July 7, 2017: A Year of PHEVing It.

Electric Vehicle Running Costs

As many of our readers will know only too well, June 30th is the end of the financial year here in Australia which means… it’s TAX TIME! Yay! Being self-employed means that part of my tax fun is figuring out what my vehicle expenses have been for the past year and how much of that was for business and how much for personal use. To help with that I keep very accurate records of my vehicle use. Every time I plug it in to charge or fill it with petrol I record the kilometers traveled, the number of kWh of electricity or litres of petrol used , the cost of petrol, the date and the purpose of the trip.

Over the last week I’ve had the intense joy of putting all of those records into a spreadsheet which allows me to, not only complete my tax return, but also to compare the running costs and fuel efficiency of running my Plug-in Hybrid Electric Vehicle (PHEV) on either electricity or petrol. The results are pretty interesting…. they confirm that driving on electricity is cheaper and better for the environment than diving on petrol but they also possibly end up raising more questions than they answer.

We’ve had our PHEV for about a year-and-a-half now and I’ve written regularly about the experience, so I won’t go into the whole history again here (Click here if you want to read all of that). Suffice to say that we love our PHEV. We have a double bed set up permanently in the back with all our camp cooking gear stowed underneath so we can, and regularly do, head off down the coast or into the bush at the drop of a hat. It does everything we need smoothly, quietly and efficiently including towing a trailer and hauling tools and materials.

Best of all it allows us to use a lot of our excess solar power (in case you don’t know, the Greeny Flat produces about twice as much energy as we consume) to charge the car during the day. This allows me to do most of my local driving on clean and almost pollution-free renewable energy. So how efficient is it?

Those who have been reading the Newsletter for a long time will know that, when we bought the PHEV it came with the following sign on the back.

1.9L/100km... an eye-catching but extravagant claim!

1.9L/100km… at least that’s what the manufacturer claims.

This is based on some sort of European testing standard that allows for lots of plugging in and charging the vehicle between petrol top ups. Having tested ours for a year and a half I can confirm that this is possible (in fact I got an email from a reader who has managed to get 1.5l/100km from their Outlander PHEV) but that I haven’t managed it myself. The best I’ve done is 2.5l/100km and the average, as you can see in the spreadsheet below, has been 5.86l/100km over the last year. This is still very good for a vehicle of this size and versatility but it’s a long way from 1.9.

A screenshot showing the averages and totals from a year's worth of PHEV driving.

A screenshot showing the averages and totals from a year’s worth of PHEV driving.

The left hand side of the spreadsheet shows the results between electricity charges and the right hand side shows the results between petrol fill-ups. Over the year we drove 19119km at a total cost of $1472 of which $1,117 was petrol and less than $354 was electricity. I say less than because I have calculated this whole spreadsheet using the worst case cost of electricity which is when we are charging the car using grid power which costs us about 25c/kWh (including GST). The fact of the matter is that I almost always try to charge the car during the middle of the day (it helps that I work from home) which means the electricity is coming directly from our solar power system. You might think that this makes it free but it doesn’t.

If we weren’t using the power to charge the car it would be exported to the grid and (for the last year) we’ve been getting 10c/kWh for our Feed-in Tariff. So charging it with solar power effectively costs us 10c/kWh which is still much cheaper than grid power. But, while I know exactly how much electricity I have used to charge the car over the year, I have no way of knowing how much of that came from the grid and how much came from our solar system. So, for the purposes of the spreadsheet I have used the grid cost.

The key results (circled in blue above) from the spreadsheet is that running the car on expensive grid power (at 2.79c/km) is still less than half the cost of running it on petrol (at 6.81c/km). Even better than that, when we run it on solar power which is less than half the cost it likely only costs us about 1.2c/km.

BUT (notice this is a big but) none of it is as simple as that because the car doesn’t run on purely petrol or purely electricity in any sort of predictable way. The car decides for itself when it will use which fuel type. I can ask it to charge the battery using petrol and I can ask it to save the power that is in the battery but I can’t tell it to only use petrol or only use electricity. What that means is that the results in the spreadsheet are completely adulterated. Almost all of the results on the left for electricity use include a certain (and undefinable) amount of petrol use and all of the results on the right for petrol include a certain amount of electricity use.

This raises the question… what is the actual cost per kilometer of running the car purely on electricity (with no petrol used at all) versus purely on petrol (with no electricity)?

And the answer is… I don’t know.

However I can estimate from a closer look at the spreadsheet results that if I run the car purely on electric I can get about 5km/kWh at a cost of about 5c/km. And running it purely on petrol I get about 7.5l/100km at a cost of about 9.5c/km. So running it on petrol is still about twice the cost of running it on grid power and about five times the cost of running it on solar power.

These estimates are somewhat confirmed by one last calculation. If I take the total cost ($1,472) of diving the total kilometres (19,119) I end up with an average total running cost of 7.7c/km which sits perfectly between the 5c/km grid electricity cost and the 9.5c/km petrol cost.

This all leaves a lot of questions unanswered but the main thing we know is that it’s much, much cheaper to run our PHEV on solar power than on petrol. But what about the effect on the environment?

Electric Vehicle Emissions

In this Newsletter back in January 2016 I showed the following chart fromĀ ShrinkThatFootprint.com

Carbon Emissions for various types of transportation

Carbon Emissions for various types of transportation

This shows that a medium sized petrol car produces about 191 grams of CO2 per km per person and an electric car produces about 43 grams (or about one fifth as much). So how does that compare to my own results?

That’s another very good question that is going to take some research and I will try to come back with an answer in next week’s Newsletter. In the meantime, if anyone can point me to a good source of information about carbon emissions from various fuel types (preferably in metric units) that would be very helpful. Thanks for reading.

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