Hydrogen out, compressed biogas in

The European Union's Joint Research Centre recently revised its comprehensive well-to-wheel (WTW) study for different automotive fuels after criticism (channeled through public consultation) had arisen over the previous study which didn't take into account biogas as a viable transport fuel. The revised version now in fact shows that compressed biogas (CBG) is the most climate friendly of more than 70 different fuels (and fuel paths used in different propulsion technologies). The fuels and pathways studied also show why hydrogen is out of business for the time being.

Even biohydrogen is not viable
The report shows that hydrogen can only be produced efficiently and in a climate-friendly manner from biomass and wind, but quickly dismisses the wind option because using dedicated wind farms is too expensive compared to biomass, whereas relying on on-site production using excess wind electricity, poses problems with reliability and availability of supply.

Hydrogen production paths based on fossil fuels (coal, natural gas, petroleum) are not more efficient than using biomass as a primary energy source, and of course have a huge CO2 burden. Moreover, using these fossil fuels for other fuel paths (Fischer-Tropsch synthetic diesel, methanol or CNG) is more efficient than using it for either compressed or liquid hydrogen. Nuclear as a primary energy source to produce hydrogen from the electrolysis of water is very clean, but extremely expensive and the most inefficient of all pathways (electrolysis requires large amounts of energy).

This leaves biohydrogen. Of all pathways, compressed hydrogen produced from biomass (in this case wood), to be used in fuel cells, is both the most efficient pathway and lowest on GHG-emissions (graph, click to enlarge). The problem is that the primary biomass can be better used for other fuel pathways, resulting in fuels with an even higher WTW efficiency and lower CO2-emissions (biomass-to-liquids or simply biogas).

When looking at the costs of the fuels over their entire well-to-tank (WTT) and tank-to-wheel (TTW) parcours, biohydrogen does not stand a chance of being introduced anywhere soon. As is well known, on the WTT-side, an entirely new and costly infrastructure to store and distribute hydrogen has to be established, whereas on the TTW-side, fuel cells are still very expensive. Furthermore, using biohydrogen in internal combustion engines is both less efficient and less climate friendly than using the biomass for other fuel paths resulting in fuels that can be used just as well in ICE's. If the ICE is going to be the propulsion technology that must overcome the high TTW costs resulting from expensive fuel cells, the detour via hydrogen is futile. This is best illustrated by the fact that biogas is one of the best primary energy sources for biohydrogen. But biogas can simply be used in an existing CNG-vehicle. Making the detour via hydrogen does not contribute to lower GHG-emissions, is less efficient, and far more expensive.

Compressed biogas, the most environment friendly fuel
The revised study recognizes the CO2 benefits of compressed biogas (CBG), or biomethane. Of all 70 possible fuel paths, the WTW-efficiency of compressed biogas used in a dedicated propulsion technology, is also (far) higher than classic biofuels (ethanol, biodiesel), roughly equal to more advanced fuels (synthetic diesel from biomass and biomethanol used in next-generation ICE's, biohydrogen in fuel cells), and almost as efficient as non-renewable advanced fuels (syndiesel from coal-to-liquids and gas-to-liquids, and methanol used in advanced ICE's).



Moreover, as an earlier WTW-study published by General Motors (which already included biogas) indicates, of all biofuels feedstocks and production pathways, biogas yields more per hectare than other energy crops. At the end of the WTT path, it results in a higher amount of energy ready to be used by the TTW path (this is especially so compared to biofuels based on low yielding crops cultivated in the North, such as corn) (see illustration).

But the main advantage is the climate friendliness of CBG. In fact, in many cases, CBG is even CO2 negative - of the 70 fuel pathways only CBG can make this claim. This is due to the fact that biomass waste-streams (from agriculture, communities and municipalities) that would otherwise be incinerated and release their CO2 without the energy being captured for useful purposes, are now used as a feedstock for automotive fuels:
ethanol :: biodiesel :: bioenergy :: biofuels :: energy :: sustainability :: hydrogen :: biogas :: well-to-wheels

Biogas can also be produced economically from dedicated energy crops (such as maize or grasses), which results in a fuel that is less costly than either first generation ethanol or biodiesel.

Compressed biogas can be used in existing CNG-vehicles (often these are bi-fuel vehicles that run on either CNG/biogas or gasoline), and it is to be expected that efficiency increases in this propulsion technology will be achieved over the coming years. The ideal (and feasible) propulsion technology would be a CBG-hybrid. According to the report, such a hybrid would be more efficient than an advanced diesel hybrid.

Many countries (especially in Scandinavia and Central Europe) have meanwhile recognized the potential of biogas as an automotive fuel and are investing in it heavily.

A chance for the developing world
But the biggest chance for the mass adoption of CBG lies in the developing world, for several reasons:

1. biogas can be produced from dedicated energy crops in a far more competitive way because biogas crop yields in the tropics and subtropics are higher and the costs of inputs are far lower (land, labor).

2. developing countries are not burdened by existing fossil fuel infrastructures. They can decide to build an infrastructure from scratch and leapfrog into a fuel efficient, energy secure, and climate friendly future. Pakistan offers the best example, with its decision to build a CNG-infrastructure, which resulted in 1 million CNG-vehicles on the road in less than 2 years time - the world's biggest CNG-fleet. Establishing a CBG-infrastructure would be similar to the way Pakistan created its compressed natural gas infrastructure.

3. as carbon markets globalise, developing countries stand to benefit financially from radically choosing for a green, CBG infrastructure today. The CO2 credits they would obtain can be traded on a global market.

In the coming days, we will be looking at other fuels mentioned in the WTW-analyses made by the Joint Research Centre. Even though such analyses are fairly complex, other WTW studies offer comparative data, from which we can derive a global picture of the efficiency and climate friendly nature of future fuels.


More information:

For the biogas energy yields per hectare, see: Reinhold Wurster, GM Well-to-Wheel-Studie - Ergebnisse und Schlüsse sowie Vergleich mit anderen Arbeiten und Ausblick auf Kraftstoffpotentiale und -kosten, L-B- Systemtechnik GmbH Ottobrunn, 06 November 2003.

The European study:
EUCAR, CONCAWE and JRC have performed a joint evaluation of the Well-to-Wheels energy use and greenhouse gas (GHG) emissions for a wide range of potential future fuels and powertrains options. The first version was published in December 2003. The documents below present the results of the second version (May 2006). The objectives of the review remained the same:

* Establish, in a transparent and objective manner, a consensual well-to-wheels energy use and Greenhouse gas (GHG) emissions assessment of a wide range of automotive fuels and powertrains relevant to Europe in 2010 and beyond.

* Consider the viability of each fuel pathway and estimate the associated macro-economic costs.

* Have the outcome accepted as a reference by all relevant stakeholders.

This new version is the result of wide consultation with relevant third parties, leaving the opportunity for each actor, stakeholder, or member of the technical/scientific community to take part in the on-going discussions, and to contribute with up-dated or corrected inputs. The process is still open, and a dedicated mailbox ([email protected]) has been created: further input data and comments are warmly welcome.

The 2006 version includes a number of new and updated pathways as well as revised cost calculations and availability estimates.

There are 10 documents available for download, offering various levels of detail:

* The Well-to-Wheels (WTW) report [*pdf] provides and integrated analysis of the complete pathways in terms of energy, GHG emissions, costs and potential availability of alternative fuels. Its two appendices cover in more detail:

o Energy and greenhouse gas balances for all pathways;

o Cost data and calculations.


* The Well-to-Tank (WTT) report [*pdf] details the WTT portion of the pathways, including cost and availability estimates. There are three WTT appendices covering:

o Individual processes and input data;

o Detailed energy and GHG balances for individual WTT pathways;

o Energy requirement and GHG emissions for gasoline and diesel fuel production.


* The Tank-to-Wheels (TTW) report [*pdf] decribes the vehicle configurations and performance.The appendix gives details on vehicles retail price estimation.

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