The Truth About Electric Cars Biggest Problem

hello everyone and welcome if you watched my video on why the combustion engine is far from dead then you saw my energy density comparison of gasoline cars versus electric cars so what we're looking at here is the same amount of energy by volume whether it's in the form of gasoline as one gallon this is representing 33.7 kilowatt hours of energy or in the form of cans of lacroix representing our lithium-ion battery cells 140 cans here in front of us now technically it should be 139 so tangerine's a close second now rightfully many of you pointed out that when i'm discussing energy density i should mention efficiency and while they are different it is absolutely a fair point because both of these while they represent the same amount of energy an electric car can go much further with its energy so this one gallon of gasoline might get a gas core 40 miles where this 33.7 kilowatt hours of electrical energy could get an electric car a hundred miles so a more fair comparison would look like this this is 2.5 gallons so now both of these can travel the exact same distance but bringing efficiency into the equation isn't nearly as simple as it sounds so in this example we're looking at a combustion engine operating at about 35 to 40 percent efficiency mazda toyota probably others have gasoline engines that can operate above 40 percent and then for the electric vehicle we're assuming today's best energy density matched with about 90 plus energy efficiency this in my opinion is the most fair way of showing this comparison when taking efficiency into consideration however it is also fair to say that most gasoline engines aren't actually operating at 35 efficiency so you'd likely need a bit more fuel so let's take this to the extreme if we were to compare a bugatti chiron capable of an impressive 11 miles per gallon combined to a tesla model s performance both with similar 0 to 60 times though very different top speeds the comparison would look more like this so the bugatti needs a gallon to travel 11 miles and the tesla model s only needs 16 soda cans to travel that same 11 miles so by volume the amount of energy they need is actually really close combustion engines can be embarrassingly inefficient when used outside of their designated purpose which for the she-run is to go really fast a tesla operates super efficiently under most circumstances but likewise not all batteries are equal and this represents today's best production lithium-ion batteries not today's average batteries and again this is just the size of the battery cells so the actual battery would be significantly larger once you incorporate the cell connections battery cooling and the housing for the battery in summary as far as energy density is concerned gasoline has about a 13 times advantage by volume and a 50 times advantage by weight and when you take efficiency into account that translates to a five times and 20 times advantage respectively so combining energy density and efficiency is challenging it's not always as simple as saying electric cars are three times as efficient they often are but here's four things to consider first it depends on the scenario an electric hyundai ioniq has a 2.5 times efficiency advantage versus a gasoline hyundai ioniq when driving in the city but it only has a two times advantage in efficiency when driving on the highway so the driving scenario plays a big role now yes the hyundai ioniq is a hybrid but its energy source is gasoline second we're assuming you're comparing similar cars apples to apples like ionic to ionic but real world people's car purchases are all over the place if you go from a hyundai ioniq to an audi e-tron you're only improving your efficiency by about 30 percent if you go from a jeep wrangler v6 to a tesla model 3 standard range your efficiency improves 700 percent third ambient temperature plays a big role studies have shown that low outdoor temperatures can result in electric cars reducing their range by up to 40 percent and cold temperatures also affect gasoline cars but not as much since electric cars use the battery pack for cabin heat while gasoline cars use energy that would otherwise be wasted to heat the cabin and fourth weight adding range to a gasoline car doesn't cause it to weigh much more so if i wanted my hyundai ioniq to go 60 miles further i just add one gallon which is only six pounds so it doesn't really change the fuel economy of the vehicle adding 60 miles of range to an electric hyundai ioniq means adding 15.2 kilowatt hours of battery which weighs 140 pounds in just the cells alone so you're effectively carrying another passenger in the car to get that extra range and perhaps you've experienced this but the more passengers you add to your car the worse your fuel economy is so adding range hurts overall efficiency more in an electric car versus adding range to a combustion car regenerative braking helps here but it certainly doesn't make up for all of it and adding any weight increases rolling resistance which is using energy any time you're moving so what's my point well my point is exactly what i said in the previous video right now passenger cars are the sweet spot for electric transportation it makes plenty of sense but because of the challenge of energy density if your vehicle gets larger it makes it more difficult for that transportation to be powered by lithium-ion batteries now i've already made a video explaining why it's tough to tow with an electric passenger vehicle so let's take this one step further and analyze an electric semi truck highway trucks are federally limited to a weight of 80 000 pounds some states allow for significantly higher but let's just use the federal limit as an example and let's assume we have a drag coefficient of 0.4 which is exceptionally good big wheels and tires the ride height and the gap between the tractor and the trailer all make it very difficult to have low drag coefficients like you see with passenger cars now you may have seen claims that the tesla semi has a drag coefficient of 0.36 but remember a big part of this number comes from the trailer you're pulling if you have a non-typical trailer for example pulling a load of cars that drag coefficient dramatically increases for the frontal area of the truck we'll go with a hundred square feet it could be a little larger but this is a fair estimate and we'll say we want our semi-truck to have a range of 500 miles starting with aerodynamics we can do the math and we need about 430 kilowatt hours of energy to overcome aerodynamic drag alone to travel 500 miles while driving at 65 miles per hour obviously that number would be a lot larger if you wanted to travel at a faster speed or if the trailer wasn't the ideal shape now we also have to include the energy for overcoming rolling resistance this isn't a big deal in passenger cars because they don't weigh that much but it's a huge deal in semi-trucks because we're talking about hauling 80 000 pounds so doing the math the energy required to overcome rolling resistance over 500 miles of driving we get 517 kilowatt hours now you might be wondering why is this number higher than the aerodynamic drag number part of it is because trucks are super heavy the other part is that our aerodynamic example has unrealistically low variables to account for all scenarios if you were to plug in a drag coefficient of 0.6 instead of 0.4 still very good for a semi truck and travel at 75 miles per hour on the highway something i've commonly seen driving in the northwest you would need 858 kilowatt hours of energy to overcome aerodynamic drag but let's go back to our original math adding the energy required for rolling resistance and drag we have a total of about 950 kilowatt hours of energy required to travel 500 miles let's say our powertrain operates at 95 efficiency again extremely good we need a total of a thousand kilowatt hours and with an energy density of 250 watt hours per kilogram for the battery cells this means our battery cells alone would weigh 4 000 kilograms or about 9 000 pounds so in the case of a highway truck with a 500 mile range 9 000 pounds of our total vehicle weight is made up of just battery cells alone this could easily be 15 000 pounds when you include all of the battery coolant battery housing and materials required for the entire battery structure and if you want to travel faster than 65 miles per hour or have a range greater than 500 miles or allow for a battery buffer of 20 percent so that the battery degradation over time is low or want a battery buffer to account for wind or elevation changes or acceleration which we've conveniently left out you could easily hit 20 000 pounds for the battery so now a quarter of your truck's weight is taken up just with the battery so you're left with 60 000 pounds to accommodate the truck the trailer and whatever cargo you're taking and because you're paid based on how much cargo you can take obviously this is a bad thing not to mention the equivalent of 10 model s battery packs will be extremely expensive and while operating costs will be lower for your truck if your carrying capacity is reduced you could also be reducing revenue per truck a quick comparison versus a diesel semi truck which gets about 6.5 miles per gallon you'd need 77 gallons or about 540 pounds in weight to travel 500 miles yes a diesel power train is heavy but so are the electric motors and inverters and controllers that we need to discuss in the electric powertrain so once again the point being that energy density with electric vehicles needs to improve okay here's the thing i'm optimistic i respect the heck out of all the engineers out there working on these problems these are very difficult problems and it's super easy for some idiot on the internet to be like no it's too difficult the emissions benefits of electric cars is very real and quite substantial i have videos diving into this in great detail if you're interested so ultimately my point isn't that we should give up on evs it's that it's going to take some time before they're viable in a lot of situations if you're an automotive engineer props to you and thank you for doing the real work and thank you all so much for watching i should probably thank automotive engineers at the end of all of my videos and in this case lacroix if you have any questions or comments feel free to leave them below

Channel: Engineering Explained

Views: 845,687

Keywords: gasoline, diesel, gas engine, diesel engine, combustion engine, ICE, EV, ICE vs EV, electric car, tesla, tesla model 3, tesla model y, gas vs electric, energy density, consumer, buy a new car, buy used car, car buying, environment, green cars, cars, trucks, profit, car makers, engineering explained

Id: oJL9MasBFvM

Length: 10min 33sec (633 seconds)

Published: Wed Feb 12 2020