IEEE Power & Energy Magazine - May/June 2018 - 77

generation exceeds the rating of the evacuation system, the output of the wind or solar plant could be
curtailed to keep the power flow from exceeding the
transmission limit. similarly, integrating wind and
solar plants can reduce the need for upgrades to the
transmission system.
✔ Sharing of operations and maintenance (O&M) expenses: another key benefit of an iwses plant is
the reduction in o&M expenses. Fewer maintenance
personnel are required to maintain an integrated
wind-solar plant compared with those needed to
maintain separately located wind and solar plants.
the skill sets needed to maintain wind and solar
plants are similar-in particular, the skills required
to maintain power conversion equipment and the
switchyard. on the operations side, savings could
be achieved by sharing the control room, communication infrastructure, and personnel necessary for
plant operation.

Benefits from Integrating a BESS
a Bess connected to the bulk power system can provide
several generation- and transmission-level services such as
energy arbitrage, reserves regulation, transmission congestion
management, and transmission asset deferral. with aggregation and suitable regulatory changes, a customer-sited Bess
can perform additional customer-level services as well as
upstream services such as distribution-level and bulk power
system services. However, a Bess integrated with a wind-

solar plant can also provide many plant-level services mandated by grid codes or regulations or incentivized through
markets. the stacking of plant-level and system-level services
can help derive more value from energy storage. a Bess integrated with a wind-solar plant can provide many of the same
system-level services as those provided by a standalone Bess,
such as the following:
✔ Energy shifting: energy storage is frequently used for
energy arbitrage or load shifting. in the United states,
pumped storage hydro plants were installed mainly to
integrate nuclear base-load power plants, charging at
night when energy prices are low and generating during the day when prices are high. Battery energy storage has been used to provide energy during peak load
hours in several niche scenarios. it will be possible to
use battery energy storage to a greater extent as costs
decline in the future.
✔ Ancillary services: Frequency regulation (i.e., the rapid
adjustment in generation or load to balance the system
in the seconds-to-minutes time frame) is one of the few
applications that can provide full cost recovery for a
commercial battery storage project. However, ancillary
services such as regulation are not explicitly procured
and compensated for in all systems. Besss have recently
found a niche in balancing ancillary services such as fastfrequency response. a Bess can also be used to provide
black-start capability to the system and support voltage
on the bulk power system in addition to balancing ancillary services, as discussed previously.

800

600
Avg Hybrid
+1.5 Sigma
-1.5 Sigma

400
MW

600
400

200

200
0

10
(b)

(a)
800

800
600
MW

600

400

400
200
200

15
(c)

(d)

figure 2. The range of hourly generation for a wind-solar plant made up of 500-MW each of wind and solar capacity.
(a) January, (b) April, (c) July, and (d) October.
may/june 2018

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2018