Audi embarks on a wind-to-wheel journey

  • 28-Jun-2011 07:51 EDT
Audi6-11CO2 system Eng.jpg

The sequence of Audi's wind-to-wheel drive toward balanced mobility.

The achievement of completely CO2-free mobility is one of the most demanding challenges facing the global auto industry. Now Audi, well aware of the hurdles it has to overcome, is investing time, money, and broad-based expertise in pursuit of successfully achieving CO2-neutral power generation and mobility.

Its project, conceived three years ago but now becoming a practical reality, involves contributing to the construction of offshore wind turbines, leading directly to the supply of three energy sources: electricity, hydrogen, and methane gas, to power, respectively, electric, fuel cell, and CNG (compressed natural gas) vehicles.

Said Audi Chairman Rupert Stadler: “On the way to achieving this, we are systematically using clean power. We are producing climate-friendly fuels and forming a mind-set for which our entire company stands. That’s the objective of Audi balanced mobility.”

Electric vehicles should run predominantly on sustainably generated electricity, he stressed. And Audi claims to be the world’s first automotive manufacturer to establish an entire portfolio of sustainable sources of energy, producing its own green power. A very significant element of this is its contribution in terms of cash and expertise in the building of wind turbines in the North Sea, with the resultant power generated fed into Germany’s national grid, which would ultimately power its electric e-tron models.

But some of the wind-sourced electricity will be used to manufacture, at an “e-gas” plant, hydrogen via electrolysis for use by fuel-cell vehicles and also (by combining hydrogen with CO2) methane gas (synthetic natural gas) to fuel internal-combustion engines.

It has been three years since Audi decided to go for “big picture” life-cycle environmental assessment. But it also realized that just producing another “worthy” study would not cut it with the buying public, so the company is taking vehicle buyers along its balanced mobility route, explaining what it is doing and why it is running a program that seems, in part at least, distinctly separate from the business of automotive design and manufacture.

For example, it can present a picture of a howling gale above the inhospitable North Sea that sends wind turbine blades whirling. Surplus power supplies could be converted to e-gas (chemically identical to natural gas) to be stored in the largest available energy storage system—the public gas network. And if needed, the energy could flow back to the grid.

Four large power plants in an offshore wind park, each rated at 3.6 mW, will supply 56g W·h of electricity annually.

Audi believes the great potential of wind-power stations has yet to be tapped. Skeptics may joke that the North Sea could have such a plethora of wind turbines and wind-power stations that shipping lanes would have to be created through them, but there is potentially a truth in the possibility.

The company is particularly enthusiastic about e-gas because methanation uses CO2 within a completely closed manufacturing/end-use cycle, and so keeps the gas out of the atmosphere.

While it has a very active EV program, Audi appreciates the need for environmentally responsible long-distance vehicle capability, which (fuel-cell examples apart) pure EVs lamentably lack. Said Michael Dick, Audi’s Technical Development boss: “We are taking the initiative and are complementing electric mobility with an equally friendly concept for long distances.”

In this, it is supported by several partners, including SolarFuel GmbH; the Center for Solar Energy and Hydrogen Research (ZSW), The Fraunhofer Institute for Wind Energy and Energy System Technologies (IWES); and EWE Energie AG.

The company is now constructing an industrial e-gas facility, which gives the whole project production momentum. Connected to a waste biogas plant, which supplies concentrated CO2 for methanation, the facility will produce about 1000 t (1100 ton) of e-gas per annum and consume 2800 t (4000 ton) of CO2 in the process. The plant will include an electrolyzer (powered via renewable energy) and methanation unit.

Even during the initial phase of the e-gas project, the electricity generated by wind power and the methane produced at the plant will suffice for a total of 2500 motor vehicles, according to the company. Some of the wind-generated energy would be enough to manufacture 1000 units of the Audi A1 e-tron (EV) and propel them 10,000 km (6000 mi) per annum. An additional share will be fed into the grid; surpluses within the power grid would thus also benefit the e-gas plant.

Audi’s four-cylinder TFSI-engined A3 TCNG could run on the e-gas from the plant. That and its exhaust system’s catalytic converter were designed for compatibility with CNG. Germany has some 900 CNG stations.

This means that A3 TCNG users could reasonably expect to fuel their cars with wind-energy-produced methane in 2013. Energy density of e-gas is similar to that of fossil-based natural gas, notably less than unleaded gasoline, but CO2 emissions are very low, not only on a comparable “well-to-wheel” basis but also at the tailpipe (tank-to-wheel). “Not one gram of CO2 is emitted via the exhaust pipe that would not have been consumed during the manufacture of e-gas. So there is a closed CO2 cycle between the fuel’s manufacture and its combustion,” stated Audi.

The 130 RON rating of e-gas allows a high-compression turbocharged engine to run efficiently. The A3 TCNG can switch to burn gasoline if an e-gas/CNG station is not available.

Considering a well-to-wheel analysis in lieu of exhaust emissions, a compact natural gas car powered by e-gas would emit fewer than 30 gm of CO2/km, claims Audi, which includes all emissions created during construction of the wind turbines and the e-gas plant. EVs directly supplied with wind-generated energy achieve less than 4 g/km. But battery manufacture requires a lot of energy and needs to be added into the equation.

Harnessing wind power is hardly new. Horizontal windmills appeared in Persia in the 9th century, and in the late 13th century a vertical windmill was used for grinding cereals in England. In the late 19th century, wind turbines were demonstrated in Europe and the U.S. They’ve slowly improved since.

Now, according to a German study for the WindEnergie association, the Fraunhofer IWES reckons that wind power could be harnessed to realistically generate some 390 TW·h of energy, which would have met almost two-thirds of Germany’s overall electricity consumption in 2010.

But because of the variability of wind power, energy storage is needed. Methanation of hydrogen via renewable energy offers a potential answer. In Germany, the power grid is linked to the underground gas network with massive storage capacity equating to 217 TW·h.

Efficiency of the e-gas pilot plant is put at 54% with a 60%-plus target.

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