Introduction to Photovoltaic Systems SECO FACT SHEET NO 11 HIGHLIGHTS N The energy needs of a typical home in Texas could be met by covering only half of its roof with sol by gregoria


									Introduction to
Photovoltaic Systems

N The energy needs of a
   typical home in Texas
   could be met by covering
   only half of its roof with
   solar electric panels.
N Photovoltaic (PV) cells
   convert sunlight directly

                                                                                                                                     City of Austin Electric Utility
   into electricity without
   creating any air or water

INTRODUCTION                             Retrofitted residential PV system The solar panels on the roof produce
                                         electricity that travels through wires to the distribution panel on the side of the home.
Photovoltaics offer consumers the
ability to generate electricity in a
clean, quiet and reliable way.         PV systems are being installed by                  can in many cases offer the least
Photovoltaic systems are comprised     Texans who already have grid-sup-                  expensive, most viable option.
of photovoltaic cells, devices that    plied electricity but want to begin to
convert light energy directly into     live more independently or who are                 In use today on street lights, gate
electricity. Because the source of     concerned about the environment.                   openers and other low power tasks,
light is usually the sun, they are     For some applications where small                  photovoltaics are gaining popularity
often called solar cells. The word     amounts of electricity are required,               in Texas and around the world as
photovoltaic comes from “photo,”       like emergency call boxes, PV sys-                 their price declines and efficiency
meaning light, and “voltaic,” which    tems are often cost justified even                 increases.
refers to producing electricity.       when grid electricity is not very far
Therefore, the photovoltaic process    away. When applications require                    HOW IT WORKS
is “producing electricity directly     larger amounts of electricity and                  PV cells convert sunlight directly
from sunlight.” Photovoltaics are      are located away from existing                     into electricity without creating any
often referred to as PV.               power lines, photovoltaic systems                  air or water pollution. PV cells are

SECO FACT SHEET NO. 11                                                          INTRODUCTION TO PHOTOVOLTAIC SYSTEMS P.1
       OF TEXAS
                                                                                                         Encapsulate seal

                                                       External circuit                                  Top electrical contact

                                                                                                         P-Type material
                                                                                                         (boran-doped silicon)
  made of at least two layers of semi-                                                                   P/N junction
  conductor material. One layer has a
                                                                                                         N-Type material
  positive charge, the other negative.                                                                   (phoshorous-doped silicon)

  When light enters the cell, some of                                                                    Base contact
  the photons from the light are
  absorbed by the semiconductor            Basic solar cell construction The sandwich of semiconductor materials
  atoms, freeing electrons from the        produce electricity directly from the sunlight without any moving parts.

  cell’s negative layer to flow through
  an external circuit and back into the
  positive layer. This flow of electrons
  produces electric current.

  To increase their utility, dozens of
  individual PV cells are interconnect-
  ed together in a sealed, weatherproof
  package called a module. When two
  modules are wired together in series,
  their voltage is doubled while the
  current stays constant. When two                     Cell                    Module                         Array

  modules are wired in parallel, their
  current is doubled while the voltage
                                           Photovoltaic cells, modules and arrays The building blocks of solar electricity are
  stays constant. To achieve the           modular in nature, allowing great flexibility in applications.
  desired voltage and current, modules
  are wired in series and parallel into
  what is called a PV array. The flexi-    THE GRID: ON                                   from their electric utility. These
  bility of the modular PV system          OR OFF?                                        homeowners can supplement their
  allows designers to create solar         Some homeowners in Texas are                   energy needs with electricity from
  power systems that can meet a wide       turning to PV as a clean and reliable          their local utility when their PV sys-
  variety of electrical needs, no matter   energy source even though it is often          tem is not supplying enough energy
  how large or small.                      more expensive than power available            (at nighttime and on cloudy days)

  SECO FACT SHEET NO. 11                                                         INTRODUCTION TO PHOTOVOLTAIC SYSTEMS P.2
and can export excess electricity         For an off-grid PV system, con-                      for use with PV systems are called
back to their local utility when their    sumers should consider whether they                  secondary or deep cycle batteries.
PV system is generating more energy       want to use the direct current (DC)                  There are two types of deep cycle
than is needed.                           from the PV’s or convert the power                   batteries: lead acid, which require
                                          into alternating current (AC).                       the periodic addition of water, and
For locations that are “off the grid”     Appliances and lights for AC are                     captive electrolyte (or gelcell) batter-
— meaning they are far from, or do        much more common and are gener-                      ies, which are maintenance free.
not use, existing power lines — PV        ally cheaper, but the conversion of
systems can be used to power water        DC power into AC can consume up                      In addition, PV systems require
pumps, electric fences or even an         to 20 percent of all the power pro-                  proper wiring, switches and fuses for
entire household.                         duced by the PV system.                              safety, controllers to prevent the bat-
                                                                                               teries from being overcharged or
While PV systems may require a            To store electricity from PV’s, batter-              overly discharged, diodes to allow
substantial investment, they can be       ies will be needed. The batteries used               current to flow in the right direc-
cheaper than paying the costs associ-     for PV systems are different from car                tion, and grounding mechanisms to
ated with extending the electric util-    batteries. The batteries best suited                 protect against lightning strikes.
ity grid. A consumer in Texas may
be asked to pay anywhere from
$5,000 to $30,000 per mile to                                                                      Charge
extend power lines.                                                                               controller                    Battery

A grid-connected PV system will                                         Photovoltaic array
require a utility interactive DC to
AC inverter. This device will convert
the direct current (DC) electricity
produced by the PV array into alter-
nating current (AC) electricity typi-               DC Load

cally required for loads such as
radios, televisions and refrigerators.
                                                                               AC Load
Utility interactive inverters also have
built-in safety features required by      Components of a typical off-grid PV system Solar electricity can be used for many
electric utilities nationwide.            purposes, either directly, or by storing in batteries for use when the sun is not shining.

SECO FACT SHEET NO. 11                                                               INTRODUCTION TO PHOTOVOLTAIC SYSTEMS P.3
                                                              F i n a n c i a l A ck n ow l e d g e m e n t This publication was developed as part of the Renewable Energy                                             Demonstration Program and was funded 100% with oil overcharge funds from the Exxon settlement as provided
                                                              by the Texas State Energy Conservation Office and the U.S. Department of Energy. Mention of trade names or
                                                              commercial products does not constitute endorsement or recommendation for use.

ORGANIZATIONS                                        RESOURCES
American Solar Energy Society
                                                     FREE TEXAS RENEWABLE ENERGY INFORMATION
2400 Central Ave., G-1
                                                     For more information on how you can put Texas’ abundant renewable energy resources to
Boulder, CO 80301
                                                     use in your home or business, visit our website at or call us at
(303) 443-3130
                                                     1-800-531-5441 ext 31796. Ask about our free lesson plans and videos available to teachers
                                                     and home schoolers.
Great list of publications

Texas Solar Energy Society                           ON THE WORLD WIDE WEB:
P.O. Box 1447
                                                     Center for Renewable Energy and Sustainable Technology (CREST)
Austin, TX 78767-1447
                                                     This site has a comprehensive list of related web sites.
(512) 326-3391 or (800) 465-5049
                                                     Florida Solar Energy Center. Information on photovoltaics, batteries, alternative buildings
                                                     systems, solar heaters. FSEC offers training courses such as, “Installation of Grid-Connected
Solar goings on in Texas
                                                     Photovoltaic Systems.”
Solar Energy International
                                                     Real Goods. Site offers introductory explanations of solar technologies. You can buy a wide
P.O. Box 715
                                                     variety of solar goods, PV modules, compact fluorescent bulbs and other gear. A worthy stop
Carbondale, CO 81623-0715
                                                     for anyone shopping for solar-powered or energy efficient items.
(970) 963-8855
                                                     Department of Energy. Web pages run by the Department of Energy. This site has a much
Info on PV design, installation workshops
                                                     more detailed fact sheet on PV basics.
Solar Energy Industries Association
                                                     Sandia National Laboratory Photovoltaic Program. This site offers descriptions of a variety
1616 H Street, NW 8th Floor
                                                     of PV systems. This rich site also includes system sizing worksheets, PV codes and standards,
Washington, DC 20006 (202) 628-7979
                                                     and PV economics.
(301) 951-3231
                                                     Department of Energy’ Photovoltaic Program
Comprehensive list of PV manufacturers
                                                     This web site contains a comprehensive directory of U.S. organizations involved in PV.
Texas Renewable Energy Industries
Box 16469                                            BOOK:
Austin, TX 78761
                                                     Just Add Sunshine, Solar Electricity Will Set You Free. J. Michael Mooney, ARC Press of
(512) 345-5446
                                                     Cane Hill, 1997. A self study guidebook on the exciting world of solar electricity. Detailed
                                                     examples of PV systems to power both large and small dwellings are included. (Available at
Comprehensive list of PV suppliers and

                             STATE ENERGY CONSERVATION OFFICE
                             111 EAST 17TH STREET, ROOM 1114
                             AUSTIN, TEXAS 78774

                             PH. 800.531.5441 ext 31796
        OF TEXAS

SECO FACT SHEET NO. 11                                                                                     INTRODUCTION TO PHOTOVOLTAIC SYSTEMS P.4

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