Page 34 - Energize March 2021

TECHNICAL

Figure 6: Peak shaving (Fraunhoffer)

output can drop by more than 50% during passing clouds. This
causes a rapid variation in the energy balance which can be
smoothed out by making use of the energy storage system. The
BESS smooths the output and controls the ramp rate (kW/min) to
eliminate rapid voltage and power swings on the electrical grid.
The PV’s DC output may be connected directly to the storage
unit. The PV plant will reduce demand from the grid during
daylight hours and where the PV plant is of a significant size
the BESS may be used to store some of the PV output and shift
usage to times outside of daylight hours to high tariff hours as
shown in Figure 7.

Distribution network support
Frequency support
This is accomplished by injecting active or reactive energy into the Figure 8: Load levelling (ABB)
network. Both over-frequency and under-frequency events can
be accommodated. Over-frequency can be handled by the BESS Load levelling
absorbing energy from the grid, and under-frequency by supplying Load levelling is used primarily in the distribution network for keeping
power to the grid. the load on the grid within certain limits as shown in Figure 8. During
under-load conditions the BESS draws power from the grid and
Voltage support during above-load conditions the battery supplies power to the grid,
Voltage support is implemented by supplying reactive power to the resulting in a high number of low-level cycles. Load levelling is used
grid from the BESS. to limit the current carrying capacity requirements of the distribution
network. Transformers, lines, cabling, and switchgear can be
optimised by applying load levelling.
Systems
There is a wide range of systems available in the market, from small
cabinet based to large multi-container installations. Most large
suppliers feature BESS systems in their product range. n

References
1. ABB: “Compact energy storage module: product overview”, ABB group,
February 2018.
2. J Wolfe: “Battery storage at the grid edge can answer all the key needs of
our future energy system”, www.rechargenews.com, June 2018.
3. H Jain, et al: “Blackstart of power grids with inverter-based resources”,
NREL (2020 IEEE PES GM) Montreal, Canada, 2 – 6 August 2020.
Figure 7: PV energy shifting using BESS (Cigré working group C6-30
brochure) Send your comments to rogerl@nowmedia.co.za

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