<ugh October has been full of blustery days, astute observers may have noticed an odd stillness to Carleton’s wind turbine. Since October 3, the turbine has been shut down and in need of repairs.
The turbine, barely three years old, needs to have its main gearbox replaced. The gears in the gearbox lost some of their teeth, causing the gearbox to overheat and forcing it to be shut down in order to avoid damaging the generator. The gearbox, a unit in the top part of the turbine called the nacelle, converts the energy of the blades, which turn at 14rpm, to a faster 1200rpm output that feeds into the generator to create power.
Since the turbine is still under warranty, the repairs will be paid for by the company that installed it, Vestas. However, these repairs are no simple matter. While only the faulty gearbox and main shaft need to be replaced, these are large components. In order to replace them, it is necessary to remove the whole blade assembly from the turbine. Since the blade assembly weighs 43 tons and the nacelle weighs 45 tons, this can only be done with a very large crane.
The crane to remove the blade assembly has to be 350 feet tall with a 280 foot boom. Such cranes are typically transported in 8-10 semi loads and must be put together on site.
“The problem has been finding a crane,” says Director of Energy Management Rob Lamppa, explaining that numerous wind farms are currently being built in Wisconsin and Iowa. Fortunately, Carleton, working with Vestas, was able to locate an available crane through the company Vic’s Crane in Rosemount, MN. The crane should be available around the first or second week of November.
Until then, however, Carleton is without wind power. Since the turbine does not directly power the college, there will not be any visible effects on campus. The energy is sold directly to Xcel Energy, who then powers the campus separately. What a month without wind power means, then, is that the college will lose around $20,000 that would go towards paying off the lease on the turbine.
“All this energy gets sold; with the turbine down, we’re just not getting any money,” says Lamppa. He points out, though, that the college’s arrangement with Xcel works out better than if this breakdown had happened at St. Olaf, where the turbine powers the school directly.
“If this happened at Olaf, they’d have to buy energy,” he says, adding that St. Olaf also pays a monthly standby fee to Xcel to insure against power outages should their turbine stop. Yet there is still the issue of money lost. Fortunately, since the turbine is still under warranty, Vestas will pay for the repair, which is considerably more than the cost of a month without the turbine’s income, as the crane time alone is around $50,000.
Such a breakdown so early in the turbine’s life is rare, but not unheard of. Lamppa points out that having to replace the gearbox every three years is the exception rather than the rule, and he adds that this malfunction will have little effect on future plans regarding wind power at Carleton.
“We’re looking at this as just unfortunate,” he says, “As if you ended up with a bad car transmission…it wouldn’t keep me from buying another car.”