Electric company cars

[openspaceman]

14 minutes ago, Squaredy said:

With electric cars, fuel economy is measured in miles per kilowatt-hour.  My Kia gives around 4 miles per Kwh.

Does it in practice?

 

My daughter is 50 miles away and says she is far too busy to check how much charge it takes and note the mileage.

 

She also got annoyed that I selected a higher regeneration setting when I used it as she was quite happy to use the brakes to slow down. Politics and economics degree don't relate much to real world common sense.

[difflock]

22 minutes ago, Squaredy said:

With electric cars, fuel economy is measured in miles per kilowatt-hour.  My Kia gives around 4 miles per Kwh.

So

 Therefore, a liter of gasoline has 8.76 kW/hr of energy in it, which is a much more manageable number.27 Sept 2021

 

And since we are getting 45mpg for every 40kW/hr(4.54 *8.76kW/hrs) of petrol

=bloody hell= nearer to 1 mile per kW/hr

how can this be correct?

 

Edited February 26, 2022 by difflock

[Squaredy]

3 minutes ago, openspaceman said:

Does it in practice?

Yes.  More in summer less in winter. 

 

We use ours on max regeneration always.  It means you effectively do the majority of the braking by just easing off the accelerator,  You only really use the brake pedal in emergency or if you fail to anticipate conditions ahead,

[difflock]

😬😬😬

[openspaceman]

2 minutes ago, Squaredy said:

Yes.  More in summer less in winter. 

 

We use ours on max regeneration always.  It means you effectively do the majority of the braking by just easing off the accelerator,  You only really use the brake pedal in emergency or if you fail to anticipate conditions ahead,

So do you measure electricity you put in by your home meter or just use the indicator in the vehicle?

[Squaredy]

2 minutes ago, openspaceman said:

So do you measure electricity you put in by your home meter or just use the indicator in the vehicle?

I did in the early days.  Fairly simple really - plug it in and it is 7kw.  So in one hour it eats 7 units of electricity.  Even after 10 hours it has only used 70 units - about £10 when we bought it.  About £15 now.

[Dan Maynard]

47 minutes ago, difflock said:

So

 Therefore, a liter of gasoline has 8.76 kW/hr of energy in it, which is a much more manageable number.27 Sept 2021

 

And since we are getting 45mpg for every 40kW/hr(4.54 *8.76kW/hrs) of petrol

=bloody hell= nearer to 1 mile per kW/hr

how can this be correct?

 

I think the engine is only 30% efficient at converting energy from fuel to motion whereas the electric motors are more 90-95% at converting electrical energy to motion.

 

The disparity is from the hidden gap when the power station converts fuel to electricity which is only 30-40% efficient. 

[doobin]

9 hours ago, Dan Maynard said:

I think the engine is only 30% efficient at converting energy from fuel to motion whereas the electric motors are more 90-95% at converting electrical energy to motion.

 

The disparity is from the hidden gap when the power station converts fuel to electricity which is only 30-40% efficient. 

Plus charging losses.

[openspaceman]

10 hours ago, Squaredy said:

I did in the early days.  Fairly simple really - plug it in and it is 7kw.  So in one hour it eats 7 units of electricity.  Even after 10 hours it has only used 70 units - about £10 when we bought it.  About £15 now.

Ok that's good so charging losses don't skew the mileage.

 

I doubt I will ever have an EV as I have 4 cars sitting here, one classic, one 4wd and mine and my wife's small runabouts.

 

What I would be interested in getting a handle on is the effect of charge efficiency as the battery ages, I'm, guessing internal losses will build up over time so would expect less of the initial electricity put in to be available. I think my home battery is warranted to give 80% of its initial capacity for 8 years but that doesn't tell me what percentage of what I put in I will get out.

[openspaceman]

10 hours ago, Dan Maynard said:

I think the engine is only 30% efficient at converting energy from fuel to motion whereas the electric motors are more 90-95% at converting electrical energy to motion.

 

The disparity is from the hidden gap when the power station converts fuel to electricity which is only 30-40% efficient. 

It needs to be a bit more refined than that but I hope someone critiques my figures; a petrol engine at maximum torque is more efficient then a naturally aspirated diesel, except most diesels are now boosted by a turbo and the common rail injection means they burn their fuel much higher up the stroke so they become more efficient. Then cars seldom work in their most efficient range (40% with a big old diesel) . Again IC cars don't recoup energy as they slow down (even though this is actually a small amount in normal driving air and rolling resistance use most energy) and tend to use fuel when stationary.

 

For our purposes we only need to consider the energy input verses mileage.

 

My little diesel fiesta when I got it at 4 years old managed 80mpg 17.6 miles per litre on a long run. As each litre of DERV contains about 10kWh of heat energy that means I did 1.76 miles per kWh of heat. An average car is probably worse than twice that.

 

Your lower figure of 30% heat to electrical power to a consumer is about right for a steam turbine power plant but only coal, nuclear and biomass power plants use them now as far as I know. Most of our electricity comes from combined cycle gas turbines which operate at 60+% heat to electricity, a lot comes from renewables which have no heat input.

 

So even at your lowest generation to consumer figure of 30% the EV doing 4 miles per kWh is doing 1.2mile per kWh of heat and if it is charged off peak it will be having input from a combination of wind and nuclear so even less heat energy and of course much lower cost if you can get an off peak tariff.

 

And that's even before we start looking at the comparative pollution levels from centralised generation versus a diesel engined vehicle.