The Key Role of Hydrogen for Reducing Carbon Dependancy in a Fossil Free System

In 2012, Danish Parliament passed a new renewable energy agreement with 7 out of the 8 parties consenting, representing 95 % of voters. The most significant implication of this agreement is that Danish wind power production shall increase from 25 % in 2012 to 50 % in 2020, measured as annual wind power production relative to electricity consumption. The Danish tradition is that a broad energy agreement is always followed, a tradition that has till now never been broken. Further, the present left wing Government has a long term energy strategy that in 2035, the heat and power sectors are fully free of fossil fuels and in 2050, both energy and transport sectors are 100 % renewable. Interestingly, the former right wing Government had the same vision of achieving a fully fossil free Denmark in 2050.

The reason for this pre-amble is to show that Denmark is committed to a renewable energy pathway, and that the country will soon be a showcase illustrating an unprecedented large scale and rapid renewable energy development.

Many studies on renewable energy system designs for Denmark have been carried out revealing the key challenges and constraints of a fossil free system. One key challenge is that also a fossil free system is dependent on a large supply of carbon; especially as feedstock for chemicals and materials and for energy dense fuels for parts of our mobility needs like aviation, sea transport and long distance transport on road. Further, renewable power production is characterized by being fluctuating, giving rise to a need of electricity storage and/or storable fuels for balancing the electricity supply and demand. The studies all point to the same overall boundary conditions, i.e. that renewable electricity is abundant, but biomass and carbon are constrained. Even with the highest possible wind power penetration, being up to 200 % of conventional electricity consumption, the system still needs substantial amounts of biomass in order to meet carbon requirements, and the various system designs quite unambiguously find that the biomass : wind power ratio is around 1:1 measured as PJ/year : PJ/year.

So even with the maximum degree of electrification in transport and heating and the minimum needs for hydrocarbon fuels, we still need just as much energy from biomass as we can get from wind, solar and wave power. This is the key challenge of the Danish renewable energy system, and it is believed to translate into the same for most other countries worldwide, also when shifting wind power to solar power in regions with higher solar radiation input than Denmark. In Denmark, we believe to have a sustainable biomass resource of 200 PJ/year available, equivalent to 40 GJ/year/capita and to around 25% of today’s primary energy consumption in Denmark. The system designs, however, all find a biomass demand much higher than that, i.e. 50 – 100 % higher.

These carbon and biomass constraints have, in the various Danish system designs, been overcome by introducing electrolysis and hydrogen in the system models. The role of electrolysis is to use excess wind power flexibly while producing hydrogen. Hydrogen is subsequently use for hydrogenation of carbon from biomass, e.g. through hydrogenation of the CO2 part of biogas or the CO part in syngas from thermal gasification – or even CO2 recycled from the subsequent energy conversion processes using the gaseous or liquid fuels from these hydrogenations. Through the introduction of electrolysis and hydrogenation in the system designs, the carbon constraint can effectively be overcome and, moreover, it seems to be the only way to overcome it in the fossil free system without unrealistic changes in transport infrastructure and technology. To fill the identified Danish carbon/biomass deficit by hydrogen as described above, compared to alternatively growing or importing energy crops, would save arable land with a food kernel production equivalent to the world average annual calorific intake of 10 million people, i.e. twice the Danish population. The production cost of synthetic hydrocarbons from this pathway was found to be 2-3 times higher than production from oil today. However, the socio-economic cost was found to be maximum 1 % the projected GDP in 2030.

Compared to global average, Denmark has a 3-5 times higher agricultural production, and agricultural biomass residues are, thus, high in Denmark. Other countries have better access to forestry biomass, but even so an availability of 40 GJ/ capita as world average is probably not realistic. Many studies striving to predict future biomass availability have been conducted, the average of which is found to be around 30 GJ/year/capita as a realistic global biomass potential. Wind power being replaced by solar power or nuclear power in other countries would imply no big difference in the overall finding. A large penetration of electrolysis and hydrogen into renewable energy systems is a way to effectively reduce the demand for biomass and a precondition for reaching a fossil free system.

These findings and their preconditions will be presented.