EV Maths Fail

Author
Discussion

Sterillium

Original Poster:

22,232 posts

225 months

Sunday 5th March 2023
quotequote all
I am pathologically stupid when it comes to maths.

A family member is in the process of ordering a new Peugeot E-2008 and they are getting a 7kw wall charger fitted at home.

Because I like cars, they've asked me how to work out what the cost of their daily commute will be, compared to the old diesel car that they have upgraded from... and I haven't got a bloody clue. hehe

Their commute is approximately 20 miles (each way) of suburban/countryside B roads.
Their old car was a Peugeot diesel running at around 50mpg.
They are already with Octopus Energy and will sometimes use the "off-peak" rate and sometimes use the "peak" rate.

Octopus Energy said:
Unit rate (23:30 - 05:30):

10.00p/ kWh
Unit rate (05:30 - 23:30):

42.90p/ kWh
Standing Charge:

51.09p/ day
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!


bearman68

4,652 posts

132 months

Sunday 5th March 2023
quotequote all
Sterillium said:
I am pathologically stupid when it comes to maths.

A family member is in the process of ordering a new Peugeot E-2008 and they are getting a 7kw wall charger fitted at home.

Because I like cars, they've asked me how to work out what the cost of their daily commute will be, compared to the old diesel car that they have upgraded from... and I haven't got a bloody clue. hehe

Their commute is approximately 20 miles (each way) of suburban/countryside B roads.
Their old car was a Peugeot diesel running at around 50mpg.
They are already with Octopus Energy and will sometimes use the "off-peak" rate and sometimes use the "peak" rate.

Octopus Energy said:
Unit rate (23:30 - 05:30):

10.00p/ kWh
Unit rate (05:30 - 23:30):

42.90p/ kWh
Standing Charge:

51.09p/ day
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!
Peugeot are claiming about 4mile per kwh, 1 days commute is 40 miles, so 10 kwh. Off peak is 10p/ unit (or KWh) , so off peak is about £1, or peak charge is about £4.20. 4m / kwh is prob a bit optimistic, so worth adding maybe 25% to those costs, especially in winter £1.25 or about £5.25) (Dunno, maybe more?) Standing charge is not relevant here, as it would need to be paid anyway.
The old car would be about £6 a day. Give or take.

I'm sure you can calculate weekly.

I'm surprised there is so little difference to be honest. Running a shed looks good value.

Hope that helps.

Nomme de Plum

4,513 posts

16 months

Sunday 5th March 2023
quotequote all
Small point but the standing charge is fixed whether you charge an EV or not so it could be argued that you exclude it from the running cost of an EV.


Nomme de Plum

4,513 posts

16 months

Sunday 5th March 2023
quotequote all
bearman68 said:
Peugeot are claiming about 4mile per kwh, 1 days commute is 40 miles, so 10 kwh. Off peak is 10p/ unit (or KWh) , so off peak is about £1, or peak charge is about £4.20. 4m / kwh is prob a bit optimistic, so worth adding maybe 25% to those costs, especially in winter £1.25 or about £5.25) (Dunno, maybe more?) Standing charge is not relevant here, as it would need to be paid anyway.
The old car would be about £6 a day. Give or take.

I'm sure you can calculate weekly.

I'm surprised there is so little difference to be honest. Running a shed looks good value.

Hope that helps.
I'd argue why would you not charge overnight at the 10p rate. The peak rate would not be required for EV charging.

They don't need to do it daily either with only 40mile per day usage.

Flumpo

3,738 posts

73 months

Sunday 5th March 2023
quotequote all
Nomme de Plum said:
Small point but the standing charge is fixed whether you charge an EV or not so it could be argued that you exclude it from the running cost of an EV.
Seems a reasonable point.

Nomme de Plum

4,513 posts

16 months

Sunday 5th March 2023
quotequote all
Flumpo said:
Nomme de Plum said:
Small point but the standing charge is fixed whether you charge an EV or not so it could be argued that you exclude it from the running cost of an EV.
Seems a reasonable point.
Bearman said the same.

TooLateForAName

4,744 posts

184 months

Sunday 5th March 2023
quotequote all
Around £6 a day for diesel, and £1/day off peak electric.


Nomme de Plum

4,513 posts

16 months

Sunday 5th March 2023
quotequote all
TooLateForAName said:
Around £6 a day for diesel, and £1/day off peak electric.
Quite compelling isn't it?

TooLateForAName

4,744 posts

184 months

Sunday 5th March 2023
quotequote all
Nomme de Plum said:
Quite compelling isn't it?
just a bit smile

I suppose the question is are they already on this electric deal or are they moving to it - and how does their usage stack up with the off peak times?

I'd also argue that long term electric prices should come down and diesel go up.

a7x88

776 posts

148 months

Sunday 5th March 2023
quotequote all
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.

dave_s13

13,814 posts

269 months

Sunday 5th 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.
Our average pence/kWh is same as you with octopus go running an old (and frankly st) nissan leaf.

We are looking to change and have the option of picking up a 2020 fiesta 1.0 petrol for a better than good price that averages about 40mpg.

So my question, because I also do not have a maths brain, is....

Given a weekly mileage of about 100miles, what s the weekly cost of current leaf Vs a petrol fiesta?

bearman68

4,652 posts

132 months

Sunday 5th March 2023
quotequote all
TooLateForAName said:
Nomme de Plum said:
Quite compelling isn't it?
just a bit smile

I suppose the question is are they already on this electric deal or are they moving to it - and how does their usage stack up with the off peak times?

I'd also argue that long term electric prices should come down and diesel go up.
No it isn't. You're not taking account of the £35k of payment for the new car. Best add another £14 per day interest payment.

Old diesel is looking compelling isn't it?

NDA

21,565 posts

225 months

Sunday 5th March 2023
quotequote all
Sterillium said:
I am pathologically stupid when it comes to maths.

A family member is in the process of ordering a new Peugeot E-2008 and they are getting a 7kw wall charger fitted at home.


10.00p/ kWh
Unit rate (05:30 - 23:30):
I'd simply work it out at 50kWh (the size of the Peugeot's battery) x 10p/kWh = £5 to fill from 0-100%. 200 mile range for £5.

You're paying the daily charge whether you have an EV or not, so I wouldn't try to calculate that into the mix.

Generally speaking you don't tend to drive it to empty and rarely fill to 100%.

anonymous-user

54 months

Sunday 5th March 2023
quotequote all
bearman68 said:
TooLateForAName said:
Nomme de Plum said:
Quite compelling isn't it?
just a bit smile

I suppose the question is are they already on this electric deal or are they moving to it - and how does their usage stack up with the off peak times?

I'd also argue that long term electric prices should come down and diesel go up.
No it isn't. You're not taking account of the £35k of payment for the new car. Best add another £14 per day interest payment.

Old diesel is looking compelling isn't it?


Keeping an old shed running is almost always going to be cheaper than buying a new or newer EV even if the actual fuel costs fabour the EV.

I’m terms of pollution it’s worse though which is why there are impending new car bans as well as low emissions zones otherwise there would be little incentive to change.


Jamescrs

4,479 posts

65 months

Sunday 5th March 2023
quotequote all
Nomme de Plum said:
Quite compelling isn't it?
Do they have to factor in the cost of installing a charging point to their home?

I.assume they don't want to constantly charge off a 3 pin plug and don't have a charger.

georgeyboy12345

3,508 posts

35 months

Sunday 5th March 2023
quotequote all
Sterillium said:
I am pathologically stupid when it comes to maths.

A family member is in the process of ordering a new Peugeot E-2008 and they are getting a 7kw wall charger fitted at home.

Because I like cars, they've asked me how to work out what the cost of their daily commute will be, compared to the old diesel car that they have upgraded from... and I haven't got a bloody clue. hehe

Their commute is approximately 20 miles (each way) of suburban/countryside B roads.
Their old car was a Peugeot diesel running at around 50mpg.
They are already with Octopus Energy and will sometimes use the "off-peak" rate and sometimes use the "peak" rate.

Octopus Energy said:
Unit rate (23:30 - 05:30):

10.00p/ kWh
Unit rate (05:30 - 23:30):

42.90p/ kWh
Standing Charge:

51.09p/ day
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!
The diesel doing 200 miles a week at 50 mpg with diesel costing £1.70 a litre will cost just under £31 a week in diesel.

The EV if charged off peak at 10p rate will cost approx. £7.35 a week.

The EV if charged at 42.9p rate will cost approx. £31.50 a week.



Downward

3,575 posts

103 months

Sunday 5th March 2023
quotequote all
£1 if you get 4 miles per KW

£1.30 ish if you get 3 miles per KW


Register1

2,136 posts

94 months

Sunday 5th March 2023
quotequote all
Nomme de Plum said:
TooLateForAName said:
Around £6 a day for diesel, and £1/day off peak electric.
Quite compelling isn't it?
Wife was using £8.00 a day diesel for her Touareg 3.0L V6
Now in her model 3 Tesla, she uses £1.10 a day electric.
Only requires overnight charging every few days at 10 pence per unit.

a7x88

776 posts

148 months

Sunday 5th March 2023
quotequote all
dave_s13 said:
Our average pence/kWh is same as you with octopus go running an old (and frankly st) nissan leaf.

We are looking to change and have the option of picking up a 2020 fiesta 1.0 petrol for a better than good price that averages about 40mpg.

So my question, because I also do not have a maths brain, is....

Given a weekly mileage of about 100miles, what s the weekly cost of current leaf Vs a petrol fiesta?
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?!?


page3

4,917 posts

251 months

Sunday 5th March 2023
quotequote all
NDA said:
Sterillium said:
I am pathologically stupid when it comes to maths.

A family member is in the process of ordering a new Peugeot E-2008 and they are getting a 7kw wall charger fitted at home.


10.00p/ kWh
Unit rate (05:30 - 23:30):
I'd simply work it out at 50kWh (the size of the Peugeot's battery) x 10p/kWh = £5 to fill from 0-100%. 200 mile range for £5.

You're paying the daily charge whether you have an EV or not, so I wouldn't try to calculate that into the mix.

Generally speaking you don't tend to drive it to empty and rarely fill to 100%.
Worth noting for the sake of the calculation, usable battery is 45kWh. Range is 130-170 miles. Based on owning one for all of two weeks now.