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TEXTO PARA AS QUESTÕES DE 51 A 53
The expression "dark doldrums" chills the hearts of
renewable-energy engineers, who use it to refer to the lulls
when solar panels and wind turbines are thwarted by clouds,
night, or still air. On a bright, cloudless day, a solar farm can
generate prodigious amounts of electricity. But at night solar
cells do little, and in calm air turbines sit useless.
The dark doldrums make it difficult for us to rely totally on
renewable energy. Power companies need to plan not just for
individual storms or windless nights but for difficulties that
can stretch for days. Last year, Europe experienced a weeks-
long "wind drought," and in 2006 Hawaii endured six weeks of
consecutive rainy days. On a smaller scale, communities that
want to go all-renewable need to fill the gaps. The obvious
solution is batteries, which power everything from mobile
phones to electric vehicles; they are relatively inexpensive to
make and getting cheaper. But typical models exhaust their
stored energy after only three or four hours of maximum
output, and—as every smartphone owner knows—their
capacity dwindles with each recharge. Moreover, it is
expensive to collect enough batteries to cover longer
discharges.
We already have one kind of renewable energy storage:
more than ninety per cent of the world's energy-storage
capacity is in reservoirs, as part of a technology called
pumped-storage hydropower, used to smooth out sharp
increases in electricity demand. Motors pump water uphill
from a river or a reservoir to a higher reservoir; when the
water is released downhill, it spins a turbine, generating
power. A pumped-hydro installation is like a giant, permanent
battery, charged when water is pumped uphill and depleted
as it flows down. Some countries are expanding their use of
pumped hydro, but the right geography is hard to find,
permits are difficult to obtain, and construction is slow and
expensive. The hunt is on for new approaches to energy
storage.
The New Yorker. Abril, 2022. Adaptado.
Na frase "But typical models exhaust their stored energy after
only three or four hours of maximum output, and—as every
smartphone owner knows—their capacity dwindles with each
recharge." (2º parágrafo), "dwindles" poderia ser substituído,
sem prejuízo de sentido, por