Biogas

The carbon base uses the following biogas emission factor: 0.0444 kgCO2e/kWhPCI.

Here is more documentation on the integration of this figure and its limitations.

We'll need to clarify what in NGC prevents us from using the lowest factor in this consumption calculation model, which is a global calculation also covering agriculture via food.

Another crucial point is that gas can be stored, unlike "green" electricity, which is why their emission factor has not yet been included in NGC.

In addition, leaks from biomethane installations, which are by nature much smaller and more numerous than fossil gas and therefore difficult to control, could be underestimated. Is this study (202200267-6) taken into account in the above emissions factor (2020)?

About land use

The carbon base link to the GRDF study is no longer online. Here it is in PDF. It shows :

The red part is detailed here:

It shows that the proportion of dedicated crops is very low, which is very reassuring.

Having said that, and I'm not sure how to define it precisely, I still have a strong impression that a large proportion of these components could be valorized differently: in concrete terms, we burn and thus valorize at a very high price (gas at wholesale price costs in September 2022 almost 2 times the biogas production price (90€/MWh)) chicken leftovers from the canteen that we could just not have produced (blue); the domestic lawn that the neighbor mows every week (light blue); manure from crops that could have been dedicated to human vegetation (mauve); and so on.

In short, if some of the energy present in the materials used by biomethane was just lost, another part simply undergoes a change of allocation, from something useful to the agricultural world to the combustion of gas to heat homes in particular. Not to mention the windfall effect for activities that emit, substitutable by others that emit less. The study seems to be very complete, so it's worth looking into. Maybe it answers all the questions I haven't seen (it's complex).

There's also an article in Reporterre that worries about bacterial contamination due to digestate spreading, as well as methane and nitrous oxide N2O leaks, which are underestimated (because they are present and therefore evaluated in the study cited by the carbon base). Please note, however, that Reporterre is not a research organization, but an opinion medium.

A very recent investigation into methanizers in Brittany points in the same direction, cataloguing the incidents that have taken place in the region: https://basta.media/des-methaniseurs-menacent-l-environnement-la-carte-inedite-des-accidents-en-Bretagne-Splann.

In my opinion, this does not call into question the inclusion of this factor in UCS. Fossil gas production is also affected by this kind of problem, by way of example.

Another question that may be answered here is: can the sector achieve x10 production without introducing negative externalities that are currently under control? It would be interesting to answer this question for the UCS user, to show him that his choice can be passed on to society as a whole. Carbone4 seems to answer in the negative: replacing fossil gas with biomethane should not lead to a failure to reduce gas consumption in general, and even less to a rebound effect!

A warning is therefore integrated into the simulation to evoke this impossible transition to scale:

Biomethane reduces enormously the CO₂ emissions of the gas you consume, but current production is unable to scale up: the overall reduction of all gas consumption remains essential, whether you consume biogas or fossil gas.