Development of the modular EP4 platform started with a blank sheet of paper in a process that managing director Nicole Fritsch-Nehring describes as a mix of evolution and revolution: "Our focus was on developing a smart turbine with the main design drivers being cost-effective large-series manufacture, optimised transport-logistics and uncomplicated site assembly and installation."
While several manufacturers now claim an extended 25-year design life for their turbines, the EP4 is thought to be the first wind turbine platform specifically developed to last for 30 years. Fritsch-Nehring believes this is an essential step in changing project financing conditions, especially as it allows asset depreciation to be spread over ten more years, driving down the lifecycle-based cost of energy (CoE).
The new E-126 EP4 shares some of the characteristics of the older E-126 Enercon model, which was launched as a 4.5MW model 12 years ago and evolved into the current 7.5MW. The E-126 EP4 is direct drive with a 127-metre rotor diameter, a mainly air-cooled electrically excited synchronous generator, and segmented blades.
But while the old E-126 has a huge 12-metre disc-shaped generator and equally large nacelle, the new E-126 EP4 looks quite different. The nacelle is substantially smaller, reduced by 9 metres diameter and 19 metres in length, the wide classic blades are replaced by slender, flat-back airfoils, and the tower is higher and slimmer.
The EP4 platform will be introduced in Germany, then sold into other European markets including France, Belgium and the Netherlands, as well as Canada. Main component and production manufacturing or assembly plants are planned in existing and new Enercon facilities in these core markets.
A prototype of the 4.2MW medium-wind model is planned for late 2015, followed by 50 pre-series and serial turbines in 2016, and an envisaged ramp-up to 100 units in 2017 and up to 500 units in 2019.
The low-wind, IEC III model is a departure for Enercon. "Enercon for a long time focused on turbine models for IEC IA and IEC IIA sites," said Fritsch-Nehring. "The EP4 platform will be our first to be expanded by an IEC class III model version with reduced power rating, but a increased rotor diameter and higher available hub heights. This prototype is planned for 2017. The third and final EP4 expansion will be a high-wind IEC class I model."
The development of the EP4 platform took two years and permanently engaged 20 lead technical experts. Enercon's R&D department comprises around 500 engineers and scientists, and additional specialists from various disciplines also worked on the project.
According to Fritsch-Nehring, the EP4 blades offer 30% load reduction compared with the "classic-shape" E-126 blades, comprising a bolted inner-steel segment and outer glass-fibre-reinforced epoxy (GFRE) segment. "This substantial loads reduction has a positive impact on the complete installation mass and cost," she said. "One example is the new concrete-steel tower with reduced dimensions and base diameter, which offers additional savings during ring segments transportation and tower installation. A second example is the new optimised foundation that requires 10% less concrete."
Weather protection
The E-126-EP4 blade structurally builds on E-115 principles and operating experiences. It again consists of a yield-enhancing flat-back airfoil in two GFRE segments, adapted to the new turbine's enlarged size and specifications. "We optimised the wrapping process of the inner blade segment and chose again not to incorporate carbon in the laminate, mainly for cost considerations. Another reason is that a lot of effort has been dedicated to developing an effective blade lightning strike protection system and the conductive properties of carbon could negatively impact this overall capability," Fritsch-Nehring said.
The E-126, EP4 and other turbine models operating in cold-climate environments can be fitted with an advanced blade anti-icing system, including an ice-detection system. It comprises a combination of electric heating elements integrated into the laminate, and a second complementary system that can blow hot air inside the blade during operation if required. Fritsch-Nehring showed validated test results indicating up to 80% reduction in blade icing-related turbine stoppages.
Segments
Enercon's 2–3MW models all incorporate a ring generator that has a 4.0-5.5-metre diameter but varies in length, and whther they are air-cooling or water-cooled (3MW E-82, E-101, E-115). For environmental and cost reasons Enercon as a policy increasingly transports raw materials, main components and complate assemblies via its own expanding train network. However, these single-piece generators are to wide, and thus have to be carried by truck, often requiring special permits and police guidance. The EP4 generator, although substantially bigger, is split in 180-degree segments, enabling train transportation and optimised road-transport logistics. The generator halves are precision manufactured and assembled on site.
Fritsch-Nehring explained that Enercon retained its standard 400V generator voltage, but with a new stator coils design offering enhanced heat dissipation capability. "The larger specific generator volume further enhances natural heat dissipation capability. The combination with the new stator coil design enabled air-cooling. The main benefits are a 35% reduction in cooling-system energy consumption, while the use of cooling fans necessary for additional generator temperature management could be reduced by 50%," she said.
Noise reduction
Enercon clients increasingly demand quiet turbines for various reasons said Fritsch-Nehring. "We therefore dedicated much time and overall effort to reducing especially generator and blade-related noise levels. These two main components are generally two primary sound power sources, and compared to the current E-126 we achieve a reduction from 108 dB(A) to 105 dB(A). Halving the sound power level allows closer turbine placement in urbanised areas and generally benefits public acceptance at noise-constrained sites."
In preparation for the future serial casting of E-126 EP4 cast components, including the four-piece hub, main pin, main carrier, and generator stator shield, in-house foundry capacity will be increased. Foundry equipment such as the ladles for pouring the liquid iron must be upgraded to able to produce the much larger components,. Fritsch-Nehring said that Enercon's foundry capacity will be used increasingly for 3MW and new 4MW class castings.
The E-126 EP4 will be available with in-house concrete-steel towers offering hub heights up to 144-metres, representing a record total installation height of 207.5-metres. The 7.5MW E-126 by comparison comes with a full concrete tower and standard 135-metre hub height.
The E-module in the tower base contains all power electronics, including a split transformer design for optimised upkeep.
When asked about her views on the future of Enercon's main platforms within the expanded product portfolio, Fritsch-Nehring said: "Despite the current key importance of our 2MW-plus E-70, E-82 and latest E-92 models, we do expect to see a smaller role for these products as part of total sales volume in the future. For the 3MW and 4MW turbines we expect a stronger and especially complementary role."
