Article - Issue 17, October/November 2003
Power for the people
Professor Alan Williams CBE FREng, Professor M. Pourkashanian and Dr J.M. Jones, University of Leeds
Concern about energy supply frequently attracts enormous interest and front-page headlines; yet when resources appear plentiful, the issue can be ignored for months or years. Increased awareness of the influence of greenhouse gases on the climate has now resulted in more constant attention from both policymakers and the general public. One of the major issues is: how can we substitute the fossil fuels with non-carbon dioxide producing sources whilst maintaining adequate supplies of energy?
The supply of energy is determined at various times by the availability of fossil fuels, or by environmental pollution constraints such as acid gas emissions, or more recently by carbon dioxide emissions. Whilst at one time the former would be the policy-controlling factor, now, as a result of climate warming and the resultant Kyoto Agreement, the emission of greenhouse gases is a major issue.
World and UK energy sources are shown in Table 1. Much of this is converted into electricity that is distributed locally or by a transmission network and this is now the most important energy vector. The contribution of the various energy sources to electricity generation is shown in Table 2.1,2 The UK energy supply position parallels the world situation in many respects. The problem that has to be solved is simply the substitution of fossil fuels by noncarbon dioxide producing sources whilst maintaining adequate supplies of energy. Of course the question of what is adequate is a debatable issue.
The UK energy review and white paper
In the UK the Government commissioned an examination of the energy situation by the Cabinet Office Policy Innovation Unit (PIU). The UK policy constraints that they had to take into consideration are as follows:
In undertaking this review the PIU requested submissions from interested bodies and amongst these The Royal Academy of Engineering made a submission that included the following points:
The PIU Report made a series of recommendations that can be summarised as follows:
In addition, a group under the chairmanship of the Chief Government Scientific Adviser considered the energy research that had to be undertaken over the next 50 years. This was fed into the PIU Report and published simultaneously. The six technologies selected were:
carbon dioxide sequestration
wave and tidal power
hydrogen production and storage
nuclear waste processing
A number of other items featured, including a proposal to increase research and development spending, and the formation of a dedicated National Research Centre. The DTI Clean Coal Committee concluded that carbon dioxide sequestration was preferable to, for example, gasification and other clean coal technologies.
The consultation document based on this report has been open to debate and many learned bodies have made submissions or personal comments.4
The Energy White Paper, Our energy future – creating a low carbon economy, was published in early 2003; the ‘four pillars’ of the report were:
Environment: to work towards cutting emissions of carbon dioxide by 60% by 2050
Energy reliability: to maintain the reliability of energy supplies
Affordable energy for the poorest: to ensure that every home is adequately and affordably heated
Competitive markets for business, industry and households: to promote competitive energy markets in the UK and beyond.
It was subject to considerable discussion including many critical remarks, especially on the lack of specific comments about nuclear power. The Royal Academy of Engineering and the Institutions of Civil Engineers and Chemical Engineers in particular have suggested that the balance is not correct and that there may be too great a reliance on imported natural gas.
A considerable number of research and development initiatives were introduced in early 2003. There was a £28m Research Council initiative in energy. The Engineering and Physical Sciences Research Council (EPSRC) in its ‘Strategic Plan 2003–2007’ identifies the same themes set out above, namely energy efficiency, the move to a low-carbon economy, carbon sequestration, renewable options, nuclear waste treatment, and environmental impacts as presenting important and urgent challenges. In order to action these, EPSRC as the lead body together with the Carbon Trust launched the Supergen initiatives, which had calls for research proposals on a number of key topics such as biomass, hydrogen, marine, future network technology, photovoltaic devices, fuel cells and lifetime extension of conventional power plant. Details of these work packages are given on the SuperGen webpage, www.supergen-bioenergy.net
The Natural Environment Research Council (NERC) and EPSRC are also establishing an energy centre to act as a hub for a proposed UK energy research network. The Carbon Trust is allocating about £10m for research in buildings and industry, and is also funding work on a broader basis for industry. The DTI has also taken a number of initiatives on renewables and the use of fossil fuels.
In the White Paper the Government stated that it will report on progress made every year; the first report is due next February.
The energy debate intensified in August 2003 as a result of the major electricity blackout in the Eastern USA followed by smaller events in London, Denmark and Italy. Generation policy and transmission issues have been subject to some scrutiny as has the influence of NETA (new electricity trading arrangements), since they all impact strongly on the capacity and reliability of the electricity system.
What are the future energy options and where is research required? This is considered next.
Carbon dioxide sequestration
Coal- and gas-fired power stations are likely to be be in significant use for several decades, so it seems likely that carbon dioxide sequestration will be necessary. For it to be economic, carbon dioxide sequestration must be applied to large combustion plant such as coal or natural gas power stations and petrochemical plants.5 There is a 10% loss in efficiency and a 50% increase in plant cost: some observers consider these figures to be optimistic. However when sequestration is coupled with enhanced oil and gas recovery, the operation could be profitable – at least for a number of years.
The UK has a considerable storage capacity of 24 Gt of stored carbon dioxide in depleted oil and gas fields in the North Sea. The capacity in coal deposits is also extremely large.
We need to improve the generation and transmission efficiency of coal-fired power stations. This can be achieved with improved design methods including CFD modelling and the use of low energy NOx and SOx control. The latter is particularly important: the impending Large Combustion Plant Directive (LCPD) requires lower levels of the emission of NOx, SOx and dust. Indeed the introduction of emissions trading suggests that cost-effective emissions control could be profitable. The greatest gains would come from investment in new plant and would use supercritical boiler plant, or high pressure, oxy-fuel combustion, chemical looping or gasification.
Combined cycle generation (CCGT) using natural gas remains a major option as a bridging fuel because of the large resource base. With clean combustion and efficiencies approaching 65%, this is a prime candidate for carbon dioxide sequestration.
The major renewable sources
The contribution of solar photovoltaic energy to world power generation is still small (several hundred megawatts) and even with very high growth rates6 will not be able to make a major contribution for several years. The major economic contribution can only be in new large commercial buildings and the rate of introduction will cover many decades. The contribution of thermal solar energy must also be increased via new architectural methods.
Solar energy is in competition with two sources of renewable energy that are already used on a commercial scale, namely wind power and biomass, but in all cases there are limitations on the maximum energy that can be provided. The average total solar irradiance is about 80–130 W/m2 whilst current solar PV cells have an efficiency of about 20%. Even with a theoretical maximum efficiency of 80% (not attainable in practical use because of dust, etc.), very large surface areas (many tens of square kilometres) are required to make any impact on the electricity needs of the UK.
The energy intercepted at a wind speed of 7 m/s is 210 kW/m2, assuming an efficiency of 20–40%, so the output of a typical generator is about 0.5–2.5 MW, although this can be up to 5 MW offshore. 7 So far the contribution onshore has not been great, with just over a 1000 wind turbines generating 200 MW of electricity. The offshore potential is considerable and the DTI has released proposals for up to 6 GW in mainly three areas: the Thames Estuary, Greater Wash and the North West. However environmental issues need to be clarified and considerable engineering advances are needed in the marinisation of wind turbines and transmission ashore if they are to be efficient and cost-effective. In the UK the present contribution to electricity generation is about 1%, but it is greater in other countries such as Denmark, where 15% of electricity is generated in this way.
The other major renewable source is bioenergy. This is seen throughout Europe as one route to meeting the EU targets for the reduction of carbon dioxide emissions. However, it accounts for only 0.25% of the UK energy provision. In the UK about 50% of all material grown becomes agricultural residues; the amount from waste potatoes, sugar beet tops and straw is about 4–15 Mt/y, with potentially large amounts from grasses and the forests. They can be utilised by combustion for heat or electricity generation, and at the present time some 4 GWe is produced from wastes, landfill gas, sewage sludge and municipal wastes, but only 150 MWe of electricity is produced in plants burning straw and other agricultural waste materials. However the total readily available energy is only about 5% of the current UK energy consumption. At present, there is a limited supply of biocrops for electricity generation, direct heating or to form liquid fuels such as biodiesel. They are increasingly being used for partial hydrocarbon fuel substitution in, for example, co-firing in power stations, where up to 20% wood or straw can be fired with coal. Bio-oils might also be blended with petrol and diesel fuels. Their widespread use in part depends on emission and taxation regulations in the near term and the incentives to farmers to provide a guaranteed production of biofuels.
The costs of these technologies have been falling as they come into more widespread use (Figure 1). Solar energy will clearly make a significant contribution once the economies of large-scale production are realised.
Wave and tidal
There is a considerable amount of energy available from wave power: 50–75 kW/m in waves off Scotland and 25 kW/m in the North Sea plus the immense energy available in the currents.9 Whilst this technology looked to be very promising in the 1980s interest dwindled for a number of reasons, particularly the difficulties in sustaining generating plant in hostile conditions. Schemes such as the Severn Barrage, which could produce 3 GWe, need considerable investment. Thus at present the main work in the UK on wave power is being undertaken using small-scale (less than 1 MW) onshore units. Wave and tidal power have large up-front costs and have no particular championing industry at present. There are also considerable environmental concerns especially in relation to tidal barrier schemes.
Hydrogen fuel gas – the hydrogen economy
Hydrogen is the clean fuel being promoted by a large number of bodies: it is an ideal fuel for fuel cells and indeed for combustion using catalytic or conventional methods. It is being strongly promoted for transportation on land and for aviation purposes, since transportation produces 20% of all carbon dioxide. Progress is being made in fuel cell technology, and more active electrode systems and catalysts are being developed. Units are currently available for vehicles and stationary power generation but they are expensive and use reformed hydrocarbon gases, so from a carbon dioxide production point of view have no advantage over conventional engines or furnaces. For hydrogen to be used widely for transport we would need large and efficient storage facilities. Whilst cryogenic storage can compete with gasoline from an energy density viewpoint, other methods such as absorbent carbons have half that storage capacity. Production is still the major concern and needs advances in photobiological production methods or some new thermochemical cycles using solar or nuclear energy. Fuel cells and the vehicles are available now for land transport but are in competition with high efficiency liquid-fuelled engines and batteries. The use of cryogenic hydrogen for aviation has been considered but the vast quantities required in many airports are a problem. It seems more likely that aviation fuels are likely to continue to be based on liquid fuels derived from bio-sources, synthesised from natural gas or from oil.
Nuclear power – the waste issue
The treatment of nuclear wastes costs many billions of pounds, causing immense economic problems to the industry, with a significant adverse effect on total nuclear power generation costs. This is one of the major difficulties facing the Government and a speedy resolution is vital. Not only do the historic wastes have to be considered, but if any new nuclear plants were to be installed then safety and total operating costs must be superior to current plant.
There are difficulties with nuclear fusion in extracting energy from a sustained nuclear plasma, and the containment vessels become radioactive, resulting in considerable nuclear waste problems. Cold fusion has been suggested by a number of research groups but these have not been successful so far.
Nuclear fission thus seems to be the only way forward for the next 50 years at least. The options must involve a replacement programme for the nuclear plant being decommissioned and new plant must be based on safe, reliable technology. The leading options include:
the Westinghouse design, which is a conventional, well tried reactor system
the AECL Advanced CANDU reactor, the ACR 700, which is a new generation reactor also based on a well tried system
the high temperature reactor, which has many advantages in that it is safe and efficient, is economic on a small scale and can be used for heating purposes.
There are many options but much depends on political decisions, as well as commercial considerations.
This is probably the most important side of the equation. Many energy conservation campaigns over the last 60 years have been aimed at reducing energy consumption and the results in industry and commercial building are significant. Energy reductions in domestic housing and in transportation are very complicated and difficult to achieve rapidly. The current Government policy is for a target 30% reduction in home energy consumption between 1996 and 2010 and there are several transport efficiency schemes in operation. The Energy Saving Trust and the Carbon Trust – administering the Climate Change levy – have considerable programmes. However, it is difficult to see a substantial reduction in energy use over the next 25 years, primarily because of the inevitable slow replacement of old housing in the major cities in the UK.
The overall picture
Demands for power and heat at the present time are met by a variety of energy sources that are both flexible and to a large degree interchangeable. They are subject to a number of factors that have been modelled by the DTI using techniques set out in Energy Paper 65.
If fossil fuel sources releasing carbon dioxide are replaced by renewable energy, it is difficult to see a contribution greater than 25–40% of the electricity supply, for example over a 25-year period, and much of this supply will be of a transient nature. The DTI has indicated its view of the generation mix up to 2020 in Energy Paper 68 and the relevant generation prediction for one typical scenario is shown in Figure 2. In this the projected electricity demand grows by one per cent or so per annum and this will require substantial new generating capacity. The figure also shows the shares of projected generation by the various types of plant. The dependence on natural gas for electricity generation is clear and of course considerable amounts of natural gas are used for heating, implying pressures on its supply. The coal-fired plant will be over 50 years old by the end of these scenarios and will have to undergo major lifetime extension. Over this time span petroleum oil will be the major component used for the transportation fuels.
Thus there is the question of the provision of a significant energy storage system or a back-up supply, which would be tested to the full in those climatic conditions when there is no wind or little sun and it is very cold. Within the industry there are growing uncertainties in planning and operation of power systems with increasing concerns about the likely impact of renewable energy sources. These are mainly relatively small, distributed electricity sources and the economics of trading are complex.11 The intermittent output of most types of distributed generation raises a number of issues about the economic balance between unpredictable outputs and requirements for reserve and frequency response. Therefore it is necessary to quantify the values of different energy sources among the market players. Additionally there is the need for the entry of contemporary software technologies and numerical methods into the power industry especially for active network management.11
Thus the most likely contributions to electricity generation in 2025 will be:
coal with some sequestration, 10–15 GWe
natural gas, 15–25 GWe
wind, 1.0 GWe
hydro, 0.3 GWe
biomass and wastes, 5.0 GWe (biomass alone, 1.0 GWe)
wave and tidal, 0.1 GWe
nuclear, 10 GWe.
It is clear that there are some significant differences to that predicted in the DTI scenario in Figure 2.
In addition there will be a distributed gas supply, initially natural gas, but ultimately used with up to 20% hydrogen, to provide heat and localised electricity. The heating load is considerable and forms an integral part of the energy supply profile. Indeed at present, in the domestic sector, the consumption of natural gas is equivalent to 32 Mtoe, whilst the electricity component is equivalent to 10 Mtoe; thus the market demands for natural gas are interestingly poised between heating and electricity generation as is clear from Table 1.
Transport will continue to be largely based on liquid fuels with battery-based units for short journeys, and increasingly fuel cells for larger vehicles. At the present time the transport sector uses 42 Mtoe of energy and is growing rapidly.
As a consequence the demands for secure, economic supplies of energy for all sectors present problems. It seems clear that, if carbon dioxide emissions are to be reduced, then the major policy issue is the retention of a major nuclear generation component. Unless there are vast reductions in the use of energy, this has to come about because renewables alone cannot provide the electricity, the heating requirements or the energy for transportation. The use of fossil fuels can help for several decades but in the long term cannot provide a secure future.
Alan Williams CBE FREng, M Pourkashanian and J M Jones
Energy and Resources
Research Institute, University of Leeds
Professor Alan Williams CBE FREng, is a Research Professor in the CFD Centre and the Research Institute for Energy and Resources at Leeds University. He is a past President of the Institute of Energy. He has been a member of a number of Government committees including most recently the Government’s Chief Scientific Adviser’s Energy Research Review Group.
Professor M. Pourkashanian is Head of the School of Process, Environmental and Process Engineering in Leeds University and holds the chair in High Temperature Combustion Technology. Previously he was a Royal Society Research Fellow working on the development of low NOx oxy-fuel burners for the process industries.
Dr Jenny Jones is a Senior Lecturer and Advanced EPSRC Research Fellow in the Research Institute for Energy and Resources at Leeds University. She is the Principal Investigator for the EPSRC SuperGen Consortium in Biomass, Biofuels and Energy Crops at Leeds University.