IEEE Electrification Magazine - March 2015 - 64

Figure 8. A bird's-eye view of the UVI St. Thomas Campus 2,099-kW
dc solar array.

Figure 9. The UVI St. Thomas Campus 2,099-kW dc solar array.

than 40% during peak production hours, defined as the
period of time when the solar system is producing power.
Because solar is not a base load power source, the solar system is oversized based on electricity consumption requirements during peak production hours and stores the energy
for off-peak production hours, the period of time when the
solar system is not producing power, using advanced energy storage. The system is also designed to eliminate the
inherent inability of renewable power production to loadfollow due to the peak power design or constantly changing
input power levels from variations in the sun, wind, or

other production sources. The solar power deployment initiative will develop a 3.3-MW ground-mount crystalline PV
system with a single-axis tracker. The system will include
the components listed in Table 4.
This system design is an ideal platform into which
new-technology battery storage should be introduced.
Table 5 shows the requirements for the energy-storage
system. A fully integrated energy-storage system that satisfies those requirements should be delivered to the site
containerized, prewired, and pretested, reducing site work
and installation time. One such solution is available from
S&C Electric and summarized in Table 6. A more detailed
description of each component follows.

Table 4. The Proposed PV System
components.

Power Electronics

System Component

Quantity

Yingli/LDK-watt crystalline PV modules

10,920

Fixed-tilt solar panels (5°)

260-kW commercial Inverter with complete
setup

16-circuit subcombiners with 100-A fuses

12-circuit combiner boxes

Data acquisition system gateways for each
inverter

Table 5. The requirements for the
energy-Storage System.

Element

Requirement

Power

St. Thomas: 1 MW
St. Croix: 500 kW

Energy

3-4 h of storage at rated power

System life

10+ years

Battery functions

Time-shifting solar generation

Ambient conditions

Tropical/salt in the air

Containerized or
indoor

Containerized

I E E E E l e c t r i f i c ati o n M agaz ine / March 2015

S&C's Storage Management System (SMS) is an example
of a utility-grade power-conversion system. It provides
four-quadrant control, acting as either a voltage or current
source (adjustable on the fly), with the ability to absorb or
provide real and reactive power. As illustrated in Figure 10,
the four-quadrant design allows the SMS to manage a
wide range of real and reactive power requirements (the
points along and within the red dashed line). The control
algorithms within the SMS support a wide variety of energy-storage use cases, including peak shaving, dynamic
islanding, renewable-energy integration, energy arbitrage,
ancillary services (including frequency regulation), load
following, and voltage control.
The SMS includes the inverters, ac and dc breakers, and
controls mounted within each international organization for
standardization (ISO) container. The building block of the SMS
is an individually controlled ±1.25-MVA/1.0-MW inverter, with
a dedicated 480-V breaker for each inverter, as shown in
Figure 11. Up to four 1-MW inverter blocks can be combined
into a single ISO container, and a total of 20 MW can be managed under a single control. The insulated gate bipolar transistor (IGBT) is the major power electronic component within the
1-MW inverter block. Each 1-MW inverter block contains
12 IGBTs and has its own local control and small ac filter components to ensure harmonic-free sine waves at the output terminals of the inverter. The SMS includes ±500-kW, dc-to-dc
converter chopper blocks, which take the variable dc voltage

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2015