Category Archives: CCS

Hydrogen and electricity for low carbon heat

Hydrogen and electricity are competing carriers, and there may be a role for both in providing low carbon heat.

There has recently been a lot of interest in the role of hydrogen as a carrier of low carbon energy, because it produces no CO2 on combustion (or oxidation in a fuel cell).  This is the first of three posts looking at hydrogen and how it might compete with electricity to provide low carbon heat.  Hydrogen and electricity may also compete in transport, but that is a large subject in its own right and will need to await further posts.

This first post outlines some of the possibilities and the issues raised.  The next post will compare electricity with hydrogen for heating in buildings.  The third post will look at the ways they may complement each other to supply heat.

There are broadly two main sources of primary energy for low carbon heat:

  • Fossil fuels with CCS, which I’ve assumed in these posts will usually be natural gas.
  • Renewables, likely in practice to be mainly wind and solar.

Each of these primary energy sources can get to the energy consumer in the form of electricity or hydrogen.  Wind and solar can produce low carbon electricity directly, or they can produce hydrogen via electrolysis of water.  Natural gas can be burnt in a CCGT to produce electricity.  It can also be processed to produce hydrogen, most commonly in a steam methane reformer (SMR).  I’ve assumed here that SMRs are used, although many are looking at alternative approaches such as autothermal reforming (ATRs) which may allow for higher efficiencies and capture rates.

If fossil fuels are used CCS is required, as both CCGTs and SMRs produce CO2.  This means they provide low carbon energy, rather than a zero-carbon energy, as a maximum of 90-95% of the CO2 produced is captured.  Any CCS built now or in the future will likely still be in use by 2050, so its capture rate must be judged against 2050 net-zero targets.  In this context, the residual emissions from any large-scale use of CCS for fossil fuels are likely to be significant, and may place limits on the extent of deployment.  SMRs produce different streams of CO2. Some of this is concentrated and so relatively easy to capture, some is more dilute.  Both streams need to be captured for the technology to play an appropriate role in a net-zero carbon economy.

Both CCGTs and SMRs also produce waste heat, which may be used, so improving the overall thermal efficiency, although applications to date have been limited.

Hydrogen can be converted into electricity using a fuel cell or CCGT (with appropriately designed turbines).  This may enable use of hydrogen for electricity storage.

Electricity for building heating is likely to come from heat pumps (likely mainly air source heat pumps) as these greatly improve efficiency.

This gives a variety of routes for primary energy to low carbon end use. These are shown in the diagram below.  In practice several of these may co-exist, and some may not happen at scale.  The pathways shown assume natural gas cannot continue to act as a carrier of energy to individual buildings.  This is because its combustion inevitably produces CO2 and very small-scale CCS for individual buildings is likely to prove impractical, for example because of the very extensive CO2 transport network that would be required.

Both fossil fuels and renewables can deliver energy as electricity or hydrogen …

Which mix of these pathways will provide the best solution? It’s not yet clear.  It will depend on various factors.

Suitability for end use.  Some industrial processes require high temperature heat or a direct flame, which heat pumps cannot provide.  Conversely, hydrogen needs to demonstrate its safety in a domestic context, though this is likely tractable.

Consumer acceptability. This is critical for residential heating, and both hydrogen and heat pumps face potential difficulties.  For example, heat pumps may be perceived as noisy, or require modifications such as installation of larger radiators which people resist.

Costs.  Which route is cheaper depends on a wide range of factors, including :

  • The capital costs of the equipment (e.g. CCGT or SMR, hydrogen boilers, and heat pumps)
  • The costs of reinforcing, creating or repurposing grids, including the extent to which the natural gas gird can be repurposed for hydrogen, and the cost of reinforcing the electricity distribution network to accommodate demand from heat pumps.
  • The cost of the primary energy, for example whether renewable energy is produced at times of low demand so might be available at a low price. If electricity from renewables is available very cheaply then resistance heating without heat pumps may make sense in some cases.
  • The thermal efficiency of the processes, for example the extent to which CCS adds costs by requiring additional energy, and the coefficient of performance (heat out divided by electricity in) for heat pump, especially in winter.
  • The costs of electricity storage via batteries or as hydrogen.
  • Load factor for heat and electricity production.

Many of these variables are uncertain.  They also vary with location and over time. The very large cost falls for renewable electricity demonstrate the need for caution in judging options on present costs.

In my next post I will take a look at how these factors may play out for building heating in the UK, and will consider the policy implications.

Adam Whitmore – 30th September 2019

 

 

How well is the UK on track for zero emissions by 2050?

By 2020 the UK will have very nearly halved its emissions over 30 years.  Reducing emissions by the same amount over the next 30 years will get the UK very close to zero.  However this will be very much more difficult.

A robust net zero target has been recommended for the UK …

A recent report by the UK’s Committee on Climate Change (CCC), the Government’s official advisory body, recommends that the UK adopts a legally binding target of net zero emissions of greenhouse gases by 2050[i], that is remaining emissions must be balanced by removal from the atmosphere.  If the Government agrees, this will be implemented by amending the reduction mandated by the Climate Change Act, from an 80% reduction from 1990 to a 100% reduction.

The target has several features that make it particularly ambitious.  It:

  • sets a target of net zero emissions covering all greenhouse gases;
  • includes international aviation and shipping;
  • allows no use of international offsets; and
  • is legally binding.

This is intended to end the UK’s contribution global warming.  It has no precedents elsewhere, although in France a bill with comparable provisions is under consideration[ii].

Progress to date has been good …

The UK has made good progress so far in reducing emissions since 1990.  Emissions in 2018 were around 45% below 1990 levels, having reduced at an average rate of about 12.5 million tonnes p.a. over the period.  On current trends, over the thirty years from 1990 to 2020 emissions will be reduced to about 420 million tonnes p.a., 47% below their 1990 levels.  Emissions will thus have nearly halved over the 30 years 1990 to 2020, half the period from 1990 to the target date of 2050.

Chart 1 shows how the UK’s progress compares with a linear track to the current target of an 80% reduction, to a 95% reduction and to a 100% reduction.  (For simplicity I’m ignoring international aviation and shipping).  The UK is currently on a linear track towards a 95% reduction by 2050.

Chart 1: Actual UK emissions compared with straight line progress towards different 2050 targets

 

Source: My analysis based on data from the Committee on Climate Change and UK Government.  Data for 2018 is provisional[iii]

The largest contributor to the total reduction so far has been the power sector.  Analysis by Carbon Brief[iv] showed that the fall in power sector emissions has been due to a combination deploying renewables, which made up about of third of generation in 2018, reducing coal use by switching to natural gas, and limiting electricity demand growth.

Industrial emissions have also fallen significantly.  However some of this likely represents heavy industry now being concentrated elsewhere in the world, so likely does not represent a fall in global emissions.  Emissions from waste have also fallen, due to better management.

Reducing emissions will be relatively easy in some sectors …

There are also reasons for optimism about continuing emissions reductions.  Many technologies are now there at scale and at competitive prices, which they were not in previous decades.  For example, falling renewables costs and better grid management, including cheaper storage, will help further decarbonisation of the power sector.  Electrification of surface transport now appears not only feasible, but likely to be strongly driven (at least for cars and vans) by economic factors alone as the cost of batteries continues to fall.

But huge challenges remain …

Nevertheless important difficulties remain for complete decarbonisation.

CCS is identified by the report as an essential technology.  However, as I have noted previously, it has made very little progress in recent years in the UK or elsewhere[v].  CCS is especially important for decarbonising industry.  This includes a major role for low carbon hydrogen, which is assumed to be produced from natural gas using CCS – although another possibility is that it comes from electrolysis using very cheap renewables power, e.g. at times of surplus.  CCS also looks to be necessary because of its use with bioenergy (BECCS), to give some negative emissions, though the lifecycle emissions from this will require careful attention

Decarbonising building heating, especially in the residential sector, continues to be a challenge.  The report envisages a mix of heat pumps and hydrogen, perhaps in the form of hybrid designs, with heat pumps providing the baseload being topped-up up by burning of hydrogen in winter.  I have previously written about the difficulties of widespread use of heat pumps[vi], and low carbon hydrogen from natural gas with CCS is also capital intensive to produce and therefore expensive to run for the winter only.  The scale of any programme and consumer acceptance remain major challenges, and the difficulties encountered by the UK’s smart meter installation programme – by comparison a very simple change – are not an encouraging precedent.

Emissions from agriculture are difficult to eliminate completely, and no technologies are likely to be available by 2050 that enable aviation emissions to be completely eliminated.  This will require some negative emissions to balance remaining emissions from these sectors.

Policy needs to be greatly strengthened …

Crucially several of the necessary transformations are very large scale, and need long lead times, and investment over decades.  There is an urgent need to make progress on these, and policy needs to recognise this.  This includes plans for significant absorption from reforestation, as trees need to be planted early enough that they can grow to be absorbing substantial amounts by 2050.

The UK’s progress on emissions reduction so far has been good, having made greater reductions than any other major economy[vii].  And technological advances in some areas are likely to enable substantial further progress.  However much more is needed.  In particular policy needs to look now at some of the difficult areas where substantial long-term investment will be needed

Adam Whitmore – 22nd May 2019

 

 

[i] https://www.theccc.org.uk/2019/05/02/phase-out-greenhouse-gas-emissions-by-2050-to-end-uk-contribution-to-global-warming/

 

[ii] The CCC report notes that Norway, Sweden and Denmark have net zero targets, but they allow use of international offsets (up to 15% in the case of Sweden).  France has published a target similar to the UK’s in a bill.  The European Commission has proposed something similar for the EU as a whole, but this is a long way from being adopted. California has non-legally binding targets to achieve net zero by 2045.  Two smaller jurisdictions (Costa Rica, Bhutan) have established net zero targets but these are expected to be achieved mainly by land use changes.  New Zealand has a draft bill to establish a target, but eliminating all GHGs will be difficult because of the role of agriculture in the New Zealand economy.

 

[iii] https://www.gov.uk/government/statistics/provisional-uk-greenhouse-gas-emissions-national-statistics-2018  The change from 2017 to 2018 is applied to the data series from 1990 produced by the CCC (the two data series differ very slightly in their absolute levels).

 

[iv] https://www.carbonbrief.org/analysis-uk-electricity-generation-2018-falls-to-lowest-since-1994

 

[v] https://onclimatechangepolicydotorg.wordpress.com/2018/04/25/a-limited-but-important-medium-term-future-for-ccs/

 

[vi] https://onclimatechangepolicydotorg.wordpress.com/2015/05/18/reducing-the-costs-of-decarbonising-winter-heating-needs-to-be-a-priority/

 

[vii] https://onclimatechangepolicydotorg.wordpress.com/2017/05/09/uk-emissions-reductions-offer-lessons-for-others/

 

A limited but important medium term future for CCS

CCS has not yet been implemented on a scale needed to make a substantial difference to climate change.  However it continues to look necessary for the longer term, with more projects necessary to get costs down.

A decade or so ago many people expected rapid development of Carbon Capture and Storage (CCS) as a major contributor to reducing global emissions.  I was one of them – at the time I was working on developing CCS projects.  However, the hoped-for growth has not yet happened on the scale needed to make a material difference to global emissions.

The chart below shows total quantities captured from large CCS projects, including 17 that are already operational and a further 5 under construction.  The quantity of emissions avoided are somewhat lower than the captured volumes shown here due to the CO2 created by the process itself.[i]

Between 2005 and 2020 capture will have grown by only around 25 million tonnes p.a..  This is only 0.07% of annual global CO2 emissions from energy and industry.  In contrast the increase in wind generation in 2017 alone reduced emissions by around 60 million tonnes[ii], so wind power reduce annual emission more from about 5 months’ growth than CCS will from 15 years’ growth – though it took wind power several decades to get to this scale.    

Chart 1: Growth of large CCS projects over time

Source: Analysis based on Global Carbon Capture and Storage Institute database[iii]

The picture gets even less promising looking at the types of projects that have been built.  The chart below shows the proportion of projects, measured by capture volume, in various categories.  The largest component by some distance is natural gas processing – removing the CO2 from natural gas before combustion – which accounts for over 60% of volumes.  This makes sense, as it is often a relatively low cost form of capture, and is often necessary to make  natural gas suitable for use.  However, it will clearly not be a major component of a low carbon energy system.  Much of the rest is chemicals production, including ethanol and fertiliser production.  These are helpful but inevitably small. There are just two moderate size power generation projects and two projects for hydrogen production, which is often considered important for decarbonising heat.

Furthermore, most of the projects separate out CO2 at relatively high concentrations or pressures.  This tends to be easier and cheaper than separating more dilute, lower pressure streams of CO2.  However it will not be typical of most applications if CCS is to become more widespread.

Chart 2:  Large CCS projects by type (including those under construction) 

Source: Analysis based on Global Carbon Capture and Storage Institute database

This slow growth of CCS has been accompanied by at least one spectacular failure, the Kemper County power generation project, which was abandoned after expenditure of several billion dollars.  Neither the circumstances of the development or the technology used on that particular plant were typical.  For example, the Saskpower’s project at Boundary Dam and Petra Nova’s Texas project have both successfully installed post combustion capture at power plants, rather than the gasification technologies used at Kemper County.  Nevertheless, the Kemper project’s failure is likely to act as a further deterrent to wider deployment of CCS in power generation.

There have been several reasons for the slow deployment of CCS.  Costs per tonne abated have remained high for most projects compared with prevailing carbon prices.  These high unit costs have combined with the large scale of projects to make the total costs of projects correspondingly large, with a single project typically having a cost in the billions of dollars.  This has in turn made it difficult to secure from governments the amount of financial support necessary to get more early projects to happen. Meanwhile the costs of other low carbon technologies, notably renewables, have fallen, making CCS appear relatively less attractive, especially in the power sector.

The difficulties of establishing CCS have led many to propose carbon capture and utilisation (CCU) as a way forward.  The idea is that if captured CO2 can be a useful product, this will give it a value and so improve project economics.  Already 80% by volume of CCS is CCU as it includes use of the CO2 for Enhanced Oil Recovery (EOR), with project economics supported by increased oil production.

Various other uses for CO2 have been suggested.  Construction materials are a leading candidate with a number of research projects and start-up ventures in this area.  These are potentially substantial markets.  However the markets for CO2 in construction materials, while large in absolute terms, are small relative to global CO2 emissions, and there will be tough competition from other low carbon materials. For example, one study identified a market potential for CCU of less than two billion tonnes p.a. (excluding synthetic fuels) even on a highly optimistic scenario[iv], or around 5% of total CO2 emissions.  It is therefore difficult to be confident that CCU can make a substantial contribution to reducing global emissions, although it may play some role in getting more early carbon capture projects going, as it has done to date through EOR.

Despite their slow growth, CCS and CCU continue to look likely to have a necessary role in reducing some industrial emissions which are otherwise difficult to eliminate.  The development of CCS and CCU should be encouraged, including through higher carbon prices and dedicated support for early stage technological development.  As part of this it remains important that more projects CCS and CCU projects are built to achieve learning and cost reduction, and so support the beginnings of more rapid growth.  However in view of the lead times involved the scale of CCS looks likely to continue to be modest over the next couple of decades at least.

Adam Whitmore – 25th April 2018

[i] CO2 will generally be produced in making the energy necessary to run the capture process, compression of the CO2 for transport, and the rest of the transport and storage process.  This CO2 will be either emitted, which reduces the net gain from capture, or captured, in which case it is part of the total.  In either case the net savings compared with what would have been emitted to the atmosphere with no CCS are lower than the total captured.

[ii] Wind generation increased by a little over 100 TWh between 2016 and 2017 (Source: Enerdata).  Assuming this displaced fossil capacity with an average emissions intensity of 0.6 t/MWh (roughly half each coal and gas) total avoided emissions would be 60 million tonnes.

[iii] https://www.globalccsinstitute.com/projects/large-scale-ccs-projects

[iv] https://www.frontiersin.org/articles/10.3389/fenrg.2015.00008/full

Deploying CCS on fossil fuel plant is more of a priority than implementing negative emissions technologies

The potential for biomass with CCS and direct air capture of CO2 should not distract from deployment of CCS on fossil fuel plants over the next few decades.  Among other things, learning from CCS on fossil fuels will help make eventual deployment of CCS on biomass cheaper and more effective.

There appears to be increasing likelihood that atmospheric concentrations of greenhouse gases will grow to exceed levels consistent with the target specified in the recent UNFCCC Paris agreement of limiting temperature rises to “well below” two degrees.  Such an outcome would require CO2 to be removed from the atmosphere faster than natural sinks allow, in order to restore concentrations to safe levels.  Near zero net emissions in the latter part of this century will also be needed to stabilise concentrations.

Many models of future emissions pathways now show negative emissions technologies (technologies that result in a net decrease in CO2 in the atmosphere) needing to play a major role for in meeting climate goals. They have the potential to remove carbon dioxide from the atmosphere in the event of “overshoot” of target atmospheric concentrations, and to balance remaining emissions from sectors where abatement is difficult with a view to achieving net total emissions of close to zero.  But the application of such technologies should not be considered in isolation.

Bio Energy with CCS (BECCS)

Bio energy with CCS (BECCS ) is the most widely discussed approach to negative emissions.  BECCS is not a single technology but a combination of two major types of CO2 removal.  Bioenergy from burning biomass to generate electricity or heat emits a substantial amount of CO2  on combustion – around as much as a coal plant.  However much of this can be captured using CCS.  More carbon dioxide is reabsorbed over time by the regrowth of the plants, trees – or perhaps algae – that have been harvested to produce the bioenergy.  Together, the capture of the CO2 from the flue gas and the subsequent absorption of CO2 from the atmosphere by regrowth of biomass can lead to net removal of CO2 from the atmosphere, although this takes time.  (The net amount of CO2, that is emitted on a lifecycle basis from burning biomass without CCS depends on the type of biomass and is subject to considerable variation and uncertainty – a controversial topic that would need another post to review.)

However at an energy system level, where the CO2 is captured – biomass plant or fossil fuel plant – is less relevant than the total amount that’s captured.  Broadly speaking, if there is a biomass plant and fossil fuel plant both running unabated the same benefit can be achieved by capturing a tonne of CO2 from either.

Indeed there may be advantages to putting CCS on a conventional plant rather than biomass plant.  It may be technically more tractable.  Furthermore, CCS require a lot of energy to capture the CO2 and then to compress and pump it for permanent storage.  Biomass is likely to be supply constrained (again, this is an issue that requires a post in itself), so using biomass rather than fossil fuels to provide this energy may limit other applications.  Only when there are no fossil fuel plants from which to capture CO2 does biomass plant become unambiguously a priority for CCS.  This is clearly some way off.

Furthermore biomass with CCS for electricity generation may not be the best use of bioenergy.  Converting sunlight to bioenergy then turning that into electricity is a very inefficient process.  Typically only 1-2% of the sunlight falling on an area of cropland ends up as useful chemical energy in the form of biofuels.  There are various reasons for this, not least of which is that photosynthesis is a highly inefficient process.  Burning biomass to make electricity adds a further layer of inefficiency, with only perhaps a third or less of the energy in the biomass turned into electricity.  Sunlight therefore gets converted to electricity with an efficiency of perhaps 0.5%.  This compares with around 15- 20% for solar cells, implying that scarce land is often likely to be best used for solar PV.  (The calculation is closer if solar PV is used to create storable energy e.g. in the form of hydrogen).   For similar reasons the use of biofuels rather than electricity in transport is inefficient, in part because internal combustion engines are less efficient than electric motors.

Limited available biomass may be better used for those applications where it is the only available lower carbon energy source, notably in aviation and (likely) heavy trucks, or for other applications such as district heating with CCS, where the ability to store energy seasonally is especially valuable.

At the very least, detailed system modelling will be required to determine the optimal use of biomass.  Suggesting that BECCS should have a major role to play simply because in isolation it has negative emissions may lead to suboptimal choices.

Direct Air Capture (DAC)

Direct Air Capture (DAC), where carbon dioxide is chemically absorbed from the atmosphere and permanently sequestered, can also reduce the stock of CO2 in the atmosphere.  However the typical concentration of CO2 in a flue gas of a power plant or industrial plant is several percent, about a hundred times as great as the concentration of 0.04% (400 ppm) found in the atmosphere.  This makes the capture much easier.  Furthermore, millions of tonnes can be captured and piped from a single compact site using CCS, generating economies of scale on transport and storage.  In contrast DAC technology tends to be more diffuse.  These considerations imply that CCS from power plants and industrial facilities is always likely to be preferable to direct air capture until almost all the opportunities for CCS have been implemented, which again is a very long way off.

Uncertainties and optionality

There are many uncertainties around negative emissions technologies, including the availability of biomass, cost, and the feasibility of reducing emissions in other sectors.  For these reasons developing optionality remains valuable, and research to continue to develop these options, including early trial deployment, is needed, as others have argued[i].

One of the best ways of developing optionality is to deploy CCS at scale on fossil fuel plants.  This will reduce the costs and enable the development of improved technologies through learning on projects.  It will also help build infrastructure which can in turn benefit  BECCS.  This needs to run in parallel with ensuring that the lifecycle emissions from the bioenergy production chain are reduced and biodiversity is safeguarded.

Negative emissions technologies may well have a role to play in the latter part of the century.  But they seem likely to make more sense when the economy is already largely decarbonised.  In the meantime deployment of CCS, whether on industrial facilities or power plants, needs to be a much greater priority.

Adam Whitmore – 21st March 2016

[i] Investing in negative emissions, Guy Lomax,  Timothy M. Lenton,  Adepeju Adeosun and Mark Workman, Nature Climate Change 5, 498–500 (2015)  http://www.nature.com/nclimate/journal/v5/n6/full/nclimate2627.html?WT.ec_id=NCLIMATE-201506