Non-fossil energy technologies in 2050 and beyond By Riso DTU

These suggest that global wind energy penetration could be 10% by 2020, 20% by 2030 and 25-30% of electricity demand by 2050. These scenarios are based on growth rates of 27% in 2008, declining to 22% in 2010, 12% by 2020 and 5% by 2030. Targets of this order are realistic, and the available wind resource is not the limiting factor: Current global electricity consumption corresponds to that generated by a wind farm measuring 1,000 kilometres square. Long-term plans should therefore be based on these growth rates.

The huge potential of wind power, the rapid development of the technology and the impressive growth of the industry justify the perception that wind energy is changing its role to become the future backbone of a secure global energy supply.

Between the mid-1980s, when the wind industry took off, and 2005, wind turbine technology has seen rapid development, leading to impressive increases in the size of turbines, with corresponding cost reductions.

From 2005 to 2009 the industry’s focus seems to have been on increasing manufacturing capacity, meeting market demand and making wind turbines more reliable. The development of new and larger turbines to some extent stagnated, and costs even rose due to high demand and rising materials costs.

We believe, however – and this is supported by recent trends – that the next decade will be a new period of technology development and further scale-up, leading to more cost-effective, reliable and controllable wind turbines and new applications. This is partly due to increased international competition, but also because the industry is increasingly dominated by high-technology international companies. The move to install more capacity offshore also favours larger wind turbines and encourages new ways of thinking.

Finally, there is an increasing awareness that renewables in general, and not least wind energy, will come to play a major role in the global energy supply as oil and gas are phased down in the period towards 2050. The cost of power from coal will also increase because of the need for carbon capture and storage.

In this chapter we discuss the current status of wind power and its prospects up to 2050, including both existing and emerging technologies.

Wind 2010: resource, deployment and technology

Studies of the exploitable wind resource demonstrate that wind energy is a practically unlimited and emission-free source of energy, of which only a tiny fraction is currently being exploited.

While the estimates differ by almost an order of magnitude, even the most conservative, such as the 2008 estimate by REN 21, show that the world’s expected electricity consumption in 2050 of 113-167 EJ/yr (31,000-46,000 TWh/yr) could be delivered by wind energy several times over. The potential of onshore wind is thus almost 400 EJ/yr (111,000 TWh/yr), even with conservative assumptions about resource and land availability.

Most forecasts predict an eventual fall in growth rates, and following the financial crisis that began in 2008 it seemed likely that future growth would be slower than in that year, when cumulative installed capacity grew by 30% to 122 GW. This did not happen in 2009, however: instead, cumulative installed capacity grew by 31% to 160 GW.

The average cumulative growth rate over the past five years has been 27.3%. While in the USA and many other countries the industry was encouraged by stimulus packages, the main growth came from China, which in 2009 installed almost 14 GW. In this light, assumed growth rates of 10-20% for the next 20 years do not seem overly optimistic.

Until the 1990s, a great variety of different wind turbine concepts were tested and manufactured. These included turbines with one or two blades, stall-controlled designs, and vertical-axis turbines. In contrast, the typical wind turbine being installed today (2010) is a three-bladed, upwind, pitch-controlled, variable-speed machine connected to the electricity grid, with a capacity of 1.1-1.5 MW in Asia and 1.9-2.3 MW in Europe and the USA.

Mainstream technological development for land-based utility-scale wind turbines is now characterised primarily by scale-up (until 2005 the size of turbines doubled every five years. But though most wind turbines now look similar on the outside, manufacturers have introduced new materials, control principles, generator and converter technologies. Together with the technical challenges associated with scale-up, these developments have called for advanced research in a number of fields.

Over the past 20 years, average wind turbine capacity ratings have grown continuously; the largest proportion of land-based utility-scale wind turbines installed globally are rated from 1.0 MW to about 3.6 MW. The largest wind turbines are installed offshore, notably in the UK and Denmark, while land-based turbines in Asia are generally smaller, at around 1.0-1.4 MW. This suggests that further development will happen in several tracks, including accelerated scale-up for offshore turbines and smaller installations on land, sized appropriately for the application and local infrastructure.

Industry trends and costs

Industrial wind turbine technology was originally developed primarily by small companies in Europe and the USA working closely with research organisations. Though this development gradually attracted the attention of established industrial manufacturers, the original small companies had made considerable progress in diversification, turbine scale-up and deployment before some of them were taken over by multinational energy companies (GE, Siemens, Alstom), while others (Vestas) grew by merging with competitors of similar size.

In Asia, new players initially licensed technology from Europe, but quickly went on to develop their own wind turbines. Wind turbines are based on a unique combination of technologies, and are gradually becoming increasingly sophisticated. The amount and diversity of research carried out will determine how far wind turbine technology will develop.

Wind turbines are complex designs, and in technical terms there are no limits to how far they can be improved. However, diminishing returns may cause the industry itself to limit future technological improvements. Whether or not this happens depends very much on the future structure of the industry, and the ability of turbine manufacturers, R&D specialists and legislators to work together to ensure that the industry remains vital, dynamic, innovative and competitive. As the motto of Roskilde University puts it, in tranquillo mors, in fluctu vita (“in stillness death, in movement life”).

We can imagine four existing industries which a future wind turbine industry might come to resemble:
“Shipbuilding” Large structures, but relatively low-tech: probably the worst case, as it would discourage investment in new technology.
“Aerospace” A handful of global wind turbine manufacturers supported by a larger number of niche suppliers. This scenario describes the wind industry until five years ago, since which time many new players have entered the scene.
“Automotive” R&D involves the component suppliers as well as the wind turbine manufacturers themselves. This scenario has the attraction of creating widely used standard components which make good use of common R&D effort.
“Power stations” Component manufacturers supply contractors who in turn are project-managed by large energy companies. This scenario could make it hard to exploit the full benefits of mass production.

The overall goal is to make wind energy steadily more cost-effective and reliable as a future large-scale global energy source. It is likely that the future wind industry will have elements of all four scenarios listed above, but of these, the third (“automotive”) offers perhaps the best opportunities for innovation and technological development. We certainly see opportunities for component suppliers to play a larger part in the development process.

Up to 2005, the industry saw learning rates of 0.17-0.09 (in other words, a doubling of cumulative installed capacity reduces the cost of electricity per kWh by 9-17%).

From 2005 to 2009, installation was limited by manufacturing capacity, higher material costs and higher margins for manufacturers, with the industry focused on increasing production capacity and improving reliability.

In future, we expect changes in industry structure and increased competition to accelerate technological development, and we see no reason to expect a learning rate of only 10% as assumed in [3] and Figure 18.

Technology trends

Mainstream technology

The 30-year development of wind energy technology, with its focus on reducing the cost of energy, has seen the size of the largest turbines increase by a factor of 100, from roughly 50 kW to 5 MW.

This is in spite of a theoretical limit to the maximum size of a wind turbine. As a wind turbine increases in size (while keeping the same proportions) its energy output increases as the square of the rotor diameter, but its mass increases roughly as the cube of the rotor diameter (the “square-cube law”). As the mass increases, the mechanical loads imposed by gravity increase even faster, until the point where the materials available are not strong enough to withstand the stresses on the turbine.

So far, engineers have avoided the limits of the square-cube law by steering clear of direct geometrical similarity, using materials more efficiently, and using stronger materials. Perhaps most importantly, designers have tailored the responses of turbines ever more carefully to the conditions under which they operate, and this remains one of the main ways of reducing the cost of energy from future turbine designs.

Issues of geometry notwithstanding, several factors favour larger turbines. However, it seems fair to assume that at some point the cost of building larger turbines will rise faster than the value of the energy gained. At this point scale-up will become a losing economic game.

As a result, it is important also to look at other ways of cutting costs. This can be done, for instance, by introducing cheaper technology or by increasing the amount of energy captured by a rotor.

Conventional wind turbines use gears to match the slow speeds of the blades and hub to the higher speeds required to drive a standard induction generator. It has been known for many years that a multi-pole generator, which can run at slower speeds, offers the chance to eliminate the gearbox. Early multi-pole generators were large and heavy, but newer permanent-magnet designs, in which the rotor spins outside the stator, are compact, efficient and relatively lightweight. The next generation of multi-MW gearless wind turbines is expected to create a step change in the industry, followed by further gradual cost reductions as with previous turbine types.

Lightweight blades

As described above, geometrical similarity says that as blade length increases, blade weight should increase with an exponent of 3 (a cubic law). In fact, several studies have shown that over recent decades the actual exponent has averaged around 2.3, and for the most recent blade designs it is 2.2 or 2.1.

Many factors have aided the move to lighter blades, of which the most important has been the development of blades that are much thicker than their predecessors, especially near the hub. Because they are stiffer at the point where the loads are highest, these new blade designs make more efficient use of materials and are lighter overall. This principle can continue to produce even larger blades that beat the square-cube law as long as it is backed by the necessary R&D into better design methods, new materials such as carbon fibre, and advanced manufacturing techniques.

One potential drawback of using thicker airfoil shapes at the blade root is a loss of aerodynamic efficiency. The answer may lie in high-lift designs such as multiple airfoils for use at the blade root, or the newly developed “flat-back” airfoil, which can maintain lift even when it is very thick.

Another way of cutting the cost of wind energy is to increase blade length while reducing the fatigue load on the blade. There can be a big payoff in this approach because material consumption is approximately proportional to fatigue loading.

Fatigue loads can be reduced by controlling the blade’s aerodynamic response to turbulence. This is already done actively via the turbine’s pitch control system, which turns the complete blade, and future turbines may also feature movable control surfaces distributed along the blades.

An especially elegant idea is to build passive ways of reducing loads directly into the blade structure. Using the unique attributes of composite materials to tailor its structural properties, for instance, a blade can be built in a way that couples its bending and twisting deformations.

Another way of achieving this “pitch-flap” coupling is by building the blade in a curve so that fluctuations in the aerodynamic load produce a twisting movement which varies the angle of attack. It should also be possible to vary the lift produced by the blade by altering the camber of the airfoil in response to flap-wise deformation, as birds’ feathers do. Such complicated blade motion will require a very good understanding of wind turbine aerodynamics and materials science.

Innovative systems of trailing-edge control could considerably reduce the fatigue loads on blades. These are now being developed in projects involving European research institutions and industry, including the large EU-funded UpWind project.

As well as reducing loads, such advanced multi-control options could help to improve turbine performance and tune the turbine’s operation to on-site conditions. For instance, a laser ranging (LIDAR) system mounted on the turbine could measure upstream wind speed and detect turbulence before it arrives at the turbine, giving an active control system more time to respond.

Indeed, aiming for cost reductions is not only a question of improving the rotor and generator as elaborated on here. The life-cycle cost of energy from an offshore wind farm comprises the wind turbines, installation and substructures, grid and O&M as the four dominating elements (Figure 21). Hence, for cost reductions to be achieved, a broad approach must be taken, addressing wind turbine technology, but also substructures, grid and O&M.

Emerging technologies

So far, most development efforts have been dedicated to an evolutionary process of scaling up and optimising the land-based, three-bladed standard wind turbines which first emerged as commercial products at the beginning of the 1980s.

To the original design have since been added individual blade pitch control, variable speed and other refinements to match the increasing size of the turbines; increasingly stringent performance and reliability requirements; and adaptations for use offshore.

One example of a technical development is “negative coning”, in which the blades point slightly forward; this increases the clearance between the blades and the tower, and also improves stability for very flexible blades. Such improvements are only possible when turbine engineering goes hand in hand with the development and application of advanced simulation and design tools. Without such tools, it would not have been possible to increase the size of wind turbines by a factor of 100 in 30 years.

Offshore wind power brings new opportunities, since offshore winds are generally stronger and steadier, but represents an even bigger challenge for turbine development, operation and cost optimisation. Operating conditions offshore are very different, so what is most cost-effective onshore may need a radical re-think for use out at sea. Figure 22 shows how future offshore turbines might diverge from their land-based counterparts.

New ideas offshore

The strength of the offshore market, and the very different conditions found offshore, make it likely that completely new types of offshore turbine may emerge. An example is the vertical-axis floating turbine illustrated in Figure 23.
Vertical-axis turbines have been tried and rejected for onshore use. The logic for using them offshore runs as follows:

The need to install turbines in deep water, where foundations are expensive, makes floating turbines an attractive idea. But conventional horizontal-axis turbines carry a large amount of weight at the top of the tower (high “top mass”), and this can cause balance problems for floating turbines. Vertical-axis turbines have lower top mass and do not need to turn into the wind, so large floating versions may become attractive.

Another idea is to harvest energy from wind and waves at the same time. The shared supporting structure and infrastructure might create a symbiosis that could accelerate the development of reliable and cost-effective wave energy solutions.

High-altitude wind systems

Various arrangements of balloons, kites and other tethered airfoils have been proposed to take advantage of strong winds at greater heights than rigid turbine towers can reach.

There are two basic approaches: Either transmit mechanical energy directly to the ground, where it can generate electricity or be used in other ways; or generate electricity aloft and send power down through a tether.
Up to around 500 metres, wind speed increases with height.

From 500 metres up to 2,000 metres, however, wind power density12 actually decreases slightly with altitude. Above 2,000 metres, wind power density again increases monotonically with height. The jet streams – narrow “corridors” of wind which move around at altitudes of 7-16 kilometres – are an order of magnitude faster than winds near the ground.

There may not be much benefit from going higher than 500 metres, therefore, unless we can place devices above 2,000 metres, or preferably in the jet streams.

Urban wind turbines

Small wind turbines and urban wind energy might seem just a curiosity in terms of their contribution to the energy supply, but this could change in future.

By 2050, our energy systems are likely to be much less centralised than at present, and people will be taking more responsibility for energy at a local level. These changed perceptions could make urban wind energy more attractive.

The challenge is to develop “urbines” that can be integrated cost-effectively into the built environment. Low sensitivity to turbulence and low noise are essential.

Wind power in context

We have shown above that the opportunities for wind energy are enormous; they expand still further if we take into account the predictability of wind energy when studying the economics of energy investments.

The report Wind Force 12 is based on the realistic assumption that wind power will continue to grow in the next ten years as it has over the past ten. If this is so, by 2020 installed wind capacity will be increasing at 151 GW/yr, representing an annual investment of €75 billion. In this scenario, wind power will produce 12% of the world’s electricity requirement by 2020, by which time it is assumed to be 30,000 TWh/yr compared to 18,000 TWh/yr today. The technological vision of Wind Force 12 is to make wind power 40% cheaper in 2020 than it was in 2000.

In 2000, global electricity production was 15,000 TWh/yr. This amount of power could be produced by a fictitious wind farm measuring 1,000 kilometres square. Such an array of turbines would fit into the Great Plains of the USA and still leave 98% of the land available for agricultural use. Supplying the world’s total energy needs from wind would require an area around four times bigger, and generating 60,000 TWh/yr. For comparison, Wind Force 12 estimates the world’s total exploitable onshore wind resource to be 53,000 TWh/yr.

Even with the predicted increases in energy demand by 2050, the idea of getting all the world’s energy from wind is still realistic in terms of the geographical area needed. This would, however, require enormous changes in our systems for converting, transporting and storing energy.

Apart from its basic role in getting electricity from wind turbines to consumers, power transmission has an important part to play in balancing local fluctuations in wind power production against fluctuations in consumption. Europe is currently placing much emphasis on strengthening and extending the transmission lines between load centres and producers, including offshore wind power plants.

Other ways of balancing demand and production include wide geographical distribution of wind power plants, better forecasting of wind, demand management and electricity storage.

Conclusions

We believe that the development of wind energy has only just begun, with respect to both technology and application. The past 30 years of R&D have established a firm foundation for wind power. While further R&D will certainly be necessary to reduce costs and fully exploit the great potential of wind, much of the earlier uncertainty about the feasibility of wind energy has now been dispelled.

The next decade is thus shaping up as a new period of technology development and further scale-up, leading to more cost-effective, reliable and controllable wind turbines and new applications for wind power.

Increased international competition is helping to reveal the great potential that exists for wind power technology and markets. The increasing dominance of the industry by high-tech global companies and the move towards offshore siting favours ever-larger wind turbines and opens up new perspectives.

Finally, there is increasing awareness that renewables in general and wind energy in particular will play a major role in the global energy supply as oil and gas are phased out in the period towards 2050, and the cost of coal-based energy increases, not least due to the cost of carbon capture and storage.

Wind energy has the potential to supply 30-50% of our electricity, and to do this cost-effectively.

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, in CHP systems based on sophisticated combustion technologies and as a source of liquid fuels for transport.

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. Biomass is a limited resource, and increases in biomass production should preferably not compete with the food supply.

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 potential for the future is huge. According to estimates by the International Energy Agency, the most probable potential for the global geothermal resource is approximately 200 EJ/yr, including 65 EJ/yr from electricity production.

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.

To date, R&D work on energy storage has focused on electricity, as electricity storage has an obvious, straightforward and urgent role in the energy market. Many types of electricity storage will be of great importance in the coming decades.

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

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. 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 fission is a proven technology, but its exploitation has grown only 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. In total, nuclear provides 14% of the world’s electricity consumption, though this figure has fallen slightly in recent years.

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 main cost of CCS relates to 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.

System aspects

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 approach 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.

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 local energy supplies such as heat pumps. Information and communications technology (ICT) will be very important to the successful integration of renewables in the grid.

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.

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 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”.

Main conclusions

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 to the extent that it can be done 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.

Several energy supply technologies with low or even zero GHG emissions are already available on the market or will be commercialised in the decades ahead.

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.