Tesla Model S weekender

Tesla Model S weekender


Tesla Model S

The car

Poweri were fortunate to be lent a Tesla Model S for a weekend in May to experience what I now consider to be a truly disruptive technology. I’m no automotive journalist and so will resist the temptation to wax lyrical about this car (too much) so the purpose of this blog is really to share my experience from a clean energy/solar/batteries point of view.

However, the car is incredible, and makes my medium range 2 litre diesel car feel positively pre-historic in comparison. There’s no doubt in my mind electric cars are the future and the big auto makers should be quaking in their boots. I doubt the people at VW, BMW, GM, Ford et al will be reading this but, seriously, stop trying to fiddle your emissions tests, get investing and do so quickly if you’re not going to fall behind. Embrace the future.

Why is the car so amazing? Oh, so many reasons, but it’s quiet; almost disconcertingly so. It’s also fast and at the risk of sounding like a boy racer I have to admit that was so much fun. The delivery of power to the wheels is instant and smooth like no other car I’ve ever experienced, even compared to normal automatic cars where you still notice the gear changes. The electric motors just never seem to run out of steam and all you can hear is a faint musical whistle at higher speeds. The acceleration is like that in a good roller-coaster but without the nausea-inducing “roller”. Add to that comfort, adaptive cruise control and auto-pilot (a bit scary at first But you get used to it) and even my wife, a self-confessed Luddite, was impressed.

Efficiency and CO2 emissions

My 2 Litre diesel car averages around 50 miles per gallon or 11 miles per litre. Over the weekend, the Tesla was averaging 3 miles per kWh, so how does this compare? (I should also point out that the kerb weight of my car is around 1400kg versus the Model S at 2200kg with some 70kWh of batteries to lug around).

The energy content of diesel oil is 11kWh/Litre (Source: Carbon Trust) so 11 miles per litre simply translates to 1 mile per kWh. So in spite of the extra 800kg of weight the Tesla has to propel it is still almost 3 times as efficient as a typical car with a diesel combustion engine! This is remarkable but actually understandable when you consider a combustion engine and gearbox might have 500+ moving parts and yet the Tesla propulsion system has only 8.

The CO2 content attributable to grid electricity is variable throughout the day but as more renewables are connected to the grid it is going down. As I write Ecotricity’s live guide suggests the carbon content of the U.K. Electricity grid is at 293g CO2/kWh. So on that basis the Tesla would produce 99gCO2/mile, which is comparable to an efficient diesel car.

Range, the practicalities of charging and cost per mile

The maximum range of the Model S when fully charged is around 270 miles, which is more than adequate for most regular journeys. For longer journeys Tesla owners have free access to their growing Supercharger network that can charge to 80% in around a half-hour. Owners of other electric cars can access the growing network of public charge points operated by companies such as Ecotricity.

There’s still the need for the regular charge at home or at work and, as the car was only on loan, I haven’t a dedicated charge point (yet) so my only option was to use a standard 13amp 3-pin domestic socket (known as Mode 1 or Mode 2 charging). Theoretically the maximum current this can charge at is 10Amps (giving 2.3kW on a 230V supply). However the actual power draw was nearer 2kW. So each hour the car charged by 2kWh and the in-car display stated this gave 6 miles of range (hence the 3miles/kWh mentioned above). A 15 hour overnight charge therefore gave me an extra 90 miles, which was limiting for the family day out I had planned. The car was delivered with 100miles of range and so to fully charge would have taken 25hrs!

Clearly then a dedicated charge point is a must if you’re looking to own an electric car. Mode 3 chargers suitable for a single-phase 230V residential supply come in two versions able to deliver 16Amps (standard charge) or 32Amps (fast charge). Had I access to a 32Amp fast charge then the power draw would be nearer 7kW and an hour charge would mean a range for the Model S of 21miles and an 7hr overnight charge would be enough for 147miles so far more than acceptable. Poweri can provide a range of charging options (and we’re accredited with OLEV so our customers can qualify for grants towards the cost of a home charger) so please contact us to discuss your requirements.

So finally what about the cost?* Assuming a price of diesel (May 2016) of £1.07/Litre then 11miles/Litre translates to 9.7p/mile for my current car. If I charged the Tesla using daytime electricity then (assuming 15p/kWh) it would cost around 5p/mile. Charging for the 7hrs mentioned above could also be done during off-peak night-time electricity (assuming you have such a tariff) at around 4.5p/kWh giving a cost per mile of a miserly 1.5p/mile.

Finally, for ultra-low cost zero emission motoring would be to have a Poweri solar PV system on your roof and charge you electric vehicle from that. Married to a stationary battery storage system to allow power to flow when and where it’s needed most is in our view the ultimate solution and got to be the future of transport.

*Footnote: clearly this comparison is just considering fuel/energy and excludes all other vehicle running costs.

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