Economy computer inaccurate

[Filmcrew]

I regularly get 3.7 to 4.2 miles to the kw on the computer on a full to empty charge journey....sometimes with as little as 3 leaves (which seems odd)! The question is if the car has a 12 kwh battery and I average 4 kwh that means I should be getting 48 miles on electric from the car. Something is not adding up....anyone know which one is right?

 

[Grigou]

Only 70 to 74 % of the battery's capacity is used, so you must take only 8.4 to 8.9 kWh in account.

 

[Filmcrew]

Many thanks....makes perfect sense.

 

[Tipper]

My good wife, a statistician, told me it was all bunkum within 2 days of getting the car.

We now ignore all data given religiously and JFDI!

Oh, and love it.

 

[maby]

As far as I can tell, it does not distinguish between the sources of the electricity consumed - it simply reports the number of miles travelled on battery including miles travelled in serial hybrid. You could never bother to plug the car in and it would still report a non-zero number of miles per kWh - despite the fact that they have all been travelled by burning petrol.

 

[anko]

As far as I can tell, it does not distinguish between the sources of the electricity consumed - it simply reports the number of miles travelled on battery including miles travelled in serial hybrid. You could never bother to plug the car in and it would still report a non-zero number of miles per kWh - despite the fact that they have all been travelled by burning petrol.

Why would you expect it make such a distinction? To be honest, I don't see thee advantage. For reporting the efficiency of the car while driving on e-motors, does it matter where the electricity comes from?

 

[maby]

As far as I can tell, it does not distinguish between the sources of the electricity consumed - it simply reports the number of miles travelled on battery including miles travelled in serial hybrid. You could never bother to plug the car in and it would still report a non-zero number of miles per kWh - despite the fact that they have all been travelled by burning petrol.

Why would you expect it make such a distinction? To be honest, I don't see thee advantage. For reporting the efficiency of the car while driving on e-motors, does it matter where the electricity comes from?

Isn't it misleading? Particularly for owners that are concerned about the environment? My car is charging at the moment and I'll go out shopping at lunchtime - four or five miles that will be covered mostly, if not entirely, on energy drawn from the grid. This evening, we'll head off to the boat and be unable to charge from the grid for four or five days - covering around 250 miles in total. Those miles will be fueled by petrol - to all intents and purposes I'll be driving a petrol car with an electric transmission and the battery is just providing a small buffer to help optimise fuel consumption. In my book, I'll be getting zero miles per kWh and something approaching 40mpg.

 

[anko]

I think what you mean is zero "miles per grid kW", which is something different then miles per kW.

As you know I am very concerned with the environment. Via the OBDII port, I get a rather accurate Wh / km reading that updates 4 times a second or more. That way I get immediate feedback on the effect of (increased) speed or opening a window or the sunroof. Very useful, as it motivates me to anticipate and such. Doesn't matter where the power comes from.

 

[maby]

I think what you mean is zero "miles per grid kW", which is something different then miles per kW.

As you know I am very concerned with the environment. Via the OBDII port, I get a rather accurate Wh / km reading that updates 4 times a second or more. That way I get immediate feedback on the effect of (increased) speed or opening a window or the sunroof. Very useful, as it motivates me to anticipate and such. Doesn't matter where the power comes from.

How can it not matter where the power comes from? From the environmental viewpoint, the car's entire raison d'etre is to use efficiently generated electricity in preference to petrol. Look, taking it to the extreme, I could limit my usage to the twenty-odd miles that I can achieve on battery, but instead of charging it from the grid, I could plug it up each night to a medium size Honda petrol generator - from the environmental point of view I would be no better (and probably a lot worse) than using a conventional 2 litre petrol car. That would be very little different to never plugging the car up to anything and just running it as a petrol vehicle with an electric transmission. The fuel economy and environmental impact might be slightly better than an equivalent size pure petrol car due to the opportunities that the hybrid drive train gives to run the engine at peak efficiency, but it will still be an order of magnitude worse than running as a genuine plugin hybrid with a lot of the miles covered on electricity drawn from the grid.

Perhaps the MMCS should give us two figures - miles per kWh of energy drawn from the grid and miles per kWh of energy generated by the ICE?

 

[anko]

How can it not matter where the power comes from?

We have not much control over whether the engine starts or not. This pretty much depends on the length of our trips. But we do have some control over how many miles we can get from 1 kW of electricity. Having this insight can help us to improve this number. Where the electricity comes from (grid, ICE or Honda generator) is of no concern for this.

Perhaps the MMCS should give us two figures - miles per kWh of energy drawn from the grid and miles per kWh of energy generated by the ICE?

These numbers would be exactly the same, wouldn't they? Unless .... now time you write "kW of energy" instead of just "kW". So, maybe you are not / no longer talking about electrical kW but about kW in general (1 liter of petrol is approx. 10 kW and such).

 

[greendwarf]

From the environmental viewpoint, the car's entire raison d'etre is to use efficiently generated electricity in preference to petrol.

Is grid electricity more efficiently generated (given all the transmission losses) than your petrol generator or PHEV? I agree it is cheaper, as a result of the tax on petrol and avoids local pollution, but overall more energy conversion efficient :?:

 

[Esparza]

At least my kWh/100km meter resets each km, so its useless to calculate the EV range based on batt capacity. Does your meter the same?

I think that with the L/100km meter we can see the petrol usage, so no need of kWh from grid and kWh from generator no?

 

[Anders]

From the environmental viewpoint, the car's entire raison d'etre is to use efficiently generated electricity in preference to petrol.

Is grid electricity more efficiently generated (given all the transmission losses) than your petrol generator or PHEV? I agree it is cheaper, as a result of the tax on petrol and avoids local pollution, but overall more energy conversion efficient :?:

In the Nordics the grid electricity has a relative low CO2 impact ( realtime data here http://www.statnett.no/en/Market-and-operations/Data-from-the-power-system/Nordic-power-balance/ ) . We bought this car to leverage this so for us it is an important metric to know how much energy came from the grid and how much came from petrol.

So the efficiency (miles per kw) is one thing and the break down of energy sources another (grid source vs petrol source). Both contributes to the mile per CO2E number we want to keep low...

 

[maby]

OK - just tried to post screen shots, but they failed to display...

Over the weekend, I checked the MMCS display on our PHEV and was told that it had a lifetime EV average of 28 miles per kWh and an "auto" average of 99.9 miles per kWh. This is in a car with 25000 miles on the clock, 90% of which were fueled with petrol and it is not driven particularly gently. The 99.9 miles per kWh "auto" readout was shown after we had driven about 100 miles on "Save" since the last full charge. So, if you want a high EV average, the answer is to use it as a petrol car! :?

 

[maby]

From the environmental viewpoint, the car's entire raison d'etre is to use efficiently generated electricity in preference to petrol.

Is grid electricity more efficiently generated (given all the transmission losses) than your petrol generator or PHEV? I agree it is cheaper, as a result of the tax on petrol and avoids local pollution, but overall more energy conversion efficient :?:

Well, it is certainly not as good as some like to paint it, but still better than running on petrol burnt within the car. It was the case a few years ago that the carbon footprint of a PHEV running on grid-supplied electricity in the UK is about half the carbon footprint of the same car running on petrol with a flat battery.

 

[anko]

So, if you want a high EV average, the answer is to use it as a petrol car! :?

How do you do that, if I may ask?

If you would be able to drive it as a petrol car EV% would be 0. When you drive it as a hybrid (like you do in the weekends), EV% is higher. Totally makes sense, doesn't it? Or would you say, EV% for an HEV is meaningless? Because I think it is very useful.

 

[maby]

So, if you want a high EV average, the answer is to use it as a petrol car! :?

How do you do that, if I may ask?

If you would be able to drive it as a petrol car EV% would be 0. When you drive it as a hybrid (like you do in the weekends), EV% is higher. Totally makes sense, doesn't it? Or would you say, EV% for an HEV is meaningless? Because I think it is very useful.

I'm talking about the miles per kWh figure here and, yes, I would say that it is meaningless if the kWh is generated by burning petrol - it's the mpg figure that counts. Is miles per kWh meaningful for a Prius? Of course not - you could have extremely efficient electric motors and a horribly inefficient generator and see a high miles per kWh figure backed by a terrible mpg figure. My car claims to have done close to 30 miles per kWh averaged over its lifetime - that is a silly figure - if it were able to achieve that, we would be getting EV ranges of well over 200 miles on its 8 (or 10, depending on how you look at it) kWh battery - do you???

 

[anko]

I must say, I did interpret "EV average" as "EV%". Different thing.

Still, we already have a quite accurate MPG number available. For this we do not know to incorporate the miles / kWh figure. With that in mind, yes I would like to know how many miles I can do per kWh, regardless of how (efficient) the kWhs are generated. It allows me to see the effect of driving 40 MPH versus 60 MPH.

 

[maby]

I must say, I did interpret "EV average" as "EV%". Different thing.

Still, we already have a quite accurate MPG number available. For this we do not know to incorporate the miles / kWh figure. With that in mind, yes I would like to know how many miles I can do per kWh, regardless of how (efficient) the kWhs are generated. It allows me to see the effect of driving 40 MPH versus 60 MPH.

Well, I would say that the definition of "EV%" that the car uses is also pretty questionable - not taking into account the source of the electricity consumed - but that is less clear. The thread started out discussing the accuracy of the miles per kWh figure and I would say that the figure displayed on the MMCS is meaningless. I can understand your interest in an effectively instantaneous figure, but that is only available through your custom built instrumentation. When the MMCS tells me that I've averaged nearly 30 miles per kWh over the last two years, it's talking through its electronic backside!

 

[anko]

Now what is it you are concerned with? Is it the accuracy of the number or is it the meaningfulness of the (a) number for a PHEV? Earlier, especially when you pulled in the Prius, I thought you were talking about the latter. Now it seems you are talking about the former.

I am not saying the number presented by the PHEV is accurate. I doubt it is. I am just saying, to me it does make sense to have such a number (assuming it is accurate) without worrying about the source of electricity.