Future energy systems will have to be much more sophisticated

Future energy systems will have to be much more sophisticated, with both central and decentralised generating units intelligently linked to end-users. This will take decades to achieve in industrialised countries. Intelligent energy systems could be developed more rapidly in developing countries with fast-growing economies, as these countries have to invest in a new infrastructure.

New energy supply technologies such as photovoltaics, and new highly efficient end-uses, are certain to influence the economics and sustainability of energy systems. However, the implications of technological development on the supply and use of energy, and on the enabling technologies used by future energy systems, are still uncertain.

We cannot create the energy systems of the future, or significantly reduce our primary energy consumption, by incrementally improving individual components of the present systems. Instead, we need to integrate and optimise the entire system – production, conversion to an energy carrier, transport and distribution of the carrier and the efficient end-use of energy, better matching the energy quality of demand and supply type – and back this up with stable energy policies. We need a paradigm shift to create revolutionary change so that, for instance, consumption adapts automatically to the changing availability of all energy sources or carriers.

In its World Energy Outlook 2009, the IEA points out that many different initiatives are needed simultaneously covering both end-use, efficiency improvements and new supply technologies if we are to limit the future atmospheric concentration of greenhouse gases to 450 ppm CO2eq. According to the 4th Assessment Report from the Intergovernmental Panel on Climate Change, this figure is needed to limit the global mean temperature increase to 2°C.

Electricity will play an even more important role in this new energy world, thanks to its ability to be created from a variety of energy sources, its ease of transmission and its convenience to end-users. Research and development in new technologies for creating, transporting and using electricity is essential, and at a greatly expanded scale.

However, new energy carriers such as hydrogen or hydrogen-rich biofuels could supplement (or compete with) electricity in the years up to 2050. Efficiency improvements in the conversion, transmission and use of energy are expected to take place at all levels.

Energy conversion and storage

Sustainable electricity generation technologies can be developed to a higher level of efficiency than we know today. Besides steady development in conventional thermal power plants, for instance with cycles operating above 700°C, there is great potential for improving the newer technologies. Examples include the aerodynamic optimisation of wind turbines, new photovoltaic cells, new materials for fuel cells and second-generation biomass conversion processes.

New low-temperature processes also need to be developed and brought to market. These systems have huge technical potential for generating power from geothermal and waste heat, but their efficiency, availability and economics first need to improve significantly.

In general, primary measures such as improvements in energy efficiency are always preferable to secondary measures such as CCS, which is highly energy-intensive and not likely to provide a sustainable solution in the long term.

Storage technologies aimed at ensuring flexibility in future energy systems include hydrogen, pumped hydro, large batteries and compressed air energy storage (CAES). Challenges in the management of energy supply exist on both long and short timescales. The long end of the spectrum (hours, days or more) covers independent fluctuations in both electricity demand and renewable energy supply, while the short term (minutes to hours) is concerned with imbalances created by uncertainty in predicting supplies of renewable energy, such as wind and solar power. Large-scale electricity storage would be able to shift demand and supply, helping to balance the power system at all timescales, and could therefore play an important role in future intelligent power systems.

Recent years have seen extensive discussion of a hydrogen economy. Among some experts, there have been great expectations of the use of hydrogen as a carrier for alternative fuels, especially in transport and as a storable form of electricity. Developing the associated infrastructure will require huge investments and new technological solutions. However, there is a long-standing debate among experts whether a hydrogen economy will indeed play a large role, or other alternatives (such as electric ones) develop further to prevent the need for such massive infrastructural changes. So it seems unlikely that hydrogen will make a major contribution before the middle of the century.

Transmission and distribution

The natural gas grid

Natural gas is often highlighted as an important enabler in the transition towards a low-carbon society. The low carbon content of methane relative to coal and petroleum means that gas demand will continue to expand: The WEO’s 450 ppm scenario predicts that world primary gas demand will grow by 17% between 2007 and 2030, though the figure for 2030 is 17% lower than in the WEO’s reference scenario. Most gas-importing regions, including Europe and developing Asia, will see their net imports of natural gas rise.

Global proven gas reserves at the end of 2008 totalled more than 180 trillion cubic metres (tcm), equal to about 60 years of production at current rates. The long-term global recoverable gas resource is estimated at more than 850 tcm.

In view of the above, it is not surprising that the world is investing in expanding natural gas grids. In Europe, a new and important gas pipeline is Nord Stream, which will link Russia and the EU via the Baltic Sea. The first line is due for completion in 2011. Natural gas grids will play a major role in most regions of the world through 2050.

District heating and cooling

District heating and cooling (DHC) grids, like natural gas grids, are often deemed to facilitate GHG reduction. Many countries with a tradition of DHC are renewing their commitment as they find new ways of using the technologies to reduce environmental impacts. DHC facilitates environmentally desirable links between energy supplies that would not otherwise be available to end-users.

District heating is a flexible technology as it can make use of any energy source, including waste heat, renewables, geothermal energy, and most significantly combined heat and power (CHP). Denmark has, along with former communist countries, been a leader in DHC for a long time.

The European CHP+ technology platform imagines that by 2050 district heating and cooling networks will constitute widespread systems of energy exchange. In this vision, DHC will be part of the infrastructure of most European cities and towns, installed together with other basic networks. Interconnected local grids will create regionwide DHC networks. Heating and cooling would be based solely on low-carbon renewable energy sources or those using state-of-the-art carbon abatement, so the network would offer customers a carbon-neutral solution for both heating and cooling.

DHC seems to have a role in the long run, but it faces a challenge in the development of new energy-efficient houses. These have low annual energy demands, but not necessarily low peak demands, and could thus require DHC networks to be oversized for much of the time. However, if buildings become very low or zero-energy, DH/DHC networks will likely not be economical any more.

Supergrids

“Supergrids” based on high-voltage direct current (HVDC) technology are attractive because they offer the controllability needed to transmit varying amounts of wind power and to act as highways for electricity trade, even between different synchronous zones.

The ultimate, global, supergrid would be able to balance power consumption, by operating across different time zones, and generation, because somewhere in the world the sun is always shining and the wind is always blowing.

Although primarily installed offshore, supergrids could include onshore nodes that might avoid the need to reinforce existing onshore grids close to the coast. It is worth nothing that the need to build new onshore transmission lines may be a limiting factor in building large offshore wind farms, due to public resistance and legal problems in obtaining the necessary rights of way. To make sure that construction costs are shared fairly, we should agree now on the roadmap for building these grid extensions.

The planned European offshore supergrid will allow electricity to be transmitted easily between the grids of participating countries. In December 2009, the UK, Germany, France, Belgium, the Netherlands, Luxembourg, Denmark, Sweden and Ireland launched the North Seas Countries’ Offshore Grid Initiative to cooperate on infrastructure for wind power in the North Sea and the Irish Sea.

Energinet.dk, Vattenfall Europe Transmission and Svenska Kraftnät are investigating an offshore grid linking the national grids of Denmark, Sweden and Germany and connecting these to the planned international wind farm at Kriegers Flak in the Baltic Sea.

Distribution and flexible grids

At the local level, there is a need for intelligent (“smart”) distributed generating systems, especially cogeneration units with climate-neutral fuels based on internal combustion engines or fuel cells. These are highly efficient in any application where electricity and heat are required at more or less the same time, or can be buffered by heat storage. Many CHP units can combine to form a virtual power plant that is centrally controlled, so that it reacts to the overall state of the grid and can even export power over long distances when necessary.

Such a mix of distributed power sources will work best if matched by flexible consumption. Electric vehicles, electric heating, heat pumps, heat storage and small-scale distributed generation from CHP or solar panels together form a promising combination. This flexibility in supply and demand is particularly important for electricity grids, which have almost no storage capacity of their own. It is somewhat less critical for gas, district heating and hydrogen grids, which by their nature include a certain amount of storage.

The combination of three grids – for power, district heating and natural gas – gives Denmark a highly efficient supply system with a large proportion of CHP. Proposed increases in renewable energy, primarily wind power, must interact as effectively as possible with these grids if they are to maximise displacement of fossil fuels in the electricity, heat and transport sectors.

End-use

A future intelligent energy system will depend on end-users to stay in balance. Power demand, for instance, must be highest when plenty of power is available and prices are low – which may well mean when the wind is blowing strongly. New end-user technologies must be introduced on a large scale; an example is houses which are almost self-sufficient in energy, with effective insulation, smart electronic equipment, heat storage, and their own energy supplied by heat pumps, solar energy and small wind turbines. Many future energy users will become increasingly self-sufficient, able to meet all their limited needs for electricity and heat over long periods.

The SuperNode configuration could be a first step towards a European supergrid. It would allow the three-way trading of power between the UK, Norway and Germany, and would include two 1 GW offshore wind farms, one in the UK and one in Germany. To balance fluctuations in wind energy, up to 1 GW could be transferred between any two of the three countries.

Supplying energy for transport via the power grid has several advantages, such as increased flexibility through closer links between the power and transport sectors, increased energy efficiency, and the chance to include transport-related greenhouse gas emissions in carbon trading schemes. “Transport” here refers not just to cars and lorries but could also cover shipping and air travel.

Higher acceptance of electric vehicles (EVs) will require lithium ion batteries with better performance: both specific energy to increase range, and specific power for acceleration. An infrastructure for charging vehicle lithium ion batteries needs to be built up while making sure that power plants and the local distribution grid can handle the resulting load.

Since ultimately it will be preferable to charge electric cars using renewable electricity, a central control system has to ensure that lithium ion batteries are charged when wind energy or solar power is most abundant. The issue with electric vehicles is not the total amount of energy they use (a million EVs require only 2 TWh/yr), but lack of grid capacity when millions of batteries are being charged simultaneously.

In each electric car, meanwhile, an intelligent controller will need to work with the battery management system, the navigation system, the driver and the power grid at the start and end points of the journey to ensure that the vehicle never runs out of charge.

Electricity is traditionally billed at standard rates for each customer, with little effort to adapt consumption to suit varying conditions in the supply system. However, a combination of liberalisation of electricity markets, an increase in renewable power and new communications technologies have made it possible – and attractive – to develop active demand response.

In households, direct electric heating and heat pumps are well-suited to provide demand response, because of the thermal inertia of buildings. In demonstration projects, switching off electric heating for up to three hours has been shown to cause few comfort problems. Several studies have analysed the value of demand response.

Today, the welfare gains are too insignificant to motivate end-users, because in most countries the production cost of electricity is small compared to the added taxes and tariffs. Switching to value added taxes, grid payments which vary according to the grid load, and variable tariffs and taxes could stimulate flexible demand and “demand shifting” and smart metering.

Demand flexibility requires smart electricity meters which communicate with the grid and adjust the flow of power to match the supply situation and customer priorities. Smart metering in turn needs communication standards to ensure that the devices connected to the intelligent power system are compatible and a system which can accommodate both scalability (large numbers of units) and flexibility (new types of units).

Integrated systems

Smart distribution systems

Local smart distribution systems will use information and communications technologies (ICT) to link end-users with both local and central energy supply as required. ICT offers a wide range of new ways of using market incentives to optimise the control of the overall energy system, from generation to consumption. For this to work, however, we need a deep understanding of the energy system; in the worst case, the result could even be worse than before, for instance if we overestimate the need for new generating capacity.

So we need to focus on better ways of modelling and analysing complex networks on timescales of up to 50 years, corresponding to the life of many parts of the energy system.

Various clustering arrangements have been suggested to manage the increasing penetration of distributed energy resources (DERs). One of these is the virtual power plant (VPP), which aggregates up to 1,000 individual DERs and manages them in such a way that they appear to the system operator as a single, reliable and integrated resource. In some areas, aggregation is already practised with larger units (above 400 kW).

VPPs could be useful in several ways. In the short term, they could act as an enabling technology for small and innovative generating units, allowing these to enter electricity markets which in some countries are restricted to large power plants. In the long term, it may be better for system operators to continue to deal with a small number of generating plants; as DERs become more common, the alternative will be to negotiate production plans, prices and contracts with thousands of small generators.

And for small consumers or producers, it may be advantageous to be a member of a larger entity with the resources to handle negotiations and stay abreast of changing regulations. Other aspects which may become issues in future include complex services, forecasting, islanding and security, control and management strategies, and market interaction.

Safety, reliability and security of supply

In all energy systems, stability is essential to ensuring that the system operates satisfactorily and serves its customers adequately. Stability is a particular concern in electricity systems if we want to maintain the existing high standard of supply in modern power systems, with a minimum number and duration of blackouts and disturbances.

Power systems are particularly vulnerable for a number of reasons. First of all, they require that voltages and frequencies remain within narrow margins; generators will trip out when there is a power surge or a drop in voltage. Furthermore, the availability of the transmission and distribution grid can be reduced by disturbances such as lightning strikes and accidents.

When renewable energy sources partly replace large central thermal power plants, the inertia of the power system often falls. Fixed-speed wind turbines with directly connected generators do contribute inertia, but typically less so than conventional power plants of the same capacity.

ICT will therefore be important to the successful integration of renewables. The benefits of distributed power systems include increased reliability and greater overall energy efficiency, for instance through better use of waste heat. Of these factors, reliability of service is one of the most important.

The rapidly increasing capabilities and falling costs of ICT open the way to two-way communication between end-users and suppliers, making this one of the most important enabling technologies for future power and gas systems. ICT systems can give market signals to both producers and consumers, allowing much more creative models of energy distribution and especially power trading. The latter is becoming increasingly important in stabilising electric grids against the inherently fluctuating nature of much renewable electricity.

A high proportion of renewable energy in the system will require a number of support technologies, including energy storage and load management, to deal with the fluctuating power from, for example, wind turbines. Such systems, in addition to the obvious benefit of providing a cleaner and sustainable environment, have the advantage that it is easy to add generating capacity as required, using local energy resources. The cost of such expansion is predictable over the life cycle of the generating plant, regardless of the price fluctuations and shortages that may affect fossil fuels in future.

The geographical spread of renewable energy sources will become important as they develop. Some renewable sources like wind, solar and wave power are intermittent and need backup from other sources which have inertia or storage. An added problem is that these resources are not evenly distributed throughout the world, and are not necessarily available where they are most needed.

Hydropower resources are unevenly distributed throughout the world, and so too is biomass. Transport of basic biomass such as straw and wood is very costly, limiting the cost-effective use of such fuels to the vicinity of production unless they can be upgraded locally to liquid fuels which are easy to transport and distribute.

Economics and politics

Low-carbon growth to meet the WEO 2009 450 ppm scenario would cumulatively cost around $10.5 trillion more than the reference scenario in the years up to 2030, in terms of global energy infrastructure and energy-related capital stock.

Around 45% of this extra investment would be in transport. The rest would be spent on buildings ($2.5 trillion, including energy-related equipment bought by households), power plants ($1.7 trillion), industry ($1.1 trillion) and second-generation biofuels ($0.4 trillion). About half the total extra investment would be in the OECD countries, and about a quarter would be needed before 2020.

These costs are partly offset by benefits to economies (lower energy costs), health, avoided climate change and energy security (lower oil and gas imports).

A future intelligent power system requires investment now. An expansion of renewable energy will first need large amounts of money to be spent on improving the transmission system, among other things, and this is not yet happening. We therefore need stable plans for government investment in the grid, and predictable regulation regimes, to guarantee the improvements in grid performance – both capacity and intelligent control – which in turn will make possible the goal of more renewable energy.

Energy and the environmental policies can strongly impact the development of future energy systems, in both directions. The main rules are:

• Politicians have to determine the overall primary goals. Further parallel goals to be defined, such as amounts of renewables or domestic heating loads, have to be chosen carefully.
• It is important to consider the effect of energy policies on economic, social, security and environmental issues.
• Goals should be stable for long periods, so as to attract investors.
• Cooperation is essential between businesses and governments, between governments and on a regional level.

Conclusion

We cannot get the future energy system we need simply by improving the components of the existing system. Instead, we need an integrated process that will optimise the entire system, from energy production, through conversion to an energy carrier, energy transport and distribution, and efficient end-use.

Similarly, significant reductions in primary energy consumption will not be reached through evolutionary development of existing systems. This will require paradigm shifts and revolutionary changes, such as the automatic adaptation of consumption to match the instantaneous availability of all forms of energy.

In this new energy world, electricity and natural gas will be even more important than they are at present. Electricity is key because of its ability to be produced from a variety of energy sources, transmitted instantly over long distances and used in many different ways, and because of its convenience to end-users. Natural gas is valued for its lower emissions compared to other fossil fuels, and the fact that it can be used as a carrier for hydrogen: Existing stoves and heaters can burn natural gas containing 5-10% hydrogen without needing adjustment.

The rising number of efficient small-generation systems such as fuel cells will create a more decentralised electricity system, especially in cogeneration applications which can use the resulting waste heat. Rising prices for conventionally generated electricity and natural gas, together with falling costs for generation based on renewables, will cause a shift in the structure and use of energy transport and distribution systems.

To accommodate the rising number of small virtual power plants, we need to develop a new electricity system with an optimum mixture of central and distributed generators; this is a challenge for the generating technology itself, and even more so for the complex instrumentation and control technologies required for smart metering, demand management and smart grids.

Large-scale and cost-effective electricity storage will form an important part of the future intelligent power system, enabling a balancing of the system over all timescales by shifting demand and supply. Small-scale electricity storage in electric vehicles will also be important to maintaining short-term grid stability as well as controlling demand over longer periods.

An important task of energy system modelling is to maintain up-to-date analyses of all the possible “least-regrets” options, taking into account the constant changes in energy prices, resource availability and politics. Three rules can help us to identify these options:

• diversify primary energy carriers to create flexibility in the energy system;
• increase the efficiency of energy use, even low-power applications, to reduce demand; and
• centralise emissions wherever possible to simplify their treatment.

Scientists and engineers cannot predict the nature of the future energy system, but in certain frames of reference they can help to separate the “no-go” choices from valid least-regrets options. Our children’s children may look back in disbelief that for so long we could tolerate an antiquated energy system without putting in place improvements that were already possible. We are already quite good at the individual components; now it is high time for the bold restructuring that will give us a flexible low-carbon energy system by 2050.

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Long-term energy security depends on the continuing availability of fossil fuels and their potential substitution by renewable energy sources. Coal and gas may well dominate the global primary energy supply for the rest of this century if no special effort is made to promote renewables. However, for many countries energy security concerns are accompanied by a preference for renewable options which can reduce their dependence on imported oil and gas, as well as helping to meet environmental policy objectives.

Policies designed to stabilise climate change have some commonality with those for energy security, since both give priority to renewable energy. However, climate change goals can also be met by fitting carbon capture and storage (CCS) at fossil-fuelled power plants, and CCS competes with renewable energy. As a result, global energy studies show that increasing the proportion of renewable energy we use will require extra effort beyond that demanded by climate change.

The increasing interest in green economics and green energy on many nations’ political agendas may change underlying assumptions rapidly. Countries like the USA, China and South Korea are aggressively promoting investment in renewable energy and energy efficiency. Given the actual expansion of wind energy installations in various global models, it seems that the fast expansion of wind farm capacity in the past couple of years is not well reflected in these projections.

To keep the global mean temperature rise below 2°C, we need serious cuts in greenhouse gas (GHG) emissions; according to the IPCC, the necessary reduction in GHGs is 50-60% before 2050. To do this globally while leaving room for development, the OECD countries, including the EU, should reduce their GHG emissions by 80-95% before 2050.

According to the analyses presented in this report, it will be difficult for the European countries to meet these targets as mitigation options from the energy sector alone do not seem to be sufficient, but have to be supplemented by action from other sectors, for example the agricultural sector.

The Danish case described in this report shows that Denmark stands an excellent chance of phasing out fossil fuels rapidly and of reducing GHG emissions at the pace needed to reach global stabilisation at 450 ppm CO2eq. Denmark’s wind and biomass resources, especially, would allow the country to phase out fossil fuels from the production of electricity and heat before 2040.

In Denmark, the combination of three grids – for power, district heating and natural gas – has produced a highly efficient supply system with a high proportion of combined heat and power. The future increase in renewable energy, primarily wind power, must interact as effectively as possible with these grids to maximise the displacement of fossil fuels from the electricity, heat and transport sectors.

Solar

Solar energy technologies either convert sunlight directly into heat and electrical energy or use it to power chemical reactions to create “solar fuels” or other useful materials. Solar heating technologies like Concentrating Solar Power have developed steadily for many years, and except for traditional biomass, solar heating is among the most abundant renewable energy technologies globally.

In past decades, two technologies for converting solar energy into electricity have dominated: photovoltaics (PV) and concentrating solar power (CSP). The global financial crisis led to a dramatic drop in PV module prices in 2009.

Concentrating Solar Power technology has been used in central power plants for more than 20 years in a few installations. Mirrors focus solar radiation on a receiver, and the resulting high-temperature heat is used to generate electricity by driving a turbine or some other engine. Heat can also be used to generate hydrogen from water, and to power more complex chemical reactions producing solar fuels.

Solar energy can be used to generate heat and electricity all over the world. Our technical ability to make use of this resource has improved dramatically in recent years, and by 2050 it is hard to imagine a society that does not rely on solar energy for large parts of its heating and electric power.

The IEA forecasts that PV and concentrated solar energy will each produce 11% of the world’s electricity by 2050. PV is by nature a distributed generation technology, whereas concentrated solar energy is a centralised technology, so their deployment will follow very different routes. PV is unique among electricity generation technologies in that its distributed nature allows it to be integrated with human settlements of all sizes, urban or rural.

Concentrating Solar Power, on the other hand, has advantages and disadvantages common to most centralised generating technologies; so, for instance, new concentrated solar energy plants will require new electricity transmission capacity. Concentrating Solar Power also has some advantages of its own: The fact that most concentrated solar energy systems separate the harvesting of energy from the electricity generation step allows them to store energy in the form of heat, and to generate power from other fuels when the sun is not shining.

Wind energy

Since 1970, wind energy has grown at spectacular rates, and in the past 25 years, global wind energy capacity has doubled every three years. The current wind energy capacity of approximately 160 GW is expected to generate more than 331 TWh in 2010, covering 1.6% of global electricity consumption. Approximately 2% of the wind farm capacity installed during 2009 was offshore, bringing the total offshore capacity to 2.1 GW, or 1.3% of global wind energy capacity.

Onshore wind power has enormous potential: at almost 400 EJ/yr. An estimate of 22 EJ/yr for offshore wind potential is conservative, as it includes only wind-intensive areas on continental shelves outside shipping lines and protected areas.

Most of the development effort so far has been dedicated to the evolutionary scale-up and optimisation of the land-based three-bladed standard wind turbines which emerged as commercial products at the beginning of the 1980s. With increased focus on offshore deployment combined with the radically different conditions compared to onshore, it is likely that completely new concepts will emerge, such as the vertical-axis turbine currently being developed at Risø DTU.

Offshore exploitation represents an even bigger challenge for wind turbine development, operation and cost-optimisation. It also brings new potential, since wind resources offshore are generally higher, and many of the constraints are very different to those onshore.

In energy scenarios involving large proportions of wind power, wind should be seen as a baseload-generating technology. For instance, in an integrated power system comprising wind and hydropower, and possibly high-efficiency pumped storage too, the best use of wind power is to deliver the baseload.

The coming decade may see new technological advances and further scale-up, leading to more cost-effective, reliable and controllable wind turbines and new offshore and onshore applications, including the introduction of wind power in the built environment. Wind energy has the potential to play a major role in tomorrow’s energy supply, cost-effectively covering 30-50% of our electricity consumption.

Hydropower and wave power

Hydropower is a mature technology close to the limit of efficiency, in which most components have been tested and optimised over many years. However, the efficiency of many old hydropower turbines could be improved by retrofitting new equipment. Hydropower has little or no potential in the low-lying terrain of Denmark.

Wave energy can be seen as stored wind energy, and could therefore form an interesting partnership with wind energy. Waves will normally persist for six to eight hours after the wind has dropped.

The technical potential for wave power in Denmark is estimated to be able to cover one-third to two-thirds of current electricity consumption. However, this would probably require an unacceptably large area in the Danish part of the North Sea. An ambitious yet realistic goal for Danish wave power by 2050 could be around 5% of electricity consumption. Globally, the potential for wave power is at least 10% of total electricity consumption, or more if we tolerate higher prices.

Bioenergy

Biomass presently covers approximately 10% of the world’s energy consumption. A realistic estimate of the total sustainable biomass potential in 2050 is 200-500 EJ/yr, covering up to half of the world’s energy needs in 2050.
However, the variability of biomass production makes such a comparison simplistic. Factors to take into account include:
• future demand for food, determined by population growth and changes in diet;
• the types of food production systems that can be adopted worldwide over the next 50 years;
• productivity of forest and energy crops;
• increasing use of biomaterials;
• availability of degraded land on which to grow biomass;
• competition between different land uses, such as reforestation on surplus agricultural land;
and
• ecological impacts.

A large proportion of biomass will probably still be in the form of wood for direct burning in less developed areas of the world. Biomass plays a special role as an easily storable form of energy, deployable in CHP systems based on sophisticated combustion technologies, and as a source of liquid fuels for transport.

Much more organic waste will be used for bioenergy in the future, solving a waste problem and recirculating nutrients to ecosystems. New forms of biomass such as algae might also contribute.

Several technologies are currently being developed with a view to improving biomass use, and these will help to make bioenergy competitive when oil prices increase. However, it is unlikely that bioenergy can provide the bulk of the world’s energy. Biomass is a limited resource, and increases in biomass production should preferably not compete with food supply.

Geothermal

Geothermal energy is used in two ways: At least 24 countries produce electricity from geothermal energy, while 76 countries use geothermal energy directly for heating and cooling. In 2008, the global production of geothermal heat was 0.2 EJ, with 10 GW of installed baseload electricity production capacity.

The last two decades have seen several projects “mining” high-temperature heat by injecting cold water into hot rocks in very deep boreholes. Known variously as hot dry rocks (HDR), enhanced geothermal systems (EGS) and engineered geothermal systems (EGS), these projects have been tested in the USA, Europe and Japan.

In Denmark, the potential for geothermal energy is substantial since suitable aquifers are available, and the technology is an excellent match for the district heating systems already widely used. Geothermal energy is therefore expected to cover a large part of the demand for future district heating. The Greater Copenhagen area has enough geothermal reserves to meet all its needs for heat for thousands of years.

Heat storage in combination with geothermal energy is at an early stage of development. In future, spare heat in the summertime from sources such as solar plants and incinerators could be used to raise the temperatures of geothermal reservoirs. In winter, it would then be possible to increase the energy output of the geothermal systems.

According to estimates by the International Energy Agency, the most probable potential for the global geothermal resource is 205 EJ/yr, including 65 EJ/yr from electricity production.

Storage

To date, R&D work on energy storage has focused on electricity, probably because electricity storage has an obvious, straightforward and urgent role in the energy market. There is no doubt that many types of electricity storage will be of great importance in the coming decades.

Several different electricity storage technologies have been developed, and systems are in operation around the world, though they are not widespread. Well-known technologies typically used for fast response include stationary batteries and flywheels, while compressed air energy storage (CAES) and pumped hydropower both provide longer-term storage suitable for spot market arbitrage.

A shift to sustainable energy sources will also require mobile storage technologies for vehicles. Capturing electricity from wind and solar sources, mobile storage technologies will need to deliver driving ranges similar to those of modern gasoline and diesel vehicles.

At a first glance, batteries may seem the obvious choice to replace fossil fuels for transport, but even with today’s advanced batteries, the driving range of electric vehicles falls far short of conventional vehicles. The fundamental problem is that batteries have an energy density almost two orders of magnitude lower than fossil fuels.

At some point in future, storing energy as hydrocarbons synthesised from hydrogen, made by the electrolysis of water, and carbon dioxide extracted from the atmosphere may become viable. The distribution system for liquid fuels is in place, so synthetic liquid fuels will not require huge investments in new distribution systems.

There is also considerable technical and economic potential for heat storage. Thermal energy storage technologies fall into two categories based on the physical processes involved: phase change materials (PCM) and sensible heat storage utilising the heat capacity of storage material. For both technologies effective thermal insulation is essential, particularly when used to store heat over long periods.

Huge underground heat storage reservoirs might become important for the seasonal storage of heat and cold in appropriate locations around the world, depending on geology and surface temperature variations. If such stores were large enough, their heat losses could be relatively small and therefore acceptable.

Energy storage has enormous technical potential, and it is likely to appear in many different guises among the building blocks of a future sustainable energy system. However, the costs associated with storing energy are often considerable and sometimes prohibitive.

Nuclear

Nuclear fission is a proven technology, but its exploitation has grown slowly in the past 30 years. However, the need for an energy supply with low fossil fuel dependence and low greenhouse gas emissions has led to renewed interest in nuclear energy. Many countries now plan to adopt or expand their use of nuclear fission.

The USA expects a nuclear renaissance, and China, India and Russia have even more ambitious plans for expanding nuclear power by 2030 through the installation of 100, 60 and 20 GWe, respectively.

Nuclear fusion power is a developing technology that will not be available for large-scale electricity production until the middle of the century. Compared to fission, however, the successful development of fusion energy would mean less radioactive waste and much less worry about the proliferation of nuclear weapons.

Nuclear fission reactors are used in 30 nations, predominantly in the OECD countries of North America and Europe, in south-east Asia and in the former Soviet Union. In total, nuclear fission provides 14% of the world’s electricity consumption, though this figure has fallen slightly in recent years.

Based on existing plans, world nuclear capacity may therefore increase from its present 340 GWe to more than 1,000 GWe in 2050, increasing nuclear’s share of the electricity supply to 20%. However, such projections are highly uncertain since they are influenced by technical, economic and especially political and social considerations.

The three existing generations of nuclear fission reactors represent an evolution of thermal neutron technology towards improved safety and economics, but with relatively minor changes to the basic concept. Generation III+ emphasises simplified designs, reducing the likelihood of system failure, and the expanded use of passive safety systems which do not rely on external power. In the next generation of nuclear energy systems known as Generation IV, reactor designs are developed for improved sustainability, meeting requirements for economics and safety while addressing concerns over proliferation and radioactive waste.

The Generation IV energy systems include fast-neutron breeder reactors that employ closed fuel cycles, allowing for a much improved utilisation of uranium resources as well as a reduction of the volume of radioactive waste. The Generation IV reactors have higher operating temperatures, which opens up for new applications of nuclear energy, such as high-temperature process heat, and liquid chemical fuels and thermo-chemical hydrogen production. With sufficient progress in research and development, first-of-a-kind Generation IV reactors could be developed around 2030, with commercial deployment starting from 2040.

Fusion research is now taking the next step with the construction of a large-scale research tokamak, ITER, in France. Expected to start operating in 2020, ITER is a worldwide collaboration that will demonstrate net energy production from controlled fusion for the first time by 2026.

Building on experience gained from ITER, plans are to build the future DEMO facility in 2030-2040 and for it to operate during 2040-2050, generating several hundreds of megawatts electricity for extended periods of time. DEMO will also test and qualify key components under realistic operating conditions. If everything goes according to plan, the first commercial fusion power plant will then be in operation by 2050.

CCS

Carbon capture and storage (CCS) can be used on large point sources based on fossil fuels such as power plants and industrial furnaces. The technology can be retrofitted at existing combustion plants without major changes, but running costs are rather high.

The CO2 produced can be stored or used in several different ways, though only ocean and geological storage have the potential to take up very large amounts. In time, CO2 stored in the oceans will reach equilibrium with the atmosphere, so this is not a permanent disposal route. CO2 injected into geological formations, on the other hand, is potentially stable for millions of years.

The main cost of CCS is for the CO2 capture stage, in terms of both its capital cost and the loss in efficiency at the power plant to which it is fitted.

To improve the chances of meeting the targets for CO2 reduction, CCS should be used worldwide, and the building of full-scale demonstration plants must be accelerated to drive down costs. Proven fossil fuel reserves, especially coal, will last far beyond this century. With CCS, we can continue to burn fossil fuels even in a carbon-neutral future. Later, CCS can even be used with biomass-fired power plants to create net negative CO2 emissions.

Technologies for the three individual steps in CCS (capture, transport and storage) already exist, and there is enough proven geological storage capacity to allow large-scale use of CCS. However, the technology needs further development and refinement through demonstration plants.

System aspects

The energy systems of today have developed gradually over the past 100 years or more. This evolution is reflected in their structure, which is based primarily on central production units delivering electricity through transmission lines to the distribution networks and thence to end-users.

Future systems will have to be much more sophisticated, with both central and decentralised generating units closely linked to end-users through intelligent communications networks. This will take decades to achieve in industrialised nations. Intelligent energy systems could be developed more rapidly in developing countries with fast-growing economies, as these countries have to invest in a new infrastructure. As a result, intelligent energy systems could be widespread by 2050.

There is also a need for a smart grid which will link production and end-use at the local level. End-users must help to maintain balance in the future energy system. New end-use technologies have to be widely introduced, including highly insulated, almost self-sufficient houses, smart electronic equipment, energy storage and heat pumps. Information and communications technology (ICT) will be very important to the successful integration of renewables in the grid.

In the past ten years, the hydrogen economy has been discussed intensively, and among some experts there have been high expectations that hydrogen will become an alternative energy carrier for transport applications. However, experts have also for a long time been debating whether a hydrogen economy will indeed come to play a large role.

Developing the necessary infrastructure will, however, require huge investments and new technology, so it is unlikely that hydrogen will make a major contribution before the middle of this century.

District heating and cooling (DHC) grids, like their counterparts carrying natural gas, are often deemed to contribute to reducing GHGs. District heating is a flexible technology which can use any fuel or heat source, including waste energy, renewables, geothermal energy and, most significantly, heat from combined heat and power (CHP) systems.

Denmark has, along with former communist countries, been at the forefront in exploiting DHC for a long time. In the long term, it seems likely that DHC will remain important, but there will be challenges following the widespread introduction of low-energy houses with a very low annual demand for heating, but not necessarily low peak demand.

Electric supergrids based on high-voltage direct current (HVDC) technology are promising because they offer the controllability needed to handle wind power effectively as well as efficient transport of electricity over long distances, even between different synchronous zones. Compared to other energy distribution systems, power grids are particularly vulnerable to disturbances and accidents. Information and communications technology (ICT) will therefore be very important to the successful integration of renewables with the grid.

High proportions of renewable energy in energy systems will also require a number of supporting technologies, including energy storage and load management, to deal with fluctuating power from renewables such as wind turbines.

Today, the welfare gains are too insignificant to motivate end-users, because in most countries the production cost of electricity is small compared to the fixed additives. Switching to percentage-type additives, grid payments which vary according to the grid load, and variable tariffs and taxes could stimulate flexible demand and “demand shifting”.

Large-scale electricity storage would be able to shift demand and supply, helping to provide balance at all timescales, and may therefore be important in future intelligent power systems.

By 2050, the sum of the potential of all the low-carbon energy sources exceeds the expected demand. The challenge for a sustainable global energy system with low CO2 emissions by 2050 is therefore to utilise this potential in the energy system in an economically attractive way. It will not be possible to develop the energy systems of the future simply by improving the components of existing systems. Instead, we need an integrated process that will optimise the entire system, from energy production, through conversion to an energy carrier, energy transport and distribution, and efficient end-use.

Similarly, significant reductions in primary energy consumption will not be reached through evolutionary development of existing systems. This will require paradigm shifts and revolutionary changes, such as the automatic adaptation of consumption to match the instantaneous availability of all forms of energy.

A future intelligent power system requires investment now, since uncertainty among investors is already hindering progress towards a higher share of renewable energy. If we do not make this investment, future generations may look back in disbelief that for so long we tolerated an antiquated energy system without putting in place the improvements that were already possible.

Hans Larsen, Henrik Bindslev and Leif Sønderberg Petersen, Risø DTU, Denmark.