Charge and fuel consumption

[krekel]

Hi all,

I have a beginners question, I haven't been able to find the answer with the search option.

I'm on the road quite a lot, on the motorway I use the "charge" option to fill up the batteries so I can use the batteries when I am back in the city. I was wondering, does charging like that cost extra fuel consumption? Is this the most efficient way?

Thanks!

Jaap

 

[maby]

Well, the "you don't get owt for nowt" law of thermodynamics dictates that the fuel consumption while you are charging will be higher than it would while you are not charging. Whether or not it makes economic sense over the full cycle of charging and subsequently using the charge is a more complex question, but I would think that the consensus would be that charging from the petrol engine rarely, if ever, makes economic sense.

 

[jaapv]

Consensus seems to be to use "save" at motorway speeds. It all depends on the pattern of the journey.

 

[Austen]

I am also a fairly new owner but maybe use the Save button when not in town, still gives you 40 Km urban per day.

 

[geoffshep69]

I agree that use of the ‘Charge’ button is very rarely a sensible strategy.

Re the use of the ‘save’ button, the other point to bear in mind is that you shouldn’t automatically use it all the time on the motorway. If you are planning to save your battery capacity for use at the end of your journey then fair enough, but if you will be coming off the motorway, going home, and arriving home with half your battery remaining then that’s not a very efficient strategy. On the basis that charging from the grid is cheaper than burning petrol, you should always be aiming to arrive home with little or no battery capacity left.

 

[krekel]

Thanks for your replies, I see your point but when I leave in the morning with the battery fully loaded and I drive on the motorway, the battery will be almost empty again within the hour. So what you are saying is that recharging on my return trip to use the battery power for the last part of the trip (from the motorway to home or office) is kind of useless?

 

[maby]

Thanks for your replies, I see your point but when I leave in the morning with the battery fully loaded and I drive on the motorway, the battery will be almost empty again within the hour. So what you are saying is that recharging on my return trip to use the battery power for the last part of the trip (from the motorway to home or office) is kind of useless?

It is not going to reduce your running costs noticeably, if at all. There has been almost interminable discussion about the relative merits of various battery management strategies for trips that are significantly longer than the EV range. Personally, I run on Save most of the time in order to keep my battery around 50% charged or more - as an ex-Prius driver, I tend to treat the battery more as an "electric turbo-charger" to provide acceleration without having to race the petrol engine. On the other hand, my PHEV use is primarily long distance journeys and it is primarily a petrol driven car for me - no battery management strategy makes much difference to my overall running costs.

People like Anko and Trex will tell you, quite correctly, that the absolute best fuel consumption on a long trip will come from running the battery down low since this will maximise the rate at which it can recoup energy from regenerative braking and give the control systems the best scope for optimising the engine power output. If you have the inclination to actively manage battery level through the use of the Save and Charge buttons, then look out some of Trex's posts on the subject. I've run some experiments over the same route, following different strategies, and any difference in fuel consumption seems to get lost in the background noise caused by variations in traffic conditions.

 

[mellwaters100]

I have had our PHEV a couple of weeks and have been comparing fuel consumption on the same journeys with our other car, a Toyota Auris Hybrid (not a plug in - can go less than 1 mile on pure electric) on the same journeys.

A typical journey I take is around 60 miles. The first 20 miles is on a 60mph road, the next 25 miles on motorway (70 mph); next 10 on 60mph and the final 5 miles at 30mph into (York) city centre. In both cars I drive cruise control at max 60mph.

On this journey, I use PHEV battery from the outset to depletion and get a couple of miles down the motorway section before it resorts to hybrid mode. Interestingly, the last 5 miles into the city centre in the PHEV I can manage almost purely on batteries, even though it is showing as depleted. The regen upto traffic lights pretty much getting me to the next set.

In the PHEV, the overall MPG for the journey is 72mpg.
In the Toyota, I only managed this mpg once; more often I am getting about 65mpg.

I find that, once the battery is depleted, the PHEV works very similar to the Toyota hybrid, putting charge into the battery when possible using the ICE / Regen, and switching to pure battery to maintain speed when it can. From my experience, it is able to do this much more effectively at 60 mph than it is at 70 mph. That is, at lower speed, it is using pure EV more than at higher speed.


Reading these forums at length, I read how people typically drive at 70mph and complain about low mpg figures. I actually worked out that, on the motorway section of my typical journey, driving 70mph would gain me about 7 or 8 minutes, which could easily be lost if the traffic lights go against me in the city.

So, to the original point, I find that letting the car "do its thing" works out the best economy-wise. Charge / Save doesn't improve efficiency when driving motorway.

The only thing I am "experimenting" with is switching to Save when going up steep-ish hill, as I find that really drains the battery in pure EV. My theory is I can use 10% battery to go up a 1 mile hill, or the same amount of charge to maintain speed for 3 or 4 miles at 60mph on the flat!

 

[maby]

I have had our PHEV a couple of weeks and have been comparing fuel consumption on the same journeys with our other car, a Toyota Auris Hybrid (not a plug in - can go less than 1 mile on pure electric) on the same journeys.

A typical journey I take is around 60 miles. The first 20 miles is on a 60mph road, the next 25 miles on motorway (70 mph); next 10 on 60mph and the final 5 miles at 30mph into (York) city centre. In both cars I drive cruise control at max 60mph.

On this journey, I use PHEV battery from the outset to depletion and get a couple of miles down the motorway section before it resorts to hybrid mode. Interestingly, the last 5 miles into the city centre in the PHEV I can manage almost purely on batteries, even though it is showing as depleted. The regen upto traffic lights pretty much getting me to the next set.

In the PHEV, the overall MPG for the journey is 72mpg.
In the Toyota, I only managed this mpg once; more often I am getting about 65mpg.

....

it's really a question of "horses for courses", isn't it? A significant fraction of your 60 miles will be done on battery at, effectively, infinite mpg. The rest is done on petrol at something between 35 and 40 mpg resulting in an overall figure of 72 mpg. Any additional distance would be done at 40 mpg (give or take) and the fuel consumption will tend towards that figure as the length of the journey increases. The Auris hybrid will never do much better than the 65mpg you report, but it will do that for thousands of miles. Our PHEV is used primarily for long journeys and has a lifetime (3 years) figure of 44mpg the last time I looked.

 

[Austen]

In the PHEV, the overall MPG for the journey is 72mpg.
In the Toyota, I only managed this mpg once; more often I am getting about 65mpg.

Does your 72mpg take into account the initial cost to charge?

 

[mellwaters100]

Does your 72mpg take into account the initial cost to charge?

Good point and, for complete disclosure, no it doesn't. So, if I take account of the 1 charge within that 60 mile trip then effective mpg drops to 60.8 mpg.

All told, I am still happy with these returns, even though the Auris is, on average, slightly more fuel efficient on these trips. 60 mile single trip seems to be a crossover point where the Auris becomes more efficient. A 250 mile trip to London returned about 65mpg in the Auris; in the Outlander, returns about 45mpg (without a pre-charge, starting on empty battery).

Plus, I console myself with the fact that the Outlander replaced a Shogun that happily consumed a gallon every 22 miles! And, with an 80 litre fuel tank, filling up every 350 miles or so plus £225 a year in road tax, plus £1,000 servicing costs - was a touch pricey to run!. Although, I am not sure how long I can "claim" cost savings between the Outlander and Shogun!!