[alancalverd]

If you take the government's annual fuel consumption figure of about 1 tonne per car (they know, because they collect the fuel tax!) at 47 GJ/tonne and utilisation of 1 hour per day, you get an actual  continuous power consumption of 1252 GW for 35,000,000 cars, so my previous estimate is a bit low.

There is no inherent aerodynamic superiority in electric cars. Current Tesla S has a drag coefficient of 0.24 against a BMW 7 of 0.22 and the ancient Citroen CX managed 0.21 on the days when it actually worked (I've had a couple, and probably spent more time under them than in them, mais quelle voiture!)

[Bored chemist]

In the UK  in 2019 we used about 50 billion litres of petrol and petrol
https://www.racfoundation.org/data/volume-petrol-diesel-consumed-uk-over-time-by-year
It delivers about 45 MJ/ Kg or about 35 MJ/Litre
That's roughly 1.8 * 10^18 Joules

A year is 3E7 seconds
So the average power is about 58 GW

UK electricity use is about 300 TW Hr per year
https://www.statista.com/statistics/322874/electricity-consumption-from-all-electricity-suppliers-in-the-united-kingdom/#:~:text=Consumption%20of%20electricity%20in%20the,301.76%20terawatt%20hours%20in%202019.

That's about 1.1 *10^18 J

So, in the UK in 2019, the energy supplied as petrol and diesel was roughly twice (more accurately 1.6 times) that supplied as electricity.

So, we need to something really stupid and triple the gird capacity, or we need to do something sensible and reduce the vehicle energy demand.

It's fair to assume that almost all of the petrol and diesel were used in vehicles.

[alancalverd]

So we agree on something! I think we are due for a wager.

I bet a pint of Greene King Abbot that I can reduce the birthrate by paying women £1000 a year not to be pregnant, before you can persuade the British public to reduce their car mileage to something sustainable. 

[Bored chemist]

OK.
I win.
The mileage is sustainable; the energy source isn't.

[alancalverd]

You mean you are going to get everyone to walk?

[Bored chemist]

You mean you are going to get everyone to walk?

I haven't made up my mind, but since the problem is not the mileage, but the energy source I don't have any problem meeting the

reduce their car mileage to something sustainable

criterion.

If we were actually able to harvest (and that might be a literal harvest) enough energy from the Sun, the mileage wouldn't matter.

[wolfekeeper]

So, in the UK in 2019, the energy supplied as petrol and diesel was roughly twice (more accurately 1.6 times) that supplied as electricity.

Um. Yes, but actually no. You've fallen into the classic trap. These things are not directly commensurate.

That's THERMAL energy. Thermal energy, except for heating spaces, is much less valuable and efficient than electricity because it's high entropy- it's highly disordered energy. Electricity has low entropy and so can be converted into other forms with very high efficiency- it's not limited by the Carnot cycle. Thermal energy; not so much, efficiency is really limited.

Overall, electric cars are about three times more efficient than petrol per kWh of energy input (the mpge measure is per unit of energy is usually well over a hundred, depending on the model and terrain etc. also depending on which gallon you use, electric cars are usually well over 100 mpge_us, the us gallon is rather smaller of course, and so way over 100 mpg_e_uk).

So, no.

So, we need to something really stupid and triple the gird capacity, or we need to do something sensible and reduce the vehicle energy demand.

No and the grid already has the capacity to carry 55+GW of demand- it's carried that before, but usually runs a demand that's more like 20-40 GW. So there's huge capacity that isn't being used, and electric cars overwhelmingly recharge overnight, when demand is low anyway.

National Grid ESO say there's absolutely no problem, and indeed want electric cars, and trucks, deployed as soon as possible, because it's going make the grid more efficient and reduce costs for everyone, from better amortisation of the hardware.

[Bored chemist]

Thermal energy, except for heating spaces, is much less valuable and efficient than electricity

Yes.
I know all that.
Are you aware that, most of the time in the UK, a car is a space that needs to be heated?

Setting that aside, the electric car may be 3 times as efficient, but that still leaves the "energy bill" in the same ballpark as the electricity supply.
Dividing 1.6 by 3 doesn't suddenly make it 0.1 or anything small enough to be very helpful.

We really should move to dropping our travel energy use.
It's possible that self driving cars will revolutionise that (provided our employers don't want us to start work at 9 sharp).

[wolfekeeper]

Oh wait, I thought you said:

So, we need to something really stupid and triple the gird capacity, or we need to do something sensible and reduce the vehicle energy demand.

And that's because you did.

Setting that aside, the electric car may be 3 times as efficient, but that still leaves the "energy bill" in the same ballpark as the electricity supply.
Dividing 1.6 by 3 doesn't suddenly make it 0.1 or anything small enough to be very helpful.

Let's do the calculation! Dividing 1.6 by 3 gives you 0.5. So the demand goes from 1 to 1.5. Oooh sounds scary.

But note that's kWhs, NOT kW.

Kilowatts would be a problem. Installing extra CAPACITY (kW) costs serious money. Pumping more kWhs through the same capacity makes things cheaper, because hardware amortises down.

Because electric cars want the cheapest electricity they recharge overnight, when the kW demand is lowest. So you're just filling in the demand gap there already is, which has actually been quietly costing everyone money for decades. That's actually why Economy 7-10 etc. was invented to try to make use of it.

Mostly electric cars these days have plenty of capacity. They drive about ~30 miles a day, but have ~150-300 mile range. So there's no big deal. They can wait for when there's a solar or wind peak and then suck down cheap electricity.

[Bored chemist]

I see you are waiting for a solar electricity peak at night.
This could be a problem.

Oooh sounds scary.

Yes. A 50% increase in average grid power at the same time that we are shutting down coal, cutting back on gas and have run out of "low hanging fruit" for renewables is a bit scary.

We could make our lives easier by staying home.

[wolfekeeper]

We haven't run out of any fruit, there's plenty of scope for more solar and wind power installation, the long pole in the tent for getting a lot of electric cars in the UK is the low availability of electric cars from manufacturers.

[Bored chemist]

there's plenty of scope for more solar and wind power installation,

Nobody said there wasn't.
But, either the people who installed the first generators were stupid, or the best locations are already taken.
That's what "low hanging fruit" actually means.

[alancalverd]

Overall, electric cars are about three times more efficient than petrol per kWh of energy input

Sadly, no. The "energy input" starts at the power station. You can get 90% conversion efficiency from a new battery, but making the electricity from gas, coal or a nuclear reactor is only about 50% efficient.

It's directly comparable to a gasoline engine: the gear train can be 90% efficient but the prime mover struggles to beat 45%.

All that electric cars do is shift the CO2 burden from the point of use to the upper atmosphere.

This is the 10th successive day with no wind above 4 GW, and the umpteenth night with no sun. Sadly, I have to go to work tomorrow, so we'll have to close a hospital ward so I can charge my car.

[wolfekeeper]

there's plenty of scope for more solar and wind power installation,

Nobody said there wasn't.
But, either the people who installed the first generators were stupid, or the best locations are already taken.
That's what "low hanging fruit" actually means.

Except that the costs/kWh of, for example, off-shore wind farms are still going down pretty fast, as are the costs of on-shore solar farms. Cameron's government basically put a moratorium on new on-shore wind turbines, and tried to cancel existing agreements with the claim that, 'nobody really wants any more on-shore wind farms' even though they were cheaper than off-shore ones at the time (and even now still), and polls showed they were really popular. That has since been lifted by BoJo, but the on-shore wind turbine industry had come to a shuddering halt.

So, no. The low hanging fruit has not been picked, the fruit is still growing towards the ground.

Overall, electric cars are about three times more efficient than petrol per kWh of energy input

Sadly, no. The "energy input" starts at the power station. You can get 90% conversion efficiency from a new battery,

Lithium ion batteries have ~98% storage efficiency.

but making the electricity from gas, coal or a nuclear reactor is only about 50% efficient.

Coal plants are usually more like 35-40%. Natural gas CCGT plants can reach ~55% but only after some hours of running.

It's directly comparable to a gasoline engine: the gear train can be 90% efficient but the prime mover struggles to beat 45%.

Gasoline car engines are more like 35% efficient in the round. Diesel engines have approached the efficiency of electric vehicles in some cases but many of them generate large amounts of particulates, and they're rapidly dropping behind as grids become greener.

All that electric cars do is shift the CO2 burden from the point of use to the upper atmosphere.

If your electricity is being generated entirely from coal plants, which until recently some parts of America (and Australia) have been guilty of (about 700g of CO2 per kWh), then it can be true that electric cars can be worse, but the UK's electrical grid is far greener, it's down at 181g/kWh (as of 2020); so it's not even close in the UK; gasoline cars are horrendously more polluting.

This is the 10th successive day with no wind above 4 GW, and the umpteenth night with no sun. Sadly, I have to go to work tomorrow, so we'll have to close a hospital ward so I can charge my car.

Doesn't matter. It's the average over the year that matters. The UK's grid is one of the greener ones in the world, and getting greener every year; but it's still got a long way to go.

[alancalverd]

Doesn't matter. It's the average over the year that matters.

Thank you, I'll tell my clients and patients that I may visit some time next year. Who knows, they may have turned green themselves by then?

[Bored chemist]

Sadly, no. The "energy input" starts at the power station. You can get 90% conversion efficiency from a new battery, but making the electricity from gas, coal or a nuclear reactor is only about 50% efficient.

Well... the point does , kind of... include not using fossil fuels to make electricity so...

If we get half our electricity from non fossil sources then the average quantity of foil fuel needed to generate a KW Hr of energy is halved.
So, even if there are no advantages to economy of scale, and the "CO2 per mile" is the same for an electric car charged by a coal fired power station as it is for a petrol car, that's just another reason to move away from fossil fuel in power staions.

[wolfekeeper]

Just to put hard numbers on this, it's been estimated that a petrol fuelled car emits about 400g of CO2 per mile driven.

An electric car can usually do about 3-6 miles per kWh. The UK grid, emits on average 181 g/kWh. But there are conversion losses between the grid and the back wheels of the electric car (about 40%), so on a very inefficient coal grid (~800g/kWh) and a relatively inefficient electric car, and comparing it to a diesel or small petrol car, the electric car could lose. But on the current UK grid, that just doesn't happen.

So for an inefficient electric car on a coal only grid: 800/(1-0.4)/3 = 440g/mile (electric)

whereas on today's grid:

181/(1-0.4)/3 = 100g/mile (same inefficient electric car)

c.f. 400 g/mile on a petrol car

So it's not remotely close, not even diesels or most hybrids can approach electric car efficiency.

Doesn't matter. It's the average over the year that matters.

Thank you, I'll tell my clients and patients that I may visit some time next year. Who knows, they may have turned green themselves by then?

Nope, just plug it in whenever you want and it will average out. Actually, on today's grid the power that goes into electric cars averages better than 181g/kWh because they're recharged at night which has a higher average percentage of nuclear and wind power than fossil; the gas generators run more during the day.

[alancalverd]

Well... the point does , kind of... include not using fossil fuels to make electricity so...

But as we have seen, there is no practical prospect of achieving this in the foreseeable future.

[Bored chemist]

400g of CO2 is 400/44 moles
9.1 moles of CO2 implies 9.1 moles of carbon.
If that's supplied as octane with a mass of 114 then each mole of carbon is an eighth of a mole of octane so that's 114/8 grams of octane. So a mole of carbon is equivalent to 14.25 grams of octane.
And thus 400g of CO2 is 9.1 *14.25 =130 grams of petrol

The density is about 0.75 so that's 173 ml
Which is 0.038 gallons.
So the figure of 400 grams per mile is equivalent to about 26 miles per gallon.

And that's the same ball park as the figure given here
https://theicct.org/sites/default/files/info-tools/One%20table%20to%20rule%20them%20all%20v1.pdf
which gives 22.1 mpg as the equivalent of 400 g per mile.
And I gather the most popular car in the UK is the Ford fiesta which runs at about 50 mpg.
So, re.

Just to put hard numbers on this, it's been estimated that a petrol fuelled car emits about 400g of CO2 per mile driven.

By whom was that estimate made, and on what basis?

[Bored chemist]

But as we have seen, there is no practical prospect of achieving this in the foreseeable future.

We are, in fact, doing it now.
As I said, even if we only shift half the generation away from fossil fuels it becomes  worthwhile.