An Innovative storage system that could enable offshore wind farms to deliver power whenever it’s needed.
Offshore
wind could provide abundant electricity — but as with solar energy,
this power supply can be intermittent and unpredictable. But a new
approach from researchers at MIT could mitigate that problem, allowing
the electricity generated by floating wind farms to be stored and then
used, on demand, whenever it’s needed.
The
key to this concept is the placement of huge concrete spheres on the
seafloor under the wind turbines. These structures, weighing thousands
of tons apiece, could serve both as anchors to moor the floating
turbines and as a means of storing the energy they produce. Whenever the
wind turbines produce more power than is needed, that power would be
diverted to drive a pump attached to the underwater structure, pumping
seawater from a 30-meter-diameter hollow sphere. (For comparison, the
tank’s diameter is about that of MIT’s Great Dome, or of the dome atop
the U.S. Capitol.) Later, when power is needed, water would be allowed
to flow back into the sphere through a turbine attached to a generator,
and the resulting electricity sent back to shore.
One such
25-meter sphere in 400-meter-deep water could store up to 6
megawatt-hours of power, the MIT researchers have calculated; that means
that 1,000 such spheres could supply as much power as a nuclear plant
for several hours — enough to make them a reliable source of power. The
1,000 wind turbines that the spheres could anchor could, on average,
replace a conventional on-shore coal or nuclear plant. What’s more,
unlike nuclear or coal-fired plants, which take hours to ramp up, this
energy source could be made available within minutes, and then taken
offline just as quickly.
The system
would be grid-connected, so the spheres could also be used to store
energy from other sources, including solar arrays on shore, or from
base-load power plants, which operate most efficiently at steady levels.
This could potentially reduce reliance on peak-power plants, which
typically operate less efficiently.
The concept is detailed in a paper published in IEEE Transactions and
co-authored by Alexander Slocum, the Pappalardo Professor of Mechanical
Engineering at MIT; Brian Hodder, a researcher at the MIT Energy
Initiative; and three MIT alumni and a former high school student who
worked on the project. The weight of
the concrete in the spheres’ 3-meter-thick walls would be sufficient to
keep the structures on the seafloor even when empty, they say. The
spheres could be cast on land and then towed out to sea on a specially
built barge. (No existing vessel has the capacity to deploy such a large
load.)
Preliminary
estimates indicate that one such sphere could be built and deployed at a
cost of about $12 million, Hodder says, with costs gradually coming
down with experience. This could yield an estimated storage cost of
about 6 cents per kilowatt-hour — a level considered viable by the
utility industry. Hundreds of spheres could be deployed as part of a
far-offshore installation of hundreds of floating wind turbines, the
researchers say. Such offshore
floating wind turbines have been proposed by Paul Sclavounos, a
professor of mechanical engineering and naval architecture at MIT, among
others; this storage system would dovetail well with his concept,
Hodder says.
In
combination, floating turbines and undersea storage spheres could
provide reliable, on-demand power, except during extended calm periods.
Meanwhile, a siting many miles offshore would provide the benefit of
stronger winds than most onshore sites, while also operating out of
sight of the mainland. “It provides a lot of flexibility in siting,”
Hodder says. The team calculated that the optimal depth for the spheres
would be about 750 meters, though as costs are reduced over time they
could become cost-effective in shallower water.
Jim Eyer, a
senior analyst with energy consulting firm E & I Consulting of
Oakland, Calif., who was not involved in this research, says the concept
“addresses some important challenges associated with wind generation in
general, especially the temporal mismatch between production and
demand, and generation variability, especially rapid output variations
that lead to excessive ‘ramping’ of dispatchable generation.” While he
calls the idea “somewhat novel and potentially significant,” he adds,
“Obviously we’ll need a proof-of-concept pilot to take the next
development step.”
Slocum and
some of his students built a 30-inch-diameter prototype in 2011, which
functioned well through charging and discharging cycles, demonstrating
the feasibility of the idea. The team
hopes to extend its testing to a 3-meter sphere, and then scale up to a
10-meter version to be tested in an undersea environment, if funding
becomes available. MIT has filed for a patent on the system.
The
researchers estimate that an offshore wind farm paired with such storage
spheres would use an amount of concrete comparable to that used to
build the Hoover Dam — but would also supply a comparable amount of
power. While cement
production is a major source of carbon-dioxide emissions, the team
calculated that the concrete for these spheres could be made, in part,
using large quantities of fly ash from existing coal plants — material
that would otherwise be a waste product — instead of cement. The
researchers calculate that over the course of a decade of construction
and deployment, the spheres could use much of the fly ash produced by
U.S. coal plants, and create enough capacity to supply one-third of U.S.
electricity needs.
The work was supported by a grant from the MIT Energy Initiative.
www.indiapowersector.com
No comments:
Post a Comment