While global renewable energy generation has grown over recent years, global energy demand is growing much faster. This has made the ‘renewables capacity gap’ a stubborn problem to solve and has led to many countries still being widely reliant on fossil fuels, particularly at peak times. Much debate is centred around which form of energy generation is best suited to bridge the gapand get carbon emissions under control.
Hydrogen has been having a moment in the spotlight. Green hydrogen, which uses renewable energy in the electrolysis process to split hydrogen and oxygen, has been hailed as a ‘silver bullet’ solution. But is it disguising the untapped potential of an already established renewable energy source? Renewable natural gas (or ‘RNG’) is a type of biogas, with a biomethaneconcentration of 90% or higher, produced in anaerobic digestion tanks in which bacteria digest a feedstock of organic waste, with the gas produced as a by-product of this process. RNG is well established in markets such as Europe, and has so far been the unloved child of the renewable energy world. But this is now starting to change.
The unique challenges of solving for peak
Peak times are characterised by a sudden large increase in the total energy demand across the grid. The form of energy generation selected to deliver extra capacity must be unaffected by external factors such as weather (counting out wind or solar) and be dialled up or down at the touch of a button. Hydrogen is a popular sustainable suggestion because it relies on a human operated chemical reaction and industrial facility to release stored energy from other renewable sources. This is the way it would likely be used in the national grids of developed countries.
But in this aspect, RNG already has an advantage over hydrogen. Its primary input is organic waste – everything from food to cow manure – from businesses and households. By sending this waste to be used in biogas plants, more effective use can be made of the energy still stored in the material, which would otherwise be lost as it decomposes in landfill. There are huge reductions greenhouse gas emissions which can be achieved by finding a more productive use for our organic waste, especially if this reduces fossil fuel usage. In addition to being abundant and under-utilised, organic waste is also a source which can be sourced locally, making the production process less vulnerable to global price fluctuations and the impact of geopolitics on supply chains.
Focus on yield and speed for RNG
Traditional biogas production methods suffer from slow production times – usually 30-120 days after waste is added to an anaerobic tank to produce gas at 50% methane. The speed and yield challenges are not ones that can be solved by simply scaling up plants (as RNG production tends to require large scale anyways). It requires them to manipulate the behaviour of the bacteria in the tank to encourage them to work faster. Since chemical additives add a cost element and risk disrupting the delicate biome in the tank, another option now being explored is biocatalytic solutions.
Similar to a catalyst used in a car, a biocatalyst does not change the chemical composition in the tank, is not ‘used up’ after time, and could potentially be retrofitted onto existing biogas plants rather than requiring facilities to be rebuilt or expanded. If some of these new solutions can be implemented widely in the industry to achieve consistently faster production, then RNG becomesmuch more viable as a ‘turn on’ source of energy at peak times.
Making the most of current infrastructure
This brings us to the question of how we can store reserves of either energy source. The main consideration with introducing large volumes of hydrogen into our energy mix is the huge amount of new construction and retrofitting required to set up a hydrogen gas network, comparable to existing supply networks for natural gas.
Meanwhile, in markets such as Europe, there are already some 24,000 established biogas plants prime for retrofitted solutions. The renewable natural gas which they produce, while net carbon negative, has a similar chemical composition and mix to the natural gas currently being used in our national networks and domestic appliances for heating and cooking. Our existing gas infrastructure is therefore ready to be used immediately for efficient distribution and abundant long-term storage of a sustainable alternative. This would make a switchover much simpler and resources focused, instead on growing overall capacity.
A viable route forward
All these elements mean that we are playing a waiting game for hydrogen to become viable, one we simply don’t have time for. Meanwhile the world’s waste has untapped potential – and an existing ecosystem ready to be levelled up. Biogas is a highly viable source of renewable energy, which if harnessed appropriately has huge potential to bridge the capacity gap. It is now down to continued willingness to invest in innovations in this field to realise this potential.
By Benjamin Howard, co-founder of Vertus Energy
