IEEE Power & Energy Magazine - September/October 2017 - 55

1 . 105
(Count)

The direction of the battery's active power depends on the
ramping behavior of the wind power plant's active power output. In particular, batteries were charging during sustained
increases in wind power and discharging when wind power
was decreasing. Figure 2 shows the frequency distributions
of positive and negative 1-min ramp rates (wind, batteries,
and total) during an 11-day observation period in November 2011. There was a significant reduction in the frequency
of large ramping rates for the total plant power (the difference is shown between the red and black plots in Figure 2).
More than an order-of-magnitude reduction in the frequency
of 1-min ramp rates was achieved for some portions of the
range, and some large ramp rates were eliminated.

1 . 104
1 . 103
100
10
1
-10 -8 -6 -4 -2 0 2
(MW/min)

Wind Power

Batteries

8 10

Total

figure 2. The distribution of 1-min ramp rates at Oahu's
Kahuku Wind Farm.

Duke Energy/Younicos BESS Project in Notrees, Texas

Texas's grid operator, ERCOT, has been evaluating its powerbalancing needs as its integration of wind generation is increasing at rapid rates (close to 18 GW of installed wind capacity
in 2016). The Notrees 156-MW wind power plant, located in
ERCOT's service territory, is owned and operated by Duke
Energy Renewables. The purpose of the 36-MW/24-MWh
battery system situated at the wind power plant's substation is
to increase the value and practical application of wind power,
alleviate intermittency issues, and demonstrate the viability of
energy storage at the utility scale.
The BESS demonstrated good performance in the fastresponding regulation service market within ERCOT, and it
has continued bidding into this market. The original advanced
lead-acid battery technology used in the Notrees project demonstrated some premature degradation under fast charging
and discharging dictated by frequency-regulation applications. The plant owner is replacing the lead-acid batteries
with Li-ion batteries from Samsung SDI. Figure 3 shows an
example time series of the BESS state of charge when providing market services within ERCOT's territory.
SCE Wind Energy Storage Project
in Tehachapi, California

State of Charge (%)

This 8-MW/32-MWh BESS installation is located in the
4.5-GW Tehachapi Wind Resource Area and owned by SCE
(see Figure 4). It uses LG Chem Li-ion batteries and ABB
Power Electronics technology. This project was constructed
to meet the following operational uses:

✔✔ transmission applications

*
*
*
*

v oltage support/grid stabilization
decreased transmission losses
diminished congestion
increased system reliability by deferring load
-shedding
* deferred transmission investment
* optimized size and cost of renewable energy--related
transmission
✔✔ system-level applications
* providing system capacity/resource adequacy
* integrating renewable energy (smoothing)
* shifting wind generation output
✔✔ market issues related to the California ISO
* frequency regulation
* spinning/nonspinning replacement reserves
* delivering ramp rate
* energy price arbitrage.
The Tehachapi battery system largely met these project objectives. While it did present a number of challenges
to SCE, these challenges were not primarily related to the
storage technology itself; rather, they were due to electric design deficiencies (such as a poor transformer design
that led to transformer failure) and control system issues.
Currently, SCE is using its experience from Tehachapi to
inform the development of other storage projects in its service territory.

60
40
20
0

1,000

2,000

3,000

4,000
5,000
Time (h)

6,000

7,000

8,000

figure 3. The measured battery state of charge when providing energy market services at the Notrees, Texas, wind power plant.
september/october 2017

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2017