Stretching more than 7,000 kilometres from Colombia in the north to Tierra del Fuego in the south, taking in Ecuador, Peru, Bolivia, Chile and a sizeable chunk of Argentina on the way, the Andes vary in width from 200 to 700 kilometres and have an average height of around 4,000 metres, with 90 peaks above 6,000 metres. Only the Himalayas offer higher ground than this.
The wind resources may be excellent, but the logistical and technical challenges posed by the unforgiving terrain and climate have largely prevented development of wind power in the region. Of the countries the Andes runs through, only Chile has managed to establish a wind power sector of any size — 375MW and growing — and it has achieved this by exploiting low-altitude sites, usually near shore.
However, there are signs that Latin-America's wind industry is ready to tackle some of the problems, and a number of projects are being planned and prepared for high-altitude sites. In May, Chinese turbine manufacturer Goldwind announced that it would provide the hardware for two of the highest wind farms in the world. Located in Ecuador, in the north-west of the continent, and at nearly 3,000 metres above sea level, the 50MW Ducal-Membrillo and 54MW Huayrapamba projects represent the country's first large-scale ventures into wind power. Ecuador currently has only 18.5MW of wind power installed, 16.5MW of which is sited at the Villonaco project, 2,720 metres above sea level. Also featuring 1.5MW Goldwind turbines, it was commissioned in early 2013.
Precisely what constitutes high altitude is a moot point. It is often defined as starting at 2,400 metres, but the medical profession recognises its effect on the human condition from 1,500 metres. And it varies according to latitude: the cooler the climate, the lower the threshold. However it is defined, the issues facing wind turbine manufacturers remain the same: how to cope with very cold temperatures and high levels of solar radiation.
Goldwind has customised its permanent-magnet direct-drive 1.5MW turbine for deployment at high altitude. Company spokesman Ian Chen points to technological improvements that range from longer blades to enhanced thermal insulation and strengthened protection against lightning and solar radiation. "With these features, the design can withstand differences in wind density, frequent lightning strikes, strong radiation from the sun and other challenging condition," he says.
Air density is another important issue for turbine makers, as US firm DeWind learned when developing its 2MW D8.2 turbine for installation at the Veladero mine in Argentina, 4,100 metres above sea level. "With every additional metre in elevation, air density decreases, and so does the energy content of the wind. At an elevation of 4,300 metres, air pressure is only about 600 millibars (mbar) (1,013 mbar at sea level), and air density drops to 0.797 kilogrammes per cubic metre (1.225kg/m3 at sea level), the company reported.
"The result is that a wind turbine operating at this elevation will have a significantly lower yield than a turbine operating at a sea-level site with same wind speed. On the upside, the lower air density means the turbine can still be operated at higher speeds."
Traditional power converters and other electric components do not always function reliably at this altitude. The DeWind turbine used a four-pole synchronous generator without slippage, connected directly to the grid. In this way, frequency regulation on the turbine is through a gearbox that is deployed as the third transmission stage.
Installed in 2008, Veladero's turbine was the highest in the world until November 2013, when the Naqu wind farm in Tibet, consisting of five 1.5MW Guodian turbines at 4,700 metres above sea level, came online.
Juan Diego Diaz, marketing director of Spanish turbine manufacturer Gamesa, explains the benefits and drawbacks of developing projects at high altitude. "The main advantage is that it is more windy. But you have to keep in mind reduced air density, so the wind contains less power and less cooling capacity," he says.
"For such projects, Gamesa has special versions of its turbine, in which special attention is devoted to power and cooling issues to optimise its performance," he adds. Specifically, Diaz refers to Gamesa's 2-2.5MW platform for sites up to 2,400 metres above sea level, and its 850kW platform for locations up to 3,600 metres above sea level. The smaller turbine is preferred for the higher applications simply because it is easier to transport and install.
"Among the advantages (of high-altitude sites) are the low effect of wake interference and the high wind speeds, which compensate, to some extent, for the loss of energy by low atmospheric density," says Rodrigo Sanchez, head of Central America and Caribbean project development for developer Juwi. But the biggest obstacle to development in these regions is down to logistics, he points out. "Developing projects in mountainous highlands implies more expensive transport," he says. "Also, the complexity of the terrain means that more time is needed for construction. Roads need to be improved, or new ones built, to allow the installation of a wind farm."
Larger turbines are less competitive for this reason, Sanchez argues. None of the projects currently being planned at high-altitude sites in Latin America (see table, above) are slated to use turbines bigger than 2MW, while several will use sub-megawatt units.