|Audi A3 TCNG for e-gas project. Click to enlarge.|
Starting in 2013, Audi will begin series production of TCNG models whose engines—derived from TFSI units—will be powered by e-gas: synthetic methane produced via the methanation of hydrogen produced by electrolysis using renewable electricity. Audi’s newly unveiled e-gas project is a component of achieving its goal of “Audi balanced mobility”—i.e., achieving a neutral CO2 balance across the entire mobility chain.
Audi says that the e-gas project, which after three years of research is now entering the practical phase, is a cornerstone of its mission to set up an entire portfolio of sustainable sources of energy. Audi will supply three sources of green 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 e-gas project consists of two main components:
Audi is contributing to the construction of offshore North Sea wind turbines which will generate clean 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 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 methanation step to produce methane. Although this methane is also known as synthetic natural gas, the company refers to it as Audi e-gas.
Audi notes that 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.
Audi says that its e-gas project provides an answer to the 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.
Along with our project partners, AUDI AG is realizing a method which puts CO2-neutral mobility within reach. 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.—Michael Dick, Member of the Board of Management for Technical Development
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 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.
Wind turbines are 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.
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% more energy than onshore stations.
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 e-gas plant has 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.
The electrolyzer runs on green electricity. Aided by polymer electrolyte membranes, the electrolyzer splits water into its components: hydrogen (H2) and oxygen (O2). Hydrogen will not be used directly for fuel cell vehicles 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.
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, Audi says.
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, with 150 metric tons of e-gas remaining 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.
In terms of the well-to-wheel analysis, a compact natural-gas car powered by e-gas emits fewer than 30 grams of CO2 per kilometer (48.28 g/mile), including 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, Audi notes a drawback in the overall energy picture regarding vehicle production: a lot of energy is needed to manufacture the batteries.
Audi says that its 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.
Renewable energies already account for 17% of electricity generated in Germany; renewable sources of energy are forecast to make up 77% of Germany’s overall electricity consumption by the year 2050.
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.
Audi argues 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%. If the dissipated heat is also used, this value is considerably higher still. The aim is to achieve an efficiency ratio above 60% in the future. Audi says that 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 Audi e-gas project can easily be replicated in any country with an existing natural-gas network.
The Audi A3 TCNG. The Audi A3 TCNG can run on the e-gas which Audi produces in the methanation unit. 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 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. 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.