There is much to recommend electric vehicles (EVs) today as we struggle with rising fuel prices, warnings that we have entered a "Post-Peak Oil World," and as concern over the environmental and societal impact of vehicle emissions grows. EVs provide clean, quiet operation, mechanical simplicity, fine driving control, excellent conversion efficiency, and the ability to generate torque rapidly and convert kinetic motion back into electricity using regenerative braking.
EVs were among the first passenger vehicles, and held many early land speed and distance records but were eventually surpassed by vehicles with internal combustion engines, which offered greater driving range and what was then a cheap and plentiful source of energy: petroleum-based fuel.
Since then, interest in EVs has grown and waned - usually in response to issues like the oil crisis of the 1970s, the California zero-emissions laws of the 1990s, and the current decade's high fuel prices. Unfortunately, the plug-in battery-electric vehicles of the 1970s and 1990s were designed for economy of operation not performance. Versus conventionally powered vehicles, they had poor handling and acceleration, low top speeds, and short driving ranges. Battery technology then in use required long recharge times and offered short life spans. And, with plug-in electrics, unless you drove in urban California, there was little access to recharging stations when away from home.
Some of these problems are addressed with today's hybrid-electric (really gasoline-assist electric) vehicles, but drivers longing for a car that is both "green" and high performance have had a long wait. It has been no small feat to reconcile the desire to go fast in style with the desire to save the planet.
That changed with the introduction of a sleek, battery-powered two-seater from startup automaker Tesla Motors (san Carlos, Calif., USA). The Tesla Roadster is not only a great-looking ride and the world's first all-electric sports car, but it has impressive performance even when benchmarked against conventionally powered vehicles. It accelerates from 0 to 60 mph in 4 seconds and tops out at 130 mph/209 kmh. Unlike earlier plug-in EVs, Tesla's Roadster uses advanced battery technology and a lightweight composite body to produce an open-cockpit sports car that should appeal to environmentalists and auto enthusiasts alike - two groups who rarely agree on anything.
One key to overcoming problems with earlier EVs is Tesla's use of lithium-ion (Li-ion) batteries, which are light, compact, maintenance-free, charge quickly, lose charge slowly, and offer the best energy/weight ratio of current commercial battery technology. Instead of a few large batteries like previous EV manufacturers, Tesla uses 6,831 microprocessor-controlled cells the size of AA batteries. This allows for better weight distribution (not to mention storage), which - coupled with aerodynamic body design and performance tires - significantly improves vehicle handling. The Roadster can travel as far on a single charge as conventional vehicles do on a tank of fuel - roughly 250 miles/402 km (EPA Highway), while providing true sports-car performance at an EPA equivalent fuel economy of 135 mpg (57 km/liter) and estimated energy costs as low as $0.01 (USD) per mile.
The other key to the Roadster's performance is significant use of composites for all external body panels - hood, decklid, roof, fenders, and doors - the center console, bumper beams and fascia, plus additional non-visible structural and semi-structural parts.
Early design goals called for the vehicle to have low aerodynamic drag to increase energy efficiency and low curb weight to maintain a high power/weight ratio for maximum acceleration. Equally important was the goal to achieve body styling that made people desire the car regardless of efficiency or performance. The engineering team also wanted body-panel stiffness equivalent to 0.04 in./0.9 mm steel panels for a "quality feel" - which necessitated options with high specific bending stiffness. Since the Roadster's target retail cost was high (fully loaded, $100,000 USD) and production volumes low (maximum 2,000 units annually), advanced composites were a logical place to start.
The team benchmarked composite-body vehicles to understand the benefits and challenges of different material/process options. Several process options were considered but rejected: autoclave was too slow and costly and had insufficient processor base; and ambient or oven-cure vacuum bagging was unlikely to meet Class A-surface requirements in the panels' complex geometries. Resin transfer molding (RTM) was finally selected for its rapid cycle times, excellent surface quality, and ability to control part thickness to increase stiffness or strength locally.
Two years of design, prototyping, testing, and redesign led to the development of unique exterior body panels of carbon fiber/epoxy sandwich construction that are strong in tension and compression. While providing bending stiffness values close to steel's, they are 50 lb/23 kg lighter per panel set than glass-reinforced polyester composites with comparable stiffness.
The RTM body and structural panels are produced by SOTIRA (France) using the "Injection Compression SOTIRA" process with in-house, epoxy injection machines and preform systems. The sandwich itself is comprised of multi-axial carbon fabrics from Zoltek Companies, Inc. (St. Louis, Mo., USA), and epoxy resins (supplier not disclosed), along with DuPont primer systems (Wilmington, Del., USA).
The vehicle was styled by Lotus Design (Hethel, UK) and engineered by Tesla's Body Engineering Team in the UK. Lotus Cars provides vehicle assembly and painting in the UK. RTM body panels are molded by SOTIRA (at St. Meloir & Pouancé plants in France). Other composite parts include an autoclaved prepreg center console by Belco Avia (san Pietro, Mosezzo, Italy); bumper beams (polyurethane foam over a carbon-fiber armature) with an RRIM polyurethane fascia from Polytec Holden (Bromyard, Herefordshire, UK); and a blow-molded ABS rear spoiler. The chassis is bonded aluminum.
The very first Roadster was delivered to its first customer - Tesla's Chairman, Elon Musk - on February 1, 2008. Series production begins March 17, 2008 and the company is currently sold out on 2008 year models but is taking deposits for 2009 models. Owing to significant global interest in the vehicle, Tesla is said to be considering development of additional versions of the Roadster for international markets.