy
      The concept is simple. People never say “the speed limit is 65 miles”, so they ought to be able to keep kilowatts vs kilowatt hours straight.

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