An urban round-around with a restricted range and relying on a trickle re-charge overnight could well be a sensible choice for those living in a large city or town. For general travel a working range of 200 miles is just not sufficient, even if you can navigate your way via Tesla’s ‘supercharger’ stations. There appear to be some 32 Tesla ‘supercharger’ stations in the UK, and not surprisingly the highest concentration is in London. Further north, on the east coast, there is only one between Edinburgh and Leeds, at Newcastle. In fact the whole of eastern England is a desert if what you need is a quick recharge. Driving south from Newcastle the first station is 106 miles away. Travelling from Newcastle to north Norfolk would require a detour of at least 20 miles to top up the charge. That could add the best part of an hour to an already long journey, and the car would still arrive with a minimal reserve, or possibly none at all.
According to ref. 16, there are another 1739 ‘rapid’ charging stations in the UK, where ‘rapid’ means 43 to 50 kW. This is only around 1/3 the rate of the Tesla ‘superchargers’, so to recharge the Tesla by 50% would still require about 1 hour. If there is one of these conveniently along the route then it would save the detour, but the slower charge rate would mean that the journey time would be much the same. And this assumes that the charger station is in working order and has an immediately available slot. Most of these stations appear to have at most 2-3 charging points.
So why do Tesla not simply increase the number of battery units to extend the car’s range?
The simple answer is weight and cost. Tesla’s choice of the battery capacity is a compromise between range, performance (acceleration and energy usage) and cost.
The Tesla model S weighs in at 2100 kg which is quite high. If the Tesla body was made from steel and not aluminium, the weight would be even higher.
The Tesla batteries use lithium ion technology. Based on figures published by Tesla, the weight of the battery works out at around 8 kg / kWhr, so the model S 85 kWhr batteries would weigh in at 680 kg. Whether this includes for the ancillary systems is not clear. For example, liquid cooling is used to control the battery operating temperature and the batteries require heating in cold weather otherwise they cannot be charged.
The battery cost is reported to be around $300/kWhr, making the cost of the battery pack in the 85kWhr model around £17,000. Increasing the useful range to 300 miles (requiring a 50% larger battery stack when the effect of the extra weight on energy use is allowed for) might cost another £8500 and increase the car weight by perhaps 340 kg. The effect of the extra weight could be expected to decrease the miles/kWhr figure by as much as 10%. The time to reach 60 mph would increase by around 16%.
EV06-0116
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