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ESS replacement cost

Discussion in 'Roadster' started by malcolm, Jun 10, 2008.

  1. malcolm

    malcolm Active Member

    Nov 12, 2006
    #1 malcolm, Jun 10, 2008
    Last edited: Jun 10, 2008
    With silly gas prices here in the UK, even buying a brand new ESS after 100,000 miles isn't looking so daft...

    Note: all mpg values are for Imperial gallons.

    What are the comparable energy costs (in £) between the Roadster and an (entry-level model) Lotus Elise S over 100,000 miles of motoring?

    Assumptions: the cost of electricity stays fixed at the present night-time rate of 5p per kWh and that (unleaded) petrol stays fixed at £1.15 per litre. (The night-time electricity rate in the UK is between the hours of 10pm and 8am).

    The other assumption is modest driving behaviour in both cars in order to achieve the manufacturer's stated 34mpg (combined) for the Elise S (25 mpg urban / 43 mpg extra-urban) and (221miles/53kWh) = 4.17 miles per kWh for the Roadster. (230 miles per charge EPA city / 211 miles per charge EPA highway)

    However, let's make it harder for the Roadster and assume that it is always re-charged at night at the fastest rate, using the Domestic Fast Charger. This means that the roadster consumes a further 17kWh running the cooling system for the battery while it charges. (Incidentally, setting the car to recharge more slowly overnight requires less power for cooling and so consumes less, cheaper electricity per recharge)

    This gives 221miles/70kWh = 3.157 miles/kWh

    So obviously for the roadster, 100,000 miles of motoring will consume a grand total of about 31,675 kWh at a cost of £1,580. (1.58 pence per mile) if you charge it quicky at night.

    (If I had used the better 4.17 figure above, this would be £1,200 for 100,000 miles)

    If you have no choice but to charge your Roadster at the fastest rate, always using the very worst UK Tier 1 daytime electricity tariff of 36p/kWh then 100,000 miles of motoring would cost you, at most, £11,455 in energy consumed. (In fact Tier 1 only applies for the first 125kWh consumed each quater by your household during the day)

    The Elise S: At 34 mpg, 100,000 miles will consume about 2,940 (Imperial) gallons
    1 (Imperial) gallon is 4.544 litres, so 2,940 i-gallons is about 13,360 litres.
    So for the Elise S, 100,000 miles of motoring will cost you £15,360 (15.4 pence per mile)

    At some point after 100,000 miles you will need to buy a new ESS; the Li-ion battery pack for the Roadster (i.e a new "fuel tank"). Or maybe have your old one reconditioned with new cells? (No prices have been set for a complete new pack - but the figure of U.S. $20,000 has been mentioned.)

    Assuming the ESS costs £13,000(?) to replace (and 100,000 miles uses £2000 of electricity) then that still works out cheaper than 100,000 miles-worth of petrol at a fixed £1.15 per litre for any car getting less that 35mpg.

    If petrol prices continue to rise, running and replacing the ESS becomes cost-effective against total 100,000 mile fuel bills for a greater proportion of higher mileage ICEs.

    If you drive predominantly in urban areas, the advantage is even greater.

    It is interesting to compare this with the approach taken by Th!nk; Purchase price for their New Th!nk City is £14,000 and the battery lease is £100 per month. The car is marketed as an urban runabout. Electricity consumption has to be added on to this.

    Data taken from:
    - Tesla and
    - Lotus prices » Find a Dealer
    - Electricity prices
    - Petrol prices Free UK fuel prices. 9,702 petrol stations covered -
  2. Cobos

    Cobos S60 Owner since 2013 - sold, S85D owner since 2017

    Jun 22, 2007
    Oslo, Norway
    Interesting comparison, but keep in mind that for the Think you get a brand new battery for "free" whenever it reaches below a certain treshold. Those £100 will supposedly also include whatever else that can get bundled with. Might be AAA membership, free electricity at certain recharge stations, free or reductions in insurance bill etc. So we need the exact details before you can pass any judgement on the financial side of Thinks battery lease.


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