Electric car engineering issues

[CraigD]

Moderation note: The first 12 posts of this thread were moved from the Community polls thread “to bailout, or not to bailout”, because they are a discussion of electric car and electric power engineering, not a discussion of the pros and cons on government bailouts of businesses.

Originally Posted by C1ay

I think vehicle development, be it private or not, is a small part of the problem of accomplishing the dream of converting our transportation infrastructure to an electrical energy source. If one calculates the amount of chemical energy currently used across the nation from petroleum fuels to find the amount of electrical energy that would be required to replace it they will find our electrical generating capacity and the distribution capacity of the power grid is but a tiny fraction of what it would need to be. The average megamart fuel station today would need to be a mini-nuclear facility to charge the same numbers of cars they see today with an equivalent amount of energy as they currently get with a fillup of gasoline.

I don’t think this is accurate. Although a bit off-topic, I think this is an important enough issue to discuss here.

According to this US DOE summary, of 101600 trillion BTUs total energy consumed in the US in 2007, 29096 was used in transportation (29%) which includes passenger cars, busses, trucks, trains, and aircraft), while 40567 (40%) was used to generate electricity. So, assuming that all transportation could be reengineered to use generated electricity (an unrealistic assumption, see below), the increase in demand for generated electricity would be about 70%, about the same as the increase that occurred between 1979 and 2007.

A large car gas tank hold about 90 L (24 gallons), about 2.3 GJ energy (). A typical US residential home (mine, for example) can deliver at a single outlet about 8800 W (the “dryer” circuit, 40 A at 220 V, limited by a breaker). So, ignoring transmission and other inefficiencies, without substantial rewiring, a typical home can deliver electric energy equivalent to a tank of gas in about 260000 s, about 3 days.

The tanks at typical neighborhood gas station hold about 60000 L (15000 gallons) of fuel, with an energy density of about 25 MJ/L, for a total energy of about 1.5 TJ (). A small nuclear reactor, such as those used on small warships and submarines, (eg: a US naval D2G reactor) generate about 150 MW power. So a small nuclear reactor delivers the energy stored in a neighborhood gas station in about 10000 s, about 2 hours 46 minutes.

There are certainly large scale engineering and planning issues that must be addressed if many vehicles are made to use stored electric power rather than fossil fuel, but I don’t think these issues are overwhelming. The big problem is not, I think, electric generation and delivery, but battery or other storage energy density. At present, a major class of vehicles, aircraft, can’t practically be made to run on stored electricity (see “Airframe design, and some daunting numbers for electric airliners”).

On a practical note, having a rechargeable electric car of the kind available today (or from 1997 to 2003, when the EV1 was in use) means you don’t recharge at fuel stations, but either at home, or in specially equipped parking places. Batteries take to long to charge to “wait at the pump” as we do when filling our fuel tanks.

[C1ay]

First consider the fact that there are power grids now that suffer rolling blackouts during peak usage times as a result of overwhelming demand. These grids are already short of capacity and loading them with the local transportation loads would simply add to that problem.

Secondly lets play with a little math to get us in the ball park. For the sake of easy computing let's assume the average fill up of gasoline is around 10 gallons. Let's also assume that by converting to electric we can gain an increase in efficiency that would allows us to fill up with only 40% of that figure since combustion engines are considerable less efficient than electrical propulsion systems. That brings our fill up equivalent to 4 gallons of gas.

Various sources on the internet give an equivalency of 120,000,000 joules to 130,000,000 joules of energy per gallon of gasoline, an average of 125,000,000 joules. That 500,000,000 joules per fill up.

Now suppose 10 minutes is a reasonable amount of time for someone to pull into the station and pump 500,000,000 joules of power into their vehicle. At 600 seconds that's around 833,333 watts per second or 3,000,000 kwh per vehicle to fill up. Multiply that by the number of cars per day filling up at a station and you'll get an idea of the power requirements.

These numbers get better of course if you allow an hour for a fill up or you build in enough capacity that cars only charge at night but I don't currently think the grids are even sufficient for that.

[Zythryn]

I believe a number of these assumptions are faulty.
First, I plan on spending no time filling up my EV as I will be plugging it in at night.
This is for convenience, yet it also has the side affect of using energy that is otherwise basically wasted. As many power plants continue to run overnight weather the power is needed or not.
Second, no one is going to flip a switch and have the entire transportation system running on electricity.
Some vehicles will be unlikely to ever make the switch (trucks hauling goods for example, or other long distance applications).
As for 3,000,000 Kwh to fill up a car, that is way off. My EV will have a 35Kwh capacity which will get it between a 100-150 mile range. Even if you double it, the stated requirement of 3 Million Kwh is still of by a factor of 40 Thousand or so.
I will see if I can find the study, but I believe there was an estimate that the current electrical infrastructure would be adequate if 20% of the cars on the road were EVs. Yes, we need improvements, but I don't think we could reach 20% in ten years time even if the big auto makers got on board.

[CraigD]

Originally Posted by C1ay

First consider the fact that there are power grids now that suffer rolling blackouts during peak usage times as a result of overwhelming demand. These grids are already short of capacity and loading them with the local transportation loads would simply add to that problem.
…
These numbers get better of course if you allow an hour for a fill up or you build in enough capacity that cars only charge at night but I don't currently think the grids are even sufficient for that.

As you note, C1ay, the inconstant demand that results in the need for rolling blackouts is a point in favor of electric cars. It’s often cited by electric car proponents.

Inconstant demand for electricity is what leads to the need for rolling blackouts. Mostly because of building cooling (air conditioning), demand for electricity is greatest during the day, and increases on hotter days. As a result, electric generator plants must be designed to produce much more power than their daily and yearly averages at peak hot day times, and much less at night and on cold days.

Because most electric cars are recharged between the time their users return home in the evening and leave for work in the morning, their demand occurs during off-demand hours, “leveling” power generation demand. Also, as an uninterrupted supply of constant voltage isn’t needed to recharge a battery, car charging could be supplied by separate supply lines, or managed by in-house systems, giving power managers more flexibility in supplying electricity.

Some have gone even further, utilizing the collective storage capacity of electric cars as part of the power grid itself. Because most cars are parked during periods of peak daytime cooling demand, their users having commuted to work earlier, if their batteries were connected to charging stations, they could actually be drawn down to make up for shortages from the power plants. After peak demand had passed, they would be charged back up.

All of these “power leveling” schemes are financially advantageous to power supply companies, savings that they could pass on to EV owners as reduced electric bills.

I couldn’t find a good reference on daily power demand, but based on the graph in this wikipedia article, typical daytime peak power demand appear to be about 40% greater than nighttime lows.

Originally Posted by C1ay

Secondly lets play with a little math to get us in the ball park. For the sake of easy computing let's assume the average fill up of gasoline is around 10 gallons. Let's also assume that by converting to electric we can gain an increase in efficiency that would allows us to fill up with only 40% of that figure since combustion engines are considerable less efficient than electrical propulsion systems. That brings our fill up equivalent to 4 gallons of gas.

Various sources on the internet give an equivalency of 120,000,000 joules to 130,000,000 joules of energy per gallon of gasoline, an average of 125,000,000 joules. That 500,000,000 joules per fill up.

I agree with the calculation so far. It agrees with the reference I gave to this wikipedia reference table in post #24.

Originally Posted by C1ay

Now suppose 10 minutes is a reasonable amount of time for someone to pull into the station and pump 500,000,000 joules of power into their vehicle. At 600 seconds that's around 833,333 watts per second or 3,000,000 kwh per vehicle to fill up. Multiply that by the number of cars per day filling up at a station and you'll get an idea of the power requirements.

: You’ve made a unit converting mistake here. “Watts per second” (which would be a unit of change in power) is not a normally used unit. 1 watt (a unit of power) is defined as 1 Joule per second.



so , not 3,000,000.

Practically speaking, there’s no current market-ready technology (at least none I know of) that will allow a car-size battery, such as the lithium-ion batteries in the Tesla roadster, to be recharged in 10 minutes. The Tesla, for example, requires at least 3.5 hours (210 minutes) to recharge its 53 kWh battery system, and is capable of this rate only because it has a motor driven liquid cooling system. It’s wise, I think, to assume that electric car recharging will remain an overnight processes for some time to come.

I’m not disputing that replacing all or a large fraction of oil-powered vehicles with electric ones would not be an engineering challenge. I am disputing that it’s an overwhelming one. As I noted in post #24, according to US energy use data, it’s less of a change than the routine electric system changes that were made from 1979 to 2007.

[C1ay]

Food for thought.....

Even with a low capacity vehicle like you mention, 35kwh, you would more than double the average household power consumption for each vehicle you connect.

[C1ay]

Originally Posted by CraigD

I am disputing that it’s an overwhelming one.

I'm not saying it's overwhelming, only that the current power grid won't support it and getting the power grid to that point is an investment that will more likely require government money instead of private money.

Originally Posted by CraigD

You’ve made a unit converting mistake here. “Watts per second” (which would be a unit of change in power) is not a normally used unit. 1 watt (a unit of power) is defined as 1 Joule per second.



so , not 3,000,000.

Ah yes, I see. It is still not a quantity our current power grid or battery technology can meet and it will likely require more funding that private funding will allow if we are to get there in the short term.

[Zythryn]

Originally Posted by C1ay

Food for thought.....

Even with a low capacity vehicle like you mention, 35kwh, you would more than double the average household power consumption for each vehicle you connect.

Even if that is the case, you again are mainly drawing power during off peak times when there is a surplus of electricity.
Are you also basing that on a full charge each day?

In my personal case, even if I did use 35kwh a day to charge the vehicle, I would still use less than my neighbor does running lights and heating his pool

[CraigD]

Originally Posted by C1ay

I'm not saying it's overwhelming, only that the current power grid won't support it and getting the power grid to that point is an investment that will more likely require government money instead of private money.

Despite the opinion of 9 of 10 respondents to this pole, I think it’s more-or-less a political and commercial given that any big investment project in the next few years in the US, and to some extent, the world, will require government money instead of private.

When it comes to this sort of infrastructure project, I suspect most of the people who replied “no” to this thread’s question “should gm or anyone be bailed out?” would reply “yes” to “should government fund large-scale power system projects?” Rather than just guessing, I’ve started a new poll thread, “Should national governments manage and pay for large power system projects”.

[C1ay]

Originally Posted by Zythryn

In my personal case, even if I did use 35kwh a day to charge the vehicle, I would still use less than my neighbor does running lights and heating his pool

That wasn't the point. Could the power grid in your neighbor and 10s of 1000s of neighborhoods across the country withstand a doubling of demand? How many families in your neighborhood will need to charge 2 or more vehicles per night at least 5 nights a week? Wouldn't such a scenario make nighttime the new peak demand period?

Yes, we can get there slowly upgrading a little at a time. The difference we're discussing though, in this side topic to the OP, is how fast private management and investment will get us there vs government agency management and investment.

[Zythryn]

Sorry, I jumped a bit ahead of myself.
First, again, you aren't going to flip a switch and have everyone running electric cars. The first few models of pure electrics will likely be bought by people who almost never take a trip longer than the range of the car, or families that will have one electric and one car capable of longer trips.
Two, and this is the part I skipped on, EVs will start to be bought by people concerned by the amount and type of energy we use. As such, I am guessing they will also be people that conserve in other ways.
I do believe there are challenges and that our grid will need expansion, but I don't believe it is as impossible as you are making it sound.