Net-Positive Solar EV Goes 600 Miles on a Charge and Carries Four Passengers
Tom Lombardo posted on July 12, 2015 | 15561 views

Many solar assisted electric vehicles (SAEVs) are built strictly for competition, but the Stella Lux (Latin for Star Light) could be the first SAEV designed to be a family car … after its prototype finishes a competition. The Stella Lux is a street legal sedan that seats four. It’s roughly the size of a 2015 Toyota Corolla, but a little shorter.

The Design Team

Stella Lux was designed by Solar Team Eindhoven (STE), a multidisciplinary group of engineering students from Eindhoven University of Technology. The car will be competing in the Bridgestone World Solar Challenge in October of 2015. The previous version - the Stella - won the 2013 World Solar Challenge in the Cruiser Class, and STE hopes to once again take home the gold. More than that, these students want to show the world that a solar assisted EV is a practical alternative to fossil fueled vehicles. 

I contacted STE team member Melvin de Wildt, who provided me with a little technical information about the car. Because the car is entering a competition, he wouldn’t go into great detail about what’s under the hood, but here is what he shared:

The Nuts and Bolts

With about six square meters of rooftop covered by monocrystalline solar cells, the car generates roughly 1500 watts in direct sunlight, which helps to charge the 15 kWh Li-ion battery pack. A pair of high efficiency in-wheel axial flux motors - a type of AC induction motor with a variable speed drive - propels the vehicle. The motors also work as generators when the car is braking, recovering much of the energy and using it to recharge the battery pack.

Since electric motors operate efficiently at a wide range of speeds, there’s no need for a transmission. This reduces weight, cost, complexity, and maintenance.

Made of lightweight aluminum and carbon fiber, Stella Lux tips the scales at a meager 375 kg (827 lbs), about one fourth that of a Corolla. With a sleek aerodynamic design that includes a tunnel down the middle, the Stella Lux can travel up to 650 km (400 miles) on just battery power. If it happens to be a sunny day, the rooftop solar panels will extend the range to a thousand kilometers (620 miles). (That’s on a sunny day in the Netherlands, which is about 52oN latitude, farther north than any part of the contiguous United States.) With an electric rate of $0.12/kWh, $1.80 worth of electricity lets the Stella Lux drive up to 620 miles. By comparison, my Corolla goes about 26 miles on $1.80 in fuel, at current gasoline prices.

Net-Positive Energy

According to its designers, Stella Lux is a net-positive energy car, which means that it generates more energy than it uses. Let’s qualify that right away: when the car is parked outside in daylight, it generates energy and uses none. When it’s on the road - even on a sunny day - it uses more energy than it generates. The net-positive energy comes from the fact that many vehicles spend more time parked than they do driving, and during their “downtime” they could be adding power to the grid. A fleet of EVs, coupled with a smart electric grid, can help balance electrical supply and demand.  

Beauty and Brains

Beauty is subjective, but I think this is one cool looking vehicle. That said, there’s no question about the Stella Lux having brains. Its navigation system can check the weather forecast and help determine the optimal route to maximize the vehicle’s range. It can synchronize with a smartphone so it knows the user’s destination. If it’s parked and plugged in, the Stella Lux can, based on one’s calendar, determine how much it can safely sell to the grid while still retaining enough charge for the next day’s commute. Door locks are automatic; when Stella Lux detects the owner’s smartphone nearby, it unlocks the doors. This car is designed for comfort and convenience, not just fuel economy.

Here is team member and mechanical engineering student Liselotte Kockelkoren describing the project:

If you would like to contribute to the Stella Lux project, click here.

Photo credits: TU Eindhoven, Bart van Overbeeke

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