IPCC: how to decarbonize the energy sector?

Here we take a closer look at Chapter 6 of the IPCC report (WGIII), which deals with energy systems. [complete pdf]

Electricity is at the heart of the prospects for limiting climate change. Indeed, it will be necessary to electrify many needs currently met by fossil fuels. Moreover, electricity is still one of the main sources of greenhouse gases. It will therefore have to be decarbonized while being deployed.

In effective cost paths, the energy sector reaches “net zero CO2” before the rest of the economy. (TS-46) For scenarios C1 to C4, net energy emissions fall by 38-52n 2030 and 87% to 97n 2050. Electricity rises from 20 e the energy used in 2019 to 48-58 e the final energy in 2050.

Between 2015 and 2020, photovoltaic and wind power electricity prices dropped by 56t 45t and battery prices by 64% respectively. The reduction is even more radical when compared to the 2000s: the price of photovoltaics has been divided by around 10 and that of onshore wind power by 2 or 3. The price of batteries has been cut by a factor of 10 since 2010. Note that the price of offshore wind power is similar to that of the 2000s. (TS, p.67;

To decarbonize uses that cannot be addressed by the direct use of electricity, energy carriers will be needed, such ashydrogen, ammonia or low-carbon hydrocarbons (biogenic or synthetic). If the principle is that unprocessed electricity is the preferred option, hydrogen is particularly interesting for storing renewable energy. The efficiency of the “electricity-to-hydrogen-to-electricity” cycle could reach 50n 2030 [rq: it is ajd of 25%]. (TS-55)

Multiple energy supply options are available to reduce emissions over the next decade. (high confidence) Nuclear power and hydropower are established technologies. Solar photovoltaics and wind power are now cheaper than fossil fuel electricity in many places. Bioenergy accounts for around a tenth of the world’s primary energy. Carbon capture is widely used in the oil and gas industry, with early applications in power generation and biofuels.

It will not be possible to widely deploy all these and other options without efforts to address the geophysical, environmental-ecological, economic, technological, socio-cultural and institutional factors that may facilitate or hinder their implementation.

(high confidence)

Translated from English, TS-56

Energy consumption and use today

Electricity generation generated 20 Gt CO2eq in 2019, with a slight increase since 2015 (2.7%). Fugitive emissions from fossil fuels (mainly methane leaks [during coal mining and natural gas exploitation-transport]) accounted for 18 e of these emissions in 2019. 2.6 Gt CO2eq are linked to oil production

Nuclear power

“Nuclear power can deliver low-carbon energy at scale”. (p.639) Nuclear power increased by 10.3 between 2015 and 2019, from 2570 TWh to 2790 TWh.

Uranium resources are sufficient for more than 130 years of current consumption. Avenues to extend this by using thorium or spent fuel were shelved due to the low price and availability of fuel. (p.639)

There are many ways to develop nuclear power:

  • Large-scale reactors, such as the 3rd generation. Projects in Europe and North America have incurred high extra costs and taken 13 to 15 years to complete. However, recent projects in East Asia have been implemented in less than 6 years. Once the first plants have learned their lesson, the price of new nuclear power should be between $42 and $102/MWh.
  • Maintaining the current fleet of power plants over the long term. This is the cheapest option, with a LCOE price of between $30 and $36/MWh.
  • Small modular reactors (SMR). Their small size would reduce total investment costs, and their factory production would improve the construction process. The manufacturers estimate prices for the first series at $131-190/MWh, which could be reduced by 19-32% later on.

“Despite low probabilities, the potential for major nuclear accidents exists and the impacts of radiation exposure could be significant and long-lasting (Steinhauser et al. 2014). However, new reactor designs with passive and improved safety systems significantly reduce the risk of such accidents (high confidence). […]The (normal) activity of a nuclear reactor results in small volumes of radioactive waste, which requires strictly controlled and regulated storage. Worldwide, around 421 kt of spent nuclear fuel has been produced since 1971 (IEA 2014). Of this volume, 2-3% is high-level radioactive waste, which presents challenges in terms of radiotoxicity and decay longevity, and ultimately requires permanent storage.” (p.640)

Nevertheless, nuclear energy has a good record on land use and ecological impact. It consumes relatively few major materials. Nuclear power plants can put a strain on water resources. However, the use of closed cooling circuits can significantly moderate water withdrawals.

The scale of the initial investment required, which can exceed $10 billion, means that 90 of the power plants currently under construction are owned or controlled by the state.


Bioenergy “has the potential to be a large-scale, high-value mitigation medium to support many parts of energy systems.” Today, biomass is mainly used for heat production, cooking, electricity or biofuels (first generation and biodiesel from oils and fats). The overall efficiency of biomass power plants is around 22%, and can be as high as 28%, due in particular to preparation (drying, conversion into pellets, etc.) (p.643)

Bioenergy accounted for 2.4 e of electricity production in 2019. Biofuel production rose from 3.2 EJ per year in 2015 to 4 EJ in 2019.

Scaling it up would require several advanced technologies:

  • Fischer-Tropsch process
  • Hydrothermal liquefaction (HTL)
  • Pyrolysis.

While promising, these processes are not yet sufficiently developed to be viable. Similarly, advanced biofuel processes are at the pilot or demonstration stage. What’s more, we need to be able to match these biofuels to existing standards. As for methanization, it tends to be less efficient than the thermochemical approach, and produces large quantities of CO2. (p.644)

Not all inputs are compatible for every process. For example, trees are not compatible with methanization, but work well with pyrolysis or combustion. Each process produces different things. For example, pyrolysis can produce hydrogen, electricity, liquid fuels and biochar.

Scaling up bioenergy production would require the creation of dedicated channels. The potential of bioenergy will essentially depend on competition with other elements: food production, forestry, water use, impact on ecosystems and land use change.

Biomass-based electricity is more expensive ($66 – 112/MWh without CCS, $74 – 160/MWh with) than fossil-based electricity, even with CCS. By contrast, hydrogen production from biomass gasification ($1.59-2.37/kg H2) would be comparable to that from methane steam reforming with CCS. What’s more, the additional cost of adding CCS [which gives a negative carbon balance, known as BECCS] is only 5% ($1.63 – $2.41/kg H2), as the CO2 stream produced is highly concentrated. The price would be much lower than electrolysis-based production.

Bioenergy’s life-cycle emissions are subject to uncertainty and could be incompatible with net-zero trajectories. Its carbon neutrality is open to debate.

Fossil fuels

Fossil fuels could play a role in the fight against climate change if strategically deployed with CCS (high confidence


IPCC, AR6, WGIII, p.646

The emissions that can be anticipated with current infrastructures are 660GtCO2eq or, including infrastructures under design, 850, which is incompatible with the C1-C4 trajectories (TS-26). To make it compatible without carbon capture (CCUS), fossil power plants would have to be retired between 17 and 23 years before the end of their lifespan (TS-53)

Coal-fired generation has declined in the USA and EU and halted its growth in China, but it continues to expand in developing countries in Asia. Between 2015 and 2019, it increased by 146GW, or 7.6%. Trade in liquefied natural gas (LNG) has expanded significantly, with exports up 160%. The price of a barrel of crude has fallen from $100 to $55 over the 5 years preceding the report (2017-2022?).

Fossil fuel reserves are tending to increase as a result of improved exploration techniques and dedicated efforts. It is estimated that 500 ZJ remain in the world, and between 15 and 20 ZJ each for gas and oil. 80 u coal, 50 u gas and 20 u oil would probably have to remain in the ground for a warming limited to 2°C. This would represent a shortfall of between 1 and 4 trillion dollars.

Fossil fuel subsidies have been estimated at between 0.5 and 5 trillion dollars a year. (p.648)

Stealth methane emissions

The exploitation of fossil fuels (coal, gas and oil) releases methane into the atmosphere. These emissions accounted for 18% of energy sector emissions in 2019. This occurs mainly (80%) at the time of extraction, but can also happen at other stages of the energy journey.

When coal is mined, 50 to 75 u of the methane released can be recovered by dedicated systems. In transport, leaks can be limited by detecting and repairing them. In total, 50 to 80 e of these emissions can be avoided with available technologies at a cost of less than $50/tCO2. (p.646)

Carbon capture

Geological storage is estimated at around 10,000 GtCO2, of which saline aquifers account for around 80 years. The main problem is the geographical distribution of reservoirs. The Middle East is estimated to have 50 th the capacity of Enhanced Oil Recovery. (p.641)

One of the challenges of carbon utilization (CCU) depends on technological constraints such as CO2 pressure and purity. For example, urea production requires gas at 122 bar and 99.9 e purity.

Current post-combustion capture technologies based on absorption are mature enough for large-scale development. Interesting progress has been made with the development of new solvents such as monoethanolamine (MEA).

New approaches based on membranes and chemical loops that reduce energy requirements are being developed at various stages of maturity, from the laboratory to prototyping. One interesting approach is the Allam cycle, using CO2 as a working fluid and operating on the basis of oxy-combustion capture.

The problem of price is central, with capture often costing over $50/tCO2. The price of a gas- or coal-fired power plant doubles with this system. What’s more, the energy requirement implies the use of 13 to 44 th more fuel.

EOR makes it possible to reduce the price of storage, and even to generate income. Nevertheless, EOR represents