Page 580 - Sustainable Cities and Communities Design Handbook

548 Sustainable Cities and Communities Design Handbook

and all except upgrading and integrating and energy management system had
ROIs of greater than 11 years.

SOLAR PV ARRAY AND SETUP

The renewable energy system to be installed at LACC consists of PVarrays, an
inverter, a controller, and other essential cables and components. Solar in-
verters are a critical component to any solar power system. Inverters change
DC (direct current) from solar panels, or the photovoltaic array, into AC
(alternating current) for use in the campus and resale back to the utility grid.
Two key categories of solar inverters are used in solar energy systems. In
systems that are not connected to the utility grid, the inverter takes DC from
the PV array and converts it to AC powering a battery or series of batteries,
from which power is drawn. In the case of this “off grid inverter” or “charge
controller,” the PV array and inverter are essentially charging batteries to keep
power supplied to the building.
The second category ties into the utility grid, again converting DC to AC,
but with this “grid-tie inverter” the power is first supplied to the building and
the remaining energy is sent back to the LADWP grid.

Solar Energy
There will be three main configurations for PV arrays at City College: carport
structures, roof-mounted structures, and ground-mounted arrays. The current

standing design has a panel slope of 5 and an azimuth of 180 . For this study,

it is assumed roof top units will be designed with a 20 and 180 panel slope

and azimuth, respectively, and the ground-mounted units will have a slope
equal to the latitude, approximately 34 with a 180 azimuth. If maximum

winter production from the ground-mounted system is desired, the array tilt

can be increased up to 15 past the location’s latitude.
Hourly solar irradiance data for the year 2005 was downloaded from
the National Renewable Energy Laboratory’s (NREL) solar radiation database. 6
Data beyond 2005 were unavailable. A monitoring station located at the
Downtown Los Angeles University of Southern California campus, the nearest
station to the LACC campus, collected the 2005 data. The data were then
analyzed using NREL PV Watts v2 program, which uses typical meteorological
weather data for a selected location and determines the solar radiation incident of
the PVarray at the given array and azimuth tilt angles. To generate solar radiation
7
data of hourly resolution, another NREL program HOMER v2.67 Beta was
employed to synthesize the desired profiles. HOMER uses an algorithm based on

6. National Renewable Energy Laboratory: Solar Radiation Database. http://rredc.nrel.gov/solar/
old_data/nsrdb/.
7. National Renewable Energy Laboratory: HOMER https://analysis.nrel.gov/homer/.