Do biofuels have a role in delivering net zero?

By Patricia Thornley, Director, Energy and Bioproducts Research Institute, Aston University

Special to The Digest

“Net zero” has become the buzz-word of 2021. By 2050 we will have emitted so much greenhouse gases that we cannot afford to emit anymore if we are to avoid dangerous climate change. But there could be 9 billion people on the planet by then, all of whom will continue to eat, breathe etc. and so there will inevitably be some carbon dioxide and other emissions still generated. That means that it will no longer be enough to be low carbon we will then need to compensate for those emissions by also removing greenhouse gases from the atmosphere. That is what “net zero” essentially means. There may still be some greenhouse gas emissions, but they will be counteracted by other things that compensate.

There are many ways of balancing the net zero equation: we can think of some industry sectors still emitting while others go negative, some countries still emitting while others compensate for those residual emissions or some parts of the planet emitting (soils) while others absorb (plants and vegetation). We can choose how to cut and allocate the emissions, but the net result must be zero.

So, we need to progress low carbon energy technologies, but also greenhouse gas removal technologies: things like biomass to energy with carbon capture and storage, enhanced weathering, direct air-capture, peatland restoration etc.

What does this mean for the future of biofuels?

Well, by 2050 it simply will not be credible to emit carbon atoms to atmosphere unless they have recently been sequestered from atmosphere. So, where we need fuels (liquids and gases that can quickly release energy), they either need to have no carbon “tail-pipe” emissions or they need to have sequestered more carbon in their production than they emit.

The first option points to urgent exploration of non-carbonaceous fuels: hydrogen and ammonia being two front-runners at present.

Much has been said about hydrogen; less about ammonia to date. Hydrogen may be new to local authorities and the general public but is tried and tested in an industrial context and up to 20% has been incorporated into the gas grid to date. There are of course concerns around its incorporation into the existing system in terms of control, energy delivery rate, etc. but these are mostly engineering challenges that will be resolved by trial and ingenuity.

The key question really is where is the hydrogen coming from and what is its net carbon impact? The crude classification of blue, green and grey hydrogen is a pretty inadequate base on which to plan net zero targets as it doesn’t give full visibility of the actual carbon impact of the delivered fuel. There is a need to look at all the options (electrolysis, anaerobic digestion, photocatalysis, gasification, methane reforming etc.) and actually evaluate their carbon (and wider sustainability) impact, including economic and social effects.

An important point to note here is that geography and scale both matter. This is not an abstract calculation where we can simply classify some fuels as good and others as bad. The impact of fuels can depend on where they are produced and deployed and the choice of fuel can be affected by location. Hydrogen may be a very appropriate energy vector where it is acting as a storage buffer at a coastal location for variable offshore renewables via electrolysis; but inland agricultural residues may present a more accessible and sustainable resource and whether that is transformed to hydrogen, methane or ammonia will depend on local conditions.

As demonstration and deployment projects are progressing, this is becoming increasingly urgent. If there is one thing we have learnt from the implementation of biofuels it is that we CANNOT wait until the fuels are being deployed to develop robust frameworks that demonstrate carbon reductions and wider sustainability of hydrogen, ammonia and other non-carbon fuels. The two issues must go hand in hand. When scientists are developing new low carbon fuels, there is a need to evaluate the life-cycle environmental performance alongside the technical performance. Only then can we make informed decisions about which fuels to prioritize in policy frameworks via legislative incentives.

So as we look to hydrogen, ammonia or other new fuels to provide our future energy requirements, we must think in advance about what we are trying to achieve and the consequences of implementing those fuels. Carbon reduction and sustainability assessment must be done in tandem with fuel development, not as an afterthought.

While it is right to focus on the long term 2050 objectives, we need to get there via a pathway that minimizes our emissions during the transition period, while remembering that the earlier we decarbonize the more valuable that carbon reduction is. Delivering modest reductions in fuel carbon intensity in the near term can have just as great (if not greater) climate benefits as delivering deep reductions in the long term.

There are many biofuels available today that can make a huge contribution to our decarbonisation targets if we facilitate their deployment. Of course, we should only support those that make real reductions, but experience with different policy mechanisms has shown the danger of having “cliff-edge” qualifiers, where systems have to achieve benchmark figures to qualify. They just don’t incentivize getting the maximum reduction from the resource being used.

Rather than abandon low carbon intensity hydrocarbon fuels (as we move away from fossil fuel vehicles) I would like to see us value the carbon reductions delivered from the biofuels and use them as a mechanism to develop sustainable production methods and verification frameworks in preparation for the real challenge of delivering BECCS at scale in a future net zero world.