Coal versus gas: explaining the CO2 intensity?

Coal provided 25% of the world’s primary energy in the past three years, but 40% of all global CO2 emissions. Gas also provided 25% of the world’s primary energy but just 15% of the CO2 (data below). In other words, gas’s CO2 intensity is 50-60% less than coal’s. The purpose of today’s short note is to explain the different carbon intensities from first principles.

Explanation #1: half the energy in gas is from hydrogen

Burning coal releases energy as carbon is converted into CO2. In other words, substantively all of the energy from coal combustion is associated with CO2 emissions.

Burning gas releases energy as methane (CH4) is converted into CO2 and H2O. In other words, just over half of the energy from gas combustion is associated with innocuous water vapor, and just less than half is associated with CO2 emissions.

This is simple chemistry. For many decision-makers, this chemistry is sufficient to explain why switching all of the world’s future potential coal energy to gas energy can directly underpin one-fifth of the decarbonization on realistic roadmaps to net zero (note below). For others, who want to get into the nerdy details of bond enthalpies, we have written the note below.

Explanation #2: bond enthalpies?

If you wish to delve deeper into the numbers behind gas and coal’s CO2 intensities, then our discussion below will help you understand the thermodynamic calculations. As an ongoing reference, the numbers are also spelled out in our bond enthalpy data-file.

Bond enthalpies. Atoms are bonded together into molecules. ‘Bond Enthalpy’ denotes the total thermodynamic energy that is contained in each of these bonds, as determined by fundamental electromagnetic forces that define the universe (note here). In other words, bond enthalpy is the minimum amount of energy that must be supplied in order to dissociate the atoms on either side of the bond; and the maximum amount of energy that could be harnessed when these atoms bond together.

Bond enthalpies are often quoted in kJ/mol. As a reminder, 1 Joule is the energy transferred when a force of 1 Netwon acts over a distance of 1 meter; or when 1 Watt of power is exerted for 1 second; or when a current of 1 Amp flows through a resistance of 1 ohm. And 1 mol is a standard for counting the numbers of atoms or atomic reactions, described 6.022 × 10²³ units. This precise number, in turn, was chosen so that 1 mol of protons would have a mass of 1g, and all larger molecules would have an atomic mass that effectively matches their atomic number of protons and neutrons.

Thus the thermodynamics of gas can be computed from bond enthalpies in the image below. Breaking the bonds in the methane molecule requires 1,652 kJ/mol of input energy. Breaking the bonds in 2 x O2 molecules requires 996kJ/mol. Total bond-breaking energy is 2,648kJ/mol. On the other side of the equation, forming the bonds in 1 CO2 molecule releases 1,598kJ/mol. And forming the bonds in 2 x H2O molecules releases 1,903kJ/mol. Total bond-making energy is 3,501kJ/mol (of which 54% is from forming water molecules). Subtract 2,648 from 3,501, and the result is 853kJ/mol of total energy being released. 1 kJ = 0.2778 Wh. So with some unit juggling, we arrive at 15kWh/kg of energy generation, or 304kWh/mcf of gas (at 48.7mcf of gas per ton; or 48.7bcf per MTpa for those who prefer LNG units).

The CO2 emissions will include 1 mol of CO2 per mol of methane. That mol of CO2 weighs 44 grams. Hence if you divide 44 grams by 853kJ, the result is 0.05 g of CO2 per kJ. Divide by 0.2778kWh/kg and the result is 0.19kg of CO2 per kWh. Multiply by 304kWh/mcf and the result is 56kg of CO2/mcf.

Likewise the thermodynamics of coal can be computed in the same way. Forming each mol CO2 from C and O releases releasing 1,598kJ/mol. That side of the equation of the easy. Next, if the coal was perfect, pure carbon then the energy that would need to be supplied for bond breaking would be 50% x 4 x C-C bonds at 346kJ/mol (692kJ/mol total), plus 1 x O=O bond (498kJ/mol), for a total bond-breaking energy of 1,190kJ/mol. But in practice, we assume that coal is usually only 80% carbon, while remaining impurities include water (which must be evaporated off), sulphur, nitrogen and other ashy impurities. It will vary grade-by-grade. But on average we think 300kJ/mol is a sensible assumption for the energy release. This yields some important conclusions…

(a) 300kJ of energy is released when 1 mol of coal combustion occurs. This is 65% less than when 1 mol of gas is burned. The main reason, as stated above, is that the coal combustion reaction does not generate any energy from producing water vapor.

(b) 20kJ/gram or 6kWh/kg of energy is released per unit mass of coal consumption. This is c60% less than when an equivalent mass of methane is burned.

(c) Minimal extra mass, as we assume methane weighs 15.6g/mol, versus coal at 15g/mol of combustible carbon (pure carbon is 12g/mol, but we assumed high-grade coal has only 80% carbon). To re-iterate, this means that 1 kg of natural gas is generating 2.5x more energy than 1kg of coal. Again, the reason comes down to hydrogen atoms in methane, which generate 54% of the energy release when they are oxidized to H2O, but in a very dense package of mass. At 1g/mol, hydrogen atoms are much lighter than carbon atoms at 12g/mol and oxygen at 16g/mol. (The hydrogen industry is currently looking for the perfect hydrogen carrier — is it ammonia? is it toluene? — in our view, a near-perfect one already exists, it is called natural gas, and it comes straight out of the ground).

(d) 1 mol of CO2 is released when 1 mol of coal is combusted. This is the same as the amount of CO2 released then 1 mol of gas is combusted. But to re-iterate gas combustion generates around 2.5x more energy.

(e) CO2 intensity is 0.5kg/kWh for coal combustion. Again this is 2.5x higher than gas combustion, and we have derived the result that gas provides the same amount of energy as coal despite emitting 60% less CO2. There is nothing here except maths and science.

Explanation #3: advanced thermodynamic considerations?

We have glossed over some important thermodynamic concepts in our explanation above. For completeness, we address them here. Those who are bored of abstruse academic details can probably skip ahead to the next section.

Strictly, the useful energy that can be obtained from combusting a fuel is not a pure function of bond enthalpies. You must also deduct a small amount for the change in entropy (Gibbs Free Energy = Enthalpy – T-Delta-S). We have not considered entropy changes in our numbers above. Neither coal nor gas combustion increase entropy by increasing the number of molecules in circulation. But both coal and gas combust with a flame temperature around 1,950C, which is going to increase the entropy of their surrounding thermodynamic systems and prevent their full bond enthalpies from being harnessed.

Another issue is higher versus lower heating values. Specifically, our schematic above showed the combustion of methane releasing 54kJ/g of energy, via the formation of CO2 and H2O. However, 5-10% of this ‘gross calorific value’ energy that is released will be lost in the water vapor. Water is a liquid at ambient temperatures and pressures. Vaporizing that water into an exhaust gas will absorb some of the energy from the combustion reaction. The amount depends on the atmospheric conditions. This is why textbooks quote the ‘net calorific value’ of methane closer at 50kJ/g at standard conditions of 0C and 1-bar. Vaporizing water is not an issue for coal combustion as there is effectively no water produced in that reaction. This narrows the ‘energy gap’ between gas and coal in practice.

Another issue is that our bond enthalpies for coal above were not quite right. We used the average bond enthalpies for Carbon-Carbon single bonds. But the carbon in coal may contain ring structures, aromatic compounds, unsaturated bonds, and particles that are not chemically bound together at all. All of this will most likely lower the bond enthalpies within coal. So our numbers for coal combustion enthalpy are imprecise, and probably a little bit too conservative.

Another issue is that ‘coal’ is a broad term, covering a range of different fuels, with different carbon contents and different impurities. These will vary. One useful online resource, suggests that energy content can range from 32.6kJ/g for the highest-grade pure anthracite coals, through to 30kJ/g for bituminous, 24kJ/g for sub-bituminous and 14kJ/k for lignite. In 2020, the average ton of coal produced in the US had a grade of 19.8 mmbtu/ton, equivalent to 5,800kWh/tonne, or 23kJ/g. This is probably a bigger issue for energy density per kg than it is for CO2 emissions per kWh.

Finally, coal may be moderately less likely to combust completely, producing small portions of soot and carbon monoxide, especially when burned in small-scale furnaces. This will detract from both the energy content and has a debatable impact on CO2 credentials.

(1) What about emissions across the supply chain?

One potential issue with the numbers we have presented above is that we also need to consider the CO2-equivalent emissions from the supply chains of producing gas and coal, respectively. If, for example, the emissions of producing natural gas were materially higher than the emissions of producing coal, then we would need to factor this in.

However, our analysis finds that often the total full-cycle emissions footprint of producing and distribution coal (usually 50kg/boe or higher) will be similar or higher than the emissions footprint of producing and distributing gas (10-60kg/boe). The free note below gives a full overview of the data we have reviewed here.

(2) What about efficiency of combustion?

A second potential issue with our analysis could be if it were easier to extract the energy from coal than from gas. For example, capturing 80% of the energy from a 0.52kgCO2/kWh fuel would result in lower emissions than capturing 20% of the energy from a 0.2kgCO2/kWh fuel.

Yet again, the data we have reviewed points to higher combustion efficiencies on gas. Our models for a coal-fired power plant assume c40% efficiencies, while our models of combined cycle gas plants average 57% efficiencies, and we are particularly excited about emerging gas-fired CHP systems that can reach 80-90% total thermal efficiencies (note below).

(3) What about ease of carbon capture and offset?

A third factor that is worth considering is the ease of capturing the carbon from combusting coal and gas. We think there is nothing wrong with continued fossil energy use in a fully decarbonized global energy system, as long as the CO2 emissions from that fossil energy is fully captured or offset.

Across our work, we find there are mixed opportunities and challenges for integrating CCS with coal and gas, but it is 2.5x easier to integrate gas with nature-based carbon removals, because there is 60% less CO2 that needs to be offset in the first place.

CCS momentum has also stepped up impressively in the past year (notes below). Coal combustion might seem to have a natural advantage, as its CO2 exhaust stream tends to be c10% concentrated, versus 4% for gas combustion. However, we also find gas’s exhaust CO2 can be concentrated towards 10% by combustion technologies such as exhaust gas re-circulation, gas benefits from fewer impurities that can poison amine cocktails, emerging technologies such as blue hydrogen can decarbonize gas at source, and there are also practical ways of blending gas back-ups with renewables in fully decarbonized power grids (notes below).

(4) What about the costs?

The dimension that has most kept coal burning in the world’s energy mix is its absurdly lost cost. A new mine requires $60/ton for a 10% IRR, equivalent to producing thermal energy for 1c/kWh (model below). Natural gas can actually beat this cost, as the best gas fields are economical below $1/mcf (0.3c/kWh), and we estimate that $2/mcf pricing can support passable IRRs in the shale industry (model also below). But on top of this, global gas value chains can bring delivered cost to $6-8/mcf (2-3c/kWh). The biggest challenge, we find, is that starving gas value chains of capital may have re-inflated marginal costs to $12-16/mcf (4-5c/kWh) (third note below).

Conclusion: coal to gas switching cuts CO2 by 50-60%

The conclusion across our analysis above is that each TWH of energy that is generated from gas rather than coal will result in 50-60% less CO2, which will lower the burden that is placed on other decarbonisation technologies in our roadmap to net zero. Stated another way, each MTpa of LNG that is developed will likely go on to obviate 5MTpa of CO2 emissions.

So far in the energy transition, however, our depressed observation is that ideological fantasies may have delayed the implementation of real, low-cost and practical CO2 reductions, such as coal-to-gas switching. We think this may change in 2022, as energy shortages deepen (note below), and the world needs more pragmatic options, to accelerate its path towards net zero. Our lowest-cost roadmap to net zero by 2050 requires global gas output to rise by 2.5x.

Border taxes: a carbon curtain has descended?

As Europe advances its decarbonization agenda, a ‘border adjustment mechanism’ has now been proposed to mitigate carbon leakage. Its initial formulation is modest. But it will snowball. And ultimately divide the global economy in two. Hence this 15-page report lays out our top five predictions for CO2 border taxes to reshape energy markets and the world.

In 1946, Winston Churchill made his famous ‘Iron Curtain’ speech, prophesizing decades of tensions between different economic systems in the West and elsewhere. The concept of a carbon curtain is similar, and is laid out on pages 2-4 of our report.

These wheels are now firmly in motion, as Europe has proposed a carbon border adjustment mechanism, in order to stem carbon leakage, as it tightens its environmental policies. For those who prefer not to read the Commission’s entire 291-page leviathan, we have summarized the key features on pages 5-6.

Expansion is inevitable. Page 7 argues for domino effects, where CBAM will be emulated by other Western economies; and then broadened, first into the manufacturing sector, then universally.

There will be five investable consequences of these escalating border taxes, which we spell out on pages 8-15. They could be extremely constructive for the gas/LNG industry, pre-existing renewables assets, and some lower carbon economies. But we also see major losers in the coal industry, higher-carbon countries and victims of inflation.

Britain’s industrial revolution: what happened to energy demand?

Britain’s remarkable industrialization in the 18th and 19th centuries was part of the world’s first great energy transition. In this short note, we have aggregated data, estimated the end uses of different energy sources in the Industrial Revolution, and drawn five key conclusions for the current Energy Transition.

In this short note, we have sourced and interpolated long run data into energy supplies in England and Wales, by decade, from 1560-1860. The graph is a hockey stick, with Britain’s total energy supplies ramping up 30x from 18TWH to 515TWH per year. Part of this can be attributed to England’s population rising 6x, from around 3M people to 18M people over the same timeframe. The remainder of the chart is dominated by a vast increase in coal from the 1750s onwards.

A more comparable way to present the data is shown below (and tabulated here). We have divided through by population to present the data on a per-capita basis. But we have also adjusted each decade’s data by estimated efficiency factors, to yield a measure of the total useful energy consumed per person. For example, coal supplies rose 40x from 1660 to 1860, but per-capita end use of coal energy only rose c6.5x, because the prime movers of the early industrial revolution were inefficient. This note presents our top five conclusions from evaluating the data.

Five Conclusions into Energy Demand from the Industrial Revolution

(1) Context. Useful energy demand per capita trebled from 1MWH pp pa in the 1600s to over 3MWH pp pa in the mid-19th century, an unprecedented increase.

For comparison, today’s useful energy consumption per capita in the developed world is 6x higher again, as compared with the 1850s. A key challenge for energy transition in the developed world is that people want to keep consuming 20MWH pp pa of energy, rather than reverting to pre-industrial or early-industrial energy levels. As a rough indicator, 20MWH is the annual energy output of c$120-150k of solar panels spread across 600 m2 (model here).

Furthermore, today’s useful energy consumption in the emerging world is only c2x higher than Britain in the 1860s. I.e., large parts of the emerging world are in very early stages of industrialization, comparable to where Britain was 150-years ago. Models of global decarbonization must therefore allow energy access to continue rising in the emerging world (charts below), and woe-betide any attempt to stop this train.

(2) Shortages as a driver of transition? One of the great cliches among energy analysts is that we “didn’t emerge from the stone age because we ran out of stone”. In Britain’s case, in fact, the data suggest we did shift from wood to coal combustion as we began to run out of wood.

Wood use and total energy use both declined in the 16th Century, and coal first began ramping up as an alternative heating fuel (charts above). In 1560, Britain’s heating fuel was 70% wood and 30% coal. By 1660, it was 70% coal and 30% wood. This was long before the first coal-fired pumps, machines or locomotives.

This is another reminder that energy transitions tend to occur when incumbent energy sources are under-supplied and highly priced, per our research below. Peak supply tends to preceed peak demand, not the other way around.

(3) Energy transition and abolitionism? Amazingly, human labor was the joint-largest source of useful energy around 1600, at c25% of total final energy consumption. But reliance upon human muscle power as a prime mover was bound up in one of the greatest atrocities of human history: the coercion of millions of Africans, slaves and serfs; to row in galleys, transport bulk materials and work land.

By the time Britain banned the slave trade in 1807, human muscle power was supplying just 10% of usable energy. By the time of the Abolition Act in 1833, it was closer to 5%.

Some people today feel that unmitigated CO2 emissions is an equally great modern-day evil. On this model, it could be the vast ramp-up of renewable energy that eventually helps to phase out conventional energy. But our current models below do not suggest that renewables can reach sufficient size or scale for this feat until around 2100.

What is also different today is that policy-makers seem intent on banning incumbent energy sources before we have transitioned to alternatives. We have never found a good precedent for bans working in past energy systems. Although US Prohibition, from 1920-1933, makes an interesting case study.

(4) Jevons Paradox states that more efficient energy technologies cause demand to rise (not fall) as better ways of consuming energy simply lead to more consumption.

Hence no major energy source in history has ‘peaked’ in absolute terms. Even biomass and animal traction remain higher in absolute terms than before the industrial revolution, both globally and in our UK data from 1560-1860.

Jevons Paradox is epitomized by the continued emergence of new coal-consuming technologies in the chart below, which in turn stoked the ascent of coal-powered demand, while wood demand was not totally displaced.

The fascinating modern-day equivalent would suggest that the increasing supply of renewable electricity technologies will create new demand for electric vehicles, drones, flying cars, smart energy and digitization; rather than simply substituting out fossil fuels.

(5) Long timeframes. Any analysis of long-term energy markets inevitably concludes that transitions take decades, even centuries. This is visible in the 300-year evolution plotted above, and in the full data-set linked below. Attempts to speed up the transition create the paradox of very high costs or potential bubbles. We have also compiled a helpful guide into transition timings by mapping twenty prior technology transitions. Our recent research, summarized below, covers all of these topics, for further information.

Source: Wrigley, E. A. (2011). Energy and the English Industrial Revolution, Cambridge, TSE Estimates. With thanks to the Renewable Energy Foundation for sharing the data-set.

MCFCs: what if carbon capture generated electricity?

Molten carbonate fuel cells (MCFCs) could be a game-changer for CCS and fossil fuels. They are electrochemical reactors with the unique capability to capture CO2 from the exhaust pipes of combustion facilities; while at the same time, efficiently generating electricity from natural gas. The first pilot plant was due to be tested in 1Q20, by ExxonMobil and FuelCell Energy, but was deferred. Economics range from passable to phenomenal. The opportunity is outlined in our 27-page report.

Pages 2-4 outline the market opportunity for more efficient carbon separation technologies, which can be retrofitted to 4TW of pre-existing power plants, without adding $50/T of cost and 15-30% of energy penalties per traditional CCS.

Pages 5-13 outline how MCFCs work, including their operation, development history, how recent patents promise to overcome reliability problems, and their emergent adaptation to carbon capture.

Pages 14-18 assess the economics, both in absolute terms, and by comparison to new gas plants and hydrogen fuel cells. CCS-MCFC economics range from passable to phenomenal, at recent power prices.

Pages 19-23 suggest who might benefit. FuelCell Energy has received $60M investment from ExxonMobil, hence both companies’ prospects are explored.

Appendix I is an overview of incumbent CCS technologies, and their limitations.

Appendix II is an overview of six different fuel cell types, comparing and contrasting MCFCs.

De-Carbonising Carbon?

Decarbonisation is often taken to mean the end of fossil fuels. But it is more feasible simply to de-carbonise them, with next-generation combustion technologies.

This 19-page note presents our top two opportunities: ‘Oxy-Combustion’ using the Allam Cycle and Chemical Looping Combustion. Both can provided competitive energy with zero carbon coal & gas.

Leading Oil Majors are supporting these solutions, to create value while advancing the energy transition.

Carbon capture remains an “orphan technology”, absorbing just c0.1% of global CO2. The costs and challenges of current technologies are profiled on pp2-4.

Energy penalties are particularly problematic. Paradoxically, the more CCS in our models, the longer it takes to de-carbonise the energy system (see pp5-6).

Next generation combustion-technologies are therefore necessary…

Allam Cycle Oxy-Combustion burns CO2 in an inert atmosphere of CO2 and oxygen. We evaluate a demonstration plant and model strong economics (see pp12-15).

Chemical Looping Combustion burns fossil fuels in a fluidized bed of metal oxide. We profile the technology’s development to-date, net efficiency and levellised costs, which are passable (pp8-11).

Oil Majors are driving the energy transition. We count ninety patents from leading companies to process CO2, including 30 to de-carbonise power. The best advances are profiled from TOTAL, Occidental, Aramco and ExxonMobil. (See pp16-19).

Oil Companies Drive the Energy Transition?

There is only one way to decarbonise the energy system: leading companies must find economic opportunities in better technologies. No other route can source sufficient capital to re-shape such a vast industry that spends c$2trn per annum. We outline seven game-changing opportunities. Leading energy Majors are already pursuing them in their portfolios, patents and venturing. Others must follow suit.

Pages 2-3 show that today’s technologies are not sufficient to decarbonise the global energy system, which will surpass 100,000TWH pa by 2050. Better technologies are needed.

Pages 4-6 show how Oil Majors are starting to accelerate the transition, by developing these game-changing technologies. The work draws on analysis of 3,000 patents, 200 venture investments and other portfolio tilts.

Pages 7-13 profile seven game-changing themes, which can deliver both the energy transition and vast economic opportunities in the evolving energy system. These prospects cover electric mobility, gas, digital, plastics, wind, solar and CCS. In each case, we find leading Oil companies among the front-runners.

Is the world investing enough in energy?

Global energy investment will need to rise by c$220-270bn per annum by 2025-30, according to the latest data from the IEA, which issued its ‘World Energy Investment’ report this week. We think the way to achieve this is via better energy technologies.

Specifically, the world invested $1.6bn in new energy supplies in 2018, which must be closer to $1.8-1.9bn, to meet future demand in 2025-30– whether emissions are tackled or not. The need for oil investment is most uncertain. More gas investment is needed in any scenario. And renewables investment must rise by 15-100%.

Note: data above includes $1.6trn investment in energy supplies and c$250bn in energy efficiency measures

Hence the report strikes a cautious tone: “Current market and policy signals are not incentivising the major reallocation of capital to low-carbon power and efficiency that would align with a sustainable energy future. In the absence of such a shift, there is a growing possibility that investment in fuel supply will also fall short of what is needed to satisfy growing demand”.

We do not think the conclusions are surprising. Our work surveying 50 investors last year found that fears over the energy transition are elevating capital costs for conventional energy investments (below).

Meanwhile, low returns make it challenging to invest at scale in renewables.

We argue better energy technologies are the antidote to attracting capital back into the industry. That is why Thunder Said Energy focuses on the opportunities arising from energy technologies. Please see further details in our recent note, ‘What the Thunder Said’. For all our ‘Top Technologies’ in energy, please see here.


IEA (2019). World Energy Investment. International Energy Agency.

Why the Thunder Said?

Energy transition is underway. Or more specifically, five energy transitions are underway at the same time. They include the rise of renewables, shale oil, digital technologies, environmental improvements and new forms of energy demand. This is our rationale for establishing a new research consultancy, Thunder Said Energy, at the nexus of energy-technology and energy-economics.

This 8-page report outlines the ‘four goals’ of Thunder Said Energy; and how we hope we can help your process…

Pages 2-5 show how disruptive energy technologies are re-shaping the world: We see potential for >20Mbpd of Permian production, for natural gas to treble, for ‘digital’ to double Oil Major FCF, and for the emergence of new, multi-billion dollar companies and sub-industries amidst the energy transition.

Page 6 shows how we are ‘scoring’ companies: to see who is embracing new technology most effectively, by analysing >1,000 patents and >400 technical papers so far.

Page 7 compiles quotes from around the industry, calling for a greater focus on technology.

Page 8 explains our research process, and upcoming publication plans.

Under-investment risks in the energy transition?

Fears over the energy transition are now restricting investment in fossil fuels, based on our new paper, published in conjunction with the Oxford Institute for Energy Studies, linked here.    

They have elevated capital costsby 4-7% for oil and by c25% for coal, compared with the early 2010s.

  • One consequence will be to concentrate capital into renewables, gas,  and shorter-cycle oil projects (i.e.,  shale).
  • But there will also be negative consequences, risking long-run supply shortages of oil and coal.
  • Companies are also being pressured to ‘harvest’ their existing assets, rather than maximising potential value in the 2020s, which may impact valuations.  

For further details please see the full paper, linked here, or contact us. 

250-years of Energy Disruption?

In 2018, we reviewed 250-years of energy transitions, arguing that another great energy transition is now on hand.

It will occur over the next century. Thus for another hundred years, today’s energy industry will remain vitally important. In addition, new sources of supply will create unimaginable new sources of energy demand.

A podcast summarising the work is available from the Oxford Institute for Energy Studies.

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