Steel forgings for windmills to be produced in joint venture

February 3, 2016
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Sumitomo Corp., Japan, and the Japan Steel Works  have formed a joint venture with Gerdau Steel, Brazil, to manufacture forged steel products for wind power generation. Gerdau is the largest long steel manufacturer in Brazil. Production of these forged parts is expected to begin in 2017.

The joint venture (tentative name "Gerdau Summit"), in addition to the existing business of Gerdau, plans to expand the business into the production and sale of wind power generation forged products.

Currently, the Brazilian government's policy is to almost double the ratio of wind power generation from a national total power supply of 6% in 2015 to 11% in 2024, in order to meet future electricity demand. To achieve this goal, the government provides support for wind power generation projects and encourages domestic manufacturing of wind power generation-related parts.

"We're working to transform Gerdau into a more efficient and profitable company, given the current and future challenges of the global steel industry," said Gerdau CEO Andre B. Gerdau Johannpeter. "We're seeking to join forces with partners who have recognized experience in their industries in order to create new business opportunities. With Sumitomo Corporation and JSW, we will develop higher-value products for our clients, which will enable them to generate higher profit margins."

JSW has long been leading the world's forging industry with its manufacturing technologies, mainly in the energy field such as power generation. Sumitomo also has significant experience and knowledge within the renewable energy and wind-related business, which has been cultivated through many infrastructure projects and related parts sales respectively. By bringing the strengths of these two companies together with Gerdau's strong production base,"Gerdau Summit" will focus on the production and sale of forged products for wind power generation in the Latin American market with a focus on Brazil.  JSW has plenty of experiences to transfer its forging and casting techniques to foreign countries. Based on such experiences, JSW launches its overseas joint venture project for the first time in the forging and casting field.

www.sumitomocorp.com

Keystone spiral welding technology enables taller wind turbines

November 19, 2014
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Keystone Tower Systems, Somerville, Mass., is developing a system that adapts a traditional pipe-making technology to make wind turbines on location at wind farms, making taller towers more economical.  A modification of spiral welding, the system involves a process in which steel sheets are fed into a machine in which they are continuously rolled into a spiral, while their edges are welded together to create a pipe.

The process allows the steel rolls to be tapered and made of varying thickness, to create a conical tower. The automated process uses  about one-tenth the labor of traditional construction, because it is made of steel to make the entire tower, instead of concrete.

With Keystone's onsite fabrication, manufactures can make towers that reach more than 400 feet. Wind that high can be up to 50% stronger and is not blocked by trees. A 460-foot tower, for instance, could increase energy capture by 10 to 5% compared with today's more common 260-foot towers. For 450-foot, 3-megawatt towers, a base 20 feet in diameter will suffice. (Increasing diameters by even a few feet can make towers almost twice as strong to handle stress.)

Keystone is now conducting structural validation of towers built by its system in collaboration with structural engineers at Northeastern University and Johns Hopkins University. For the past year, the startup has been working toward deploying a small-scale prototype (about six stories high) at the MIT-owned Bates Linear Accelerator Center in Middleton, Mass., by early 2015.

www.keystonetowersystems.com   

Tapping energy from the sun through heat and light

January 20, 2014
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A new approach to harvesting solar energy, developed by Massachusetts Institute of Technology, Cambridge, researchers, could improve efficiency by using sunlight to heat a high-temperature material whose infrared radiation would then be collected by a conventional photovoltaic cell. This technique could also make it easier to store the energy for later use, say researchers.

Adding the extra step in this case improves performance because it makes taking advantage of wavelengths of light that ordinarily go to waste possible. A conventional silicon-based solar cell "doesn't take advantage of all the photons," explains associate professor of mechanical engineering Evelyn Wang. That's because converting the energy of a photon into electricity requires that the photon's energy level match that of a characteristic of the photovoltaic (PV) material called a bandgap. Silicon's bandgap responds to many wavelengths of light, but misses many others.

To address that limitation, the team inserted a two-layer absorber-emitter device—made of novel materials including carbon nanotubes and photonic crystals—between the sunlight and the PV cell. This intermediate material collects energy from a broad spectrum of sunlight, heating up in the process. When it heats up, as with a piece of iron that glows red hot, it emits light of a particular wavelength, which in this case is tuned to match the bandgap of the PV cell mounted nearby.

This basic concept has been explored for several years, since in theory such solar thermophotovoltaic (STPV) systems could provide a way to circumvent a theoretical limit on the energy-conversion efficiency of semiconductor-based photovoltaic devices. That limit, called the Shockley-Queisser limit, imposes a cap of 33.7% on such efficiency, but Wang says that with TPV systems, "the efficiency would be significantly higher—it could ideally be over 80%."

There have been many practical obstacles to realizing that potential; previous experiments have been unable to produce a STPV device with efficiency of greater than 1%. But Lenert, Wang, and their team have already produced an initial test device with a measured efficiency of 3.2%, and they say with further work they expect to be able to reach 20% efficiency—enough, they say, for a commercially viable product.

The design of the two-layer absorber-emitter material is key to this improvement. Its outer layer, facing the sunlight, is an array of multiwalled carbon nanotubes, which very efficiently absorbs the light's energy and turns it to heat. This layer is bonded tightly to a layer of a photonic crystal, which is precisely engineered so that when it is heated by the attached layer of nanotubes, it "glows" with light whose peak intensity is mostly above the bandgap of the adjacent PV, ensuring that most of the energy collected by the absorber is then turned into electricity.

In their experiments, the researchers used simulated sunlight, and found that its peak efficiency came when its intensity was equivalent to a focusing system that concentrates sunlight by a factor of 750. This light heated the absorber-emitter to a temperature of 962°C.

This level of concentration is already much lower than in previous attempts at STPV systems, which concentrated sunlight by a factor of several thousand. But the MIT researchers say that after further optimization, it should be possible to get the same kind of enhancement at even lower sunlight concentrations, making the systems easier to operate.

Such a system, the team says, combines the advantages of solar photovoltaic systems, which turn sunlight directly into electricity, and solar thermal systems, which can have an advantage for delayed use because heat can be more easily stored than electricity. The new solar thermophotovoltaic systems, they say, could provide efficiency because of their broadband absorption of sunlight; scalability and compactness, because they are based on existing chip-manufacturing technology; and ease of energy storage, because of their reliance on heat.

Some of the ways to further improve the system are quite straightforward. Since the intermediate stage of the system, the absorber-emitter, relies on high temperatures, its size is crucial: The larger an object, the less surface area it has in relation to its volume, so heat losses decline rapidly with increasing size. The initial tests were done on a 1 cm chip, but follow-up tests will be done with a 10 cm chip, they say.

Zhuomin Zhang, a professor of mechanical engineering at the Georgia Institute of Technology who was not involved in this research, says, "This work is a breakthrough in solar thermophotovoltaics, which in principle may achieve higher efficiency than conventional solar cells because STPV can take advantage of the whole solar spectrum. … This achievement paves the way for rapidly boosting the STPV efficiency."

The research team also included MIT graduate students David Bierman and Walker Chan, former postdoc Youngsuk Nam, and research scientist Ivan Celanović. The work was funded by the U.S. Department of Energy through MIT's Solid-State Solar Thermal Energy Conversion (S3TEC) Center, as well as the Martin Family Society, the MIT Energy Initiative, and the National Science Foundation.

More information:

MIT

Image caption — A nanophotonic solar thermophotovoltaic device composed of an array of multi‑walled carbon nanotubes as the absorber, a one‑dimensional silicon/silicon dioxide photonic crystal as the emitter, and a 0.55 eV photovoltaic cell. Courtesy of John Freidah.