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  • Efficiency: Electric vs. Gas

    I know there are many ways to look at this issue, but I'll try to boil it down to simplest terms:

    With our current technology, is it more efficient to burn a barrel of oil at an electrical generating plant, and then send that electricity along wires into the storage batteries of an electric car? Or, to take that same barrel, and put it into the gas tanks of your average gas-powered car?

    I'm talking about mass-conversion efficiency, not cost-effectiveness (the two may be related, but not precisely).

    Electric vehicles are not the solution to our energy woes, if we have to burn an equivalent or greater amount of fuel to power them. I really don't have an answer here, I'm just wondering.

    And, to confuse matters, let's say that the electrical power is coming not from fuel but from hydro power. Then it should be easy, right? But we don't have enough hydro capacity if every car converted to electric. We would need to build more generating plants. Which means burning lots of fuel. Which wipes out any efficiency gains you might have had.

    Like I say, a lot of variables. But I am not yet convinced, when all is factored in, from raw materials ultimately converted to miles driven, that electric is the way to go.

  • #2
    Centralised power generation is the traditional way to consider energy management, however there is another school of thought that suggests power generation may best be served by millions of micro generating systems. Indeed that's precisely the push that's going on in Australia now, where there are quite good financial incentives to installing photovoltaic solar cells on individual houses to both supply the house and feed any surplus back into the grid. While this solution clearly can't supply the grid 24/7, it may go a long way to relieving base demand during daylight hours.

    Typically in Australia (and it's not dissimilar in most other Western countries), there may be coal power stations (other countries may use a different fuel but the principle is the same) to supply base demand, with regional small stations using something like gas turbines to supply peak loads. The regional stations are not especially efficient, therefore expensive to run, but MUCH cheaper overall that building another big station just for peak loads. With the new push on you may find that there aren't as many big stations being built any more, just the smaller ones, with the base load instead handled by generation at or near the consumer.

    Pete

    Edit: Now I see your location is China ... having said all that they're sure as heck building a s%&t-load of new coal powered stations. IIRC there's a new one coming on line every week or two!!
    Last edited by PeteF; 08-21-2010, 03:18 AM.

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    • #3
      The answer is a very large "it depends". It depends on the source of the electricity and it depends on the electric car vs the petroleum fueled vehicle type. It depends on the type of batteries and it depends on the usage of the vehicle. It greatly depends on what time of day the electric vehicle is recharged. We have enough generating capacity in North America to support about a 70% conversion of the general fleet of gas vehicles to electric as long as the charging is done off peak only. Of course there are a long string of dependencies in that calculation too.

      The current answer is that you can easily manipulate the numbers to show whatever you like. Even efforts to level the field of comparison by calculating the well to wheel efficiency must make a series of assumptions that can heavily skew the outcome.
      Free software for calculating bolt circles and similar: Click Here

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      • #4
        Electric may be more efficient, but it is the most expensive. Take a home for example. You could heat your home with electricity and that would be nearly 100% efficient in converting electric power into heat. Your costs to heat your home would also go up by about a factor of 10 or more over Natural Gas.

        Lets take just the cost of purchasing and running a car.

        The Chevy Volt sells for $40,000
        The Kia Soul sells for under $20,000 and gets about 30 MPG

        Assuming that gasoline costs $2.00 per gallon, you could buy the Soul and pay to drive it for 300,000 miles for just what a Volt costs.

        The Volt has a max range of about 40 miles before recharging.
        The Soul has a maximum range of about 360 miles.

        Pound for pound gasoline has the most energy potential of any viable automotive energy source including batteries.

        In the end efficiency isn't all you should be looking at, but also the total cost of ownership.

        So which is more efficient? Overall electric powered cars are lots more efficient emptying your bank account compared to a gasoline powered car.

        Be careful what you ask for...you might get it.

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        • #5
          It's a long, circuitous route: from radiant solar energy, to complex organic life, to hydrocarbons, to electricity, and back to radiant heat.

          I'm inclined to believe the most realistic option is small-scale local generation to compliment big grid power plants. That sounds like a best-case scenario to me.

          But here's a question about the big power plants, which I don't know much about: let's say the plant is running off-peak. How do they scale down the power generation? Do they run fewer power turbines, or keep the same number of turbines running but at half-speed, or the turbines continue to run continuously but they disconnect them from the grid, or some combination of these? Forgive me if this question is obvious to some of you, but hey, we all gotta learn somehow.

          The point is, what is the most efficient way to run a big station and how do they do this with variable demand? Would it be better to run the big stations at a steady state 24/7, and let the small local power supplies (even down to the level of the individual car) handle the variable power demands?

          Come to think of it, let the plants run at max. efficiency 24/7, and store the excess power in supercapacitors scattered throughout the grid that people can draw from as demand requires.

          I don't know, just thinking out loud.....

          But, back to cars. I don't think the economy of the electric vehicle is going to ever match that of gasoline in any kind of timeframe that will matter to those of us reading this. It's too late for electric cars if we assume we can use them in any way like we've become accustomed to using gas cars. Those days are gone.

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          • #6
            Just my dumb opinion

            A few years back my freind got a golf cart to play around with he claimed
            it to use a qt. of gas a day using it with trimmers shovels chain saws in
            the back. I thought a cool thing i could use. Not long after I came upon
            an EZE GO for free being 36Volt six batt. golf cart. It ran well went pretty
            fast wife always using it, kids too. The charger had an 8hr timer. When
            I got my electric bill for that month, that thing went out the door as fast
            as I got it. I remember years back driving a T950 with a 534v8 ran cheaper
            than that! OR mow 10 ac/ with a 8N Ford on 5gal......

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            • #7
              I'm pretty sure electric generators at power plants only run one speed; 60Hz. So to scale back individual generators are shut down rather than run slower. To restart they need to be brought up to speed, connected to line, then pour on the steam.

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              • #8
                Ive been looking into all sorts recently

                our government are now providing us with a feed in tariff

                which on the surface looks very good ..thats until you look into it.

                Our price for electricity is roughly £0.13 a unit

                the feed in tariff is £0.42 a unit for feed in electricity back into the grid.

                PV

                To be able to do this you need to have a government accredited installer sell you the panels install the panels...and charge you a yearly inspection charge

                probably works out in excess of £15,000 plus the maintenance charge

                air source heat pump

                £0.075 given back to you for every unit you use,, under the renewable heat incentive scheme that isn't passed yet..if passed will roll out on April 2011

                gov have my house worked out at using 10,500 units kWh heating plus 3500 units hot water a year...means they give you £900 ish back each year

                again usual government accredited installer...whole job around £5-8 thousand.........lots of companies trying to sell you these systems to run with conventional radiators...i have great doubts weather they would work with anything but underfloor heating ..as the units only heat the water to 55 degrees c.

                CHP combined heat and power unit ..

                based on sterling engine generator

                £8000 plus ..all those service charges..£0.42 feed in tariff ............great doubts hanging over their reliability and spares cost


                Wood fuelled pellet stoves and log burners biomass ..that have been passed to use by the gov

                very expensive appliances ...have to be installed by gov accredited insataller..........£10,000 - £18,000....motors electronics lambda 02 sensors....masive stainless flues costing lots of money

                £0.09 per unit given back to you under the renewable heat incentive scheme.

                so

                about £1100 a year will be given back to you buy the gov ..

                cant see theses units lasting beyond ten years without spends and brake downs

                and some have a massive service charge check every year .........as much as £400 -£500...lowest service charge £180

                as you see every one i look into ..it looks great on the surface until you delve behind it .

                having said all this ..i now realise thast you are talking vehicles and not heating systems ..GAS in my UK brain always says to me mains gas for heating...and gas in vehicals says ..to me lpg propane.

                all the best.markj
                Last edited by aboard_epsilon; 08-21-2010, 08:28 AM.

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                • #9
                  Originally posted by strokersix
                  I'm pretty sure electric generators at power plants only run one speed; 60Hz. So to scale back individual generators are shut down rather than run slower. To restart they need to be brought up to speed, connected to line, then pour on the steam.


                  Yes I think that's the way its done also, but there's some lee-way within the system as individual turbine generators have vast flexibility even though the 60hz's needs to be maintained - it's done by load demand and so when its not not great or they need more they just match the pressures to the turbine accordingly to come up with the proper hz's, as long as its in the turbine/gens operating range then all is good - if not they either drop one or add another to compensate - if its a potential to add then yes they have to get one spinning up to speed but I really don't think it takes all that long,

                  What im curious about is how do they match up all the individual hz's ?
                  or properly segregate them for 3 phase ?


                  For the record --- I don't think electric will be practical in comparison for a long long time,

                  The Cons;

                  coal is still the main driving force, it takes more fuel to mine, Then the inefficiencies start at the furnace and then are transfered to the blasphemy of the boilers and then to the tyranny of the turbines - they then continue with the degeneration of the generators then are further pillaged by the step up transformers and quickly wisked away only to be sodomized by the line transportation then to the final domestic dispute of the step down transformers --------- It's not over -------- from here it is ran into another heat creating transformer to then attempt to charge the batteries on the electric car, while most of the electricity goes to charging the batteries some goes to heating them up and is therefore wasted ,,, Now to power the car ---------- the batteries then give up their energies but not all of it goes to the electric motor as once again the batteries heat whilst doing this, meanwhile the electric motor gobbles up the energies and puts most to use but also heats itself up in the process,,, Meanwhile it's winter time - and the electric car has no real means to heat the cabin ----- so instead of having most of its waste heat handy and in one spot like the IC engine much of the waste heat for the electric car is sitting back at the power plant -- so what does the ass backwards electric car have to do ------------------- it takes the end result and small percentage of power that has made it through the fuqueing archaic maze and dumps it into a dead short electric grid to keep its moronic occupants from freezing to death ------- Real nice....

                  So ------- doesn't sound that great does it?
                  And that's not even comparing it to the efficiencies of a little 1.3 liter turbo diesel ----- oops - guess i just did...

                  Just to be fair here's the Pro's -------- inner city electric vehicles can use their brakes to recharge the battery's for the next take off, But please don't make me go through all that is lost in this process...........................
                  Last edited by A.K. Boomer; 08-21-2010, 10:04 AM.

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                  • #10
                    A gas or diesel vehicle has a lousy energy conversion rate...... they have a low efficiency vs the carnot limit. maybe half, if you are lucky....(that's one of those assumptions)

                    If we were not limited by NOx limits, the efficiencies could be much larger. Utilizing the heat at higher temperatures near the flame temp, if possible, extracts more energy. But high temps also drastically explode the NOx output, requiring heavy and bulky equipment for mitigation in order to meet pollution limits

                    A central station plant has a very high efficiency, usually quite close to the Carnot limit. But the losses of distribution really hurt that when it comes to "at the outlet" efficiency.

                    Then, an electric car has batteries. Charging a battery has an inherent loss also. yes, it varies by battery type, but it is generally at least 10%, may be up to 25%.

                    Finally, an electric car is not lossless. It cannot convert 100% of the input energy to motion/work, and it loses energy in all the auxiliaries, etc. And, you have to heat the car somehow, during half the year.

                    An electric car is also of no use for a trip longer than about 30 to 50 miles (you have to get back after all). This is something which precludes it being your only vehicle, unless your passport is only good in your native city (we may get to that point).

                    It is best to think of the electric car, for the foreseeable, as a way to move the pollution source, and potentially slightly reduce overall pollution. In a city, there is obviously no exhaust, same reason electric has been used in mines.

                    If you want an overall efficiency improvement, an electric car varies from a minimal improvement, to a net loss, depending on the assumptions, or hard numbers if you have them in any particular case.

                    At present, it would be a mistake to assume that there is a bright future of clean transport simply by using electric cars. The relative cleanliness of the electric central station is reduced by the inefficiency all along the delivery path, since that means more fuel must be burned for the same energy output "at the wheels"

                    OH, yeah, "but we'll just charge them with solar and wind power"......

                    Sorry to burst your pretty bubble, but there is not now, and may never be, enough solar and wind power to waste any of it on charging vehicles...... All the solar and wind power there is now cannot do the job.

                    Naturally, solar is "out"..... When solar is available, you are not generally charging, unless you are on swing shift.... so some storage process with a relatively crummy efficiency must be used, DOUBLING the storage and "charging" losses.

                    Maybe you will be REQUIRED BY LAW to work at night in order to allow solar charging........
                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #11
                      The Tesla Roadster people have done some very detailed studies of electric efficiency and performance. They have the platform that represents the current driveable state of the art complete with electric heating and and conditioning.

                      Here is a detailed explanation of the best case power consumption that can be expected from the Tesla.

                      http://www.teslamotors.com/blog4/?p=70

                      Here is their comparison of Well to Wheel efficiency:

                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        In 2004 a Harvard Science Professor published a report of his long study that stated the USA would need 3 and 1/2 times more Power Stations if the entire fleet of Trucks and Cars in the US went to Electric power. You may recall, that was when the Media was in love with Hydrogen Power, another looser. In addition, we would need to completely triple our grid and update it. The latter being the impossibility, with NIMBY
                        Some feel that small local or home power units are the answer, but just as our friend in Wales has found out, the fingers of regulation will control that and it will never be cheap.
                        We live in an age where reason and logic no longer exists in our Leaders.
                        Witness the fact that our local Nuclear Power Stations produce electricity at 2 cents per KWH and we paid 8 cents to buy it. (1994). Then the "leaders' decided to have Gas units built, and a California Utility built a gas unit here with a published "cost" of 12 and 1/2 cents per KWH ( I know, I protested at the hearing).Today we pay 14 cents and they tell us it is still not enough.
                        To address this shortfall, our State has mandated that 25 % of our power should come from wind in the next 10 years. Must be "inbreeding ?"
                        But back to cars..
                        Batteries, Hydrogen,Natural Gas,Propane all suffer a Major fault when compared to Oil, and that is they lack ENERGY DENSITY....simple
                        When you have a mobile consumer like an automobile, the cost to carry your fuel efficiently cannot be ignored, and oil is king in this important (but often ignored) area. Now couple this with Storage issues, where Hydrogen and Electrical storage have diminishing returns (natural bleed off) and we can say, " let the folly begin"

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                        • #13
                          you also have to remember this

                          in the winter .........on a cold day .a lot of the so called heat losses in IC engine...will be going into the cars interior via the heater to keep the occupants warm, and de-mist the windows..so will not be such a loss

                          with an electric car ..this heat has to come from somewhere .so will be using valuable battery energy keeping occupants warm ..demisting etc.

                          think trams and tubes and busses are the future.

                          all the best.markj
                          Last edited by aboard_epsilon; 08-21-2010, 11:06 AM.

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                          • #14
                            Lots of assumptions, and also some outright lies or "falsefacts".

                            They give it as a "best case" and that is what it is. In spades.

                            The driving conditions are unrealistic...... good for a few weeks in fall and spring, in daylight.

                            The kw used for travel at various speeds are "interesting", but don't accord with general usage..... In a gas vehicle, fuel use does NOT go along with that power curve*..... There is no particular reason why the tesla should follow it either. I am forced to the conclusion that teh Tesla folks assumptions are driving that.

                            I am sure it is a good vehicle. For their price it should be.

                            Will anyone actually get the range they quote? maybe. Some folks. The same group that can nearly double the mileage of their gas vehicle by extreme driving techniques.

                            *I get no degradation of mileage that is findable/relevant at any speed between 55 and 75 mph. And, I am talking about 9 hour trips over the same route at the same general weather conditions, not mileage spread over days or weeks. The variation is about 7% at max, and much of that is due to an actual fault in the vehicle which was since repaired.

                            According to the Tesla curve, I should have seen a 50% change, but that does not happen in reality.
                            Last edited by J Tiers; 08-21-2010, 11:14 AM.
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #15
                              Same old sales pitch
                              "So here are some of the critical inputs that we have assumed:
                              • Single driver ~180lbs
                              • Soft top or Hard top on vehicle (with windows up)
                              • No air conditioning usage
                              • No heat usage
                              • No headlights or cabin air blower (large 12V loads)
                              • Tires inflated to recommended efficiency setting 30/40 front/rear psi"

                              I question any study that makes unreal assumptions !

                              Also Even, I can't find the study you posted for the assumption on efficiency.
                              The CERTAINLY don't have "cost" as a factor
                              Rich

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