Audi balanced mobility – The route to CO2-neutral mobility

Audi balanced mobility - Audi A3 TCNG

INGOLSTADT : May 13, 2011 - Audi is blazing utterly new trails to shape the future. Under the motto of “Audi balanced mobility,” the company wants to realize a considerable goal: a neutral CO₂ balance across the entire mobility chain. A core aspect of this mission is the Audi e-gas project: a milestone not only for Audi but also Germany’s entire energy-supply industry.

Audi balanced mobility - Wind Energy

Audi begins comprehensive initiative on sustainable and CO₂-neutral power generation and mobility

Audi wants to take the lead in the automotive industry regarding sustainable approaches to the use of natural resources. Under the motto of “Audi balanced mobility,” Audi is gearing its efforts to pursue a major goal: completely CO₂-neutral mobility. And the Audi e-gas project is a pivotal aspect of this initiative. The brand thus ushers in a milestone from which the energy-supply industry and society can benefit. Audi will be unveiling the e-gas project to the public for the first time in Hamburg, the Green Capital of 2011, on May 12 and 13.

Audi balanced mobility refers to a sustainable approach which addresses every aspect of the automotive value-added chain and provides new impulses for all gas and power suppliers in Germany. “Ecology and economy in unison: that is the greatest challenge of the future. To attain this we must bring mobility completely into equilibrium – with people and their new values and with the environment. CO₂-neutral mobility is our goal,” says Audi Chairman Rupert Stadler. He continues: “On the way to achieving this we are systematically using clean power. We are producing climate-friendly fuels and forming a new mindset for which our entire company stands. That’s the objective of Audi balanced mobility.”

The e-gas project, which after three years of intensive research is now entering the practical phase, is a cornerstone of this mission: Audi is the world’s first automotive manufacturer to set up an entire portfolio of sustainable sources of energy. Whereas some competitors limit themselves to purchasing green power from third parties, the brand with the four rings is becoming directly involved in producing it.

For this purpose, Audi contributes to the construction of offshore North Sea wind turbines, which generate green power that is then fed into the public power grid. Audi wants to use green power to produce and also operate its electric-drive e-tron models in the future.

A production unit will use some of this wind-generated electricity to manufacture hydrogen by means of electrolysis. Hydrogen can be used in the future as a source of energy for fuel-cell vehicles or, in an additional step, it can be used to manufacture methane. Such methane is known at Audi as e-gas. It is chemically identical to natural gas and can power combustion engines. Starting in 2013, Audi will begin series production of TCNG models whose engines – derived from TFSI units – will be powered by e-gas.

Ernst Ulrich von Weizsäcker, an environmental scientist and the co-president of the International Resources Panel, explicitly welcomes Audi’s initiative: “What I want is eco-friendly, sustainable mobility. Audi’s e-gas project, with its practical applicability, fits in extremely well with this, and goes a long way toward achieving CO₂-neutral mobility.”

In the medium term, Germany’s energy-supply industry can benefit from the Audi e-gas project. It provides an answer to the pressing question as to how green power can be efficiently stored, irrespective of location. If there are strong sea winds, for instance, then surplus power supplies can be converted to e-gas and stored in the largest available energy-storage system: the public gas network. If necessary, this energy can flow from the gas network back to the power grid at any time.

The Audi e-gas project

En route to the CO₂-neutral mobility of tomorrow, Audi is systematically relying on renewable energies – and the Audi e-gas project will be a milestone along this route. It consists of two main components. Wind turbines will generate clean power, part of which Audi will use in the future to build its e-tron vehicles. Clean power will also play a key role in powering e-tron vehicles. Rupert Stadler, Chairman of the Board of Management of AUDI AG, declared in May 2010: “Electric Audi vehicles ought to run predominantly on sustainably generated electricity.”

A new plant, the e-gas project's second component, will use the remaining green power to produce hydrogen by means of electrolysis. This source of energy, generated in a climate-friendly manner, can be used to power fuel-cell vehicles in the medium term. Audi will also combine hydrogen with CO₂ in an additional step to manufacture methane. Although this methane is also known as synthetic natural gas, the company refers to it as Audi e-gas. It can power combustion engines designed for use with natural gas; as of 2013, Audi will begin series production of such models, designated TCNG.

Methanation is particularly advantageous in that the reaction occurs with the aid of CO₂, which consequently is not discharged into the atmosphere. This results in a completely closed CO₂ cycle, which in turn facilitates climate-friendly long-distance mobility.

The Audi e-gas project furthermore exhibits a tremendous advantage from which Germany’s entire energy-supply industry can benefit: In the form of methane, electricity generated via renewable energy can be fed into the natural-gas network – which helps to solve the problem of how to store surplus wind or solar energy. If necessary, this energy can flow from the gas network back to the power grid at any time.

“Along with our project partners, AUDI AG is realizing a method which puts CO₂-neutral mobility within reach,” says Michael Dick, Member of the Board of Management for Technical Development. “Our technology has the potential to give new direction to the discussion on expanding renewable sources of energy. We ourselves are taking the initiative and are complementing electric mobility with an equally eco-friendly concept for long distances.”

Audi has completed the research phase of the e-gas project and will take the second step in mid-2011: investing several tens of millions of euros in the construction of an industrial facility. Audi will thus kick off this large-scale energy project together with its project partners: SolarFuel GmbH from Stuttgart; the Centre for Solar Energy and Hydrogen Research (ZSW), also based in Stuttgart; the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) in Kassel, Germany; and EWE Energie AG.

Electricity from offshore wind turbines

Wind turbines constitute the first significant component of the Audi e-gas project. During the project’s first phase, four large power plants at an offshore wind park in the North Sea are being financed by Audi and a regional power-supply company. Rated at 3.6 MW each, these four turbines are to supply some 53 GWh of electricity annually. This is equivalent to the requirements of a medium-sized city.

Concerning the use of wind power in Germany, offshore wind-power stations currently play a minor role. Located far from the coastline, they harness wind averaging 30 km/h (19 mph) to produce about 40 percent more energy than onshore stations. It goes without saying that great potential has yet to be tapped.

The e-gas plant

The project’s second large component is the e-gas plant, which will produce hydrogen and methane on an industrial scale. Ground is scheduled to be broken in Werlte, Germany in July 2011. The e-gas plant is connected to a waste-biogas plant, which supplies the concentrated CO₂ necessary for methanation and which would otherwise pollute the atmosphere. The plant will annually produce some 1,000 metric tons of e-gas while consuming 2,800 metric tons of CO₂.

The plant will comprise two main components: an electrolyzer and a methanation unit. There is also piping technology, tanks, open-loop and closed-loop control electronics, and compressors for feeding e-gas into the natural-gas network. In January 2011, a lab facility with an output of 25 kW was set up for testing purposes; it was possible straightaway to produce gas which meets feeding-in quality requirements.

The electrolyzer runs on electricity generated via renewable energy. Aided by polymer electrolyte membranes, the electrolyzer splits water (H2O) into its components: hydrogen (H2) and oxygen (O2). In the future, hydrogen will be able to power fuel-cell vehicles such as the Audi Q5 HFC; such vehicles, however, have not yet reached product maturity. Hydrogen therefore will not be used directly during the project’s first phase; instead, after being separated and dried, it is placed into a storage tank and then the methanation unit.

Here, the hydrogen is combined with carbon dioxide (CO₂) to create methane (CH4) as per the Sabatier reaction; water (H2O) forms as a by-product. Methane, a synthetic natural-gas substitute, is thus produced; it is subsequently conveyed to Germany’s natural-gas network as well as the network of CNG stations.

A long-proven technology in the chemical industry, it can in principle function wherever there is water, electricity and a CO₂ source. Fundamentally speaking, CO₂ can also be obtained from the surrounding air, but doing so entails more resources.

Even during this initial phase of the e-gas project, the electricity generated by wind power and the methane produced at the plant will suffice for 2,500 motor vehicles in total. Some of the wind-generated electricity would be enough to manufacture 1,000 units of the A1 e-tron and propel them 10,000 km (6,200 miles) per year. An additional share will be fed into the grid; surpluses within the power grid would thus benefit the e-gas plant, too.

By means of the e-gas generated via renewable energy, 1,500 units of the A3 TCNG could each be driven 15,000 km (9,300 miles) annually. And there would still be 150 metric tons of e-gas for the public gas network. As needed, this gas could also flow back. All in all, that represents a big boost to the power grid and equates to far more than 30,000,000 climate-neutral kilometers (18,700,000 miles) driven every year.

With regard to environmental impact, e-gas dazzles as fuel for vehicles. If one considers the well-to-wheel analysis in lieu of exhaust emissions, then a compact natural-gas car powered by e-gas emits fewer than 30 grams of CO₂ per kilometer (48.28 g/mile). And that includes all emissions created during construction of the wind turbines and the e-gas plant. Only electric vehicles which are directly supplied with wind-generated electricity perform even better: they emit under 4 g/km (6.44 g/mile). However, they exhibit a drawback in the overall energy picture regarding vehicle production: a lot of energy is needed to manufacture their batteries.

Storage of green power in the gas network

The Audi e-gas project is capable of solving several pressing problems faced by the sustainable energy-supply industry all at once. In the process chain, clean power, hydrogen and methane are produced: three key sources of energy for future mobility. In the medium term, this technology has the potential to establish a highly flexible power-supply infrastructure for electricity, heating and motor vehicles which is based entirely on renewable energies; in addition, the respective percentages of the three sources of energy can be adjusted as required.

The future of Germany’s power supply belongs to renewable sources of energy. Last year, their share of overall consumption of electricity, heating and fuel exceeded 10 percent for the first time. Renewable energies already account for 17 percent of electricity generated, whereby wind energy constitutes the largest share and figures vary considerably among German states. Renewable sources of energy are forecast to make up 77 percent of Germany’s overall electricity consumption by the year 2050.

Wind power has great potential. The Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) was commissioned to conduct a study by WindEnergie, a German association. According to the study, wind power could be harnessed to realistically generate some 390 terawatt hours (TWh) of energy – this would have satisfied 64.7 percent of Germany’s overall electricity consumption in 2010 (603 TWh). Overall output in the computational model amounts to 198 gigawatts (GW).

The production of electricity via wind and sun, however, is subject to natural fluctuations and the necessary storage capacity is currently very low. Pumped-storage power plants are capable only of short-term storage: during an emergency in Germany, they could supply power for all of an hour. All other solutions, such as compressed-air energy storage plants, are similarly very limited regarding capacity and period of storage.

The methanation of hydrogen using renewable energy helps solve this problem: the power grid is linked to the underground gas network, which can store surplus power supplies for months. The gas network has a potential capacity of 217 TWh, in contrast to the power grid’s storage capacity of just 0.04 TWh. The latter’s transport capacity, moreover, is just one tenth of that of the gas network.

Energy can be conveyed from the gas network – perhaps by means of gas-fired power plants or, in a decentralized manner, in block-type thermal power stations – back to the power grid at any time. New, decentralized cogeneration power plants can boost efficiency even more. In addition, methane is also suitable for the supplying of gas to private residences or providing high-temperature process heat.

The efficiency ratio of the e-gas pilot plant – from wind turbine to methane gas – is about 54 percent. If the dissipated heat is also used, this value is considerably higher still. The aim is to achieve an efficiency ratio above 60 percent in the future. The potential to store large quantities of energy – made possible by pairing electricity with gas on the one hand as well as wind energy and solar energy on the other – can truly invigorate the expansion of renewable sources of energy. The fact that the Audi e-gas project can easily be replicated in any country with an existing natural-gas network hints at the technical and economic significance of this project.

The e-gas project’s cars

Audi will supply three sources of energy in the scope of the e-gas project: electricity, hydrogen and methane gas. Respectively, each one is suitable for a very different type of drive concept: for electric cars, fuel-cell vehicles and CNG vehicles.

The Audi A1 e-tron
The A1 e-tron is the concept of a purely electric vehicle. If necessary, a range extender can recharge its battery; the A1 e-tron is propelled exclusively by the power of its electric motor. The four-seater is a zero-emission vehicle during short city drives.

This small compact car’s electric motor supplies a continuous output of 45 kW (61 hp) and a peak output of 75 kW (102 hp), transmitted to the front wheels via a single-stage transmission. The peak torque of 240 Nm (177.01 lb-ft) is available right from the off. The A1 e-tron dashes from zero to 100 km/h (zero to 62.14 mph) in 10.2 seconds and boasts a top speed above 130 km/h (80.78 mph).

It draws its energy from a package of lithium-ion batteries arranged in a T pattern beneath the center tunnel and rear bench seat. The liquid-cooled battery stores 12 kWh of energy, which suffices for more than 50 km (31.07 miles) of driving. High-voltage current will recharge the battery in less than an hour. As of longer distances, a range extender operates. A small rotary-piston engine underneath the luggage compartment recharges the battery by means of an alternator.

Audi balanced mobility - Audi A3 TCNG

The Audi A3 TCNG

The Audi A3 TCNG, a technological standard-bearer, can run on the e-gas which Audi produces in the methanation unit. Its four-cylinder TFSI engine and the exhaust system’s catalytic converter were designed with natural gas in mind. In Germany alone, natural gas is available at some 900 CNG stations and counting.

Via the “balanced cycle method” – similar to the purchasing of green power – A3 TCNG owners should be able to fuel their vehicles with wind energy starting in 2013. When a driver refuels with e-gas, the corresponding amount of renewable energy required to produce this e-gas is fed into the grid.

The volumetric density of e-gas is equal to that of fossil-based natural gas and is thus lower than premium unleaded. Similarly to natural gas, the combustion of e-gas also creates far less CO₂ than premium unleaded does. Concerning the e-gas project, this means that CO₂ emissions are very low not only in the overall picture (well-to-wheel), but also at the exhaust pipe (tank-to-wheel). Not one gram of CO₂ is emitted via the exhaust pipe which would not have been consumed during the manufacture of e-gas. In other words, there is a closed CO₂ cycle between the fuel’s manufacture and its combustion.

The high octane rating of approx. 130 RON for natural gas, biomethane and also for e-gas facilitates a high compression ratio in the turbo engine – which ensures high efficiency. Like all Audi models, the A3 TCNG in no way sacrifices driving enjoyment or everyday practicality. Its gas tanks, which store the e-gas at a pressure of 200 bar, offer enough capacity for long drives. The Audi A3 TCNG also boasts a bivalent configuration: if the natural-gas tanks run empty and there is no CNG station nearby, the vehicle can run on conventional gasoline with no drop in performance.

Images : Audi balanced mobility

[Source : AUDI]