Nissan Leaf - The Maths

Friday 19th March, 2010
After reading this piece, please see my updated "One Year Later" article.

Nissan have this week announced that the new Leaf model will be made at their Sunderland assembly plant. Great news for the UK and particularly good news for the North East of England with hundreds of jobs secured for the foreseeable future making possibly the most appropriately named "green" car ever.

The Leaf is entering a new market for Nissan in that it, like a milk float, will be powered completely on electricity from on-board batteries. Between uses it will be charged from the mains and the stored charge will be enough to give the car a claimed range of around 100 miles. They also claim (through @neilatnissaneu on twitter ) that a full charge will cost "something like 1.20 Euros". This left me wondering, after all electricity is many things but it really isn't cheap. Would 1.20 Euros really get a UK owner 100 miles? What will the true running costs be? Let's do the maths...

There are 2 ways to charge the Leaf. There is a 50kW "quick charger" that will charge the car to 80% in about half an hour. Of course, in a UK domestic set-up, this kind of power draw might blow a few fuses as our 220V sockets are limited to 13amps of current - a maximum 3kW. For these purposes, a 220v plug-in charger is supplied which takes around 8hrs for a full charge. Not really handy for a quick top-up, but OK to leave overnight for use the next day.

It's easy to verify these claims. The on-board battery pack stores 24kWh of charge, with a 50kW charger it's obviously going to take about half an hour to charge fully. With the 3kW plug-in charger, 8hrs is a fair estimate as it will charge up to 3kW each hour it's plugged in. Notice here that 3kW is the maximum current draw from a domestic socket, similar to that used by a kettle - so charging this think is like boiling your kettle for 8 hours solid. Still sound green? Well it didn't to me, so I did some more maths.

From my latest electricity bill, e.on charge me about 10 pence per kWh of electricity used. This only applies after the first 900 units which are charged at a higher rate of 24p/kWh. This is my standard domestic tariff before discounts like dual fuel but inclusive of VAT @5%. Notice here that domestic fuel doesn't command the full 17.5% rate of VAT, it's discounted as it's essential for people to stay warm and stay alive. This is in direct contrast to petrol/diesel which is taxed very heavily as a luxury. I wonder what might happen to VAT in the future if people start powering their vehicles from it.

So, back to the maths, the cost for a full charge is pretty easy to work out. 24kWh x 10p = £2.40 - Somewhat more than the claimed 1.20 Euros but still pretty reasonable. If you're a light electricity user, the higher rate would apply, putting the price of a full charge charge up to £5.76. With some clever timing, you could work Economy 7 discounts in here, but it would require some inconvenience and only charging the car during off-peak hours. In my experience, with an electric heater, running 3kW through a plug-in timer isn't ideal and may actually melt or catch fire - I speak from experience. For these reasons, I think it's fair to ignore Economy 7 discounts and work on a full charge cost of £2.40 to £5.76 depending on total power usage in your home.

This full charge may get you around a claimed 100 miles. I'm assuming this excludes any current usage from headlamps, wipers, air-con, electric windows, heaters etc. Without a combustion engine on board, heating is going to be a considerable cost to the on-board batteries - although the car can be pre-heated, at additional cost, from the mains charger. Pre-heating won't be an option in office or supemarket car parks so we'll take 100 miles range as an absolute maximum. Note, this is each way...a 50 mile return journey - unless you have the ability to charge at the destination.

So, up to 100 miles on a minimum of £2.40 - which would buy you 2 litres of petrol at today's prices. I make that an easy comparative figure of 50 miles per litre - a very impressive claim.

Unlike many, I'm not going to draw a comparison of this to a standard petrol car, instead I'll compare it to a modern hybrid - in this case the 3rd Gen Toyota Prius, which has an official figure of 72.43mpg or 3.9litres per 100km. A quick search (many people clicking that link are going to be introduce to the god-like Google Calculator) and we can equate this to a figure just over 19miles per litre of petrol. Of course, in the case of the Prius, I know this to be not a claim but a real-life figure. My father in-law takes his Prius hybrid from Weybridge to Basingstoke and back with a genuine 70+ Winter...using headlights, heaters etc.

The Prius is bigger than the Leaf and has a petrol fuel tank that is 45 litres in size offering a range of (45 x 19) 855 miles. Based on the (almost) current price of £1.20/litre, that's a £54 fill from empty or £6.32 for 100 miles of range equivalent to that claimed by Nissan for the Leaf.

I'm trying not to draw too many conclusions here but you can take a car, with 100 miles of range that costs £1.20 to £5.76 to refill and can only be charged in selected locations or take a bigger, more practical, car that currently costs £6.32 to go the same distance but can go over 800 miles and be filled up at any petrol station.

After discussion with my wife, she pointed out that 100 miles wouldn't even get her to Bluewater and back so I'd be a dead man if I got her one of those...even if my credit card bills may be easier to settle ;O)

Note: I've completely overlooked exhaust emissions in this article. Whilst the Leaf doesn't directly generate any emissions, the majority of electric power in the UK currently comes from coal fired power stations which have their own exhaust that is high in CO2, NOx and SOx. It is this authors current belief that, if we switched all vehicles in the UK to EVs overnight, the output of these gases would not go down and would potentially go up with the extra electricity that would need to be generated. In the future, for sure, renewable energy will help with this scenario, but we aren't there yet and won't be for a long time.

Update: I've now done some comparitive figures for CO2 emissions resulting from running a Nissan Leaf in the UK. The article can be found
here. I've also done some stats for charging on an Economy 7 Tariff here.

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