Page 85 - Solar Power in Building Design The Engineer's Complete Design Resource

STORAGE BATTERY TECHNOLOGIES 55

and installed by utility companies that provide grid-connection service systems. Net-
metered solar power cogenerators are subject to specific contractual agreements and
are subsidized by state and municipal governmental agencies. The major agencies that
undertake distribution of the state of California’s renewable energy rebate funds for
various projects are the California Energy Commission (CEC), Southern California
Edison, Southern California Gas (Sempra Power), and San Diego Gas and Electric
(SG&E), as well as principal municipalities, such as the Los Angeles Department of
Water and Power. When designing net metering solar power cogeneration systems, the
solar power designers and their clients must familiarize themselves with the CEC rebate
fund requirements. Essential to any solar power implementation is the preliminary
design and economic feasibility study needed for project cost justification and return-
on-investment analysis. The first step of the study usually entails close coordination
with the architect in charge and the electrical engineering consultant. A preliminary PV
array layout and a computer-aided shading study are essential for providing the
required foundation for the design. Based on the preceding study, the solar power
engineer must undertake an econometrics study to verify the validity and justification
of the investment. Upon completion of the study, the solar engineer must assist the
client to complete the required CEC rebate application forms and submit it to the
service agency responsible for the energy cogeneration program.

Grid-connection isolation transformer In order to prevent spurious noise trans-
fer from the grid to the solar power system electronics, a delta-y isolation transformer
is placed between the main service switchgear disconnects and the inverters. The delta
winding of the isolation transformer, which is connected to the service bus, circulates
noise harmonics in the winding and dissipates the energy as heat.
Isolation transformers are also used to convert or match the inverter output voltages
to the grid. Most often, in commercial installations, inverter output voltages range
from 208 to 230 V (three phase), which must be connected to an electric service grid
that supplies 277/480 V power.
Some inverter manufacturers incorporate output isolation transformers as an inte-
gral part of the inverter system, which eliminates the use of external transformation
and ensures noise isolation.

Storage Battery Technologies

One of the most significant components of solar power systems consist of battery
backup systems that are frequently used to store electric energy harvested from solar
photovoltaic systems for use during the absence of sunlight, such as at night and dur-
ing cloudy conditions. Because of the significance of storage battery systems it is
important for design engineers to have a full understanding of the technology since
this system component represents a notable portion of the overall installation cost.
More importantly, the designer must be mindful of the hazards associated with han-
dling, installation, and maintenance. To provide an in-depth knowledge about the