Avoiding excess erosion in a sandy environment

Operations and maintenance: Brazil has built much of its growing wind-power capacity in scenic coastal locations, creating specific operations and maintenance challenges.

Pretty tough Building wind farms on sand dunes increases the need for monitoring (pic: Iberdrola)
Pretty tough Building wind farms on sand dunes increases the need for monitoring (pic: Iberdrola)

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Brazil's first commercial wind farm was installed on the sandy seaside pier in Fortaleza, the windy capital of Ceara state in the north east. The Mucuripe project, which started operating in 1996 with four 300kW geared Tacke turbines, was a pioneering co-operation contract with the German government, but the climate and conditions were radically different from anything the Germans were used to. Temperatures hit 40 degrees Celsius in summer and fine grains of sands are whipped up from the beaches by constant wind.

The Mucuripe experience was to prove useful in the coming years as the country started building up its wind power in earnest. In 2002, just six years after it was constructed, Mucuripe was totally refurbished by Wobben Windpower, the Brazilian subsidiary of German turbine manufacturer Enercon, doubling the installed capacity to 2.4MW. The old turbines were dismantled and handed over to a local university for research.

"We replaced those turbines with our direct-drive E44-600kW units, which, because they had no gearboxes, were more appropriate to sandy conditions," says Eduardo Lopes, Wobben's commercial director. "Even though maintenance of the turbine is easier because of its gearless technology and aluminium nacelle, care has still to be taken to cool the equipment, keep salinity out and repair abrasion from sand, doing preventive maintenance to the concrete or steel towers," he says.

Monitoring trips to the towers are required almost twice as often as at non-sandy sites. According to Lopes, geared turbines in sandy and high-temperature locations often need to be replaced as often as every four years because of abrasion.

Brazil's more recently installed wind farms tend to be sited inland, but the bulk of the projects constructed since Proinfa - the country's incentive programme for alternative electricity sources - was implemented in 2004 are in sandy, seaside locations. Many are sited on sand dunes in states such as Rio Grande do Norte and Ceara in the tropical north-eastern region of the country, and in the cooler, temperate state of Rio Grande do Sul in the south.

Driving over sand

"The first wind farms built on dunes required innovations because of the moving sands," says Odilon Camargo, co-founder of wind-sector engineering consultancy Camargo Schubert. According to Camargo, engineers needed to place a layer of clay and rocks to stabilise the ground for trucks to reach the location. Even so, when the wind farms were completed and commissioned, the shifting sands continued to hinder access by large maintenance vehicles.

"In some cases, companies opted to use a kind of surf-break made of palm leaf or other local fibrous material," says Camargo.

Bloomberg New Energy Finance (BNEF) analyst Amy Grace recognises that the problem raises operations and maintenance (O&M) costs, although by how much is hard to quantify as there has been an overall global reduction in costs, according to the BNEF's Wind Operations and Maintenance Price Index.

"Harsh environments such as sandy and seaside locations do raise maintenance prices because of corrosion and the infiltration of sand in the turbines," Grace says. "On the other hand, competition, new availability-guarantee contract clauses and improved technology have brought down O&M costs."

According to the BNEF index, annual O&M costs have decreased by more than 30% since 2008 to around EUR 20,000 per megawatt in 2012, and continue to fall. In fact, wind farm operators throughout the world have been moving towards availability contracts, most of which guarantee around 98% availability. More than 90% of O&M contracts are now based on availability clauses, Grace says, compared with just 10% before 2011.

In any case, since Proinfa in 2002, owners have been modifying the turbines in Brazil to withstand saline conditions and high temperatures. Changes include refrigeration and protection against erosion or corrosion of parts. "In some cases, the nacelle had to be dismantled and taken to the factory to implement the changes, which resulted in high costs and loss of revenue," says Camargo.

Modifications also had to be made to towers and electrical components, says Lopes of Wobben, which operates about 1GW across 45 sites in Brazil, with 18 of these located on beaches or dunes. Its contracts include a 97% availability-guarantee clause and replacement of parts. "Some are simple, such as painting the towers with marine anti-corrosive paint, but these conditions require more frequent in-loco monitoring," he says.

Adapting the design of towers and nacelles to prevent the full force of sand and salt-laden winds entering whenever maintenance doors are opened, together with rubber seals around the doors, are among the changes that have been implemented. The electricity transformer components in Wobben's machines are now located inside the tower, says Lopes. This avoids exposing transformers to harsh environments or having to build specially designed shelters.

Although Brazil has more than 30 research groups in universities and technology centres developing wind-power equipment and regulation, most of the design changes made by international manufacturers located in Brazil are done at the companies's headquarters.

An exception is Argentinian turbine maker Impsa, which is investing BRL 150 million ($62 million), with funds from Brazil's federal research financing authority, Finep, to develop a locally made turbine adapted to climatic conditions. US manufacturer GE will also invest in local development when its research centre in Rio de Janeiro is completed in March 2014.

Spanish turbine manufacturer Acciona uses its experience from Chile's coastal regions and the state of Oaxaca in south-west Mexico, according to Christiano Forman, head of the company's Brazilian operations.

Applied knowledge

Acciona operates 371 turbines in Oaxaca, where wind speeds are very high and carry a great deal of salt and sand. The company's maintenance teams have to check the corrosion protection and have tropicalised some electronic components to withstand the condensation caused by changes in temperature and humidity.

But some of the changes are made locally, since Brazilian financing rules come with local-content levels in excess of 60%. According to Forman, Acciona is working with local steel-plate suppliers. "[They] are offering us Brazilian steel with mechanical properties adapted to the local conditions," he says. "For example, we generally use steel grades with mechanical requirements up to -20 degrees Celsius for standard climate conditions or up to -40 degrees for cold-climate conditions. Temperatures in Brazil are far from these limits, so we can improve our design with this steel."

Acciona has a kit for these conditions that includes anti-sand sealing for nacelle and nose cone, special gearbox and generator ventilation grids that open only when the turbine is working, levers that open under air pressure; and special cabinets that seal electrical and electronic components in dusty environments according to international market standards.

Acciona has just signed a contract with French firm Voltalia to supply 70 AW3000 3MW turbines for the 120MW Sao Miguel do Gostoso and the 90MW Areia Branca projects in Rio Grande do Norte, in the north-east. Both are sited on sand dunes, and according to Forman, Acciona's AW model can be adapted to the local conditions, which is included in contracts.

"If there is a specific environmental condition affecting a project it will be taken into consideration when evaluating the commercial terms and technical specifications we offer each client," says Forman. Although he says these differentials do not affect O&M prices, equipment monitoring and revision is carried out more often, especially in sealing and in the overall cleanliness of the turbine.

Tough on blades

Gamesa also "imports" experience from its operations in other parts of the world to deal with Brazilian conditions. Its main area of concern is with the turbine blades that suffer abrasion from the sand.

"The blades require a specially designed coat to reduce accelerated wear and tear from the abrasion, while the nacelle has to be more hermetic without interfering with the cooling of the components. The metallic parts also have to be protected from humidity," says Fernando Valldeperes, Gamesa's director of service sales and marketing. But all this does not affect the life of a turbine designed to last 20 years, he insists. "The accumulated experience from O&M services is what makes the difference to optimise capital and operating expenditure of the wind assets," he adds.

The O&M processes must be adapted to dusty and corrosive environments to reduce the aerodynamic loss of blades, he explains. First, regular inspection and cleaning of the blades needs to be carried out to ensure their aerodynamics are maximised. Then, a cleaning of the nacelle interior is programmed during the preventative maintenance schedules to limit the adverse effects of sand storms on the nacelle cooling system. Also, specific attention is given to lubrication and all metal parts, such as bolts, that will suffer from corrosion and could generate extra maintenance costs.

Gamesa has turbines operating in desert areas such as Egypt, Algeria and Mexico, but conditions are slightly different in Brazil. And, with most of the wind farms operating for less than a decade, the company is continually building its experience.

According to BNEF's Grace, with most O&M contracts by turbine makers now featuring availability guarantees, costs caused by environmental conditions are being absorbed by manufacturers, which are responsible for substituting turbine parts and blades. The real cost of operating on a beach or hot desert region will soon hit home as parts start to require replacement after five to ten years of constant operation.

The strategy Grace has observed in these contracts is that operators are not only paying more attention to preventive maintenance, but are also reducing costs by scaling up the number of turbines at wind farms in order to better allocate man hours and reduce maintenance costs per turbine.

Going inland

In Brazil, however, new wind developments are going inland. Land availability, real estate prices, complex environmental licensing processes and a lack of grid connections are forcing developers inland, where more recent measurements have registered more constant winds at 100 metres and above. According to Fabiano Lima, technical director at Camargo Schubert, less than 20% of the roughly 10GW of new wind projects planned in the past two years are located on the seashore.

The exception, however, will be the southern state of Rio Grande do Sul, where most of the 77GW regional wind power potential mapped in 2011 is located in the coastal areas, says Lima. "Temperatures are cooler in Rio Grande do Sul, but there is a lot of sand and salinity, which added to the fact that winds are more irregular there, means adaptations to turbine and blade still need to be made," he says.

Brazil's federal power regulator, Aneel, understands the need to improve turbine adaptation. Its research and development rules for the sector, published last year, give one basic criteria - adaptations of turbines to local environmental and climatic conditions.

According to Maximo Pompermayer, Aneel's R&D director, five power companies have submitted requests for approval of research projects in wind that include the adaption of turbines. Protecting turbines from sand and salt continues to be a hot topic.

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