environmentalresearchweb blog
May 18, 2013
Nuclear & Renewables: Backup/Grid Costs
A study by the OECD Nuclear Energy Agency (NEA) Nuclear Energy and Renewables: System Effects in Low-carbon Electricity Systems, looks at the interactions of variable renewables and ‘dispatchable’ energy technologies, such as nuclear power, in terms of their effects on electricity systems. The report focuses on “grid-level system costs”, the subset of system costs mediated by the electricity grid, which include the costs of extending and reinforcing transport and distribution grids as well as connecting new capacity, and the costs of increased short-term balancing and maintaining the long-term adequacy of supply.
While all technologies generate system costs, those of dispatchable generators are seen as at least an order of magnitude lower than those of variable renewables. The study says that ’ the system costs of variable renewables at the level of the electricity grid increases the total costs of electricity supply by up to one-third, depending on country, technology and penetration levels’. While grid-level system costs for dispatchable technologies are claimed to be lower than $3/MWh, they can reach up to $ 40/MWh for onshore wind, up to $ 45/MWh for offshore wind and up to $ 80/MWh for solar.
Their UK data is as follows:
The back up cost is put at zero for nuclear, $4.05/MWh for wind at 10% market penetration, $6.92 at 30% penetration; $26.08 and $ 26.82 respectively for PV solar Balancing cost is put at $0.88 (@10%) and $ 0.53 (@30%) for nuclear; $7.63(@10%) and $14.15 (@30%) for both wind and solar
Grid connector costs are put at $2.23/MWh for nuclear, $3.96 for on land wind, $19.81 for offshore wind, $15.55 for PV.
Grid reinforcement and extension costs- zero for nuclear, $2.95/MWh ((@10%) and $5.20 (@30%) for on land wind, $2.57 (@10%) and $4.52 (@30%) for offshore wind, $8.62 (@10%) and $5.18 (@30%) for solar
Totals: Nuclear $3.10 /MWh (10%) $2.76 (30%) On land wind $18.60(10%) and $30.23 (30%) offshore wind $34.05 (10%) $45.39 (30%), PV solar 57.89 (10%) and 71.71 (30%)
So at 30% penetration, they say wind can cost at least ten times more, PV 20 times more than nuclear! Are they right? The nuclear costs look very low. In its 2010 study of the cost of maintaining adequate frequency response via the grid Balancing Services Incentive Scheme (BSUoS), National Grid estimated that ‘the risk imposed by six additional 1800 MW [nuclear] power stations on the system could increase from £160m to £319m’. That works out at about $3.2 /MWh, assuming an 80% load factor. Not $0.53-0.88.
And some of the figures for renewables look very high. The extra cost for onshore wind backup and balancing services has been put by Milborrow at up to $4/MWh for contributions to supply of up to 20%, and up to £11.3/MWh for a 40% contribution. Not ~ $21 (at 30%)! In any case, the cost will depend on what measures are used to ensure balancing- output from gas plants is only one option e.g. interconnector links with the continent could lead to wider system benefits, exporting excess UK wind power. A big £bn p.a income gain. By contrast having nuclear on the grid imposes some costs. If it has to be run 24 7 then some output from renewables may have to be curtailed (i.e wasted) at low energy demand times. It is possible to vary the output from nuclear plants to some extent, but that too imposes operational losses and costs.
The NEA says that, currently, grid-level costs are absorbed by consumers through higher network charges and by the producers of dispatchable electricity in the form of reduced margins and lower load factors. It says ‘Not accounting for system costs means adding implicit subsidies to already sizeable explicit subsidies for variable renewables. As long as this situation continues, dispatchable technologies will increasingly not be replaced as they reach the end of their operating lifetimes, thereby weakening security of supply.’
They add ‘Maintaining high levels of security of electricity supply in decarbonising electricity systems with significant shares of variable renewables will require incentives to internalise system costs, as well as market designs that adequately remunerate all dispatchable power production, including low-carbon nuclear energy’
So it comes down to the simple message that renewables are a bad idea and if we persist in using them, then technologies like nuclear will need extra support and protection!
Of course you could argue that if you don’t have nuclear then the problems are much less-it is not too much use for balancing after all, and there are plenty of good balancing options. The NEA however are unable to contemplate heresies like this. They simply say ‘significant changes will be needed to generate the flexibility required for an economically viable coexistence of nuclear energy and renewables in increasingly decarbonised electricity systems’. Although actually they see co-existence as problematic ‘In systems that currently use nuclear energy, the introduction of variable renewables is likely to lead to an increase in overall carbon emissions due to the use of higher carbon-emitting technologies as back-up.’
Really? Surely when wind is high, we wont be burning gas so, even if there are some emissions from gas plants run when wind is low, there will still be a large overall carbon saving. There is certainly a cost to providing backup, although it can clearly be exaggerated. Most of the backup plants needed for now and for a couple of decades ahead already exist, so it’s just their occasional use of fuel that costs extra. Longer term we might need a few more, though that wont will be just for balancing- we may need them anyway to replace old plant. In a report to the Committee on Climate Change, in March 2011, consultants Poyry noted that, in a scenario with renewables supplying up to 94% of UK electricity by 2050, new peaking plant would not be needed until after 2030, and that by 2050 around 21GW would be needed. And, over time, we can switch to balancing with biogas and green gas generated from excess wind to avoid all fossil emissions.as was perused in the Pugwash report. www.britishpugwash.org/recent_pubs.htm
Developing radically new systems like, along with smart grids and supergrids, will certainly cost money, but will balance supply and demand, provide us with a way to switch to renewables, reduce the use of ever more costly fossil fuel and avoid the costs and risks of nuclear. Not something NEA would like! http://www.oecd-nea.org/press/2012/2012-08.html
May 11, 2013
Renewables- a state of play review
I have just finished writing a new book entitled ‘Renewables’, which should be out later this year. It looks at the state of play around the world, drawing in part on this Blog. There is a lot of technological progress to report, and lot of inspiring plans. Some renewables are already competitive with conventional sources in some locations, and many more may well be soon. The down side is that, despite good progress, globally the climate policy picture is still grim. The use of coal is expanding, undermining emission reductions. In the absence of tight, globally agreed, emissions targets, market trading arrangements like the EU Emission Trading System are not very effective. Indeed the EU-ETS seems to be near collapse, with carbon credits trading at 2.6 euro/tonne.
Fortunately the feed in tariff approach seems to be spreading, and that is much more effective, as I report in my new book. Soon we should have 300GW of wind in use globally and we have just passed 100 GW of PV solar, with FiTs helping a lot. The retreat from nuclear in some countries is also helping, although the nuclear v renewables issue continues to rumble on, and I have covered it briefly in the new book. The simple point is that most renewables are getting cheaper, moving down their learning curves well, while nuclear is displaying a negative leaning curve,with costs rising. In parallel, the Energy Return on Energy invested (EROEI) ratio for nuclear is low (around 15:1) and is likely to fall as uranium ore grades decline (maybe to 5:1 or less) while the EROEI’s for renewables are all higher and improving (pv solar up to 20:1, CSP 40:1, wind up to 80:1,hydro 200:1 or more).
Renewables do have their problems (e.g they are mostly diffuse and variable) and much of the new book looks at how they might be overcome. It covers grid integration issues, supergrid links, and so on. I hope I have managed to get the balance right, being realistic about what can be done, while still conveying a positive message.
I will be interested in reactions.
(A short blog this week, as I’m on holiday in Spain)
May 3, 2013
Supergrids still on the agenda
The aim of the German led Desertec Industrial Initiative is to support and link up solar and other renewable energy projects in the desert areas of North Africa and the Middle East via supergrids, with some power being brought back to the EU. Certainly many countries in the region are embracing solar, including Morocco, Algeria, Tunisia, Saudi Arabia, Egypt, UAE, and Jordon. Egypt already has a large Concentrated Solar Power (CSP) plant just outside of Cairo, and also a significant wind programme. Qatar is to invest up to $20bn in a 1.8GW solar plant, scheduled for 2014. Tunisia is developing a 2 GW CSP project. Morocco also has ambitious plans for CSP, and the Saudi’s plan to have 41GW of PV/CSP solar capacity by 2032, via $109bn programme. Whether its CSP of large scale focused PV (CPV) it seems to be a booming area: Algeria, which already has a 130MW hybrid CSP plant, took out a full-page ad in the Financial Times last November, which proclaimed that Algeria was “creating the path beyond oil”.
However, these projects may well just stay as local energy suppliers, at least for a while. According to a report last year in European Energy Review (29/11/12), the success of Germany’s Energiewende green energy programme has led some of Desertec’s original supporters, like Greenpeace Germany and the German Greens, to conclude that Germany doesn’t need Desertec. Even Germany’s environment minister Peter Altmaier said recently that ‘Desertec has become much less important since Germany’s renewables boom.’ The European Energy Review report concluded ‘Germans may see Desertec as a welcome helping hand, they do not view it as a crucial part of their Energiewende’.
Siemens and Bosch pulled out of the Desertec programme last year, but Desertec remains confident given that it still has wide industrial support (including from E.ON and ABB) and it is still working with and supporting projects in North Africa, with CSP being only one of the options- there is also a huge wind potential in the region. There are also new potential project links elsewhere, for example in Asia. One such envisages HVDC supergrid links to wind projects in Mongolia, while, separately, the Gobitec initiative proposes links to CSP projects in the Gobi desert. http://www.gobitec.org/ and www.desertec.org/press/press-releases/1210 24-01-wind-power-from-the-gobi-desert/
Even more ambitiously, why stop at just generation? Although HVDC can be very efficient at shifting power long distances, there may be local excess generated at times, so why not store it until demand at the other end of the link is high? This could avoid grid congestion problems, which some see as becoming an issue, although initially more in the EU than at the source end of the grid: www.sciencedirect.com/science/article/pii/S0378779612003197
However, with large projects, local storage might be very valuable. There is the option of creating vast new lakes in depressions in desert areas for seawater storage and pumped storage operation using power from Concentrated Solar Power plants. The huge below-sea-level Qattara Depression in Libyia might be a possible site, or the Danakil Depression in Eritrea /Ethiopia. That’s pretty speculative, but if an when CSP or CPV gets going on a significant scale, it might prove worthwhile: http://elpipes.blogspot.co.uk/2011/01/pumped-storage-at-danakil-depression-in.html
Perhaps a little less fanciful, there is a very large renewable energy potential in Northern Russia and Siberia, which might be exploited. Despite the huge wind potential, put at over 350GW, Russia has a very small renewable energy programme aiming to supply 4.5% of its electricity by 2020, with only around 11MW of wind capacity so far, and although it’s now planning to expand that a bit, to 150MW, it is still clearly leaving most of it untouched. Instead it is focusing on exporting gas and developing nuclear power. But there have been suggestions that opportunities exist for exporting ‘green’ energy from Russia to the EU, which might help stimulate development of its huge renewables resource more rapidly.
A recent paper in Energy Policy argued that ‘EU-Russian cooperation in the renewable energy field would present a win-win situation: (EU) Member States could achieve their targets on the basis of Russia’s renewable energy potential, while Russia could begin to develop a national renewable energy industry without risking potential price increases for domestic consumers—a concern of great political sensitivity in Russia.’
Some of this might simply involve importing biomass from Russia, but there is also the option of electricity imports via new supergrid interconnections, although clearly there are huge political and economic issues involved. See ‘RUSTEC: Greening Europe’s energy supply by developing Russia’s renewable energy potential’, Anatole Boute, Patrick Willems, Energy Policy 51(2012) 618-629.
Long distance transfer using High Voltage Direct Current grids is quite efficient (with energy loses of around 2% /1000km compared to maybe 10%/1000km for conventional AC grids), butt there are plenty of problems with the supergrid idea, not least its high initial high capital cost. And for schemes like Desertec to work there will be need for careful local negotiation over way leaves and, for the local generation plants, over the distribution of costs and benefits: see http://www.spiegel.de/international/europe/competitors-and-local-opposition-threatens-desertec-solar-plan-a-892332.html. But the Desertec scheme only envisages most of the CSP power being used locally -only 15 % being sent to the EU, so local use would dominate.
Despite the problems, enthusiasm remains high. In a joint declaration last year the Desertec Industrial Initiative and Medgrid, the French led transmission group, along with lobby groups like Friends of the Supergrid, the Renewables Grid Initiative and the Climate Parliament group, said there could be ‘No transition without transmission’, and backed grid upgrade links across the EU and to and in nearby regions. See, www.medgrid-psm.com/en/
Political and economic pressures may slow them but supergrid projects of various kinds seem bound to spread as more renewables are added to networks. There are already plans for linking up wind projects in and across the north sea; given it huge renewables expansion programme, Germany need to reconfigure and strengthen its national grid system; enthusiasts in Japan are looking to supergrids to help top up and balance their new renewables programme; and China is building large HVDC links to integrate in its massive hydro and wind projects. And there is the ambitious Atlantic Wind Connection offshore grid proposed for off the east coast of the USA, linking up 7GW of offshore wind projects: http://atlanticwindconnection.com/
It may be developed piecemeal, and a long way from some of the wilder dreams about global supergrids, but the elements of regional supergrid systems look like they will emerge.
Mathematics of Planet Earth Year - free content
The IOP Publishing journals Nonlinearity and Inverse Problems, from the same stable as environmentalresearchweb and ERL, have made all content relevant to the Mathematics of Planet Earth Year free to read.
To read these recent papers, along with additional information from authors, for free, head to Nonlinearity or Inverse Problems.
April 27, 2013
UK Marine Renewables
A report by RenewableUK says the Electricity Market Reforms could act as a springboard for the growth of wave and tidal energy, or could undermine investor confidence in marine power at a crucial stage of the industry’s development. It also highlights challenges such as delays in getting grid connections for wave and tidal projects, and the high cost of transmission charges.
The report, “Conquering Challenges, Generating Growth”, lays out the progress made so far: 12 full-scale single devices with a capacity of 9 megawatts deployed in UK waters generating clean electricity - more than the rest of the world combined. It notes that commercialisation of the tidal sector is just around the corner, with the deployment of the first arrays (multiple devices) beginning in 2014, and an expected increase to 100-200MW of wave and tidal installed by 2020. Major engineering firms such as Siemens and Alstom are working with the UK and Scottish Governments, universities and electricity companies to develop British marine power. The Crown Estate has awarded leases for more than 1.8 gigawatts of capacity at nearly 40 sites in UK waters. The British Isles has 50% of the total European wave energy resource and 25% of tidal energy resource - these technologies could generate up to 20% of the UK’s electricity needs. Based on independent research, RenewableUK estimates that wave and tidal energy could be worth £6.1 bn to the UK by 2035, creating nearly 20,000 jobs - up from the 1000 employed now
However, this growth could be stifled if the Government fails to get the details of Electricity Market Reform right. The most crucial factor is the level of financial support technologies will receive. The report states that the initial strike price for the first generation of tidal arrays should be set at £280 to £300 per megawatt hour. For wave technology, the initial strike price should be £300 to £320/MWh. This will catalyse the marine energy industry, leading to economies of scale and learning through experience, which will lower the strike price for the second generation of arrays in 2018. Also, under EMR, contracts would only last for 15 years - the report argues that this must be extended to 20 years to give investors an adequate return - otherwise the strike price would have to be higher. It’s notable that there is talk of EDF being offered 40 year CfD contracts for its nuclear projects.
RenewableUK’s Wave and Tidal Manager, David Krohn, said: “The wave and tidal energy industry has reached an exciting period as it moves from single device demonstrator projects to the first small proving arrays. The world’s leading projects are being developed in the UK waters thanks to a comprehensive package of support granted by the UK and Scottish governments, which has ensured that the UK leads the world in wave and tidal energy. However, there are significant hurdles that need to be overcome to ensure the sustained growth of the industry. It’s time to get real about the potential risks so that we can work with Government and others to find the solutions as early as possible. Wave technology in particular will need tailored capital support in the coming years if we are to maintain pole position in this promising and strategically important sector. It is essential that Electricity Market Reform provides a level of support that will allow the most cost effective projects to be taken forward.’ www.renewableuk.com/en/publications/index.cfm/wave-and-tidal-energy-in-the-uk-2013
It is true that wave and tidal stream technology is still relatively expensive, but costs are falling, thanks to the support via the revised Renewables Obligation and special development grants, amounting in all to 25-30p/KkWh. By contrast, onshore wind gets 10p/kWh or less and offshore wind 15-17p/kWh. Max Carcas, previously a device developer with Pelamis, told the Financial Times (28/1/13).’While 25-30p/kWh seems quite expensive it is often forgotten that there has never been a new energy technology that has been economic ‘out of the box. The cost of generating from wind and solar energy has fallen by about 80 % since the mid-1980s, The fact that the opening costs of marine energy are lower than many preceding energy technologies puts this sector in a very good position to be competitive in the longer term.’
So it is good to hear that the Crown Estate is investing up to £20m in two new wave or tidal energy projects. The funding will be used to construct arrays (multiple devices). Projects with an installed capacity of at least 3 MW are eligible to apply, as long as they are expected to reach final decision on investment by March 2014. RenewableUK said: ‘The funding will accelerate a crucial step forward - from successful individual devices to the deployment of full-scale arrays in the water. It will also help to attract the right level of private investment to commercialise the sector’
In parallel, two tidal power projects in north Wales and Scotland are to receive grants worth £10m each. Sea Generation Wales, a joint venture between Siemens, and RWE,, will develop a 10MW project off Anglesey, with five 2MW of MCT’s SeaGen type generators, running by 2015, while MyGen, in a joint venture between Morgan Stanley and International Power, an independent power generation company, will develop an 86MW project in the Pentland Firth between the northern Scottish mainland and the Orkney Islands. This is the first phase of a 400MW array which will feature the turbines developed by Atlantis Resources and Tidal Generation Limited, the partly Rolls Royce initiated project now owned by Alstrom. More should follow. For example Siemens, is planning a MCT SeaGen project at Kyle Rhea in the Orkneys, expected to be operating tidal farms of 20MW to 50MW by 2020.
But it’s not all good news. Neptune Renewable Energy’s Proteus tidal stream ducted- vertical axis turbine has been found to be technically flawed and therefore not commercially viable. Their full-scale demonstrator was deployed in the Humber estuary in January 2012 and has been subject to much testing and a number of modifications. But it became apparent that the device would not be able to achieve a high enough level of electrical output, despite indications to the contrary resulting from earlier work done at fortieth and tenth scale. The plan was to supply the Deep marine attraction in Hull with around a third of its power.
The company said ‘Since November, a significant amount of work has been carried out, some independently, to establish the reasons for the technical problems and to understand whether the company was facing issues of adjustment and tuning, rather than a challenge to the overall concept of using a vertical axis turbine within a duct, in estuarine locations. This work has included looking at an alternative lift turbine, rather than drag turbine,” said the company’. But having looked at the options they have decided to abandon the project and liquidate the company. Source www.neptunerenewableenergy.com/
More positively, Pulse Tidal has secured a site for its 1.2MW commercial demonstration of its oscillating double hydrofoil system at the SW Marine Energy Park, Lynmouth. That’s a very novel design, so it will be interesting to see how it fares.
April 20, 2013
Biomass battles
The ‘Dirtier than Coal’ report from Friends of the Earth, Greenpeace and RSPB, argued that burning trees would produce more CO2 net than burning coal, in part due to the delay before CO2 was reabsorbed by new planting. See my earlier Blog: http://environmentalresearchweb.org/blog/2013/02/biomass-burning—worse-than-co.html and www.rspb.org.uk/Images/biomassreporttcm9-326672.pdf
It referred to a report by North Energy Associates (NEA) and Forestry Research (FR) produced for DECC, which tried to answer the question: ‘Is it better to leave wood in the forest or harvest it for timber, other wood products (e.g. panel boards) and/or fuel?’ They concluded that: ‘Management of UK forests for wood production can contribute to UK carbon objectives e.g. to 2050…Using wood for bioenergy can also reduce carbon emissions, compared to burning fossil fuels for energy….These results suggest that policy should support managing UK forests to produce wood for products and bioenergy’.
However, the NEA/FR report specifically rejected the ‘whole tree burning’ scenario picked by the FoE/Greenpeace/RSPB report’s researcher Tim Searchinger, in favour of using trimmings, offcuts and other wastes with no other market: www.gov.uk/government/uploads/system/uploads/attachment_data/file/48346/5133-carbon-impacts-of-using-biomanss-and-other-sectors.pdf
The Biomass Energy Centre, which is a government backed advice and information agency, has produced a critique of the Searchinger study, which it says ‘appears to have been neither peer-reviewed nor submitted to any journal for formal publication, contains no new research but numerous factual errors and misinterpretation’. For example, he ‘chooses just one scenario from the peer reviewed study by FR and NEA for DECC, amongst the hundreds examined,’ allowing him ‘to allege that biomass is “dirtier than coal”, ignoring all the other scenarios that show carbon saving benefits in the form of lower GHG emissions ranging from marginal to very substantial’.
The Biomass Energy Centre says.’The DECC study shows that there are many ways of using forests and that, for managed forest in the UK, almost all of the scenarios provide considerably greater GHG emissions reductions than simply leaving the trees unharvested. It also shows that there is an unrealistic scenario, selectively picked by Searchinger, which is slightly less good under certain circumstances, in GHG emissions terms, than leaving them unharvested. This scenario does not make economic sense, and does not represent UK practice. In addition, the UK government sustainability requirements demand genuine GHG emissions reductions, so this scenario would not attract government support in the form of ROC payments and, hence, there is no incentive to power generators to use it’.
The Biomass Energy Centre point out that UK sawmill practice basically involves the selection and use of timber of sufficient size and quality for construction or joinery, purposes, and it backs this approach as being both economically and environmentally sound. The left overs have many uses including for paper, wood-based panels and sometimes for fuel. They insist that the use of whole trees including all of the roundwood for energy in the UK is simply not an economically realistic approach. What may be viable is the use of forestry thinnings, chips, sawdust, offcuts, etc. In addition, ‘Broadleaf trees also have a significant proportion of branches (conifers typically much less), while conifer tops taper to wood of small diameter. If these types of wood are not used for wood-based panels (for which they are not always suitable), paper or energy, they will simply be disposed of, and will still break down to carbon dioxide. Consequently the appropriate use of these types of wood for energy, displacing fossil fuel, is beneficial.’
They note that ‘the research undertaken by FR and NEA for DECC and related research by FR clearly demonstrates that the production of mixtures of sawn wood, wood-based panels, paper and fuel (including a proportion from small, young thinnings as whole trees) results in significant overall greenhouse gas benefits’.
Clearly, although they don’t meet the re-absorption delay issue head on, they don’t see using marginal and left over wood as a problem, and also claim that, even if biomass fuel prices rose, that would be unlikely to divert high value timber from other markets, so it would not be a problem for other uses of wood, including those which ensured continued carbon sequestration. www.biomassenergycentre.org.uk
One time Greenpeace and FoE senior energy campaigner, Stewart Boyle, now active in the biomass industry, also joined in the critique. He produced a heartfelt Blog for the Renewable Energy Association claiming that the NGOs had got it badly wrong. He also saw the co-firing of wood chips in coal plants like Drax as a helpful interim step and was worried about DECC’s attitude. www.r-e-a.net/blog/modelling-our-way-to-biomass-paralysis-22-03-2013
Not everyone thinks that importing wood chips from North America to co-fire in large old inefficient coal plants like Drax is a good idea. The High Renewables scenario for 2050 produce for British Pugwash avoided all biomass imports: www.britishpugwash.org/recent_pubs.htm
But in the interim some might be condoned, while we get busy developing smaller scale high efficiency Combined Heat and Power plants, linked to district heating networks, and fed by UK sourced biomass or biogas. Short Rotation Coppice still has its advocates, while AD biogas production from farm and food wastes has a lot of attractions.
The latter would avoid land use conflicts, but if we want to go for green gas and biomass in a big way they may not be avoidable. The Pugwash 70% renewables scenario had 10% of UK land area being used for biomass by 2050, with the implication being that faming practices and diets might have to change. But 2050 is a long way off and by then we may well be generating (and storing) synthetic green gases, using the excess electricity that wind, wave and tidal projects will generate, when energy demand is low, to power electrolysers. Germany has started doing that now, in part as a way to balance variable renewables like wind and PV solar. But this ‘power to gas ‘idea also helps avoid excessive land use for biogas production, with an extension being to use CO2 captured from the air to convert electrolytic hydrogen into methane. See, for a UK input by ITM: http://www.itm-power.com/wp-content/uploads/2013/04/Platts-April13.pdf
Meanwhile, although burning trees is out of the question, we do need to see what biomass can offer. UKERCs estimate for SRC was 4% of UK electricity and that’s just for starters. http://www.ukerc.ac.uk/support/tiki-index.php?page=Biomass+Resources+and+Uses
April 13, 2013
Heat pumps v CHP/DH
There has been a long and interesting debate over whether Heat Pumps or Combined Heat and Power plants linked to district heating networks are the best option for efficient low carbon home heating.
In theory a heat pump, working like a refrigerator in reverse, can deliver heat with around three times the energy value of the electricity fed in to run it, though in practice they may not always achieve these high levels of return, especially in cold damp weather (Roy et al, 2010). But heat pumps do offer a way of upgrading low-grade heat, from whatever source, including the air, ground, water, direct solar and geothermal, and if they are run using electricity from renewable energy sources, their carbon emissions will be low.
Steam-raising thermal power plants by contrast are much less efficient. However they can be operated in Combined Heat and Power (CHP) mode, so that some of the heat that would otherwise be wasted in the conversion process is captured for use in district heating networks (DH). CHP/co-generation can increase the energy conversion efficiency up to 80% or more, compared with around the 35% typical of conventional stream raising plants, and so it makes a lot of sense, as long as there is a suitable local heat load e.g. a city or urban area. It has been claimed that CHP plans linked to district networks are far more efficient than heat pumps, especially small domestic scale heat pumps.
Heat pumps have an energy output/input Coefficient of Performance (COP) of maybe 3, but since they are using some of the heat that would otherwise be wasted, CHP plants linked to DH can deliver a COP equivalent of up to 9, or more, depending on the grade of heat that is required (Lowe 2011). And if CHP plants use a renewable source of heat, like geothermal or biomass, their carbon emissions, already low/kWh, should be even lower, and cost less/tonne of CO2 saved than heat pumps (Kelly and Pollitt 2009). Though, there is some debate on this; it may depend on the carbon content of the electricity used by the heat pump and the grade of heat that you want out (Woods 2011; MacKay 2013).
It is true that installing district heating (DH) mains can be disruptive, more so than installing heat pumps in individual houses. But once installed and linked to the central heating radiators of houses and other buildings, unlike with domestic heat pumps, there is no in-house device to maintain. Moreover, once installed DH pipes can be fed with heat from any source, as they become available, including solar and geothermal energy and it become a major infrastructure asset. That helps make large scale solar heating linked to heat stirs viable in Denmark- it’s claimed to be much more economic than individual house solar heating, if you already have the DH network.
Note also that heat can actually be sent quite long distance without significant losses: for example Oslo’s district heating network is fed via a 12.3 km pipe from a waste burning plant in the city outskirts, and in Denmark there’s a 17km link from a CHP plant to the city of Aarhus, while heat is delivered by a 200 MW capacity heat main to Prague from a power station 65 km away.
With a CHP/DH system at Odense claimed to have a COP equivalent of near 12, three times that of a heat pump, surely CHP/DH wins hands down? Well no, sadly it’s more complex than that. These systems are not operating in a vacuum. If there is a lot of spare electricity available at night (e.g. from a large nuclear and/or wind programme) then heat pumps can use it, and in off- gas grid areas, which are also to be unlikely to be candidates for DH, domestic heat pumps can be very useful .
It has also been pointed argued that, while CHP may convert 1 unit of combustible fuel into, typically, 0.5 units of heat and 0.3 units of electricity, and so is overall 80% efficient, a heat pump converts 1 unit of electricity into ~2 or more units of heat, so its 200% efficient. Ah, but where did the electricity come from? If it’s from a fossil or nuclear plant running at 35% efficiency, you are back down to 70%. And retaliating further, the CHP buffs say that, in theory since CHP delivers heat that would otherwise be wasted, its COP is infinite- since it gives us heat for no new fuel input!
It certainly can get complicated. For CHP operation, taking heat out from the near final stages of a power turbine reduces its electrical generating efficiency slightly, but to confuse things further, stream is sometimes taken off at several stages at different temperatures- and times. So there is no one efficiency figure: CHP plants can vary the heat to power ratio depending on market and weather conditions. And of course you can use heat pumps with heat from CHP! And big heat pumps can be good in some locations, taking heat from rivers, lakes or even the sea, as is done in Sweden. The debate goes on…
References
Kelly, S. and Pollitt, M ((2009) ‘Making Combined Heat and Power District Heating (CHPDH) networks in the United Kingdom economically viable: a comparative approach’ Energy Policy Research Group, Cambridge University: EPRG Working Paper 0925: www.eprg.group.cam.ac.uk/wp-content/uploads/2009/11/eprg09251.pdf
Lowe, R (2011) ‘Combined heat and power considered as a virtual steam cycle heat pump’, Energy Policy Volume 39, Issue 9, pp 5528-34 http://dx.doi.org/10.1016/j.enpol.2011.05.007
MacKay, D (2013) ‘Sustainable Energy without the Hot Air’- on line book, p147 et passim http://www.withouthotair.com/
Roy, R., Caird, S. and Potter. S (2010). ‘Getting warmer: a field trial of heat pumps’, The Energy Saving Trust, London.
Woods, P and Zdaniuk, G (2011) ‘CHP and District Heating - how efficient are these technologies?’ CIBSE Technical Symposium, DeMontfort University, Leicester UK 6/7th September
April 12, 2013
EGU2013: tree spotted in poster halls
It’s not often you see vegetation at the Austria Center Vienna, particularly inside the poster halls. But this year Rolf Hut of Delft University of Technology in the Netherlands positioned one of his research subjects, a tree, next to his poster display.
Whilst an unexpected encounter with plants can be pleasant for conference delegates, for those interested in measuring the moisture content in the top 5 or 6 cm of soil by satellite, vegetation can be a problem. The water it contains may be a source of noise in the radar backscatter signals they need, particularly as plants’ water content tends to fluctuate during the day.
And that’s where the tree comes in. Hut and colleagues are measuring the natural vibration frequency of trees in order to assess changes in their water content. Assuming the tree has a constant stiffness, any alteration in this frequency indicates a change in mass, and hence water content.
By ‘plucking’ the tree, which had accelerometers attached to its trunk, Hut was able to show delegates the principle of his technique. The oscillation data provided by the accelerometers enabled calculation of the tree’s Eigenfunction, or natural frequency. Leaving the tree in the wind would also see it start to oscillate at its natural frequency, Hut said.
Hut’s colleague Bouke Kooreman has been testing the approach in Ghana, where good satellite data are available.
Ultimately, understanding how vegetation water content changes during the day and its effect on radar backscatter could not only help remote soil moisture measurements but also provide a new technique for measuring plant water stress remotely.
Hut, whose work was featured in the session on ‘Innovative techniques and unintended use of measurement equipment’, has also used the Kinect motion detector for the Xbox 360, which incorporates a 3-D scanner, to improve the accuracy and efficiency of determining in situ soil moisture content.
April 11, 2013
EGU 2013: climate change hard to reverse
It’s early days, but scientists are developing techniques to remove carbon dioxide from the atmosphere, either directly through technologies such as artificial trees or, less directly, by biomass burning with carbon capture and storage. Even if these methods are implemented, however, the Earth will feel the temperature effects of climate change for centuries to come.
That’s according to Andrew MacDougall of Canada’s University of Victoria, who gave a press conference at the European Geosciences Union’s General Assembly in Vienna. His simulations using the University of Victoria Earth-System Climate Model indicate that without any artificial carbon removal, and assuming that fossil fuels run out, around 60-75% of near-surface warming will remain 10,000 years into the future.
With a middle-of-the-road scenario for carbon dioxide removal, however, a 20th century-like climate could be restored by the late 24th or early 25th century, MacDougall found. But simulated surface air temperature would still be above the pre-industrial temperature by the end of the 30th century, even for the fastest carbon removal scenario he modelled, as oceans gradually release their stored heat.
Restoring climate will require removal of more carbon from the atmosphere than was originally emitted by man, MacDougall said. In some scenarios, 115-190% of anthropogenic emissions will need to be sequestered. Currently land and the oceans remove around half of the carbon dioxide man emits to the atmosphere each year. Once atmospheric carbon levels fall, this stored carbon will start to emerge. In addition, melting of permafrost as temperatures rise has released methane and carbon dioxide to the atmosphere. “There’s no easy process to put this back in,” said MacDougall.
The simulations indicate that it’s much easier to return ocean pH levels to normal than temperatures. But sea-level rise from melting of the Greenland ice sheet seems largely irreversible - while atmospheric carbon levels of less than 350 ppm could stabilise the ice sheet, water from the oceans would only be refrozen into the ice very slowly.
MacDougall simulated carbon concentrations that followed the representative concentration pathways RCP 2.6, 4.5, 6.0 and 8.5 used in the IPCC’s forthcoming fifth assessment until they reached their peak, in 2050, 2150 and 2250, respectively. Then he reduced carbon concentrations at the same rate that they had increased, as well as restoring pasture and croplands to their pre-industrial area.
April 10, 2013
EGU 2013: stormy times ahead
Thunderstorms are getting stronger and more frequent, according to Eberhard Faust of Munich Re, speaking at a press conference at the European Geosciences Union General Assembly in Vienna.
In 2011 losses from thunderstorms east of the Rockies reached a record value of $47 billion, with two cities hit by outbreaks. For comparison, Hurricane Sandy caused losses of $60 billion.
Together with scientists from the German Aerospace Center (DLR), Faust examined data for severe US thunderstorm losses east of the Rockies from March to September each year from 1970 to 2009. Both the mean level of loss and the variability went up. Some have ascribed this rise to an increase in the value of building stock. But by correcting for socio-economic changes, Faust found that the change was due to altered thunderstorm activity.
Faust sees this increase in thunderstorm activity as due to changes in climate, which have boosted humidity at low levels of the atmosphere and increased seasonal aggregated potential convection energy. These storm changes are consistent with the modelled effects from manmade climate change, he said, but he currently can’t make a call on whether they are down to natural climate variability or to man.
To come up with the results, which are published in Weather, Climate and Society, Faust and colleagues looked at thunderstorm severity potential, a measure of the potential energy in the atmosphere available for convection, and the strength and direction of the wind between ground level and 6 km. The team counted occurrences of thunderstorm severity potential of more than 3000 J per kg. The mean value of occurrences increased by a factor of two between1970-1989 and 1990-2009, while standard deviation, a measure of variability, changed by a factor of 1.5.
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