energy conversion and CO2
20 May 2011 : Under the "e-gas
project" title, Audi is presenting a clear plan to reach what it
calls "balanced mobility", a completely CO2-neutral
mobility, in an initiative from which both the energy-supply industry and
society should benefit.
Audi says that the e-gas project can even help to solve
the problem of how to store surplus wind or solar energy, as such a surplus
energy can be fed into the natural-gas network (see: methanation
below) and from there, it can even flow back from the gas network back to the power grid at any
First, the Audi e-gas project consists of two main
components: wind turbines and a new plant.
The wind turbines will generate clean power, part of
which Audi will use in the future to build its e-tron vehicles (it will
also play a key role in powering these vehicles).
The new plant 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
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 cleaner long-distance mobility.
The German luxury car brand says that its e-gas project
adds another advantage from which Germany’s energy-supply industry can
benefit: in the form of methane, electricity generated via renewable
energy can be fed into the natural-gas network – which can help 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
Having completed the research phase of the e-gas
project, Audi will soon take the second step (mid-2011): 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.
A neutral CO2
balance across the entire mobility chain. Press
on the e-gas
project image to enlarge it in a different window.
Wind turbines constitute the first significant
component of the 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 (equivalent to the requirements of a medium-sized city).
Offshore wind-power stations currently play a minor
role in Germany. But when located far from the coastline, they harness
wind averaging 30 km/h (19 mph) to produce about 40 percent more energy
than onshore stations.
The second large component of the project 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.
electrolyzer runs on electricity generated via
renewable energy. Press
on the electrolyzer
image to enlarge
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
The electrolyzer (picture above) 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. Since such vehicles have not yet reached
product maturity, hydrogen 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.
Methanation: hydrogen is combined with carbon dioxide
to create methane. Press
on the methanation image to enlarge it.
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. Although CO2 can also be obtained from the
surrounding air, doing so requires 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
With regard to environmental
impact, 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
The Audi e-gas project is capable
of solving several 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 Audi A1 e-tron's electric motor supplies a continuous output of 45 kW (61 hp) and a peak
output of 75 kW (102 hp).
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
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
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 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
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
The small compact Audi 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.
The Audi A1 e-tron'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
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
The Audi A3 TCNG 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
A3 TCNG can run on e-gas
produced 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 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, says Audi.
words, there is a closed CO2 cycle between the fuel’s manufacture and
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 A3 TCNG's 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.