360 Ë 9 HTS Maglev bearing and flywheel energy storage system
during ever operation processes, the HTS FESS unit can save 345,000 kWh of electric
energy over 6000 working hours per year, which is an excellent result. Moreover,
there are other benefits from the usage of HTS FESS units. One benefit comes from
the improvement of the power quality: namely, the relaxation of serious fluctuation
of voltage and current in the subway supply network can improve the service life and
operation performance of the electric equipment. Another benefit is the reduction of
power demand, which reduces the huge cost associated with expansion of the supply
network under the need for ever-increasing transport capacity of the subway system.
9.6.2Renewable energy system
The renewable energy systems like solar power generation and wind power generation
need energy storage systems to improve the quality and stability of generated electri-
cal energy. The principal technical point of the running test of this 5-kWh HTS FESS
prototype in renewable energy system is power capacity. For example, the power of
an individual wind turbine generator is about 2–5 MW, which is much higher than the
100-kW power of our HTS FESS prototype. Application in renewable energy system
requires a high power level, so the maximal I/O power should be improved to 400
or 500 kW for a single HTS FESS unit. This is the next upgrade for this HTS FESS
prototype. For a renewable energy station with hundreds of megawatts power level,
there would be thousands of HTS FESS units in operation.
9.6.3Power grid system
Their application in power grid is the optimal and most beneficial usage of FESS units.
The FESS units can supply protection or improvements on the power grid system, such
as the power angle stability, the grid voltage stability, the grid frequency excursion
suppression, and the regulation control. Those protective applications in a power
grid require large power capacity, as much as hundreds of megawatts, but with a
short working time, such as several minutes. The single HTS FESS unit used for the
protective applications should have enough ESC to support the maximal I/O power at
least 1–5 minutes. This HTS FESS prototype has an available ESC of 5.75 kWh of 75%
DOD, which can support the I/O power of 100 kW for 3.45 minutes. Thus, it can be
tested for the protective applications. Because the 100-kW power of this HTS FESS
prototype is much smaller than the actual power of the grid, its I/O power needs to
improve to 300–500 kW, and at least 10–20 prototypes are needed to run the test.
Another application of FESS units in the power grid is for long-term load shifting (LS),
such as 3 or 7 hours LS, which is used to adjust the power demand of the gird or store
electrical energy at valley times to sell later [84]. The long-term LS applications require
the HTS FESS have enough ESC to support the maximal I/O power for several hours.