Environmental Engineering Reference
In-Depth Information
Circuit breaker panels that protect and control the AC systems are required.
The circuit breakers should be implemented using appropriate relays or con-
tactors so that power routing can be accomplished by the system control-
ler. These relays also function as protective circuit interrupt elements. In the
case of tying the grid inverter to the utility meter, the system controller must
monitor and verify that the frequency and voltage waveforms are compat-
ible with the grid. At that point, the system controller will close the circuit
breaker connecting the system to the grid.
A transformer with its primary winding connected to the 480 Vac system
is utilized to provide 60 Hz AC power to the low voltage circuit breaker
panel. This panel houses either traditional passive circuit breakers for the
user loads or externally controlled relays (or contactors) if additional auto-
mation is desired.
The system controller is responsible for the overall control and protection
of all the other elements of the electric system. It has several important func-
tions, with its primary job to appropriately route power to or from the stor-
age system, the local power sources, and the loads. To implement energy
storage management, the controller monitors the amount of power generated
by the local power sources, the load demand power present, and estimates
the status of the energy storage system (full, empty, 50% full, etc.). Based on
this information, it initiates one of the following actions:
• If energy is being generated but not used by the loads, power is
routed to the motor pump drive and water is pumped to the surface,
until the surface reservoir is full.
• If power is demanded by the loads, but no power is generated, stored
energy is released by putting the storage system into generating mode,
until storage reserve is deleted.
• If power is demanded by loads, the energy storage is depleted, and
no local power generation is online, electricity is routed from the
utility grid to supply the load demand.
• If more power is produced by the local energy source than is being
used and the storage reservoir is full, power will be “net metered”
or routed to the grid.
Direct energy from the utility grid can also be stored. This option would be
used if time-of-day pricing of grid electricity is in effect. For example, if less
expensive grid electricity is available at night than during the day, this inex-
pensive electricity can be stored and later used when grid prices rise. The
efficiency of the storage system must be traded against the cost differential
of the time-of-day pricing to determine whether this choice is economically
beneficial.
In addition to energy storage management, the system controller performs
monitoring, protection, and power routing functions. System status including
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