Audi E-diesel made from water, CO2 and green power
audi-mediaservices.com
audi-mediaservices.com
The normal problem is that the cheapest/easiest source of hydrogen is from the stream reformation[1] of natural gas, but here there are using high temperature electrolysis[2] of water powered from green energy (they don't seem to specify exactly what this is).
The CO2 comes from atmospheric capture using a device from Climeworks[3], and biogas. This is CO2 neutral as all this CO2 is either in the atmosphere already, or will naturally end up in the atmosphere.
This is of course a very small-scale pilot by Audi, but I've often thought that using hydrocarbon fuels manufactured from atmospheric CO2 and water might be an excellent solution for transport and space heating. We have all the infrastructure for distributing these fuels, they are manufacturable using something like solar energy, and can be easily stored and transported themselves.
[1] http://en.wikipedia.org/wiki/Steam_reforming [2] http://en.wikipedia.org/wiki/High-temperature_electrolysis [3] http://www.climeworks.com/
1) There is only one source of "new" energy on the Earth: nuclear. Whether it's from a nuclear reactor, or the Sun's rays, that's the only way you get new energy.
2) All conventional sources of energy (petrol, natural gas, diesel, ethanol, etc) are extraction of previously stored energy. Fossil fuels are just a solar energy store on a geologic time scale.
3) Any time you hear about a process that involves creating fuel from lower energy-state molecules (molecules that react on their own), there must be another source of energy involved.
4) There is no such thing as 100% efficiency in transmission of energy, so all forms of energy extraction/conversion involve some loss of energy to the surrounding environment. This prevents any such systems (non-nuclear extraction/conversion) from being run in a feedback loop that provides a net positive energy output.
For example, the explanation of the process starts with:
"First, water heated up to form steam is broken down into hydrogen and oxygen by means of high-temperature electrolysis. This process, involving a temperature in excess of 800 degrees Celsius, is more efficient than conventional techniques because of heat recovery, for example".
Heating water past its boiling point requires energy. Electrolysis requires energy. Where does that energy come from?
The above question does not automatically make Audi's efforts a failure. One of the problems with green energy sources (solar, wind, geothermal, etc) is that they aren't terribly portable. Solar panels can produce enough energy to drive a car, but you'd need a panel array that is many times the surface area available on a typical passenger car; assuming you want to keep the same performance and amenities that we've come to expect. Instead, we store the energy in a short term storage mechanism and extract it as we drive.
The most popular solution to this problem so far has been to use a chemical battery. Lithium-ion batteries are the go-to energy store right now, but it's conceivable that they won't be forever.
The key metrics (some of them, anyway) for an energy store are:
* The energy density per volume and per mass.
* The rate of transfer in/out (how fast you can charge/discharge the battery).
* The efficiency in which you can transfer energy in and out of them.
* Self-discharge rage (how much energy the store loses when it is idle).
Diesel handily beats lithium-ion batteries by a very wide margin when it comes to energy density. Diesel is around 13,700 Wh/kg. A good Li-Ion battery comes in at around 150 Wh/kg. Li-Ion energy density is improving, but not at a rate that would surpass fossil fuels any time soon.
The problem with diesel is that you can't readily create diesel from other forms of energy efficiently. That's what Audi is working on here, and it's a pretty big deal.