Charging Electric Vehicles at Night Can Cause More Harm Than Good, Says CMU Study

1 year ago by Mark Kane 102

Tesla charging point

Tesla Model S Receiving A “Destination” Charge

Top Gear's Jeremy Clarkson isn't sure whether he will be able to connect before nightfall

Top Gear’s Jeremy Clarkson isn’t sure whether he will be able to connect before nightfall

Carnegie Mellon University’s study, recently published in the journal Environmental Research Letters, poured anxiety on the night charging of electric cars.

So far, we have been accustomed to think that night charging is not only suitable to EVs that sit in garages, but could take advantage of unloaded power plants/grids from a cost perspective.

According to the study there is however question about environment impact of night charging.

Jeremy Michalek, a professor of engineering and public policy and mechanical engineering, and his colleagues modeled the PJM region, which includes Washington, D.C., Philadelphia, Pittsburgh, Cincinnati and Chicago, and whether there is someting wrong in generating electricity at night instead during the day?

CMU’s study concerns coal-fired power plants suggesting that at least in some cases night charging could indeed cause more harm over daytime than good.

“Researchers at Carnegie Mellon University find that while charging electric vehicles at night is more cost-effective, it increases air emissions.

Charging electric vehicles late at night, when demand is low and electricity is cheapest to generate, is preferred by grid operators. However, CMU researchers found that it produces substantially higher greenhouse gas emissions and air pollution than simply charging as soon as the driver returns home.”

Michalek explained:

“We looked at how power plant operations would change in response to electric vehicle charging load, and we modeled emissions from those plants and their downwind air pollution consequences for human health and the environment. We found that charging late at night reduces power generation costs by a quarter to a third, largely by shifting to cheaper coal-fired power plants. But the extra emissions released as a result can cause 50 percent higher costs to human health and the environment.

Coal (Lithium?) rail cars


Sounds like just another reason to not like coal-fired power plants.

“According to the study, coal-fired power plants often operate below full capacity at night, so they are available to be dispatched in response to new nighttime load, like electric vehicle charging. These coal-fired power plants produce sulfur dioxide, which is the largest single source of cost to human health resulting from electric vehicle charging.

In a separate study, published in the journal Environmental Science & Technology, Michalek and colleagues looked at greenhouse gas emissions from electric vehicle charging across the United States.

“In nearly all U.S. regions, charging later at night increases greenhouse gas emissions,” he said.”

““For now, if you live in a coal-heavy region like the Chicago, Washington, D.C., Philadelphia area, delaying charging until late at night can cause more harm than good.””

If the findings are right, the only way to not increase environment impact per energy unit produced and delivered would be switch a from coal-fired power plants to some other cleaner sources, but on the other hand we have the costs and time needed to see those gradual improvements in the energy sector.

source: Carnegie Mellon University

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102 responses to "Charging Electric Vehicles at Night Can Cause More Harm Than Good, Says CMU Study"

  1. ModernMarvelFan says:

    It sounds like using peaky gas plants is still better in emission than using backbone coal plants…

    We just need a cleaner grid regardless whether we all drive EVs or not.

    Transportation sector (private cars) only account for about 20% of the total CO2 emission anyway. Not that we shouldn’t reduce that to zero. But Power plants generate almost as much if NOT more in CO2 emission than transportation.

    It is time to reduce on all fronts.

    Time to go clean nukes, geothermal, solar and wind.

    1. Grendal says:

      Your reasoning is right on. I think your mix for electrical generation is the most healthy, balanced, and sustainable.

      1. Thomas J. Thias says:

        Caution is advised before reading to much into this Carnegie Mellon study, paid for in part, by Toyota Motor Corporation.

        The last big “EV (BEV) Attack Study” in January of 2015, by the University Minnesota, as reported on this site, was subsequently refuted by numerous organizations including the Union of Concerned Scientists and by my own comments posted here on Inside EVs on January 6th, 2015.

        Link Goes To InsideEVS 01.06.2015-


        Thomas J. Thias



        1. M Hovis says:

          Right on Thomas. It even smells of a common Toyota tactic of mixing future and present to spin the outcome. A study was just released that US solar will double in 2016 primarily due to utilities rapidly entering the renewable market. Just once I would like to see a study that actually “studies” how many EVs currently and in the future power off of renewables. You nailed it Thomas.

        2. Alpha777 says:

          I smell Koch Money.

          This is the same as global warming denial propaganda.
          Yesterday’s high was 81 in Philadelphia in January.

          So now we have June in March.

          1. SJC says:

            Koch Industries, where piles of petroleum coke blow into the rivers…

          2. zzzzzzzzzz says:

            Are you hired by Koch? :/
            As you advocate for battery car agenda to ignore the obvious fact that battery cars despite all their advantages to some extent just shift pollution from tailpipe to power plants.

            Li-Ion batteries are not suitable for long term storage and are not helping intermittent solar/wind to advance as they leave solar/wind to compete with fuel cost part only of natural gas plants, and it is low price level.

            1. Nix says:

              Even if you accept your incorrect premise that EV’s just move the emissions from tailpipes to smoke-stacks, that would be a good thing.

              Tailpipes emitting pollution at body level directly in and around where we work and live where we breath it all the time is much more dangerous to our bodies than the same pollution being released from the top of a 75 foot smoke stack far from heavily populated regions.

              1. ericonline says:

                Well said. I’m surprised more people don’t share this view. The adverse impact of living in a carbon emission cloud in many major cities is undeniable.

    2. MikeG says:

      I agree with everything you said, except clean nukes.
      There is no such thing–we don’t have the political will to handle the high-level waste.
      We do not have the necessary regulations to prevent another nuclear disaster, whether caused by human error, earthquake, solar storms or intentional sabotage.

      1. David M says:

        You clearly don’t know about thorium Reactors Which can not meltdown even when intentionally sabotaged. Thorium also cannot be weaponized. That nuclear waste is fuel; waste is just material that we fail to utilize. Just like that stuff you flush down the toilet everyday. Thanks to the regulation that you think we don’t have enough of we cannot build new CLEAN Nuclear reactors so we are stuck with 50 year old dirty reactors. We have the technology; let’s use it!

        1. MikeG says:

          David–I do know about thorium reactors.

          I know that no one has built a successful one beyond scientific prototypes.

          Talk to me again when they are widely in use. Until then, I won’t be convinced that nuclear is a viable option.

        2. MikeG says:

          Also, if thorium was a solution why aren’t there any commercial scale units now?

          Saying something is technologically possible (thorium) is not the same thing as mature technology.

          I lump thorium reactors with fusion reactors. They won’t be feasible for at least 30-50 years. As me again in 30-50 years and I’ll give you the same answer.

          1. SJC says:

            Fast reactors use waste plutonium and depleted uranium for fuel, they don’t melt down.

            1. zzzzzzzzzz says:

              There are all kinds of fantasy reactors that are possible technically and prototypes are made and even function. But none of them make any sense commercially. Even old relatively cheap proven reactor designs have priced itself out of the market in places like US. That is with huge subsidy of legislated liability insurance waiver that most likely would be unobtainable in commercial insurance market. Nuclear energy is legacy of nuclear weapon development. Forget it just for commercial purposes.

              In addition, it doesn’t help intermittent solar/wind energy, as most nuclear plant costs are fixed capital costs for many decades. You may reduce power (in theory) of nuclear plant while sun is shining, it will save almost no money as it would be running at full power all the time. Solar/wind is redundant with nuclear.

              1. SJC says:

                Russia has been running a fast reactor generating power for more than 30 years, it is NOT a “fantasy”. GE has the PRISM fast reactor that is ready to be deployed.

                1. zzzzzzzzzz says:

                  That is exactly what I’m telling, they exist as prototypes, but never made commercial sense for wider deployment. Commercial use of such reactors is fantasy.
                  And Russia has well known (lack of) safety record in nuclear industry. When you skip on safety, you can make many things cheaper – until things go wrong and then it becomes very expensive.

                  1. SJC says:

                    The GE PRISM design is safe, some politicians oppose fast reactors because they think they will proliferate plutonium. That is absurd because they USE plutonium for fuel.

                  2. Bill Howland says:

                    A few comments:

                    In view of the horrific Japanese Fukushima Daichi experience, where 3 reactors experienced China Syndromes (all 3 reactors melted down to the ground water – they still remain to be ‘recovered’), and the fact that the US AEC ‘grandfatherd’ this Mark I reactor design because 23 of them still exist in the states, and to ban them would “Kill the Nuclear Industry in the United States”, and that 3 of the GE engineers quit in protest – agreeing with the AEC that the containments are too small to be safe – for all the preceding reasons I’m not interested in anything GE plans to do, or what catchy names they call their new Designs.

                    Jeffrey Inmult said GE will rebuild all the reactors at Fuku Daiichi – maybe that was before he was briefed on the scope of the job, namely around $500 Billion for the cleanup alone over the next 50 years. I’d hold him to it even though it would bankrupt his company.

                    As far as fast breeder reactors go, Russian companies from all appearances are far, far more technologically advanced than anywhere else on the globe.

                    “…From Wikipedia, the free encyclopedia
                    External images
                    BN-800 reactor. Photo from Rosatom
                    The BN-800 reactor is a sodium-cooled fast breeder reactor, built at the Beloyarsk Nuclear Power Station, in Zarechny, Sverdlovsk Oblast, Russia. Designed to generate electrical power of 880 MW in total, the plant is the final step to the commercial plutonium cycle breeder. The plant started producing electricity December 10, 2015, with a reduced power of 235 MW…”

                    This is the successor to the BN-600 in operation from 1980.

                    While these are commercial reactors, continuing tests are ongoing to try to finese the construction of better fuel assemblies, prior to the construction of larger machines (BN-1200, and BN-1600) in the 2020’s.

                    The encouraging thing to me is that, with this new commercial BN-800 fast breeder, they are carefully ramping up the power (currently 235 MWe, on the way to 880 MWe), and developing fuel assemblies for use on this and the previously mentioned larger machines.

                    I contrast that experience with the rusting hulks we have in this country, besides all the ‘routine releases’ the Nuclear Industry in this country is given a pass on. In my state, the Indian point #2 and #3 plants have been leaking radioactive water for the past 30 years, such that monitoring wells now show, initially 65,000% over the regulatory limit, and then a week later, they found another place where it was 80% worse than even the 65,000% overage.

                    What with transformers exploding on a regular basis, it gives the impression that these Nuclear Firms in the states are doing the absolute minimal amount of maintenance necessary to keep their plants limping along, such that organizations far more conversant with the day to day details are now calling, (RiverKeeper for instance), the Indian Point facility “Chernobyl on the Hudson”.

                    Its 35 miles to NYC. If anything ever goes really wrong at this facility, what will millions of people do?

          2. Ambulator says:

            Even without thorium, nuclear reactors are better for the environment than solar or wind. The Earth is a big place. There’s plenty of room to store a small amount of high-level waste.

            Thorium or even uranium molten salt reactors are better still, but there is no need to wait to build them.

          3. Pushmi-Pullyu says:

            MikeG said:

            “I lump thorium reactors with fusion reactors. They won’t be feasible for at least 30-50 years.”

            That seems unnecessarily pessimistic. The current Chinese-American project to develop “Generation IV” thorium commercial reactors hopes to have a demonstration plant running by 2020, and start selling the plants worldwide by 2030.


      2. Pushmi-Pullyu says:

        MikeG said:

        “…we don’t have the political will to handle the high-level [nuclear power plant] waste.”

        Unfortunately that’s true in the USA; too bad we can’t imitate France in that regard.

        But you’re ignoring the fact that the amount, the volume, of waste generated by commercial nuclear power is incredibly minuscule compared to the amount of waste generated by coal-fired plants.

        You’re also ignoring the fact that (aside from extremely rare accidents) nuclear waste only affects soil and water, not air. In fact, coal-fired plants put out more radioactive air pollution than do commercial nuclear plants.

        1. Nix says:

          Sadly, while nuclear power production doesn’t impact air quality, nuclear accidents, explosions, and nuke weapon testing certainly does.

          In fact, all biological matter everywhere in the world can be tested for cesium-137. Items that do not contain cesium-137 was alive prior to humans releasing massive amounts of cesium-137 into the atmosphere, polluting the entire world. Biological matter that does contain cesium-137 was alive at some time after humans released cesium-137 in the atmosphere. (There are no natural sources of cesium-137 on the earth, it is entirely unnatural and is purely something that is man-made by nuclear reactions)

          We can even use this to test for forged antiques, like faked paper documents and fake old wines. The cesium-137 pollution is so mind-bending in its ubiquity, that it is a reliable way to test ALL life-forms around the world to see if they were alive when any number of nuclear power plant disasters and weapon tests were conducted.

          Literally all life forms everywhere in the world that were alive through our nuclear age are contaminated with man-made cesium-137 released into the atmosphere.

          1. Pushmi-Pullyu says:

            Correct me if I’m wrong, but most of that is from atmospheric and above-ground tests of nuclear weapons, which are now banned by international treaty… altho perhaps North Korea is still doing that, I dunno.

            I imagine some was released during the Fukushima accident, but I suspect relatively little into the air, despite a lot of hysterical shrieking by the media. Likewise, the radioactive contamination of sea life has been enormously exaggerated by alarmist media stories… which, again, single out nuclear waste contamination as if somehow that is the one and only form of industrial toxic waste which is unacceptable in even very small amounts.

            Humans are rather poor at putting relative dangers into perspective.

            1. Nix says:

              Yes, nuke weapons testing and actual nuke weapon attacks are the largest source of human made radioactive pollution. But nuclear power plant disasters are also a major source of human-made radiation.

              Going directly to your comment: “In fact, coal-fired plants put out more radioactive air pollution than do commercial nuclear plants.”

              This only holds true if you ignore radioactive air pollution from nuclear power accidents. Yes, burning coal releases about 1000 terabecquerels of radiation per year.

              But Fukushima released 14,000 to 17,000 terabecquerels and Chernobyl released 85,000 terabecquerels.

              So you can’t simply claim that nuke power releases less radiation by trying to minimize these nuclear accidents.

        2. Cao says:

          A piece of Uranium the size of the eraser on a pencil has the equivalent energy of 100 Train Cars of Coal… Think about that for a while and try to picture it…

          Anti nuclear energy people always group it with Bombs and the few failures where men were responsible for not following proper procedures… Thanks to a over reactionary bill pushed by the Carter administration we can’t use more modern technologies that we just sell to other countries…

          Oh well

    3. Speculawyer says:

      Close down the coal plants and install lots of: onshore wind, geothermal, solar PV, nuclear, offshore wind, concentrated solar power, biomass, hydropower, tidal power, and some natural gas peakers.

      Long DC transmission lines will be needed to couple different areas so that the power can be moved around as needed.

      1. Larry says:

        I thought DC was much less efficient than AC power transmission.

        1. Pushmi-Pullyu says:

          HVDC (High Voltage Direct Current) is used for moderately long distance transmission of power in certain areas. I don’t know about the details, but apparently it’s at least not much less efficient than AC transmission when that method is used.

          That shouldn’t be confused with local distribution of power. By analogy, HVDC is one method of bulk transmission on the wholesale level, but it has to be converted to lower voltage DC for local, “retail” distribution.

          1. Pushmi-Pullyu says:

            Edit: …it has to be converted to lower voltage AC for local…

      2. Mark C says:

        To that list { lots of: onshore wind, geothermal, solar PV, nuclear, offshore wind, concentrated solar power, biomass, hydropower, tidal power, and some natural gas peakers}, I’d add energy storage. Otherwise, I agree completely.

    4. Joeski1 says:

      Clean nukes?absolutely ridiculous. such thing..they emit heat , radioactive waste and kill sea life 24/7/365

      1. SJC says:

        Fast reactors use waste plutonium and depleted uranium for fuel, they don’t melt down.

      2. Pushmi-Pullyu says:

        Nuclear power absolutely qualifies as “clean”, as compared to other methods of generating electricity. The amount of waste generated per year is incredibly tiny; arguably the industrial waste from the concrete needed to build a hydroelectric dam and power plant is more damaging to the environment.

        In fact, some studies show that nuclear power plant is the safest form of power, if you consider all the totality of hazards to humans on the basis of per-kWh of power generated over the lifetime of the power plant.

        It’s unfortunate that the media, manipulated by Big Oil, has created the boogeyman that “RADIATION!!”, or more accurately radioactive waste, is somehow the only form of industrial waste that’s unacceptable. That ignores the reality: An estimated 15,000 to 30,000 Americans are killed each and every year by the air pollution generated by coal-fired plants. Obviously the death toll is much greater worldwide. Nuclear power is orders of magnitude safer in that regard.

        If humans were rational animals, we would long since have replaced every single coal-fired power plant with a much safer, clean energy nuclear power plant.

        1. Nix says:

          Yes, nuclear energy is clean and safe — as long as there are no Fukushima level disasters.

          The problem is that decades of operation that was cleaner, safer, and released less radiation than burning coal, all gets wiped out with a single accident.

          Fukushima released 14,000 to 17,000 terabecquerels of cesium-137 into the atmosphere, while about 3,500 terabecquerels directly flowed into the ocean.

          In the 1986 Chernobyl nuclear disaster, 85,000 terabecquerels of cesium-137 were released.

          So while nuclear power releases way less radiation than the estimated 1,000 terabecquerels per year globally that burning coal releases, a single nuclear disaster can release the equivalent of decades worth of burning coal.

          Unfortunately we can’t simply ignore accidents.

          1. Pushmi-Pullyu says:

            Nix said:

            “The problem is that decades of operation that was cleaner, safer, and released less radiation than burning coal, all gets wiped out with a single accident.”

            Nonsense. The World Health Organization estimates only about 4000 deaths worldwide from the worst-ever nuclear disaster, Chernobyl. The death toll due to Fukushima is estimated to be orders of magnitude less.

            Both together are far less than the death toll caused by one single year of coal-fired power plant pollution.

            The biggest “toll” from the Fukushima disaster was all the stress caused by hysterical over-reaction to a relatively low-level nuclear reactor leak, followed by the permanent evacuation of residential areas, of which about 85% isn’t contaminated enough to pose any danger to human health.

            As a matter of fact, I saw a news report on that just yesterday; I think it was on the NHK (English language news from Japan) news site. They showed a reporter wandering around in a sadly deserted area of the Fukushima evacuation zone, accompanied by a scientist explaining that the background radiation level there was less than twice the normal amount for Japan, and far less than the normal background level in many parts of the world.

            The over-reaction in Japan of all places is understandable, but still a result of public hysteria and government officials too craven to educate the public on the realities.

            1. Nix says:

              Pushy — Based upon your response, I think you are conflating two different issues.

              The numbers I provided are purely with regard to the the radioactive materials released by burning coal vs. nuclear plant accidents.

              But your response conflated in the effects of other harmful emissions released by burning coal, which are by far the bigger causes of death than the radiation itself. You have not presented numbers comparing radiation deaths from burning coal, to radiation deaths from nuclear accidents.

              If you check my numbers, you will see they are absolutely correct when comparing the radiation released by burning coal and the nuclear accidents I mentioned. At current rates of burning coal, it would take 100+ years to release the same amount of radiation released by just the 2 accidents I documented, and those are in no way the total amount of radiation released from human nuclear power plant related activities.

            2. Nix says:

              As for bashing the Japanese for “hysteria” regarding radiation, I would think twice about that from your safe home in the United States, considering the devastating effects of the US dropping nuclear bombs on the Japanese cities of Hiroshima and Nagasaki.

              I think their “hysteria” is warranted considering their unique history of being the only nation in the world to suffer the massive long-term effects of radiation.

    5. Lad says:

      This is a grossly flawed study; it linkings coal fired plants to EV charging. the load could be anything that uses the electricity that time of night. It could be any load; how about an oil jack. In that case, the conclusion would be pumping oil at night increases more pollution, Dah!
      The pollution is caused by the fossil fuel used by the plant. not by what the load is.

      The readers have been suckered into commenting on nonsense and this University should be embarrassed by this flawed study.

    6. Jim Whitehead says:

      This is a great example of lame “static analysis” and straight-line extrapolation. Make a paper airplane out of it, please. 🙂

      Why do you think NIGHT RATES are so low? Because most utilities can’t give away most of their power at night. That’s why utility-scale Tesla PowerPacks generate great interest.

      Just because a surprise large load at night is done by high polluting coal plants, doesn’t mean that (static thinking) they will be routinely used at night in an EV car heavy USA. This is a FICTITIOUS CRISIS.

      When in 10+ years, night charging becomes common, utilities will adjust their plant schedules, so that less polluting plants, like gas, will be left on longer from the day, to handle charging at night. Coal Plants can remain as old emergency backups.

      1. liberty says:

        I think its worse than static analysis, its misleading, and focuses on a non problem.

        1) get 20 million plug-ins running in US running an average of 10,000 electric miles a year to substitute 2000 GWh of electricity for 6.7 Billion gallons of gasoline.

        2) Build enough fast cycling ccgt and wind to cheaply charge all these at night, while reducing ghg from the grid during the day.

        Note the carnegie type study tries to pretend we need to do 2 before 1, but these plug-ins help pay for the grid improvements.

        Just 4 500 mw ccgt power plants and 1.2 GW of wind can supply that in 6 hours at night for a double high capacity. That is something very inexpensive when looking at the oil independance. With that you can retire a lot of stinky coal.

    7. manbitesgas says:

      Clean up, absolutely, but “clean nukes”?… Is that like “clean diesel”? Unless you’re talking LFTR, let’s not even open that can of worms. The cost alone of decommissioning nuclear could probably pay for all the batteries we’d need for 100% renewable grid.

      1. Pushmi-Pullyu says:

        Exaggerate much?

        Stabilizing and permanently storing nuclear waste is a political problem, not a technological one. France solved the problem long ago.

  2. Get Real says:

    Ridiculous, this supposed problem is rapidly going away as coal is quicklying being replaced by RE.

    1. Doug B says:

      RE is mostly daytime Solar, Wind is available at night but most nightime energy for most utilities is coal, so when you look at how clean energy is, midday during peak solar is often best.

    2. Speculawyer says:

      Lots of new renewable generation capacity is being added. However, since the capacity factor is pretty low, much much more needs to be added.

      And we’ll need more transmission lines to move the electricity around as needed.

  3. lewl says:

    All this confirms is you need to ditch coal already.
    Our baseload is nuke and hydro, and wind if it’s blowing that night.
    Definitely cleaner than the peak time gas plants. Which are cleaner still than the best coal plants.

  4. ericonline says:

    I agree this is ridiculous. Coal is being steadily replaced, and natural gas is so cheap now that these units run all nite. It makea little difference. Coincidentally I am an electricity trader in PJM. The average electron may be cleaner during the day. But marginal electrons will likely come from natural gas whenever you plugin. This study is junk science.

  5. bingo says:

    Hello. We all know the obvious answer–storage. Just talk to Tesla and get PowerPacks.

    1. Jychevyvolt says:

      Bingo, you win the model 3.

    2. Priusmaniac says:

      Or charging at work from the office solar panels for free.

  6. patrick says:

    Simple, put a price on carbon and electricity rates will be cheapest when there is the most renewable power available. Here in the NW we typically have a lot of wind at night. So this article title does not apply.

  7. ffbj says:

    B.S. from CM. Oh by the way is it just coincidence that two of the bigger robber-barons Carnegie and Mellon, who name is on this school created this study? Who funded it?

    Since 18GW of coal fired power plants were retired last year, mostly the older dirtier ones, CM should probably do a new study.

  8. ericonline says:

    In addition, charging at nite causes a flatter load shape (demand shape) for the grid. So there is less need for power plants to turn on and off altogether. This flatter shape increases efficiency in the system and leads to fewer carbon emissions. Turning units and off is both costly and energy inefficient. Also higher night time demand makes wind power more viable, so power companies are more likely to invest in new wind turbines as Electric cars become more common. Very disappointed in Carnegie Mellon on this one.

    1. ffbj says:

      Sure, and very predictable, as you suggest.

  9. Jeff Songster says:

    Just saw an excellent TED talk by Al Gore from the latest session in Vancouver BC Canada. He has a slide that shows the number of new coal power plants denied approval and the large number of decommissioned existing plants… so RE is rapidly replacing the stinkers. Just need to add more batteries to the grid and get solar on as many roofs as possible. Won’t be long now before we don’t need coal or oil.

  10. evcarnut says:

    WE won’t need , coal or oil, or them!….Good ridens!

  11. Anon says:

    Old, filthy tech, needs to be replaced by cleaner sources. Sorry Koch Bros.

    In my area, we have some wind turbines and (scary, old steam style that really should be decommissioned) nuclear. Solar hasn’t hit here big yet. But as people combine affordable, increasingly efficient panels with batteries for local grid / home use, it will spread widely.

    Small wind generators would work well here on the gusty prairie. They would just as easily attach to a powerwall type solution.

  12. wraithnot says:

    I bet the conclusion would be very different in Texas due to all the wind power they have there. In the “early hours of Sunday the 13th of September [2015]” the wholesale cost of electricity there actually went negative due to all the wind power. Although the power producers didn’t actually lose money because the subsidies they got for wind generation more than offset the negative wholesale cost:

  13. James says:

    How many cars are in their model? If it’s the current number, I find the study to be dubious, but if we are talking 100% penetration, sure, it would be bad on the current grid.

    I tend to charge my car while solar feeds it, and my wife’s car in middle of night.

    1. Nix says:

      They base their study on 10% of all cars in the US being 2011 Volts, 2012 Tesla Model S’s, and Toyota Prius PHEV’s, and that the power grid is from 2005/2010.

      The other 90% of cars in the US are all Toyota Prius Hybrids in their assumptions. No other ICE cars are mentioned besides hybrid Prii.

      They also assume that nothing will improve between now and when 10% of cars are EV’s charging late at night. The grid stays as bad as it was in 2005/10 (even though it has already improved since then), and pure EV’s will not ever be any more efficient than the 2012 Model S. Even though Tesla isn’t anywhere near the most efficient EV, and even Tesla offers newer versions of the Model S that are more than 10% more efficient than the original Model S

  14. William says:

    I don’t get this stupid report. The whole point of charging at night is to use electricity that’s already there, it’s been wasted because the demand is low, there are not enough EV to cause the power plants to increase production.

    If there are millions of EV charging at night and cause the power plants to increase production, then this report makes some sense.

    1. ericonline says:

      Capacity is there but electricity is not being wasted. When you plug your car in or flip a switch, a power plant somewhere ramps up a little.

      1. Spec says:

        No, that’s not true. A lot of power is wasted at night. It is difficult to ramp coal & nuke plants up and down so a lot of energy is just burned off and wasted.

        William is right. The number of EVs out there right now is so low that it really isn’t changing how they operate plants at night.

        1. JakeY says:

          That’s not quite right. What you say implies the electricity is 100% free, but in actuality what charging at night does is help raise the efficiency slightly (by not requiring the plants to ramp too low). That means while there is some advantage, it is not really from wasted electricity.

          1. Pushmi-Pullyu says:

            Both you and Spec are oversimplifying. Some base load coal-fired power plants are run 24/7, never powered down, because it takes hours to cool down or heat up the boilers, so they are run day and night whether there is enough demand for them to supply power to the grid or not. In that respect, Spec is correct.

            Where the argument Spec is quoting is oversimplifying is to state or imply that the average EV is getting all its electricity from such a base load plant, which otherwise would be wasted. Grid power is supplied from numerous sources, not just one. So yes, some of that power used at night might well have gone to waste otherwise. But most of it comes from other sources; sources which can be ramped up and down to meet demand.

            Spec’s argument is often repeated on pro-EV websites, so I don’t blame him personally for that. No doubt he thinks it’s entirely true.

            It’s unfortunate that some EV advocates are willing to throw out arguments using cherry-picked facts and half-truths. I wish we would leave that sort of dishonesty to the EV bashers, because the Truth is on our side. Far better that we stick to the standards of “The truth, the whole truth, and nothing but the truth.”

        2. ericonline says:

          Spec and William are completely wrong. Power is not wasted at nite. At any point in time the amount of electric generation matches exactly demand. This keeps the system frequency at about 60.0 hertz. Nuke and some coal units may always stay on and then natural gas units ramp up and down to balance out the system. So the instant you flip a lught switch on a natural gas units ramps up a little bit. Stop spreading misinformation.

          1. Nix says:

            ericonline — Sort of true.

            Actually, when you flip a single switch for a light, power plants don’t react at all. It is too small for the power plant to even notice.

            In the United States, our 120 V residential electric power is actually delivered at a range of 114 V to 126 V (RMS) (−5% to +5%).

            When you switch on your light, the voltage on the grid drops ever so slightly that it impacts nothing anywhere. The power plant continues to generate the exact same amount of power into the grid. Small variances in draw from the grid are essentially absorbed by small variances in grid voltage.

            Now when enough people turn on their lights to drop the voltage from (for example) 120 to 118, and it stays there, then maybe your local power plant might ramp up a generation source, and bring it online to bring up the voltage to 120.

            Then if enough people shut off their lights, the grid voltage will go up until they pull a power plant offline, and ramp it down. For example, your grid might hit 123 V, and then your electricity supplier would bring a plant offline, or a boiler at a plant offline.

            Over-generation above 120V is essentially waste. It is electricity that didn’t need to be generated.

            Energy used for ramp-up before a plant goes online is waste.

            Energy used after a plant goes offline during ramp-down is waste.

            Sometimes when a power source is brought on and offline, electricity that is produced during ramp-up/ramp-down is diverted to the earth/ground. This is waste.

            When your local power supplier (the guys who send you your bill every month) gets electricity, they may get it from power plants they own, or from power plants they contract with. Based upon those contracts, it may be cheaper for your provider to keep the power plant running all night than it is to shut it off and on. So you might see voltage on your grid start pushing 126 V. That is waste. They are over-generating to the grid.

            Many times, it is cheaper for the power company to sell this electricity at a very low price than it is to take production off-line.

            1. ericonline says:

              Nix, all conventional power plants have governors that respond to frequency (wind and solar plants cannot do this since) to conform the frequency to 60.0. This is largely done automatically and is a NERC requirement.

              You can read about it here if you are bored enuf.

              If a power plant pushes extra power onto the grid, other plants MUST ramp down to compensate. This is why prices often go negative in Texas when the wind blows. Otherwise prices would never go negative. The opposite happens when wind turbines suddenly stop producing. Fossil fuels must ramp up accordingly. This is one reason why wind plants are not as clean as people think. Conventional plants must be on and ready to ramp up when the grid is relying on wind power. Otherwise we’d risk blackouts every time the wind stopped blowing in Texas.

              Yes, obviously flipping a light switch is too small for anyone to notice. But my point is that plants have governors that are required by NERC to respond to deviations in frequency.

              I am a professional electricity trader and a NERC certified System Operator. I’m not sure why so many Pro-EV people seem to think electricity is largely wasted. Perhaps someone knows who started this misinformation? There is lots available capacity for units to stay on all nite rather than cycle off or ramp down.

              1. Bill Howland says:

                Yeah, I don’t know where Nix gets that nonsense. Perhaps he just thinks it works that way.

                The 114-126 volts at his house is more determined by nearby loads or by capacitors being thrown on the line (within a mile of the house), or else voltage regulators a few miles back at the last substation.

                In extreme cases the frequency can droop a bit on an isolated relatively low power grid suddenly trying to cope with a huge step increase, and vice versa.

              2. Bill Howland says:

                Incidentally, the voltage at my house is the worst I’ve seen in the Western World.

                On August 1st, my voltage is typically 108 volts (216 on the car charger) with absolutely nothing on in the house except clocks. It goes down from there.

                On the same day, houses in the first ring suburbs of the Buffalo Ny 60 hz substations (designed and built in 1920) remain at a pretty even 120 volts overall, even with the greatly increased air conditioning load.

                I’ve thoroughly examined why my relatively ‘modern’ installation is so inferior to stuff put in 95 years ago. If there’s any curiousity, I’ll explain.

      2. Bill Howland says:

        Hehe, you must appreciate this is turning into a comedy hour. Other than the coal issue, we agree.

        Spec I think is not using the term ‘wasted’ as the others are, he just seems to mean inefficient.

        Pushy says ‘some’ electricity is wasted, probably in the sense that it is discarded, which as you know is untrue. The fact that he is criticizing Jakey means Pushy as usual is totally clueless.

        It is always fun to watch a dunce take on the ‘aura’ of a big-expert.

        Now, Nix, man, you are knowlegeable in things youve talked about in the past, but that last post caused side-splitting laughter here.

        …”Actually, when you flip a single switch for a light, power plants don’t react at all. It is too small for the power plant to even notice.

        In the United States, our 120 V residential electric power is actually delivered at a range of 114 V to 126 V (RMS) (−5% to +5%).

        When you switch on your light, the voltage on the grid drops ever so slightly that it impacts nothing anywhere. The power plant continues to generate the exact same amount of power into the grid. Small variances in draw from the grid are essentially absorbed by small variances in grid voltage.

        Now when enough people turn on their lights to drop the voltage from (for example) 120 to 118, and it stays there, then maybe your local power plant might ramp up a generation source, and bring it online to bring up the voltage to 120.

        Then if enough people shut off their lights, the grid voltage will go up until they pull a power plant offline, and ramp it down. For example, your grid might hit 123 V, and then your electricity supplier would bring a plant offline, or a boiler at a plant offline.

        Over-generation above 120V is essentially waste. It is electricity that didn’t need to be generated…”

        “Power…114-126…(root mean square)”. Uh, yeah, the juice made generally is sinusoidal alternating current at roughly 60 HZ (exact over time since some clocks still depend on it – the governors ‘count cycles’ with respect to elapsed time and correct as necessary). My utility says ‘network areas are 5 % higher’. I’d say its 4 % (125 volt design).

        “When you turn on your lights, the voltage drops to 118….Utility ramps up….”.

        No – the juice to your neighborhood comes from medium voltage lines which are all locally regulated by the time you get it at your house.

        Ok, Nix, now here’s your side-splitter:

        “…Over-generation above 120V is essentially waste. It is electricity that didn’t need to be generated…”

        That is so wrong on so many levels.

        1). There is nothing magic about 120 volts. When a Tesla Model S dual charger draws 80 amps from the line, neighboring houses (if on the same can) will go down at anytime of day. It has nothing to do with generation.

        2). If the ‘generator’ is far away from the interstate ‘tie’ and the full output of this particular plant is desired, the voltage at the power plant MUST be HIGH to compensate for the presure drop in the transmission line. If powerfactor correction is also to be done, thats another complication I’m not getting into here.

        So, when many ‘lights’ are on so to speak, the generated voltage at the plant is higher, not lower.

        3). Again, the voltage at your house is TOTALLY INDEPENDENT of the juice coming out of any of the power plants ultimately feeding your house. Either with station type regulators at the neighborhood substation, or pole-mounted regulators on the individual feeder itself.

        When the juice is over 120 volts at my house, there is nobody dumping the juice into the ground. What a hare-brained idea.

  15. Friend o EV says:

    This is the whole premise behind the power wall and battery storage solutions. There is plenty of solar power available even in overcast climates as Germany has proven. We just need to eliminate coal power production – NOW – the whole research topic bugs me because it is regressive not forward thinking.

  16. EVs says:

    Maybe we shouldn’t watch TV at night, or use electricity to heat our pools and saunas since it is bad for the environment

    1. kdawg says:

      That’s what I was going to post too. No more TV at night, and don’t pop that microwave popcorn, unless you are an evil person.

  17. William says:

    Pump water uphill in the day and run hydro at nite. This can be done where elevation and lakes are not used to capacity!

    1. Priusmaniac says:

      Or pump less at night and charge the ev with excess wind power.

  18. Michael Will says:

    Destination daytime charging perhaps paired with bidirectional grid power control is the answer. Charge at work. Also solves the availability for people without garages, i.e. Apartment renters. Install more solar.

  19. jstack6 says:

    -Most Power plants have excess at night and can’t store it or Ramp down and meet the next days peaks. So they dump power at night.
    -The transformers and transmission lines are running at max during the day, they have very little loads at night.
    -Wind power comes a lot at night when there is already peak excess. In Texas one utility pays you to charge at night. All Utilties have low Time Of Day night prices.
    =So charging at night is best in many ways, even using excess COAL generated excess Off Peak. GET ALL THE FACTS =D–

    1. Spec says:

      This is a great post.

    2. ericonline says:

      Absolutely inaccurate. If a baseload power plant doesn’t ramp down at nite some other type of plant does (usually a gas plant) to balance out supply and demand. No electricity is wasted as you guys keep implying. Otherwise the system frequency would rise above 60 and your electronics would get fried.

      The point is though the coal units will produce the same amount of power weather you charge or not.

      1. patrick says:

        Excess generation on the grid does not change the frequency. It increases the voltage. And Yes, there is often surplus at night.

        1. ericonline says:

          There is usually a surplus of generating CAPACITY at nite, not energy being largely wasted. You guys need to stop spreading this misinformation. Who started all this? Power generation needs to closely match load (demand) at all times. This is exactly why power is so cheap at nite. There are lots of units on to meet daytime demand that have to either ramp down or cycle off at nite.

        2. Bill Howland says:

          “Excess generation does not increase the frequency,… it increases the Voltage.”

          Wrong on both counts Patrick. There is no such thing as ‘excess generation’ in the first place, and the voltage at your house is not determined by the generating plant.

          Its analogous to saying ‘my headlights are dim in my car, so therefore the car is out of gas’.

    3. Bill Howland says:

      “…GET THE FACTS…”.

      They aren’t getting them from you. A power plant with excess capacity does not generate ‘excess power’. That would be stupid.

      A lightly loaded plant uses less fuel than when it is going full boat.

      When you drive do u floor the accelerator and control the amount of speed you need by operating the emergency brake? Its that dumb.

  20. Joeski1 says:

    CMU is wrong… bunch of dweebs… they wasted energy on their inaccurate report.. the bottom line is an EV cuts down on greenhouse gases because it doesn’t burn oil.. by over 95%… if one creates just a bit of extra pollution at night.. it is a very small amount and meaningless in the grand scope of how much pollution is avoied by NOT burning gasoline to begin with.. they may be smart.. but they have no flipping common sense!!

  21. wavelet says:

    The study is idiotic; its conclusion is world-of-duh obvious “using more coal-based generation is more polluting than using less coal-best generation”. I hope it wasn’t funded by public money. They’re looking at things the wrong way around: Once there’s a significant number of people charging, that will drive significant changes in the generation mix as well.

    However, InsideEVs doesn’t have to help by reporting on this “study”, and if it feels it has to, at least reword the headline. There’s nothing inherent about the time-of-day here.

  22. Nix says:

    I started laughing when I started reading the assumptions of the study.

    First off, they assumed that PHEV’s would never get any better than the 2011 Volt with 35 miles of EV range, and EV’s would never get any more efficient than the 2012 Model S. Then they threw in the Prius PHEV, which isn’t even sold anymore. Then they extrapolated as if these cars magically became 10% of the total US fleet of vehicles.

    But both the Volt and the Model S have already improved, and it is literally impossible to go back in time and massively increase the number of 2011 and 2012 cars produced in the past.

    Then for grid numbers, they use 2010 and 2005 grid numbers, even though all of us here know that the grid has gotten cleaner since then.

    So they are pretending that older car technology, on an older grid, will magically still exist by the time 10% of all car drivers charge late at night at some unnamed date in the future.

    That simply won’t happen. It is a study of a point in time that will never exist. It is like writing a movie about humans riding dinosaurs and claiming it is a documentary.

    To add insult to injury, they simply assume that the power will come from coal power plants because it is currently cheap, without actually bothering to find out where late night power is ACTUALLY coming from.

    Even more absurdly, they assume that as Wind power increases, it will displace Natural Gas instead of Coal. But we’ve seen exactly the opposite, where Coal has been dropping while NG and Wind both increase power generation share.

    Finally, their assumption is that the other 90% of cars will all be Toyota Prius hybrids, and regular ICE cars are never even mentioned — as if they simply don’t exist.

    I laughed until I cried. Bad science at its worst. All they managed to prove is that if you make enough assumptions that are wrong and cherry pick data from different points in time that will never happen at the same time, that you can prove anything.

  23. Pushmi-Pullyu says:

    Is this “study” by Carnegie Mellon University just another hatchet job funded by Big Oil?

    The article says:

    “We found that charging late at night reduces power generation costs by a quarter to a third, largely by shifting to cheaper coal-fired power plants.”

    Looks like B.S. to me. The reason that electric utilities are shifting so rapidly from coal-fired to natural-gas-fired power plants is because it’s far cheaper to run them on natural gas; and the latter is also less polluting. If the night-time electric demand rises above the amount of power provided by “base load” power plants, which are almost all nuclear and coal-fired, then wouldn’t most utilities use a natural-gas-fired plant to make up the difference?

    Suggesting that on average, utilities would increase usage of burning coal, sounds like cherry-picking facts to fit an anti-EV FUD agenda. I have no doubt one could find specific instances where that would be true, but on average it simply makes no sense for utilities to choose to buy more more coal than to buy more natural gas, when the latter is much cheaper.

    I trust what the Union of Concerned Scientists says about EVs vs. gasmobiles, and greenhouse gas emissions. Most other sources reporting on these issues seem to skew their results to fit a political agenda, either promoting Big Oil or promoting an extremist “Green” agenda that ignores reality. (As an example of the latter, consider how “Green” advocates have been co-opted to support the counter-productive “hydrogen economy”.)

    1. Nix says:

      “The reason that electric utilities are shifting so rapidly from coal-fired to natural-gas-fired power plants is because it’s far cheaper to run them on natural gas;”

      They base their numbers on 2005 and 2010 grid statistics. It sounds like their assumptions about coal being cheap is based upon 2005/2010 numbers too.

      1. Pushmi-Pullyu says:

        Nix, I wish I had read your masterful analysis of the absurd premises this idiotic study is based on, before writing my response. I need not have bothered, because you really got to the heart of the study’s fallacies, and I only nibbled around the edges.

        Well done, sir! And thank you most sincerely.

        1. Nix says:


  24. Bill Howland says:

    A new low in idiocy.

    Any activity that tends to level electric consumption over a 24 hour period is more efficient, since more plants can run at more efficient rates. And transmission facilities will run at lower percentage losses.

    I agree with the sentiment that for a research result to be this bad, someone must have paid for it.

  25. martinwinlow says:

    Wow! Who knew? Using more electricity causes more CO2 emissions at the power plants! Not exactly rocket science but this is basically what this (no-doubt) hugely expensive bit of ‘research’ has concluded.

    The point is, it is better to have emissions at one central point than millions of distributed ones and the energy generated is, over-all, more efficiently used by powering EVs.

    With the number of EVs where it is now (and probably for a good 5 years yet) charging EVs at night allows the already stretched grid to cope. It wouldn’t cope if *all* vehicles suddenly became EVs, of course but we have a few years to sort it out. That together with the imminent boom in PV+storage should allow a transition to a much brighter future for sustainable transport.

    As a matter of interest, I did some sums and concluded that in the UK we would only have to find an extra 10% of electrical generation capacity to cope with the electrical demand of all the cars currently plying our roads.

    As an indication of how that relates to required PV installation, fully 2/3 of the electrical energy used by my small EV (Mitsubishi i-MiEV) that I use for a 45 mile daily commute (50% more than the national average, BTW) has been offset by the 1.2kW PV array I installed nearly 2 years ago on my garage roof. And it isn’t even a very ideal situation due to tree shading issues.

    Martin Winlow

  26. Someone out there says:

    I’m sure there are specific places and times where these conclusions are true but I very much doubt it’s valid for the general case. This leads me to believe that this study is more propaganda than science. Somebody wanted these results so these “researchers” set out to find a circumstance where it happened to be true.

  27. Rick says:

    When I read the title, I thought it’s a general problem… thankfully doesn’t apply to this part of the world 🙂

    1. Scramjett says:

      Yes, here either. California is all gas boilers or Combined Cycle Gas Turbines with simple cycle gas turbines for peak loads.

  28. Scramjett says:

    Ok, I obviously didn’t read all 70 comments so this may have been addressed, but here goes. I wonder if the study authors took into consideration the fact that most of these plants are in operation during the night already? One of the arguments in favor of night time charging was the unused capacity that power plants generate. I recall reading a number of years ago that the unused night time capacity of power generation could handle night time charging if some 70% to 80% of the vehicle fleet were converted to plug-ins. It seems to me that the point here (as has been mentioned) should be that we should get off of coal and that the results of this study are:

    a) Applicable to a very few special cases, and
    b) May not have as significant an impact on emissions if the emissions are already being produced anyway.

    I’d be curious to see if the study assumes that these coal plants would have to be ramped up to a higher capacity rather than idled (note that “idling” power plants still generate power, hence the unused night time capacity).

  29. Nix says:

    Scramjett —

    It is important to know the difference between “capacity”, “generation”, and “consumption”.

    “capacity” is how much electricity COULD be generated if every power plant were running at full load.

    “generation” is how much electricity IS generated.

    “consumption” is how much electricity is actually used by consumers after losses.

    It is correct that we have enough unused capacity at night to charge around 80% of vehicles in the US. This means that we would not have to build any new power plants at all to provide this electricity. We could simply leave these power plants online, and not shut them down.

    This is often used to fight the FUD that if we shift to EV’s, we will have to build thousands of new power plants. We won’t.

    But “capacity” doesn’t have much to do with actual electricity production or consumption.

    To your point b), capacity isn’t the same as generation, so emissions aren’t necessarily being produced when a plant is offline (it depends upon the plant).

    The study ASSumes that at night coal plants will be ramped up, based upon 2005/2010 grid data, and that natural gas generating will be taken off-line. They don’t base this on actual data from power companies doing this, they just assert that coal is the cheapest source, and will always be the cheapest source. And that on some unnamed future date when 10% of the US fleet are EV’s charging late at night, that coal will still be kept online while other greener sources are brought offline.

    This is one of the ASSumptions of the study that is highly questionable.

    Here is a link that might help:

  30. JR says:

    This is a typical example, how to create FUD again. It is all ways possible to find some examples, and create some general truth from this.
    Well in DK we shut down wind turbines sometimes during nights, becourse we cant use the electricity they produce

  31. Phr3d says:

    I am late to this party, as usual, and presume I’ll get no response.

    My understanding is much like Nix’s, Bill, and I hafta’ wonder if I am lacking in correct terminology, a la kW vs kWh.

    I have electricians throughout my family and have had many ‘interesting’ classes that I managed to pass.

    so my basic 5th grade understanding is that AC is great for some things, DC is great for others. my understanding is that AC is Not great for efficiency, but who-cares as central generation and improved distribution outweighed the efficiency aspect.

    simplest terms, from my substandard knowledge is that a generator creates kWh’s for use in a loop – if the devices on that loop use All of the kWhs created, you have 100% utilization and perfect efficiency (simplification here, ok?). This is where I begin to use the term Waste, which seems absolutely laughable to you and Your experience as I am missing some very important factor. If the generator supplies 1kWh of power at a given cost, and only .5 kWhs are actually Needed, where does that remaining .5 kWh Go?

    Obviously many questions continue from this, i.e., a given generating facility uses power (often referred to as Excess power) to move water for hydro, overnight. Why would they do that, unless there was ‘surplus’ as moving water to generate electricity is necessarily inefficient, so my humble neurons concluded that That energy creation (and used to move the water) would be.. wasted.. unless they performed -some- work with it.

    So, to the many that ‘cannot get’ where these ‘ideas’ came from, this is a miniscule slice of why we thought it was the case, and I have not found anything that refutes my conclusions, and I have looked around a Lot.

    I hope that this gives some illustration of why our laughable conclusions seem well researched and reasonable to me, and look forward to any education (using small words) that you are willing to convey.

    Thanks to all for a very interesting commentary.

  32. G2 says:

    This study sounds like it was funded by the Koch brothers; in other words it is complete propaganda.