EV Maths Fail

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Discussion

OutInTheShed

7,368 posts

25 months

Sunday 5th March 2023
quotequote all
Sterillium said:
What they want is:

1. Weekly cost of the old diesel (assuming five days commute per week).
2. Weekly cost of the new EV when charged during "off-peak" rates (assuming five days commute per week).
3. Weekly cost of the new EV when charged during "peak" rates (assuming five days commute per week).

I think the answer to number one is £31.80, but I have no clue about the others!
Loads of money on finance/depreciation, buttons on fuel.

Even the old diesel, the fuel will not be half the true cost.

dave_s13

13,813 posts

268 months

Sunday 5th March 2023
quotequote all
a7x88 said:
Assuming your leaf does around 3 miles per KWh - 33KWh per 100 miles = 33x0.22p= £7.26

40mpg for 100miles is 2.5 gallons or ~11.4 litres. £1.50 a litre is £17.10

Think that is about right?!?
Cheers...

silentbrown

8,793 posts

115 months

Sunday 5th March 2023
quotequote all
Don't forget charging losses of about 10-15%...

In other words, to put 40kWH of charge into your car will consume around 45kWH of electricity.

Discombobulate

4,794 posts

185 months

Sunday 5th March 2023
quotequote all
Just watch the cheap rate trap that we EV owners tend to fall into. Charging actually costs much more than than off peak rate as you have to allow for the offset higher rate during the day.
Likely to be more like 20-25p average per kWh depending on how heavy day time use is.

dmsims

6,450 posts

266 months

Monday 6th March 2023
quotequote all
Load shift into the cheap rate as well

My average rate is 19p

Discombobulate said:
Just watch the cheap rate trap that we EV owners tend to fall into. Charging actually costs much more than than off peak rate as you have to allow for the offset higher rate during the day.
Likely to be more like 20-25p average per kWh depending on how heavy day time use is.

Maracus

4,229 posts

167 months

Monday 6th March 2023
quotequote all
dmsims said:
Load shift into the cheap rate as well

My average rate is 19p

Discombobulate said:
Just watch the cheap rate trap that we EV owners tend to fall into. Charging actually costs much more than than off peak rate as you have to allow for the offset higher rate during the day.
Likely to be more like 20-25p average per kWh depending on how heavy day time use is.
We've managed 68% usage on the cheap 7.5p/Kw period this month.

At 5p above the capped rate, the normal rate cost us £102 last month using 260kW, at the capped rate of 34p/Kw it would have been £88. The capped rate total cost would have been higher as we'd have had to run the dishwasher @ 39.5p/Kw.

In this case, the gap between the two is marginal in order to gain the cheap rate.


Edited by Maracus on Monday 6th March 06:30

dmsims

6,450 posts

266 months

Monday 6th March 2023
quotequote all
No idea what you are trying to say

Couln't you just say: My average rate was xx p ?

Maracus said:
We've managed 68% usage on the cheap 7.5p/Kw period this month.

At 5p above the capped rate, the normal rate cost us £102 last month using 260kW, at the capped rate of 34p/Kw it would have been £88. The capped rate total cost would have been higher as we'd have had to run the dishwasher @ 39.5p/Kw.

In this case, the gap between the two is marginal in order to gain the cheap rate.


Edited by Maracus on Monday 6th March 06:30

Maracus

4,229 posts

167 months

Monday 6th March 2023
quotequote all
dmsims said:
No idea what you are trying to say

Couln't you just say: My average rate was xx p ?

Maracus said:
We've managed 68% usage on the cheap 7.5p/Kw period this month.

At 5p above the capped rate, the normal rate cost us £102 last month using 260kW, at the capped rate of 34p/Kw it would have been £88. The capped rate total cost would have been higher as we'd have had to run the dishwasher @ 39.5p/Kw.

In this case, the gap between the two is marginal in order to gain the cheap rate.


Edited by Maracus on Monday 6th March 06:30
That the increased day rate is negligible if you can use the cheap rate enough. HTH.

JonnyVTEC

3,001 posts

174 months

Monday 6th March 2023
quotequote all
I’m lucky still on Go Faster.
13.4p day/ 5.5p for 5 hrs off peak.

For last bill average was 7.95p /kWh so you can see the bulk use is off peak 722kWh versus 321kWh, my rate starting at 8:30pm also massively helps this ratio.

But then I do fairly high miles and in a performance car - hence it uses a lot of kWh. Nothing to do with efficiency before someone starts comparing a polo blue motion to an Audi RS3 mpg in some sort of odd ball EV top trumps that always pop up.

Otispunkmeyer

12,557 posts

154 months

Monday 6th March 2023
quotequote all
Some addtional food for thought.

EVDatabase UK - Pug 2008 Electric.

They have the following for consumption:

City - 281 Wh/mi (cold), 191 Wh/mi (warm)
Highway - 409 Wh/mi, 321 Wh/mi
Combo - 346 Wh/mi, 250 Wh/mi

Having checked on Spritmonitor.de these cars are averaginging 18.63 kWh/100 km. with the spread being 14.58 to 24.77 kWh/km

in old money this is approx 300 Wh/mi average (234 - 400 Wh/mi spread). So this seems pretty bob-on with the estimates from EV Database.

So worst case is looking like 400 Wh/mi. 40 miles = 16 kWh consumed. You can easily get this amount charged in that "cheap window" where it is 10p/ kWh = £1.60 (or £3.20 for there and back and again should probably just squeak 32 kWh charging in the 4 hours, it'll be a little short, but not much). Probably add 10% for "losses".


50 MPG diesel will do you 80 miles in 1.6 gallons, or 7.2 litre. Diesel is a bout £1.70 a litre so £12 or there abouts.

If you have to pay 42.9p for a kWh all this then it comes out at about £7 for the 40 miles (£14 for the round trip). Which is awfully close to the diesel really. And if you have to start charging at public conveniences I suspect the EV is going to cost you even more than this. But this is worst case consumption remember whereas the diesel is presented more like "best case".



Edited by Otispunkmeyer on Monday 6th March 10:23


Edited by Otispunkmeyer on Monday 6th March 10:26


Edited by Otispunkmeyer on Monday 6th March 10:27

OutInTheShed

7,368 posts

25 months

Monday 6th March 2023
quotequote all
20 miles each way. Call that 800 miles a month.
Diesel roughly 10 miles per litre, 17p per mile.
£136 per month.
Other costs, like depreciation, maintenance, allow at least £100 a month.
More expensive, maybe nicer diesels are available if these numbers don't fit the narrative.
So bare minimum ~£240 a month or so, up to whatever you want to pay to have a nicer car.

EV
'Fuel' anything from £50 to £100 a month.
Lease, depreciation or whatever?
£400 a month?
So maybe £500 a month?

You can add in tyres, insurance and other costs which will be similar if you want to be accurate.

If all that matters is cost per month, then petrol might be worth a look.

Unless you do big miles and/or drive a gas guzzling Vee monster, fuel costs are not a big part of 'economy'.

The other thing is that the true cost of driving even a horrible car is 'hundreds a month' so paying a little more to have the car you want is entirely sensible. It's fine by me.

Just don't try to justify your shiny car to me on its fuel cost per mile.




dmsims

6,450 posts

266 months

Monday 6th March 2023
quotequote all
Nope

Maracus said:
That the increased day rate is negligible if you can use the cheap rate enough. HTH.

Maracus

4,229 posts

167 months

Monday 6th March 2023
quotequote all
dmsims said:
Nope

Maracus said:
That the increased day rate is negligible if you can use the cheap rate enough. HTH.
Wrong.

820kW used in total.

820kW @ the Capped rate of £0.34 = £278.80

560kW @ £0.075 = £42
260kW @ £0.395 = £102.70

£42 + £102.70 = £144.70

If I used the dishwasher on the capped rate, it would be a larger gap.


JD

2,769 posts

227 months

Monday 6th March 2023
quotequote all
OutInTheShed said:
20 miles each way. Call that 800 miles a month.
Diesel roughly 10 miles per litre, 17p per mile.
£136 per month.
Other costs, like depreciation, maintenance, allow at least £100 a month.
More expensive, maybe nicer diesels are available if these numbers don't fit the narrative.
So bare minimum ~£240 a month or so, up to whatever you want to pay to have a nicer car.

EV
'Fuel' anything from £50 to £100 a month.
Lease, depreciation or whatever?
£400 a month?
So maybe £500 a month?

You can add in tyres, insurance and other costs which will be similar if you want to be accurate.

If all that matters is cost per month, then petrol might be worth a look.

Unless you do big miles and/or drive a gas guzzling Vee monster, fuel costs are not a big part of 'economy'.

The other thing is that the true cost of driving even a horrible car is 'hundreds a month' so paying a little more to have the car you want is entirely sensible. It's fine by me.

Just don't try to justify your shiny car to me on its fuel cost per mile.
Why would a diesel depreciate £100 a month, but an EV £400?

Nomme de Plum

4,191 posts

15 months

Monday 6th March 2023
quotequote all
JD said:
Why would a diesel depreciate £100 a month, but an EV £400?
Old car versus new car I suspect.

The new car provides betterment so should not normally be included in the calculation unless it was new diesel for new EV equivalent.

I think poster may have bee in his bonnet about EVs

dmsims

6,450 posts

266 months

Monday 6th March 2023
quotequote all
At last an answer (and I was saying no to HTH!)

Maracus said:
Wrong.

820kW used in total.

820kW @ the Capped rate of £0.34 = £278.80

560kW @ £0.075 = £42
260kW @ £0.395 = £102.70

£42 + £102.70 = £144.70

If I used the dishwasher on the capped rate, it would be a larger gap.

Maracus

4,229 posts

167 months

Monday 6th March 2023
quotequote all
dmsims said:
At last an answer (and I was saying no to HTH!)

Maracus said:
Wrong.

820kW used in total.

820kW @ the Capped rate of £0.34 = £278.80

560kW @ £0.075 = £42
260kW @ £0.395 = £102.70

£42 + £102.70 = £144.70

If I used the dishwasher on the capped rate, it would be a larger gap.
Gotcha beer

OutInTheShed

7,368 posts

25 months

Monday 6th March 2023
quotequote all
JD said:
Why would a diesel depreciate £100 a month, but an EV £400?
I reckon £100 a month is about the bare minimum for depreciation and repairs anyone should budget on for an old diesel.
As I said, it's not hard to spend more.

£400 was a guess at monthly leasing or depreciation for the EV in the OP.
It's possible to run other EVs for less, but not tons less.
Even if you were to look at the lower end of the used EV market, you'd want to be writing down the value by a few £k a year if you were being realistic.

It's not an anti-EV point, it's just pointing out that motoring is an expensive game and the fuel cost is not generally the most of it.

Big Nanas

1,341 posts

83 months

Monday 6th March 2023
quotequote all
a7x88 said:
I don’t always get how some people use the off peak charging costs for their EV.

Yes, you can charge at the off peak rate, but then your normal usage is at higher cost and this never seems to be considered. You really need to calculate it using your average price per KWh. For example - I’m an EV driver and I use an overnight tariff. I only have an overnight tariff because I have an EV (if you would have one anyway this obviously does not apply). My average p/KWh is ~22p, so it would only be fair to use this average to calculate my journey cost.
We are with OVO energy and have an EV 'add-on', called "Charge anytime". Our standard tariff remains the same, but charging using the App costs 10p per kWh.
You set the time you want a full charge in the app, and then it talks to the car to charge only when the grid is greenest/low usage/excess energy. This can be at anytime during the day or night.
We've been using it for about 6 weeks now and it works very well, and we don't have to worry about daytime rates being higher.

JD

2,769 posts

227 months

Monday 6th March 2023
quotequote all
OutInTheShed said:
I reckon £100 a month is about the bare minimum for depreciation and repairs anyone should budget on for an old diesel.
As I said, it's not hard to spend more.

£400 was a guess at monthly leasing or depreciation for the EV in the OP.
It's possible to run other EVs for less, but not tons less.
Even if you were to look at the lower end of the used EV market, you'd want to be writing down the value by a few £k a year if you were being realistic.

It's not an anti-EV point, it's just pointing out that motoring is an expensive game and the fuel cost is not generally the most of it.
Where does one by a new old diesel?