In today's fast-paced world where technology is advancing at fantastic speeds, the trend is bigger, better, faster and more complex, whether talking about smart grid technology or renewables. No sooner than the latest generation of technology is installed, it is out of date. The latest widget is not only bigger — or in some cases smaller — it is full of new features that suddenly one cannot live without.
Remember when wind turbines were 50 ft (15 m) tall with rotor blades 130 ft (40 m) in diameter, generating 50 kW? That wasn't so long ago. Today, the typical wind turbine rating runs between 1 MW and 3 MW, with 5 MW becoming more commonplace and 10 MW under test.
Fairly representative of today's technology is the V80-2.0 MW wind turbine from Danish manufacturer Vestas Wind Systems. The V80 is one of the workhorses of the industry. It stands over 410 ft (125 m), depending on the tower selected. Its nacelle, the generating equipment housing, weighs about 74 tons (67 metric tons), the blade assembly is roughly 40 tons (36 metric tons), and the tower is another 173 tons (157 metric tons), depending on the configuration, bringing the total weight close to 290 tons (263 metric tons).
The American Wind Energy Association (AWEA) reports that the typical transport of a turbine this size takes about eight semi loads: one nacelle, one hub, three blades and three tower sections. For a 150-MW project, the transportation requirements can be as much as 689 truckloads, 140 rail cars and eight ships to the United States.
Megawatts, Mega Turbines
In 2009, Belgian developer WindVision began construction of the Estinnes wind farm in Belgium. This wind farm will have installed in it 11 of the world's largest wind turbines — the Enercon E-126 7-MW wind turbines.
The E-126 was originally nameplated for 6 MW but improvements have allowed Enercon to increase the rating to 7 MW. The E-126's hub height is approximately 440 ft (134 m), and the rotor diameter is about 415 ft (127 m).
Since January 2010, five of these huge turbines have been operational. Video of two of these turbines, erected in Emden, Germany, can be seen in operation on YouTube.
Is There a Limit?
The paint is hardly dry on the E-126 and there is a new challenger for world's largest wind turbine on the scene. In early 2010, the Norwegian company Sway AS announced it was partnering with the Norwegian state utility Enova and Clipper Marine of the U.K. to bring to life an offshore wind turbine rated at 10 MW. This wind turbine will have a rotor diameter of 475 ft (145 m) and a hub height of 525 ft (160 m). It will be located in Oeygarden, Norway, and is scheduled for completion in 2013.
One of the forces driving this trend to larger wind turbines is economics, of course. AWEA has compiled data showing the cost of electricity generated by wind turbines has dropped by more than 80% since the early 1980s. At that time, electricity cost between $0.30/kWh and $0.40/kWh. Today, it is costing between $0.03/kWh and $0.05/kWh, similar to fossil fuels. AWEA accredits this reduction to larger wind farms and improved technology.
Cost is only part of the equation. As AWEA experts stated, there also is the advancement of technology. From the pure physics of the situation, the total amount of energy the turbine can remove from the wind is directly proportional to the sweep of the turbine's blades (total area). In other words, the longer the blades, the greater the power generated by the turbine.
To increase the length of the blades, the hub needs to be higher, and it gets heavier because of the increased generator rating. As the tower gets taller, the wind speeds increase. Mathematically, the energy generated from the wind is proportional to the cube of the wind speed the turbine encounters. If the wind speed can be doubled, more than eight times the energy can be extracted. That is the incentive for turbine manufacturers to push the technology envelope to allow for longer blades and higher hub heights.
Increase the Rating, Not the Size
If a manufacturer can increase the rating of the turbine without increasing the size, the manufacturer becomes popular. If it can increase the rating and reduce the size of the turbine while improving reliability, the manufacturer becomes really popular. Since technology is progressing at an exponential rate, it is reasonable to expect improvements are close at hand. Direct-drive wind turbines hold the promise of answering these problems.
The Global Wind Energy Council reports that direct-drive systems have been around for several years. Enercon has been a pioneer in direct-drive technology for years. The direct-drive technology simplifies the nacelle by doing away with the gearbox, which reduces weight. As a result, they are lighter, cheaper and more reliable (the gearbox causes most of the maintenance problems). Much of the weight reduction comes from the elimination of the gears and the use of permanent magnets instead of electromagnets that require starter brushes, coils and power from the grid every time they are started.
Recently, Siemens and GE Energy announced designs using direct-drive technology. Siemens has developed the SWT-3.0-101 DD 3-MW turbine. The company recently announced that Minnesota Power has decided to modify its original Bison 1 Wind Power Plant turbine order to include 15 of the Siemens SWT-3.0-101 direct-drive machines. According to Siemens, the SWT-3.0-101 DD 3-MW nacelle weighs 12 tons (11 metric tons), about 25% less than its 2.3-MW turbine's nacelle.
GE Energy also has developed a direct-drive wind turbine for offshore installations. The company plans to supply its 4.0-110 4-MW direct-drive wind turbine for the first freshwater offshore wind farm in the United States. GE is partnering with the non-profit Lake Erie Energy Development Corp. for a 20-MW wind project in Ohio's Lake Erie shoreline.
Chinese manufacturers also see the advantage of direct-drive wind turbines. Consequently, it was not surprising when Chinese conglomerate Xiangtan Electric Manufacturing Corp. Ltd. (XEMC) purchased the Dutch company Darwind. Darwind has been developing designs for a 5-MW direct-drive wind turbine. The new company XEMC Darwind announced it will have two prototypes of the DD115 5-MW offshore wind turbine beginning trial testing, with one unit installed in China and one in Europe.
Superconducting Technology Meets Wind Technology
Another interesting technology twist is from American Superconductor Corp. (AMSC) in the form of a 10-MW class high-temperature superconducting (HTS) wind turbine. AMSC is developing the turbine by combining the wind turbine engineering experience of its Windtec division with its leadership in the superconductor arena.
“The 10-MW turbine is called the SeaTitan,” said Martin Fischer, general manager for AMSC Windtec. “It is a direct-drive wind turbine that will use AMSC's Amperium HTS for the rotors rather than copper. AMSC has developed a 36.5-MW HTS motor for the U.S. Navy that is being tested on a ship. Converting that technology to generation is not a problem.”
AMSC estimates the generator system will weigh in at roughly 138 tons (125 metric tons), which is about 192 tons (174 metric tons) less than a conventional generating system of the same rating.
With all this interest in larger wind turbines, it is only natural that wind farms are growing larger, too. Huge wind turbines require huge wind farms around them. On average, about 50 acres (20 hectares) per megawatt is a good model. Turbine spacing is dependent on the nature of the terrain, the wind rose (a graphic tool used by meteorologists to describe wind conditions for a particular location) and the manufacturer's recommendations.
Wind farm turbines are typically placed in rows perpendicular to the prevailing wind direction. A typical rule of thumb for separation within a row is two to four rotor diameters and 10 rotor diameters between rows to avoid wind turbulence.
It gets more complicated when factoring in the variable-direction winds. The Global Wind Energy Council recommends the use of wind farm design tools (WFDT) for detailed wind farm layout. WFDT computational optimization may result in substantial gains in energy production over manually derived layouts.
Records Are Made to Be Broken
The world's first commercial wind farm was built in the United States by U.S. Windpower on a few acres on Crotched Mountain in southern New Hampshire in December 1980. It had 20 30-kW wind turbines. Compare that with the world's largest wind farm (currently) located in Roscoe, Texas. The Roscoe Wind Farm covers more than 100,000 acres (40,469 hectares) with 627 turbines to produce 781.5 MW of electricity. It was built at a cost in excess of $1 billion. Interestingly, the previous world's largest wind farm, Horse Hollow, also in the United States, held the record for less than two years (covering 47,000 acres [19,020 hectares] of land with 421 turbines to produce 735 MW of electricity).
One thing is for sure, Roscoe will not hold the title long. There are many new wind projects on the drawing boards. The proposed Caithness Shepherds Flats in Oregon will generate 845 MW from 338 turbines at an estimated cost of $1.3 billion.
Solar has followed the same technology trend as wind. It started off slowly but has been gaining market share as the technology becomes more efficient and the cost per watt drops. Basically, there are two types of solar technologies: concentrating solar power (CSP), also referred to as thermal solar, and photovoltaic (PV).
PV offers a direct conversion of sunlight to electricity but varies as the sun's energy varies and is gone when the sun is down. The first utility-scale solar PV power plant went on-line in 1982 in Hesperia, California. ARCO Solar developed a 1-MW solar farm consisting of 108 PV dual-axis tracker panels.
Since then, PV projects have grown to utility-scale proportions. First Solar will develop the Desert Sunlight solar project. It will be a 550-MW PV solar project covering about 4,500 acres (1,821 hectares). The project will consist of a 250-MW solar farm near Desert Center, California, and the 300-MW Stateline solar project located in northeastern San Bernardino, California. Pacific Gas & Electric Co. has signed a contract for 300 MW of the output. Southern California Edison will buy the remaining 250 MW.
CSP technology uses the sun's energy to heat a fluid to a very high temperature. The fluid is then circulated through pipes to transfer the heat to water to produce steam. At that point, electricity can be generated. For utility-scale solar generation, the most common CSP technologies are the parabolic trough and power tower designs, but there also are solar dish designs and Fresnel reflectors. Thermal solar offers the ability to provide electricity after the sun goes down, which is very attractive to utilities using renewables for generation.
The largest active solar energy facility in the world is the Solar Energy Generating Systems plant located at Kramer Junction, California. It started life as the world's first large-scale CSP facility, with 30 MW of capacity in 1986.
Today, it is made up of nine solar plants. Solar Energy Generating Systems has an installed capacity of 354 MW using 936,384 parabolic mirrors, reaching operating temperatures of over 750°F (399°C). It covers more than 1,600 acres (647 hectares).
How long the Kramer Junction facility will remain the largest solar farm is anyone's guess. The Los Angeles Times reports that BrightSource Energy Inc. started construction on the Ivanpah solar project on Oct. 28, 2010, in the Ivanpah Valley in Southern California. The CSP facility will have a capacity of 392 MW using three 459-ft (140-m) solar towers. The U.S. Department of Energy has guaranteed a loan worth nearly $1.4 billion for the project.
According to Bloomberg, the joint developers (Solar Millennium, LLC and Chevron Energy Solutions) received approval from Secretary of the Interior Ken Salazar for their $6 billion Blythe solar project. The Blythe project will have a capacity of 1000 MW and cover 7,025 acres (2,843 hectares). Southern California Edison will purchase all of the output from the project and will build a 230-kV transmission line to connect the Blythe project to its system.
The New York Times reports that there are nine solar plants in permitting currently. If approved, they will cover 41,229 acres (16,685 hectares) of Bureau of Land Management land and have the capacity to generate 4580 MW of electricity. As if those statistics are not mind-boggling enough, there is the $550 billion DESERTEC solar power project to consider. It will be located in the Sahara Desert and is purported to be the size of Wales. Wind-wise, the story is the same — big facilities.
Google plans to invest in the Atlantic Wind Connection project, a $5 billion 6-GW, 350-mile (563-km)-long offshore wind farm planned to be located along the U.S. Atlantic Seaboard. The energy harvest is getting serious, but how can the industry intellectualize a wind farm 350 miles long or a solar farm the size of a country? Has the industry's reach exceeded its grasp? Only time will tell.