Category: Test Drives

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Tesla Model S Vs Sunswift eVe.. 500 km range on 1/5 the battery capacity

Recently EV News had the opportunity to test drive two electric vehicles with 500 km range within a fortnight of each other. One, a world record breaking electric car, the University of New South Wales Sunswift eVe solar race car and the other a Tesla Model S P85+.

I wrote last year how in many ways the two share a common heritage with technology in the Tesla having a direct evolutionary path from the inaugural World Solar Challenge in 1987. While I was massively impressed by my short drive in the top-of-the-line Model S, it's interesting to analyse the strengths and weaknesses of two EVs that both achieve the holy grail of plug-in vehicles, 500 km range on a single charge.

Following Sunswift eVe's World Record run in July, Wired magazine hailed the student-run university project as being Tesla's new competitor, ahead of the likes of BMW or General Motors. Hyperbole? Perhaps as eVe is not a road registered vehicle let alone production ready. But that doesn't detract from the fact that during the world record run, Sunswift eVe achieved 500 km range at highway speeds of 107 km/h (66 mph), without solar array assistance, using a battery pack made of the exact same Panasonic cells used by Tesla but with 1/5 th the capacity of the Model S.

When you take into consideration that much of the Model S design, from the large wheelbase to the all Aluminium body construction, is dictated by the 500 km range goal and the size and weight of the battery pack required to achieve that, any vehicle that achieves energy efficiency sufficient to reduce the 18650 battery cell count from 7,104 to 1,200 must offer some advantages.

Number one on the list is direct drive in-wheel motors. Sunswift eVe is RWD and powered by 2x 1.8 Kw (10 Kw Peak) Australian developed direct drive CSIRO wheel motors, that give eVe a top speed of 140 km/h. These axial flux BLDC wheel motors are 98.3% energy efficient and because they are inside the wheel with the rotor turning at the same RPM as the tire, there is no mechanical transmission gearing losses which typically range from 20-30%.

Sure, rated power of only 1.8 kw is barely enough to run a 4 slice toaster but the driving experience proved that 20 kw peak (27 horsepower) provides enough performance to accelerate and maintain highway speeds with minimal fuss. Each wheel motor weighs in at only 15 kg with the 99.2% efficient motor inverters adding less than 1 kg each to over-all powertrain weight.

Next up is aero efficiency. Because the car was deigned for a 3,000 km race with a high average speed on extremely limited solar power, aerodynamic efficiency is king. Sunswift eVe has a 1800 x 4500 mm footprint (larger than a Tesla Roadster). Although the car has twice the frontal area of its blade-like solar car predecessor, Sunswift has achieved a similar drag coefficient. It’s managed this partly through a unique high-set “tunnel” underside design, giving the car the look of a catamaran.

Where the Tesla Model S has the lowest drag coefficient of any production vehicle of 0.24, Sunswift eVe, designed exclusively using Computational fluid dynamics (CFD), achieves a Cd of 0.16. During my test drive of eVe, even though the vehicle had both doors removed for easy access, the lack of aero drag was noticeable while coasting. One team member told me it takes eVe several kilometers to coast to a stop from 100 km/h.

While Tesla claimed that every panel on the Roadster was carbon fibre, UNSW has taken that a step further and fabricated the entire chassis from the material. Manufactured through a sponsorship deal with New Zealand firm Core Builders Composites, the company that build much of the America's Cup fleet, the vehicle has a kurb weigh of just 320 kg. A Tesla Model S weighs 2100 kg.

The main benefit of light weight is reduced rolling resistance. Approximately 5–15% of the fuel consumed by a typical car may be used to overcome rolling resistance. Michelin special order low rolling resistance tyres are used which are run at 80 psi. While not exactly the same kind of road car tires as the 285/30 R21 used on the rear of a P85+, they are possibly not too far removed from the bicycle like 155/70 R19 tires fitted to the BMW i3.

The combination of electrical energy efficiency, low aero drag and rolling resistance means a 16 kWh battery made from 1200x Panasonic NCR18650 cylindrical Lithium Ion cells with a weight of only 63 Kg is enough to give eVe a single charge highway speed cruising range of over 500 km. That's the same battery capacity as a Mitsubishi iMiEV which has a maximum range of 155 km.

Although carbon fiber is roughly 20 times more expensive than steel, BMW have invested €400 million to launch the first carbon fibre reinforced plastic (CFRP) production car, the all electric i3. BMW’s goal is to get the expense of a carbon-fiber frame down to the level of aluminium by 2020. While only the passenger cabin of the i3 is made from carbon fiber with the drive train, battery and suspension attached to an aluminium chassis, it seems only a mater of time before 100% CF chassis like eVe become economically viable for mass produced road cars.

The next challenge for the Sunswift team is to make the eVe the first road-legal solar-powered car in Australia. They expect it to meet Australian road registration requirements within as little as one year.

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A ‘quick’ test drive in a Tesla Model S P85+

Earlier this week EV News had the pleasure of test driving a Tesla Model S P85+ around the streets of Sydney. It was only a very brief experience compared to the week long test drives we've had with most other EVs, but it was long enough to confirm Tesla Motors electric vehicles are in another league.

The first thing you notice about the Model S is that it's a big car. All dimensions including wheelbase and track are larger than a Holden Commodore VF. The upshot of this being the Model S has more interior storage space (1,796 L) than the Mitsubishi Outlander PHEV SUV we tested a few weeks ago. The overall size of the wheelbase seems governed by the size of the flat-pack battery enclosure which makes up 700 kg of the vehicles 2,100 kg kerb weight.

For such a heavy car the weight wasn't noticeable while driving, although the test route didn't allow for any high speed loaded cornering. In acceleration the P85 Model S is stunning! Unlike all other EVs I've driven which have synchronous BLDC permanent magnet motors, the asynchronous AC induction motor in the Model S really has a kick in the back off the line. So much so it might be a good idea for Tesla reps to wear a neck brace on test drives.

The BMW i3 I drove in Munich earlier this year was the fastest EV I had previously driven but full acceleration in the i3 didn't really come on strong until over approx 25 km/h. With 310 kw and 600 Nm peak torque from zero RPM from the 3 phase AC induction motor, the P85 Model S launches from a standing start to 100 km/h in just 4 seconds. That's faster than your average Porsche.

As with all EVs, mid-speed acceleration was impressive but with the Tesla, mind blowingly so! The main reason I've been so keen to sample a Model S was because my daily driver has 255 Kw / 500 Nm with a 1600 kg chassis, so on paper the two are broadly comparable. My 5.7 Lt 4 door sedan does 0-100 km/h in around 5 sec which is faster than both a standard Model S 85 (5.6s) the 60 version (6.2s). I've clocked up over 300,000 km in my current car so am fairly familiar with impressive acceleration, yet the Model S P85 absolutely kills it!

I've been trying to get my head around how the Tesla Model S P85's mid-speed acceleration felt twice as fast as my car. The Tesla's 600 Nm multiplied by the 9.73:1 reduction gear ratio gives 5,898 Nm at the rear wheels. Divide that by the 2,100 kg kerb weigh and the Model S has 2.8 Nm /kg. Running the same numbers for my Corvette engined family sedan gives 4,476 Nm (in first gear only) divided by 1,600 kg kerb weigh surprisingly gives the same 2.8 Nm/kg figure.

So why does the P85 feel twice as fast at mid speed? The 3 phase AC copper rotor induction motor's torque curve gives a flat 600 Nm between 0 and 5,000 rpm. Like with all EVs this broad torque curve allows the Tesla to have a single speed transmission. This means it's effectively in first gear all the time. So while my ICE powered car, even in 1st gear, doesn't reach peak torque until 4,400 rpm (although it has approx 80% of that from 1,500 rpm), cruising in top gear reduces maximum rear wheel torque to 'only' 1,500 Nm at mid-speeds. By comparison, the Tesla has approx 6,000 Nm available from standstill up to approx 70 km/h.

The bottom line is, at mid-speeds, the Tesla has up to 4x as much peak torque available at the flick of the throttle pedal compared to my ICE car and I can confirm, you can certainly feel the difference. The rep spotted the "Tesla grin" immediately. It's no surprise that Mercedes, Audi and BMW are already working on their own versions of the Model S. I don't think it's much of an exaggeration to say this car is revolutionary!

The Model S P85+ as driven was priced around $190k. A basic P85 option package with the full 310 kw / 600 Nm and 21" wheels is $130,600. Unfortunately luxury tax and other government charges add another $25k bringing the total cost to $155k in Australia.

(dyno torque curve from a Tesla Roadster - the Model S P85 has 2x more torque @ the wheels)

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On Holiday in Hawaii with the Nissan Leaf

During a recent holiday in Waikiki, a beach front neighbourhood of Honolulu in Hawaii, EV News took the opportunity to rent a Nissan Leaf for the day. Having scanned the available cars on the Enterprise Rent-A-Car web-site and noticing they had Nissan Leaf available and for approx the same price as others in the same bracket I couldn't resist test driving one.

We picked up our Silver 2013 Leaf with 544 miles on the odometer with a full charge and only a vague idea where we were going. Earlier in the week we'd hired a 3rd generation Toyota Prius to lap the Island of Oahu a couple of times. (I've driven a Holden Volt and a Mitsubishi iMiEV, but not a Prius so I had to tick that box)

Having just hopped out of a Prius the controls in the Leaf were immediately familiar. It wouldn't be a wild guess to say the mouse-shaped gear selector in both could be from the same supplier. The start procedure in both is almost identical too, put the wireless key in the centre console, foot on the brake pedal, push button to start, select 'D' on the 'mouse', foot parking brake off, push the throttle and start moving forward - silently.

Aside from the steering wheel being on the wrong side of the car and having to drive down the wrong side of the road, (we're RHD here in Australia) we were still a bit navigationally challenged after only a few days in Hawaii. For a start, we hadn't been able to source an old fashioned paper road map of the place and being cheap skates (read: having a strong aversion to being ripped off) neither my better half nor myself had set-up International roaming on our iPhones so consequently they only worked when-ever WiFi was avaliable. Infrequent checking of Google maps required a quick visit to the nearest McDonalds to use their free WiFi.

Of course, the Leaf has GPS as standard built into the dash but a) you can't type in an address unless stationary (which frustrates the passenger no end) b) the address look-up isn't as good as Google and more often than not failed to return a result so it becomes a two device routine to actually find the route to any particular land mark.

I soon discovered range anxiety is real, at least within the first hour of being in a unfamiliar car. Like any typical Hawaiian day it was 30c so having driven out of the hire car lot and straight onto an expressway with the air conditioning on (i.e. maxium possible energy consumption)... the range indicator started to fall rapidly. Obviously if you owned a Leaf you would soon grow accustomed to it's range capabilities, but in unfamiliar terrain and in an unfamiliar electric vehicle, straight off the bat, it's all an unknown.

When we got the keys the range indicator said 84 miles (134 km). We hit a few outlet stores, hill climbed the 1,186 feet (361 meters) elevation to the Nu'uanu Pali Lookout, depleting indicated range to less than 20 miles - which we regenerated back up to 37 miles (60 km) by the time we returned to our hotel by late afternoon.

Fortunately Hawaii has plenty of accessible public changing stations, which most of the time are very popular. (see above) Even though the parking itself isn't free, the charging is and as luck would have it, there was a charging station within 5 mins walk of our hotel. It was not being used when we arrived with our Leaf (although it had been ICE'd by a minivan – who promptly moved and starting asking questions about the Leaf) and after a quick 3 hours plugged in we set off for dinner with the dash showing 100 miles (160 km) of range.

When confined to level ground, city driving, as opposed to expressways and hill climbs, the Leaf consumes amazing little energy. What you use during heavy acceleration is mostly regenerated while pulling up at the next set of traffic lights. The leaf has the same blended brake set-up as the Prius and Volt so any use of the brake pedal kicks in more regeneration as opposed to dissipating energy through the friction brakes.

In fact, having driven 2 full laps of Ohau in a Prius, I now understand why Prius owners are often quoted as saying brake wear is minimal even after 200,000 km as like the Volt, the Prius uses full regen braking most of the time. Incidentally, on a recent trip to Darwin to cover the World Solar Challenge it was interesting to note 80% of the taxis in Darwin are Prius – frugal on both fuel consumption and brakes - sounds like a perfect combination for a taxi.

From a drivers perspective, due to the “pedal feel simulator” in most hybrids and electrics, it's hard to tell the difference between regn and friction braking based on pedal feedback alone. The tell-tale is watching the dash displays and how they ramp up to full any time the brake pedal is pressed while the vehicle is at speed.

For urban driving the Nissan Leaf is a great choice. It's surprisingly big for a 'small' car, costs virtually nothing to run, takes only a few hours to get back to fully charged on a 240v outlet and as we have seen with DC fast chargers it can easily cover 500 miles (800 km) in a day.