Chapter 29: PHOTOVOLTAIC SYSTEMS
Summary
Photovoltaic (PV) generation of electricity is becoming more common in the building sector as PV costs
have come down and interest in “green” energy alternatives has gone up. Typical PV costs are indicated
as $1.50-2.50 per watt of capacity and $0.50-0.25 per watt produced. Net-metering regulations for power
“buy-back,” utility interest in alternative power sources, several federal government programs, and the
advent of building-integrated photovoltaic options are noted as trends encouraging the use of PV
systems. PV systems may be designed as stand-alone or as grid-connected systems; a hybrid standalone system is also described. Direct connected systems feed power directly to loads without the
provision of storage; these systems are noted as being rarely used. Battery storage permits system
output to better match building loads across time. Grid-connected PV systems permit a building to use
either PV or utility-generated power to meet building loads.
Codes and standards that will affect the design of photovoltaic systems are reviewed. Terminology and
definitions applicable to PV systems are explained. The difference between irradiance and insolation is
emphasized; the elements of a PV system are described; types of PV cells are defined. The photovoltaic
effect is discussed in some detail and conversion efficiencies for PV cells outlined. Older large-crystal
silicon cells are compared to newer polycrystalline, thin-film, amorphous cells. Fixed versus tracking
arrays are discussed. Battery types appropriate for use in PV systems are examined in detail, including
performance characteristics and capacity ratings.
The design process for a stand-alone PV system is described and illustrated by means of a worked
example. A different design process applicable to a grid-connected system is also described. Various
examples of PV applications are presented.
A case study of the Lillis Business Complex at the University of Oregon is provided as an example of a
recent building-integrated photovoltaic application. The case study provides context and background for
the project (including design intent, criteria, and validation approaches). Key building design features are
described.
Chapter Outline
29.1 A Context for Photovoltaics
29.2 Terminology and Definitions
29.3 PV Cells
29.4 PV Arrays
29.5 PV System Types and Applications
(a) Stand-alone systems
(b) Grid-connected systems
(c) Economic considerations
29.6 PV System Batteries
29.7 Balance of System
29.8 Design of a Stand-Alone PV System
29.9 Design of a Grid-Connected PV System
29.10 Codes and Standards
29.11 PV Installations
29.12 Case Study: PV (Lillis Business Complex)
References
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Key Concepts
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photovoltaic or PV (as a “green” means of generating electricity)
net metering (as a photovoltaic power billing approach)
stand-alone versus grid-connected PV systems (as alternative design approaches)
avoided cost (as a means of establishing utility payments for PV power)
PV system terminology (as a means of fostering design team communication)
insolation versus irradiance (as distinct metrics of solar availability)
photoelectric effect (the reason PV cells generate electricity)
building-integrated photovoltaics or BIPV (as an emerging PV installation trend)
Terminology and Metrics
Important Terminology
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rectifier
battery (lead-acid, lead-calcium, lead-antimony, nickel-cadmium; sealed; shallow-cycle, deepcycle)
photovoltaic (PV)
cell
module
panel
array
thick-crystal
thin-film
polycrystalline
amorphous
stand-alone PV
grid-connected PV
interactive PV system
hybrid stand-alone PV
direct-connected PV system
building-integrated photovoltaics (BIPV)
inverter (power conditioning unit, power conversion system)
safety cutoff
kWh meter
PURPA (Public Utilities Regulatory Policy Act)
avoided cost
net metering
insolation
irradiance
energy
power
tilt angle
fixed array
tracking array (single axis, dual axis)
charge controller
Important Metrics
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watts per square foot (irradiance, solar power received)
watt-hours per square foot (insolation, solar energy received)
nanometer (wavelength)
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electron-volt (a measure of energy at the atomic scale)
efficiency (dimensionless)
A-H (ampere-hour; battery capacity)
Links to Resources
U.S. Department of Energy, Energy Efficiency and Renewable Energy, Photovoltaics:
http://www.eere.energy.gov/solar/photovoltaics.html
Florida Solar Energy Center, Photovoltaics:
http://www.fsec.ucf.edu/pvt/pvbasics/
Sandia National Laboratories, Photovoltaics:
http://www.sandia.gov/pv/
Solar Decathlon Competition
http://www.eere.energy.gov/solar_decathlon/
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