For all the energy required to propel a vehicle, not all of it makes it to the wheels. Some of it is lost to friction and heat. Vehicle inefficiency can be classified into two categories of losses: road-load and energy conversion. At Tesla, careful attention is given to both to achieve the maximum range. The Tesla Roadster leverages both an incredible electric powertrain and an engineer’s obsession with efficiency to be the most efficient production sports car on the market today.
ROAD-LOAD
All vehicle types, regardless of what powertrain they use, need to overcome road-load. It includes wind resistance, mechanical friction (bearings, hubs, driveshaft, etc.), and tire rolling resistance. Road-load affects all vehicles. As a car speeds up, wind resistance increases; there is more air for the car to “push” out of the way. Therefore, road-load is greater at higher speeds and is dependent on the aerodynamics of the vehicle. Tesla engineers are focused on decreasing aerodynamic losses while achieving beautiful styling. Road-load can be minimized by designing brakes, bearings and other rotating components with less friction. It is also important to use tires that have low rolling resistance and make the vehicle as light as possible. Energy saved by decreasing road-load can have a significantly positive impact on range. The Model S will be one of the most aerodynamic sedans ever built with all components tuned to minimize friction and achieve the highest possible range.
ENERGY CONVERSION LOSSES
Two theoretical cars with identical road-load could have very different overall efficiency based on how effectively they convert energy before it turns to the wheels. Electric vehicles have the lowest overall energy conversion losses.
ELECTRIC VEHICLE EFFICIENCY
In an electric vehicle, chemical energy is stored in a battery. Lithium-ion batteries are used in Tesla vehicles because of high energy density. Converting the chemical energy to free electrons (electrical energy) can be greater than 90% efficient – some energy is lost to heat in cells and other battery pack components such as current conductors and fuses. The remaining components of the Tesla powertrain – the drive inverter and motor – are also extremely efficient. Overall, drive efficiency of the Tesla Roadster is 88% - almost three times more efficient than an internal combustion powered vehicle.
INTERNAL COMBUSTION VEHICLE EFFICIENCY
Chemical energy is stored as gasoline in a conventional car. Combustion is used to convert the chemical energy into thermal energy. Pistons convert the thermal energy to the mechanical work that turns the wheels. The conversion process is, at best, 35% efficient. The majority of the energy stored in the gasoline is lost as heat.
HYBRIDS AND PLUG-IN HYBRID VEHICLE EFFICIENCY
The energy conversion process in a hybrid is a combination of the process in an internal combustion vehicle and battery electric vehicle. Overall efficiency for a hybrid is a bit higher than a conventional vehicle because it can recapture some road load energy, but is still much lower than an electric vehicle. When Hybrids operate in all-electric mode – overall efficiency can be quite high. However, once the gasoline engine kicks in, the overall powertrain efficiency includes losses due to both the ICE conversion process and the battery. A world of 100% hybrid vehicles is still 100% dependent on oil.
FUEL CELL VEHICLE EFFICIENCY
Fuel Cells, like batteries, convert chemical energy directly to electrical energy without an intermediate thermal step, but do so less efficiently. Conversion efficiency for this step is no more than 50%. There are additional losses associated with reforming and converting stored hydrogen for the fuel cell stack. Post-processing of byproducts also affects overall conversion efficiency. Total efficiency is quite similar to conventional ICE powertrains.
WELL-TO-WHEEL EFFICIENCY
Comparing an example of each technology reveals that Tesla electric technology uses energy most efficiently. As utility companies build more efficient power plants and bring more renewables online, the well-to-station efficiency will significantly increase. In turn, the overall vehicle efficiency increases to levels never to be recognized by internal combustion or hybrid technologies.
PETROLEUM WILL NOT LAST FOREVER
Petroleum is a limited resource and a vexing source of price spikes, geopolitical instability, and environmental disasters of epic proportions. Petroleum currently fuels 95% of the United States transportation sector, a sector that demands nearly 28% of total energy usage. Globally, demand for personal transportation is increasing while reserves are decreasing. Not only is petroleum a diminishing resource, but it is also a significant source of greenhouse gas emissions.
Fortunately, reducing the use of oil for transportation can quickly increase independence and reduce emissions. Tesla vehicles are semianl to developing a cleaner, more independent transportation paradigm.
CLEAN ENERGY IS THE FUTURE
Reducing the transportation sector's dependence on petroleum means increasing dependence on electricity. As transportation increases its use of the electricity grid, the demand for energy will rise. This demand can be met by bringing online increasingly efficient power plants and renewables. Many countries have committed to decreasing dependence on fossil fuels by increasing their renewable energy portfolios. The United States Federal Government has pledged to reduce greenhouse gas emissions by 28% by 2020. In Europe, renewable energy should account for 20 percent of energy consumption by 2020. Germany alone has more than quadrupled the amount of renewable energy feeding its grid in less than a decade.
Some may argue that electric vehicles simply replace one polluter (petroleum) with another (coal). To use the United States electricity grid as example, Tesla vehicles cut in half the carbon dioxide emissions of its petroleum-burning rivals, despite the fact that about half the grid is powered by coal. We can do better. Over the past five years, United States electricity generation from renewables has increased while coal decreased. As this shift happens, electric vehicles become even cleaner. In California, renewables (13%) contribute more to the grid than coal (12%).
BOLD ACTION
Many Tesla owners around the world take emissions into their own hands. Increasingly, they rely exclusively on solar for their complete energy needs and in doing so, they tread more lightly on the planet. Some utility companies offer their customers the opportunity to buy energy generated exclusively from renewable sources. In both cases, Roadster owners lead a truly emission-free lifestyle
CHARGING
With a Tesla, waiting until the fuel needle hits "empty" is a distant memory – owners simply plug in when convenient to maintain vehicle charge. The Roadster’s charger is incorporated into the powertrain system, enabling the use of any conventional 110-volt or 220-volt power outlet for charging. The Roadster and its connectors are designed to offer owners the freedom to charge whenever and wherever they want. Charging at night provides an extra financial advantage as many utility companies offer special rates during off-peak hours, when demand for electricity is low. When paired with a residential solar array, the Roadster offers complete driving independence. Plug in before bed and wake up with 245 miles of driving range.
Sports cars are meant to be driven. The Roadster infuses every trip with new life. Connect not only to the car and road - delight in the surrounding sounds and scenery of the route. Roadsters have driven across the United States, throughout the European countryside, and on countless other adventures. California's Highway 101 has a series of Tesla High Power Wall Connectors as a shining example of the future of the electric highway.
See more at http://www.teslamotors.com.
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