Tag Archives: power generation

A chance to change some dubious climate accounting

The UK should change the way it accounts for emissions under its legally binding carbon budgets, whether or not it remains part of the EUETS.

An apparently technical question about the UK’s accounting for its carbon budgets raises broader questions about alignment of targets and policy instruments.

The UK’s carbon budgets are legally binding obligations under the Climate Change Act (2008) to limit total emissions from the UK.  Checking whether emissions are within the budget ought to be simple.  Measure the UK’s emissions to see if they are at or under budget.  If not there’s a problem.

But it does not work that way.  For sectors not covered by the EUETS actual emissions are indeed used.  However for those sectors covered by the EUETS – power generation and large industry – emissions are deemed always to be equal to the UK’s allocation under the EUETS (which is made up of both auctioned allowances allocated free of charge[1]), whatever emissions are in reality.  Actual emissions from the covered sectors could be much higher and carbon budgets would still be met

While this may sound bizarre, there was a logic to it when the rules were established.  If UK emissions from the traded sector are above the UK’s allocation UK emitters need to buy in EUAs.  If the scheme were short of allowances, as was expected when present accounting rules were set, the additional EUAs bought by UK emitters to cover emissions above the UK’s allocation would lead to reduced supply of EUAs for others.  There would in consequently be reduced emissions elsewhere matching the increased emissions in the UK.  The approach was therefore to some extent a reliable measure of net emissions.  It also aligned with the EUETS having clear National Allocation Plans (NAPs) for EUAs for each Member State, something that no longer exists.

Now this type of accounting no longer makes sense.  With a large surplus of allowances in the EUETS, if the covered sectors in the UK emit more than their budget they will simply buy surplus allowances.  These allowances would otherwise almost all eventually be placed in the Market Stability Reserve (MSR).  Under current proposals (and indeed most likely eventualities), these EUAs would eventually be cancelled.  Additional emissions in the UK are therefore not balanced by reductions elsewhere – they simply result in buying surplus EUAs which would never be used.  This type of situation is sometimes called “buying hot air”.

To avoid this occurring in future, accounting for carbon budgets needs to change to actual emissions.  This will necessarily happen anyway if the UK leaves the EU ETS.  UK allocations under the EUETS will no longer exist. Accounting cannot be based on a non-existent allocation.

But even if the UK stays part of the EU ETS the basis of accounting should change to prevent the UK is meeting its carbon budgets by simply buying in surplus EUAs.

The possibility of buying in surplus to cover UK emissions appears quite real.  UK emissions were above allocation until quite recently.  This was not too serious a problem then, because carbon budgets were being met fairly comfortably anyway.  However the situation may recur under the 2020s and early 2030s under fourth and fifth carbon budgets, which will be much more challenging to meet.  Total UK emissions could be allowed to rise above those carbon budgets simply as a result of an accounting treatment[2].

When a target applies to a jurisdiction that does not wholly align with the policy instrument there will always be a need to consider circumstances in assessing whether targets are being met.  The UK should not be able to meet its carbon budgets simply due to an accounting convention.  Current rules were put in place before the current oversupply under the EUETS arose.  It is no longer fit for purpose.  It should be changed to accounting based on actual emissions whether or not the UK is part of the EUETS.

Adam Whitmore -20th June 2017

[1] This consists of auctioning plus free allowances plus UK allocation under the NER. In Phase 4 it would also include any allocation from the Innovation Fund. Future volumes placed in the MSR and thus excluded from auctioning would also be deducted from the total. If the UK were to leave the EU ETS and backloaded UK allowances currently destined for the MSR were to return to the market this would have a significant effect on measured performance against carbon budgets under current accounting.

[2] Whether this led to total actual emissions being above carbon budgets would depend on the performance of the non-traded sector.

Half way there

The UK has made excellent progress on reducing emissions.  But the hard part is yet to come.

The UK’s Climate Change Act (2008) established a legally binding obligation to reduce UK emissions by at least 80% from 1990 levels by 2050.  This is an ambitious undertaking, a sixty year programme to cut four in every five tonnes of greenhouse gas emissions while simultaneously growing the economy.

The story so far is, broadly, an encouraging one.  2016 emission were 42% below 1990 levels, about half way to the 2050 target[1].  This has been achieved in 26 years, a little under half the time available.  And it has been achieved while population has grown by about 15%[2] and the economy has grown by over 60%.  The reduction in emissions from 1990 to 2015 is shown on the chart below, which also shows the UK’s legislated carbon budgets.   There is of course some uncertainty in the data, especially for non-CO2 gases, but uncertainties in trends are less than the uncertainty in the absolute levels, and emissions of CO2 from energy, which is the largest component of the total, are closely tracked.

The UK is half way towards its 2050 target, in a little under half the available time …

Source: Committee on Climate Change

The chart below shows the sectoral breakdown of how this has been achieved, and this raises some important caveats.

Progress in some sectors has been much more rapid than others …

Source: Committee on Climate Change

The largest source of gains has been the power sector, especially if a further fall of a remarkable in emissions from power generation in 2016 is included (the chart only shows data to 2015).  While renewables have made an important contribution, much of this fall has been due to replacing coal with gas.  This been an economically efficient, low cost way of reducing emissions to date, to which UK carbon price support has been a major contributor.  However coal generation has now fallen to very low levels, so further progress requires replacing gas with low carbon generation – renewables, nuclear and CCS.  This is more challenging, and in some cases is likely to prove more expensive.

The next largest source of gains, roughly a third of the total reduction, is from industry.  However, while detailed data is not available, a large part of this reduction may have been due to broader economic trends, notably globalisation of the world economy leading to heavy industry becoming more concentrated in emerging economies.  This trend may also have had some effect on electricity demand and thus emissions.  The aggregate reduction in global emissions may thus be smaller than indicated by looking at the UK alone.  Reducing global emissions still requires a great deal more progress on industrial emissions, especially in emissions intensive sectors notably iron and steel and cement.

Progress in reduction of emissions from waste, especially methane from landfill, has been a third important contributor.  Again, this has been highly cost-effective reduction.  However about two thirds of emissions have now been eliminated so further measures will necessarily make a smaller contribution, though there is much that can still be done with the remainder such as eliminating organic waste from landfill.

Other sectors have done much less, and will need to do more in the years to come.  Progress on f-gases may be helped by the recent international agreement on HFCs, although more will still need to be done.  Transport emissions have made only slow progress in recent years.  It is essential that electrification is encouraged so that a large change similar to that achieved in the power sector can be achieved in transport.  The buildings stock remains an intractable problem, and the first priority must be to at least make sure that new buildings are built to the highest standards of insulation.

So continuing the trend of falling emissions in future will be difficult and will require new and enhanced policy measures.  But in 1990 the prospects of achieving what has already been achieved doubtless looked daunting, and progress to date should encourage further efforts in future.

Adam Whitmore -25th April 2017

Material in this post draws on a presentation by Owen Bellamy of the Committee on Climate Change at a British Institute of Energy Economics seminar on 5th April 2017.

[1] The UK’s domestic emissions need to go down slightly more rapidly than the headline target would suggest due to the role of international aviation and shipping.  This is shown on the chart.  However the broad message is the same.

[2]https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationestimates/articles/overviewoftheukpopulation/mar2017

The constrained role of biomass

The role of biomass in the world energy system looks likely to be constrained, so there will be a need to focus on high value applications where there are few low-carbon alternatives.

This is the second of two posts looking at the role of biomass.  Here I focus on potential resource constraints.

A wide range of possibilities

The amount of biomass available to provide energy depends a lot on the amount of land available to grow energy crops, and how much that land can yield.   Different assumptions on these variables produce quite different estimates of the total resource, and numerous studies over the years have produced a wide range of results.    The amount of waste biomass available also matters, but potential availability from this source is smaller.

A comprehensive review of estimates of the biomass resource was carried out two years ago by researchers at Imperial College[i] (see chart).  It showed a variation in estimates of a factor of around 40, from of the order of 30 EJ to over 1000 EJ (1EJ =1018 J, or a billion GJ, or 278 TWh).  This compares with total world primary energy demand of just under 600 EJ, transport demand of around 100 EJ, and at least 250 EJ to produce present levels of electricity, assuming biomass combustion to remain relatively inefficient[ii].

Estimates of available biomass resource

biomass chart processed

Source: Slade et. al. (2014)

The authors examine reasons for differences in estimates, which I’ve summarised in the table below.  The differences are largely assumption driven, because the small scale of commercial bioenergy at present provides little empirical evidence about the potential for very large scale bioenergy, and future developments in food demand and other factors are inevitably uncertain.

Reasons for variation in estimates of total biomass supply

Range Typical assumptions
Up to 100EJ Limited land available for energy crops, high demand for food, limited productivity gains in food production, and existing trends for meat consumption.  Some degraded or abandoned land is available.
100-300 EJ Increasing crop yields keep pace with population growth and food demand, some good quality agricultural land is made available for energy crop production, along with 100-500Mha of grassland, marginal, degraded and deforested land
300-600EJ Optimistic assumptions on energy crop availability, agricultural productivity outpaces demand, and vegetarian diet
600 EJ + Regarded as extreme scenarios to test limits of theoretical availability

 

Reasons for caution

In practice there seem to me to be grounds for caution about the scale of the available resource, although all of these propositions require testing, including through implementation of early projects.

Land Availability

  • There will rightly be emphasis on protection of primary forest on both carbon management and biodiversity grounds, with some reforestation and rewilding.
  • There is little evidence of a shift away from meat consumption. With the exception of India, less than 10% of people in  most countries are vegetarian despite many years of campaigning on various grounds[iii].   In China meat consumption is associated with rising living standards.
  • Demand for land for solar PV will be significant, although a good deal of this will be on rooftops and in deserts

Yield

  • The nitrogen cycle is already beyond its limit, constraining the role of fertiliser, and water stress is a serious issue in many places (agriculture accounts for 70% of current fresh water use). The UN Food and Agriculture Organisation has projected fairly modest increases in future yields.

Policy support

  • Difficulties in limiting lifecycle emissions from biofuels are likely to lead to caution about widespread deployment.
  • Concerns about food security may limit growth of biofuels.

Small scale to date, despite many years of interest

  • There has been little progress to date compared with other low carbon technologies. Though traditional biofuels remain widely used, modern biofuels account for a very small proportion of demand at present.  World biofuels consumption currently accounts for only 0.2% of world oil consumption[iv] .  Many biofuels programmes have had subsidies cut and there is still limited private sector investment.

In this context some estimates of the potential for biomass to contribute to energy supply seem optimistic.  For example, Shell’s long-term scenarios (Oceans and Mountains) show biomass of 74 EJ and 87 EJ respectively for commercial biomass, 97-133 EJ including traditional biomass by 2060[v].  These totals are towards or above the more cautious estimates for the resource that might ultimately be available (see table above).  A recent review article[vi]  suggested that by 2100 up to 3.3 GtCp.a. (around 12 billion tonnes of CO2) could be being removed, and producing around 170EJ of energy.  However the land requirements for this are very large at about 10% of current agricultural land.  The authors suggest instead a mean value for biomass potential of about a third of that, or 60EJ.

On balance it seems that biomass is likely to account for at most less than 10% of commercial global energy (likely to be around 800-900EJ by mid-century), and potentially much less if land availability and difficulties with lifecycle emissions prove intractable.

It thus seems likely that biomass energy will be relatively scarce, and so potentially of high value.  This in turn suggests it is likely to be mainly used in applications where other low carbon alternatives are unavailable.  These are not likely to be the same everywhere, but they are likely often to include transport applications, especially aviation and likely heavy trucking, and perhaps to meet seasonal heat demand in northern latitudes.  For example, according to Shell’s scenarios aviation (passengers + freight) is expected to account for perhaps 20-25EJ by 2050, and biomass could likely make a useful contribution to decarbonisation in this sector.

None of this implies that biomass is unimportant, or has no role to play.  It does imply that policies focussing on deploying other renewable energy sources at large scale, including production of low carbon electricity for transport, will be essential to meeting decarbonisation targets.  And the optimum use of biomass will require careful monitoring and management.

Adam Whitmore  – 11th April 2016

 

[i] Slade et.al., Global Bioenergy Resources, Nature Climate Change February 2014

[ii] Data on final consumption and electricity production from Shell and IEA data.  35% efficiency for biomass in electricity is assumed, which is likely to be somewhat optimistic, especially if CCS is employed.

[iii] https://en.wikipedia.org/wiki/Vegetarianism_by_country

[iv] BP Statistical Review of World Energy

[v] http://www.shell.com/energy-and-innovation/the-energy-future/shell-scenarios.html  These totals include biofuels, gasified biomass and biomass waste solids, and traditional biomass.

[vi] Smith et. al., Biophysical and economic limits to negative CO2 emissions, Nature Climate Change, January 2016.  The paper estimates land requirement for 170 EJ of 380-700 Mha, around 10% of total agricultural land area in 2000 of 4960Mha.

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

 

 

Grains of rice, Japanese swords and solar panels

Even Greenpeace has underestimated the growth of renewables.  In particular, solar has been growing exponentially, and may continue to be so for a while, though likely at a slower percentage rate.

Greenpeace did much better than many at projecting the growth of renewable energy sources in the 2000s.  Their projections were very close to outturn for wind – the 1999 projections were a little below outturn, the 2002 projections a little above.  However even Greenpeace underestimated the growth of solar.  The projections were nevertheless startlingly better than those of the IEA, who have, as I’ve previously noted, consistently underestimated the growth of renewables by a huge margin.  Growth of solar has been exponential, as has that of wind (at least until recently).  Greenpeace appears to have done well by following the logic of exponential growth.

Greenpeace’s projections for wind growth in the 2000s were close to outturn, but they underestimated the growth of solar …

Capture

Exponential growth is so powerful that it can confound intuition about how large numbers can become.  The counterintuitive power of exponential growth is illustrated by the process of making a traditional Japanese steel sword.  The supreme combination of strength and flexibility of such a weapon is said to derive from the way an exponential process layers the metal.  As the metal is beaten out and folded repeatedly to forge the sword the number of layers in the metal doubles up each time.  Following this simple process 15 times creates 215 layers, well over 30,000.  This would be impossible in any other way with traditional methods, and the number of layers created would be hard to comprehend without doing the formal calculation.  This property of producing very large numbers from simple repeated doublings may have contributed to previous projections for renewables seeming implausible, because they were so much greater than the then installed base.  This may have contributed to even Greenpeace being a little cautious in its projections for solar.

Nevertheless exponential growth inevitably runs into limits as some stage.  This is captured by the classic fable of grains of rice on a chessboard, where one grain is put on the first square, two on the second, four on the third, eight on the fourth and so on, doubling with each square.  Half way through the chessboard the pile of grains, though very large, is manageable – around 50 tonnes for the 32nd square.  However amounts then quickly begin to go beyond all reasonable physical constraints.  The pile on the final square would contain 263 grains of rice, which is about 230 billion tonnes.  This is about 300 times annual global production, and enough to cover not just a square of the chessboard but the entire land surface of the earth (to a depth of about a millimetre or two).

Extrapolating growth rates for solar PV from the period 2000 to 2013, when cumulative installed capacity doubled every two years, runs into similar limits.  At this growth rate the entire surface of the earth would be covered with solar panels before 2050.  This would provide far more energy than human civilisation would need, if there were room for any people, which there would not be because of all the solar panels.   So are there constraints that imply that renewables are now in second half of the chessboard – or, if you prefer a more conventional model, the linear part of an s-curve for technology adoption?

Looking at solar in particular, as I’ve previously commented, it needs a lot of land, but this is unlikely to be a fundamental constraint.  Some have previously suggested a limit as technologies reach scale, defined as about 1% of world energy supply, after which growth becomes more linear.  However solar manufacture and installation are highly scalable, so there are fewer obstacles to rapid growth than with traditional energy technologies.

Costs are rapidly falling, so that solar is becoming competitive without subsidy, both compared to other low carbon technologies and, increasingly, with high carbon technologies, especially if the cost of emissions is taken into account.  There is no obvious limit to how low the costs of solar cells can go that is likely to bind in the foreseeable future, although the ancillaries may show slower cost falls.  The costs of lithium ion batteries are also falling rapidly, having approximately halved in the last five years and continuing to fall at a similar rate.  As a result daily storage is becoming much more economic, reducing the problem of the peakiness of solar output and easing its integration into the grid, although seasonal storage remains a daunting challenge.

Solar still accounts for only around 1% of world electricity generation so globally there are plenty of opportunities globally in new electricity demand and from scheduled retirement of existing generating plant.  The vexed issues around grid charges, electricity market structures and role of incumbents may slow growth for a while, at least in some jurisdictions, but seem unlikely to form a fundamental barrier globally as long as costs continue to fall.

In short there seem few barriers to solar continuing to grow exponentially for a while, although likely at a slower percentage rate than in the past – each doubling is likely to take longer than two years given the current scale of the industry.  Solar can still continue moving quite a long way up the chessboard before it hits its limits.  How large the industry will become will need to await a future post, but provisionally there does not seem any reason why solar PV should not become a 300-600 GW p.a. or more industry.

Policy has played an important role in the development of solar to date mainly by providing financial incentives.  It will continue to play an important role, but this will be increasingly around removing barriers rather than providing a financial stimulus.

Of course I cannot know if this fairly optimistic view is right.  But it does at least to avoid some issues that might bias projections downwards.  First, it recognises the potential validity of counter-intuitive results.  In a sector such as energy which usually changes quite slowly the numbers resulting from exponential growth can seem implausible.  This can lead to rejection of perfectly sound forecasts, as the intuition of experienced professionals, which is based on long experience of incremental change, works against them.  Second it avoids assuming that all energy technologies have similar characteristics.  Finally, it takes into account a wide range of possibilities and views and considers the drivers towards them, helping to avoid the cognitive glitch of overconfidence in narrow limits to future outcomes.

The rate of growth of renewables is intrinsically uncertain.  But the biases in forecasts are often more towards underestimation than overestimation.  If you’ve been in the energy industries a while it’s quite likely that your intuition is working against you in some ways.  Don’t be afraid to make a projection that doesn’t feel quite right if that’s where the logic takes you.

Adam Whitmore – 25th November 2014

Notes

In the calculations of the results from exponential growth I have, for simplicity, assumed very rough and ready rounded values of 40,000 grains of rice = 1litre = 1 kg.  I’ve assumed 10m2/kW (including ancillaries) for the area of solar panels. The land surface of the earth is 1.5 x108 km2.  Solar capacity doubled around every 2 years from 2000 to 2013, growing from 1.25GW in 2000 to 140 GW in 2013 (source:  BP statistical review), reaching a land area of around 1400km2.  217 times its current area takes it past the land surface of the earth, so it would take to 2047 (34 years from 2013) with doubling of installed capacity every 2 years to reach this point.  The source of the story about sword-making is from the 1970s TV documentary The Ascent of Man and accompanying book.

For data on Greenpeace’s historical projections see:

http://www.greenpeace.org/international/Global/international/publications/climate/2012/Energy%20Revolution%202012/ER2012.pdf See pages 69 and 71

 

Tranmission links to enable wind power

The availability of long distance transmission systems can help smooth out variations in availability of wind power, but helps solar less.  Policy needs to enable long-distance links to allow continuing increases in wind generation.

One of the challenges of moving to an electricity system running with a large proportion of wind and solar is that electricity output from these sources is variable, because the wind does not always blow and the sun does not always shine at any particular location.  With small proportions of these sources on the system this is not much of a problem.  However as a system becomes more dependent on these variable renewables, production is potentially curtailed in periods of high output, while there is a shortage of power at other times.  I’ll refer in this post to wind and solar photovoltaic (PV) power, which is by far the predominant form of solar electricity.  The issues with concentrated solar thermal power are different because there is some potential for storage in the power plant.

Difficulties with balancing supply and demand typically begin to become more severe as each type of variable renewable power, for example wind, begins to supply more than (very roughly) around 15% of annual electricity.  In practice the extent of the challenge of integration depends on a range of factors.  One influence is the amount of inflexible generating capacity such as nuclear on the system.  Another influence is the correlation between variable supply and demand.  For example, there is some seasonal correlation between electricity demand and wind output in Europe (in winter demand is higher and it’s windier), and there is some daily correlation between electricity demand and solar PV output in Australia (the demand peak is in the daytime).  Nevertheless, in any case there will be challenges in reliably meeting demand while accommodating very large amounts of variable supply.

To address this problem variable supply can be moved to different times, using storage, and to different places via transmission capacityDemand management can help, especially for a demand peaks, and some thermal back-up capacity is likely to be needed anyway in most cases.

The extent to which transmission links can help system balancing depends on the extent to which generation in different places is correlated.  If distant power sources tend to produce power at different times then transmission can greatly help smooth out variations in production, because when output is low in one location electricity can be moved there from another.  But if distant sources tend to produce power at the same time the advantages of long distance transmission will be reduced, because if output is low in one place there will be little electricity in the other place to move to fill the gap.  This is especially so if patterns of demand are also similar in the different places

Typically, correlations of output across regions for solar PV are much higher than for wind, especially as distances increase (see chart).  This is because solar output tends to depend strongly on time of day and season, which is quite similar even across an area as large as Western Europe, whereas wind varies with weather systems, which are less strongly related over distance of the order of 1000 miles or so.  Looking at the correlations between hourly output in different countries in Western Europe shows that the correlation between solar output in Germany and France is 88%, much greater than for wind at 44%.  Moving further away, the correlation between output in Germany and Spain is close to zero for wind, but still as high as 84% for solar.  The match of solar output is is actually greater than these figures imply due to the large number of times when solar output is zero for both countries.

Correlations of hourly output between different Western European countries are much greater for solar than for wind …

Correlations chart

These factors mean that increasing interconnection will tend to enable higher proportions of wind more than it will enable higher proportions of solar.  (This is assuming transmission is for load balancing.  Interconnection to transport power from sunnier to less sunny regions may well be valuable.  Also, this conclusion would change if intercontinental of transmission of large amounts of power were possible, but this remains a distant prospect.)

Incidentally, the correlation between solar and wind output is negative (when it’s windy it tends to be less sunny and vice versa), so having some of each on the system tends to increase the combined total that can be accommodated, compared with a system only having either one or the other.

A recent study of the USA by the National Oceanic and Atmospheric Administration (NOAA) confirmed very large benefits from High Voltage Direct Current (HVDC) long distance transmission for systems with large amounts of variable renewables.   The study used very detailed weather and load data, and data on existing power plants.  It concluded that with optimistic projections of wind and solar costs it is possible to reduce CO2 emissions by 82% with somewhat lower electricity costs, provided sufficient transmission capacity is in place.  The study emphasised the importance of the transmission network encompassing a large geographical area, such as the 48 contiguous US states, due to the large geographical scales over which weather is variable.

However, interconnectors are not always quick, cheap or easy to build.  They often link or cross different jurisdictions – US States, Chinese provinces or European countries – and will often link different types of electricity trading arrangement.  This can impose substantial barriers around permitting, and also around operation.  Policy can help the growth of wind by reducing these barriers and recognising the growing role of internconnection, although the precise policy measures necessary will be quite locally specific.  Enabling increased transmission is likely to be an important step in enabling the continuing growth of wind power in particular, and is likely to become increasingly urgent as growth continues.

Adam Whitmore – 16th September 2014

References

Thanks to Mathieu Ecoifier for providing the correlation coefficients between wind and solar in Europe.  Correlation coefficients are a rough and ready indicator of independence.  Actual effects on system operation will depend on many factors.

For analysis of the inverse correlation of wind and solar see for example Correlations Between Large-Scale Solar and Wind Power in a Future Scenario for Sweden, Joakim Widén, IEEE Transactions on Sustainable Energy, Vol. 2, No. 2, April 2011

The US study mentioned is Alexander MacDonald et. al., NOAA Earth System Research Laboratory, Low Cost and Low Carbon Energy Systems Feasible with Large Geographical Size (2014) – Presentation at Imperial College London 27th May 2014

The EU’s recent proposal for a 2030 EUETS target does not look very ambitious

The EU’s recently announced greenhouse gas emissions target for 2030 looks like just enough to keep the 2050 target credible, but seems unlikely to be perceived as highly ambitious by other jurisdictions.  

The European Commission has recently proposed a target of reducing EU greenhouse gas emissions to 40% below 1990 levels by 2030.  Sectors covered by the EUETS (power generation and large industry) will be required to reduce emissions to 42% below 1990 levels.  This post takes a look, using some rough-and-ready analysis, at how onerous the EUETS target would be if implemented.   The Commission also announced a proposal to establish a “market stability reserve” for the EUETS.  I will return to this proposal in a future post, but for now the analysis excludes its effect.  The analysis also excludes the temporary delay of allowances sales over the next few years (backloading), which does not affect cumulative totals to 2030 in the absence of the stability reserve.

A target of a 40% reduction by 2030 is on a straight line track from the 20% mandated by 2020 towards the least stringent end of the 2050 target, which is an 80-95% reduction from 1990 levels.  This appears to be the minimum reduction likely to retain the credibility of the 2050 target, especially given the current surplus of allowances in the EUETS.  A smaller reduction by 2030, requiring deeper cuts to be achieved more rapidly towards 2050, would likely have increased the perceived probability that the 2050 targets would not be adhered to.

There is currently a surplus of EU allowances of around 2.2 billion tonnes, equivalent to about one full year of emissions covered by the scheme.   This scale of surplus has arisen mainly due to the severity of the recession in Europe.  Emissions currently remain below the cap, and even as the cap tightens it will take more than a decade for the surplus to disappear.

This is illustrated in the chart below.  The cumulative cap on emissions between now and 2030 (green line) starts at level of the current surplus.  It then increases, but less rapidly each year as the annual cap comes down.  This is compared with the illustrative case of annual emissions are constant at 2012 levels (solid blue line), so cumulative emissions grow linearly.  In this case, with no reduction in annual emissions, the surplus disappears in around 2026.  However in practice power sector emissions are expected to fall over the period (see below), reducing cumulative emissions (dashed blue line).  This leads to the surplus disappearing only in 2029, and reduces the cumulative shortfall by 2030 to quite low levels, assuming emissions from industry are constant.  Aviation is excluded from these totals.  Although internal flights remain covered by the EUETS, the associated cap remains unclear.

Cumulative emissions (excluding aviation) and the cumulative cap (including current surplus) show a deficit emerging only in the late 2020s …

 Cumulative surplus

The power sector is the largest source of emissions covered by the EUETS, so is crucial to demand for allowances.  There may be some increase in electricity demand over the period, and hence in demand for allowances.  The increase may be smaller with strong efficiency measures, or larger if there is very rapid uptake of electric vehicles, and will also vary more generally with GDP growth over the period.  There is also likely to be a decrease in nuclear generation to 2030 as older plant comes to the end of its working life and is not replaced by an equal amount of new plant.

However the growth in demand and fall in nuclear output seem likely to be more than offset by continuing growth in generation from renewables.  This implies a net decrease in the need for fossil generation, leading to lower emissions in the absence of changes to the fossil fuel mix.  However there may be some increase in emissions from internal EU  aviation, although any increase is likely to be much smaller in absolute terms than the decrease from the power sector.  Trends in emissions from industry, assumed to stay constant here, will also affect the total.

Together these trends might lead to a cumulative excess of expected emissions over the cap of around a billion tonnes by 2030 (about 3% of the total), including some growth in emissions from domestic aviation.   Projections of emissions over more than a decade and a half are obviously uncertain, and the cumulative total could easily vary by a billion tonnes or more from this total.  Nevertheless, it seems likely that the shortfall in allowances cumulatively over the period will be somewhere in the low- to mid- single figures percent of the total over the period, with the market remaining in surplus until the late 2020s.   The additional abatement required to eliminate the shortfall in this case could be achieved by a moderate amount of fuel switching.  And scenarios where a surplus of allowances persists through to 2030 are not hard to construct.  (The shortfall is somewhat increased if you take the view that there is a permanent stock of allowances needed to enable hedging in the market,  Some estimates indicate that this is around a billion tonnes, which would increase the shortfall to around 6% in the scenario above.  However it is by no means clear that this is needed through the 2020s, and anyway it remains easily accommodated by fuel switching,  Conversely around an extra 800 million allowances unused from the New Entrant Reserve  may come into the market at the end of Phase 3 in 2020, further reducing any shortfall )

Any substantial scarcity that does emerge seems likely to be as a result of banking of allowances into the period after 2030, either as a result of private sector banking or the operation of the market stability reserve, which effectively mandates a certain amount of banking of any large surplus.

The EU’s apparent intention to (just about) keep on a track towards its 2050 targets is surely welcome.  However the proposed 2030 target for the EUETS thus does not seem very demanding.  It seems unlikely that such a cap will be to be taken by other countries as a sign of strong EU leadership on emissions reduction.  It also seems unlikely that the EUETS alone will become effective at stimulating large scale investment in low carbon technologies over the next decade and a half.  This risks endangering progress to reduce emissions after 2030.  Additional policy instruments will likely be needed if the EU is to succeed in building the low carbon infrastructure needed to put itself on a path to largely decarbonising its economy by the middle of the century.

Adam Whitmore  –  14th February 2014

Notes on data and assumptions  

The 40% target requires a 20% point reduction by 2030 from the already mandated 20% cut due by 2020.  If this were followed by 40% points (40% down to 80%) over the subsequent two decades an 80% cut would be achieved by 2050.   20% of 1990 levels per decade thus takes the cap towards the top end of the 2050 target range of an 80-95% cut by 2050.

2012 emissions include the industrial emissions additionally covered in Phase 3.  Emissions from large industry are assumed to remain constant over the period.  The linear reduction factor is assumed to increase from 1.74% p.a. to 2.2% p.a. in 2021.

The estimates of power sector trends are based on the IEA 2013 World Energy Outlook New Policies Scenario.  This scenario shows demand growth in EU power generation of 0.4% p.a. over the period, leading to an additional 260TWh of generation by 2030 compared with 2011.  It also shows a decline of 10% in nuclear, but his may include optimistic assumptions about new build.  A decrease in nuclear generation of 20% (180 TWh p.a.) seems plausible, and I’ve used this estimate.  This leads to potential additional demand from fossil generation of 440TWh (260TWh + 180TWh).  The IEA estimates that generation from renewables, including hydro, will approximately double between 2011 and 2030, increasing by 730TWh p.a..  This leads to a net reduction in demand for fossil generation of around 290TWh (730TWh – 440TWh) by 2030.  The estimate of the saving takes account of the profile of these trends, for example the more rapid fall-off in nuclear in the 2020s.  Additional TWh of low carbon power are assumed to reduce emissions by 0.4t/MWh, equivalent to displacing mainly gas. 

The electricity sector projections take their base year as 2011 while the emissions data base year is 2012, but this is taken account of in the calculations. 

Internal aviation emissions are currently around 84 mtpa, but the position of aviation within the EU post-2020 is currently unclear.  The calculations assume that international aviation is dealt with under a separate agreement through ICAO, or not at all. 

The calculations exclude any additional reductions if other jurisdictions take action.  Any reductions in the cap due to international action may in any case be accompanied by increased use of offsets within the EU.