The last two decades have seen amazing changes in wind turbine technology – from 50 kilowatt (kW), 15 metre rotor diameter machines on land to multi-megawatt, 100 metre rotor diameter machines installed in the sea.

In terms of technology there has been a change from stall controlled, fixed speed machines with gearboxes, to pitch regulated, variable speed, and gearless turbines.

The two machines differ in regards to their normalised tower head mass, which refers to the tower head mass divided by the swept area of the rotor. This disparity even occurs amongst turbines that use similar technology and is, in part, due to the application of sophisticated controls that create an ‘intelligent turbine’.

In using stall controlled turbines the wind direction is monitored to ensure the turbine faces into the wind. Pitch control is used to monitor the output and to adjust the pitch of the turbine. With variable speed, torque control is introduced to reduce drive train loads. Nacelle accelerometers have allowed nacelle vibrations to be monitored and limited by pitch adjustments. Most recent developments include load sensors within the blades themselves, and the application of individual blade pitching to control those loads.

In short, wind turbines have gone from tractor to helicopter technology over the last 25 years. The application of intelligent controls has allowed loads to be controlled, and turbines to become lighter. However, there is still some debate in the industry over which approach is better ‘light and twitchy’ or ‘heavy and dumb’.

In the drive train there are a number of approaches. There is the typical configuration of a three stage gearbox and a high speed generator. There is the Enercon approach of a large, low speed generator, and no gearbox. There is also a hybrid possibility of a one or two stage gearbox, and a medium speed generator, which is used by Winwind. The jury is still out on this issue.

In other technology developments, there is a trend to full power conversion, as it allows more flexibility in complying with grid codes. There is also increasing possibilities for the deployment of permanent magnets and superconductors within wind turbines.

Until recently the obvious trend for wind turbines has been ‘bigger and bigger’, which in turn is changing to a trend of ‘better and better’. In terms of size, we expect an ongoing demand for 1-2 megawatt (MW) machines simply due to transportation limitations. Offshore market turbines will continue to get bigger and bigger, and there may also be a market for bigger turbines in some onshore locations. Garrad Hassan also sees a developing market for smaller turbines where transportation is a limitation, as well as perceiving opportunities for new kW class wind turbines.

In terms of technical challenges to the wind industry the key issues are gearbox reliability and understanding what the loadings are, generator reliability, capital cost reduction, long term operation and maintenance costs and quality.

Market

The three largest wind markets today are Germany, Spain and the US. The German market is politically driven and has been consistently the largest market for a number of years. The Spanish market is political-cum-commercial, and has also been a consistent market. In contrast, the US market has been inconsistent as the production tax credit (PTC) has been turned on and off, however more stability has been achieved recently with the advent of a longer term PTC.

At present the world market demand is close to maximum turbine manufacturing capability which could lead to major bottlenecks in the supply of forgings, gearboxes, and ironically perhaps, carbon for high quality steel manufacture.

Although there are a large number of new turbine manufacturers coming onto the market, it is unlikely that they will relieve the supply shortage, as the supply bottlenecks are in the upstream manufacturers, and the new turbine manufacturers will rely on the same sources of gearbox and forgings supply as the existing manufacturers.

Industry

The top nine wind turbine manufacturers account for 95 per cent of the production of wind turbines. Recent years have seen the arrival of the large multi-nationals such as GE, Siemens and most recently Alstom in wind turbine manufacturing. The involvement of companies such as these cannot be overestimated as it signifies the move of the wind turbine manufacture into the main stream power industry.

Within the industry there is a significant divergence between manufacturers on the proportion of in-house manufacture; manufacturer or assembler. On the one hand there are manufacturers like Enercon, which manufactures almost everything in house because of the unique design of its turbines. There are also companies such as MHI, which has the capability to manufacture almost everything in house and takes advantage of this, while other companies have the same capabilities but choose not to use them. Vestas, Gamesa, Suzlon and Siemens are some of the companies that have significant in-house capability while still having significant sub-suppliers.

There have been some manufacturers moving towards more in-house supply, notably Suzlon, however this is not seen as a general trend. Most new manufacturers, including approximately 40 Chinese manufacturers of 1.5 MW wind turbines, tend to be toward the ‘assembler’ end, but there may also be some that arrive at the manufacturer end of the spectrum.

On the developer side, historically there has quite a division between markets. Germany has been dominated by small projects run by individuals or small groups, using large turbines, while India has mainly focused on small projects using small turbines. On the other hand, the US has produced large projects using medium sized turbines. On the whole there is a general trend towards big utility wind farms, i.e. large projects using large turbines.

The new utility owners not only bring new contract structures, but also create opportunities for new players, and mean that new suppliers will arrive, especially from Asia. Funding trends are also changing; there is less ‘simple’ project finance, more balance sheet building and portfolio funding, lots of assets changing hands, and lots of banks chasing deals.

Future

Region specific wind turbines: The wind industry evolved in northern Europe, however the places where wind is now being deployed have significantly different characteristics. There are likely to be opportunities for regional specific turbines to develop in order to take advantage of, or cope with the conditions of a specific region. In general, a mean wind speed makes money while an extreme wind speed costs money. If companies create an index based on a ratio of the extreme to the mean, the differing conditions of each region becomes clear. For example in Brazil, the ratio of extreme to mean winds is low, whereas in many parts of Asia the occurrence of typhoons causes a high ratio.

Offshore wind turbines: The conditions offshore are different to those experienced by land based turbines. To date, most offshore turbines have been marinised versions of land based turbines. Offshore there is low turbulence, low shear and no human neighbours. This may pave the way for shorter towers, faster running rotors, different blades, larger turbines, and perhaps two-bladed machines. Offshore is technology limited – an engineer’s dream.

Forecasting: Accurate forecasting means that wind energy can ‘look like’ conventional generation. Garrad Hassan is now forecasting for 2,000 MW in five countries. Forecasts for a portfolio of wind farms are more accurate than for a single wind farm. Wind is variable, but predictable. It is not an intermittent energy supply nor does it disappear instantaneously.

The grid: The grid is the key. 25 years ago, when wind was small and environmentally driven, the energy source was treated with ridicule by grid operators. At present, driven by environmental and security of supply reasons – for example, Europe does not want to be dependent on Russian gas – wind is treated with a mixture of animosity and co-operation. The attitude of the Transmission Service Operator depends on experience – in general the more experienced the more co-operative. In a few years time, when wind truly becomes least cost, full co-operation from grid operators may be possible.