Page 84 - Solar Power in Building Design The Engineer's Complete Design Resource

54 SOLAR POWER SYSTEM DESIGN CONSIDERATIONS

GRID-CONNECTED SOLAR POWER COGENERATION SYSTEM

With reference to Figure 3.5, a connected solar power system diagram, the power cogen-
eration system configuration is similar to the hybrid system just described. The essence
of a grid-connected system is net metering. Standard service meters are odometer-type
counting wheels that record power consumption at a service point by means of a rotat-
ing disc, which is connected to the counting mechanism. The rotating discs operate by
an electrophysical principle called eddy current, which consists of voltage and current
measurement sensing coils that generate a proportional power measurement.
New electric meters make use of digital electronic technology that registers power
measurement by solid-state current- and voltage-sensing devices that convert analog
measured values into binary values that are displayed on the meter bezels by liquid-
crystal display (LCD) readouts.
In general, conventional meters only display power consumption; that is, the meter
counting mechanism is unidirectional.

Net metering The essential difference between a grid-connected system and
a stand-alone system is that inverters, which are connected to the main electrical serv-
ice, must have an inherent line frequency synchronization capability to deliver the
excess power to the grid.
Net meters, unlike conventional meters, have a capability to record consumed or gen-
erated power in an exclusive summation format; that is, the recorded power registration
is the net amount of power consumed—the total power used minus the amount of
power that is produced by the solar power cogeneration system. Net meters are supplied

Figure 3.5 Grid-connected hybrid solar power system with standby generator.