When it comes to renewables, a hot desert can be an oasis for solar power, but there are two big reasons why wind farms rising among sand dunes were — until recently — just a mirage. “Heat and sand make it difficult for normal wind turbines to operate in the desert,” says Rebeca Calderon, a program manager at GE Renewable Energy in Barcelona.
Just like our bodies, a turbine’s electronic components are prone to heatstroke and can fail in extreme heat, similar to a smartphone that has been left out in the midday sun. So it seems brave to install a 50-megawatt wind farm in Oman, one of the world’s hottest countries, whose landscape is mostly treeless, waterless and covered with sand. Temperatures regularly exceed 40 degrees Celsius (104 degrees Fahrenheit) in Oman, which lies on the tip of the sweltering Arabian Peninsula. Sandstorms are also frequent during summer months. Violent winds blow sand up to a mile high, forming dark, menacing clouds that can swallow entire cities. What Oman needed were turbines as tough as a desert fox, and Calderon and her team have delivered the goods. “We modified a standard turbine to do the job,” she says.
Fortunately, keeping out heat and keeping out sand go hand in hand. Calderon and her team started by cutting four openings into the nacelle of a standard turbine. The nacelle is the box at the top of a turbine tower that houses the power production kit: the gearbox, generator and controller. Next, they installed four sets of louvers — angled slats — to cover these openings. Imagine plantation shutters instead of glass panes in the tropics, and you’re getting close. The louvers act as a kind of filter, allowing air to breeze in and out of the nacelle but physically blocking the wind-whipped grains of sand. “In a sandstorm, sand is flying in all directions, but this system keeps the air that is circulating through the top of the turbine filtered and clean,” Calderon says.
There’s more sand-proofing lower on the tower. If you’ve ever been to the beach, you’ll know that sand has a habit of getting everywhere. That’s why the designers installed small wiry brushes in the small gaps between the tower and nacelle. They block windborne grains of sand from infiltrating the turbine’s nether regions. Engineers have also added sand-blocking louvers to the turbine tower’s door.
In doing so, the team achieved dual purposes. These angled air vents at either end of the turbine keep the whole structure cooler by allowing air to rise and circulate. “There’s no refrigeration — we’re just using the power of convection,” says Calderon.
The interior of any wind turbine needs to stay below the crucial level of 55 degrees Celsius (131 degrees Fahrenheit). Anything hotter knocks out heat-sensitive electronic components. Extreme temperatures also punish turbine machinery. For example, the lubrication oil for the turbine’s gearbox goes runny in the heat, which causes grinding in the gears.
A standard, unmodified wind turbine can work at full power only up to an outside temperature of 35 degrees Celsius (95 degrees Fahrenheit). A temperature of between 35 and 40 degrees Celsius reduces its power capacity. It shuts down completely when the mercury tops 40 degrees Celsius (104 degrees Fahrenheit).
But Calderon says that a modified turbine can work 5 degrees Celsius above normal levels. That’s enough, she says, for Oman, where the average maximum summertime temperature is 45 degrees Celsius.
Calderon says that the self-cooling, vented turbine can produce electricity at 100 percent of its generation capacity until the outside temperature reaches 40 degrees Celsius. It still cranks out some power between 40 and 45 degrees Celsius.
This means that the wind turbines could stay online in Oman’s broiling midday heat. This is a boon for the country’s 13-turbine wind farm in Dhofar, which will produce a maximum of 50 MW when it comes online in July 2019. That translates to hundreds of extra megawatt hours per day for both Masdar, the developer, and the country’s grid.
Calderon’s work is not just about squeezing out extra hours of power production. Desert-resistant turbines can open up huge swathes of barren, unused land in North Africa and the Middle East for renewable electricity generation. The vast deserts of the region are all potential homes for a sandstorm-proof and heat-resistant turbine, says Calderon.
Says Calderon: “There are lots of sites across the region that have extreme hot weather and sandy areas, where wind may be an option now because of this design.”
This is not the first time GE engineers designed a turbine to deal with extreme weather. Calderon’s colleagues in Barcelona are also working on a wind turbine that can handle typhoons and hurricanes. You can read the story here.