2011-11-29

More on EV Batteries

I've been doing some more thinking about Electric Vehicles and the battery technology that will drive it to eventually replace internal combustion cars.

In the previous article I pointed out that Electric Vehicle Battery Packs need to have an energy density of around 675 Watt-hours per kilogram (Wh/kg) if they are to have an equal range to today's petrol-powered cars. I also pointed out that the Nissan Leaf - the world's first truly mass-produced electric car - has a battery pack with an energy density of around 131.57 Wh/kg. This means that the Leaf only has an effective range of approximately 117km (72 miles). "Range Anxiety" is truly a problem for Leaf owners - even though the total cost of charging the Leaf is lower per kilometre than the cost of filling up regular cars with petrol (the equivalent fuel efficiency for the Nissan Leaf is 2.4 litres per 100 km - 99 miles per gallon).

As a result of this study, I've done some more number crunching - this time taking into consideration various different types of vehicle. The Nissan Leaf is essentially a "Compact Car" or "C-Segment" vehicle. The other electric car that is dominating the EV market is the Mitsubishi i-Miev. The i-Miev is different to the Leaf in that it is a "Subcompact" or "B Segment" vehicle (also known as a Kei Car). This means it has a smaller engine (47kw compared to 80kw in the Leaf) and is lighter (1080kg compared to 1521kg). Thus the cars can't really be compared.

So what I did was examine the various different types of cars and work out just how much battery density needs to increase before the range of that particular vehicle class can be effectively equaled by an EV.

The image from my spreadsheet is too large to post here, so click here to see it directly. I obviously need to explain it, so have it open in one tab while looking at this page and flick between them.

Each different column colour represents a vehicle class. We have Subcompact / B Segment all the way up to Full SUV / J Segment. In each of those columns I have also included a base vehicle to use by way of comparison. Since we recently bought a VW Caddy, I decided to stick pretty much with Volkswagens as far as possible, with the notable exception of the Australian Ford Falcon and Range Rover. Each of these vehicles is given a fuel economy figure in Litres per 100km (to convert to mpg, click here). I've also included the size of each fuel tank, in both litres and in weight, as well as in kilowatt hours of storage. The cars I used all had petrol, not diesel, engines.

Column B shows energy storage in Wh/kg. This assumes that, as technology improves, more and more power is able to be stored in an EV battery.

All those numbers from column 9 downwards, and from column D onwards, are the range (in kilometres) of each vehicle class according to the energy storage numbers in column B. The most important cell in this section, and the spreadsheet, is F19, showing 117km range at 131.57 Wh/kg for a compact car. This is the base figure for the Nissan Leaf that I mentioned above and in my previous post.

The important figures are shown there in bold. I'll dot point them here:
  • Subcompact (VW Polo): 600 Wh/kg for 600km range.
  • Compact (VW Golf): 675 Wh/kg.
  • Mid Size (VW Passat): 785 Wh/kg
  • Compact SUV (VW Tiguan): 950 Wh/kg
  • Full Size (Ford Falcon): 1100 Wh/kg
  • Mid SUV (VW Toureag): 1300 Wh/kg
  • Full SUV (Range Rover): 2800 Wh/kg
As you can see, it is obvious that 675 Wh/kg may be enough to completely control the Subcompact and Compact markets, but as soon as you take bigger vehicles into consideration, the energy density needs to be higher. And this shows how the market will react as time goes by: the smaller, lighter vehicles will become more dominated by EVs than the bigger, heavier vehicles.

I've also placed another figure to look at: the energy density needed for the vehicle to have a range of 1000km. This is an important figure (though arbitrary) that will affect EV design. If we assume, for example, that battery energy density reaches 1300 Wh/kg (and thus control the mid sized SUV market), what would happen to the subcompact market? Well according to the spreadsheet, such a vehicle would have a range of 1300km, more than twice what is probably needed. When this occurs, it is very likely that EVs will have less space dedicated to battery packs and more space dedicated to other aspects, such as greater boot space and leg room. Thus the cars will have an ever increasing usability.

This is not outside the realms of possibility. Think about the battery packs needed to power your mobile phone or laptop - they have been decreasing in size and increasing in energy intensity for some time. The same should be true for EV battery packs.

Now the second part of the graph needs some explanation. It is essentially the application of Moore's Law to battery technology in column B (column C is the multiplier for the spreadsheet, so ignore that unless you wish to check my figures - which you are welcome to). Moore's Law, in this case, assumes that battery energy density will double every two years. If we take this year (2011) to be the year when battery packs of 131.57 Wh/kg are currently available to the market (ie the battery packs for the Nissan Leaf), then you can see the sort of battery energy density that could be theoretically available as years go by.

If we take...
  • a range of 300km to be the sort the market will respond to positively (and thus begin to be competitive with petrol driven vehicles),
  • and if we see a range of 600km to be the sort that will completely control the market (and make petrol driven vehicles obsolete),
  • and a range of 1000km to be the point at which these vehicles begin to reduce the amount of space needed for battery packs (and thus increase usability by having more space),
  • and if we apply Moore's Law to battery technology...

...then we will see the following:

  • Subcompact EVs will begin to be used in number from 2014. They will begin to control the market in 2016. They will begin to increase usability from 2017 onwards.
  • Compact EVs will begin to be used in number from 2014. They will begin to control the market in 2016. They will begin to increase usability from 2018 onwards.
  • Mid-Size EVs will begin to be used in number from 2015. They will begin to control the market in 2016/2017. They will begin to increase usability from 2018 onwards.
  • Compact SUEVs will begin to be used in number from 2015. They will begin to control the market in 2017. They will begin to increase usability from 2019 onwards.
  • Full Size EVs will begin to be used in number from 2015. They will begin to control the market in 2017. They will begin to increase usability from 2019 onwards.
  • Mid-Size SUEVs will begin to be used in number from 2016. They will begin to control the market in 2018. They will begin to increase usability from 2020 onwards.
  • Full-Size SUEVs will begin to be used in number from 2018. They will begin to control the market in 2020. They will begin to increase usability from 2022 onwards.
Now I don't really know too much about how the car market reacts to new vehicles and how long it takes for them to be taken up by the market, but it is probably likely that 2014-2016 will be the years when the electric car begins to hit world markets in number.

2 comments:

ryanturcotte said...

Why do you think Moore's Law can be applied to battery technology?

Ana said...


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