Your choices:
1 Biomass (digestible sludge); 2 Fuel: gaseous; 3 Transport
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| 1 Biomass (digestible sludge) | District cooling | Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | 2 Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | 3 Transport |
| Residual oils/fats etc | Local heating (ind. house) |
For cars, there are mainly two gaseous fuels competing, namely methane (LNG) and LPG. These two may not be confused. LPG mainly consists of propane and/or butane and though it is distributed and may be filled in liquid form it readily becomes gaseous already at ambient temperatures. Methane, in contrast, is handled as a compressed gas. Its heating value is different and so are its combustion properties. Hence the two are not freely interchangeable. Thus, filling stations for LPG, which is basically a fossil fuel, cannot readily be converted into methane filling stations.
Like for injection into the fossil gas pipeline system, also the use of biogas for vehicles require a bit of "topping", i.e. the addition of heavier hydrocarbons like propane or butane to make the gas quality freely interchangeable with the LNG commonly used. However, there is an upper limit since the addition of these components tends to lower the octane number and therefore may induce engine knock.
Therefore, not only the Wobbe index but also the octane number becomes important in the case of vehicle gas production. Those of you not familiar with the terminology are referred to the Wikipedia, articles on Wobbe index and on octane number.
This is one major option at municipal-scale biogas plants such as digesters in connection to wastewater treatment plants or dump sites designated for organic waste fractions.