This document discusses stand-alone photovoltaic (solar electric) systems that are independent from any power grid. It describes the key components of stand-alone systems including solar modules to convert sunlight to electricity, batteries to store energy, inverters to convert DC to AC current, and provides guidance on properly sizing, installing and maintaining these systems for off-grid use. Stand-alone systems generate and store solar power to provide electricity day and night without connection to the existing utility grid.

1. There are 2 types of photovoltaic
applications: those connected to an
Residential Photovoltaic existing power grid (Grid-Tie), and
those independent from any power
(Solar Electric) Stand Alone Systems grid (Stand Alone).
STAND ALONE SYSTEMS
Photovoltaic systems are appearing
across the Arizona landscape. HOW TO CHOOSE A Choosing a System
Current trends show an increasing PHOTOVOLTAIC (P.V.) System choice is based on OTHER APPLICATIONS
number of urban and rural install- SYSTEM *What do you need it to do? • SOLAR WATER PUMPING
ations as Arizonans search for *How much power do you • POOL PUMPS
energy stability and security. want? • IRRIGATION CONTROL
DO NOT THINK ABOUT PV *What is the daily & annual • LIGHTING
In response to the Arizona Corpor- WITHOUT CONSIDERING profile of power use and • DC POWERED
ation Commission implementation ENERGY EFFICIENCY. projected need?. • EVAPORATIVE COOLERS
of the Environmental Portfolio PV only makes sense when *What happens if the power
Standard directing Arizona utilities electricity is consumed efficiently.. system fails?
to provide a portion of their energy Energy efficiency is the key goal
from renewable sources, utilites are before considering any PV system, STAND ALONE SYSTEMS
installing solar power lants; pro- since it will have a direct impact Stand alone systems are totally self-
viding incentives and buydowns to upon the type and quantity of PV sufficient with no connection to the
their customers who purchase and equipment needed. utility grid system. They generate
install solar systems; and some are electricity during daylight hours, and
even offering packaged units of FIRST STEPS store excess for nighttime use. ALLIED EQUIPMENT TO BE
stand-alone systems for remote USED WITH STAND ALONE
settings. * Consider an energy audit APPLICATIONS
* Consider energy efficiency Stand Alone Systems • Propane generator
While the economics of photo- • Insulation * Total independence from utility • Gas stove and dryer
voltiacs continues to get better and • Effective windows and covers power. • Solar Cooker
better, the obvious advantage is in • Roof exposure and impacts * Provide for all electric needs • Solar water heater
locations where there is no utility • Efficient appliances * Require large battery bank • Wind generator
grid, and remote enough to make • Time of use utility rates for night and cloudy days.
extensions of the existing power • Site conditions * Consider a backup
grid costly. Rural Arizonans • Architecture and construction generator/inverter in case of
continue the incorporation and use * Use Passive solar techniques to system failure.
of solar, and leading the State into a mitigate negative conditions, * Minimize electricity use
solar future. and take advantage of site Energy Efficient appliances
resources to reduce power Use only electric appliances
requirements. * Minimize “parasitic loads” that
are always on but don’t need
to be (VCR, clocks,etc.)

2. WHAT WILL IT DO? INVERTERS
Inverters convert DC (direct Cur-
Stand Alone systems rent) electricity to AC (alternating
* Provide power whenever current) electricity. There are 2
the sun is shining, eliminating types of Inverters – sine wave and
dependency on utility provid- non-sine wave (for non-critical
ed electricity, and reducing power requirements like power
utility bills tools, etc,) Inverters. Non-sine wave
* Provide power for a variety inverters are cheaper and should BATTERIES
of applications other than ONLY be used in stand Alone
residential use. Can be used
SYSTEM INFO Batteries store DC electricity for
applications, N E V E R in grid later use.
for pumping water from a well, SOLAR MODULES connected systems.
outdoor lighting, etc..
* Care must be taken to
correctly size and maintain
the system.
* Amount of solar power
available depends on array *Use ONLY deep cycle batteries.
and inverter.
*Wet batteries need to be checked
* Back-up power and time
for fluids and tightness at least
depend on Battery and every 6 months
Inverter choices. *Sealed batteries do not need water
Solar modules that convert sunlight
to electricity are very similar for all Inverter Choice but may not last as long as wet
STAND ALONE COMPONENTS systems, with larger modules being batteries.
PV array – The part of the system
Consideration
normally cheaper in terms of dollars * How much power is needed? *Capacity – Larger capacity store
that converts sunlight to electricity per watt delivered. Modules more energy and are more
Stand Alone Inverter – The part of * How flexible is the battery
produce more power when cooler. charging? expensive.
the system that changes the quality *Voltage of the batteries MUST
of the electricity the panel produces * Will the Inverter control a backup
A current development in photo- generator? ALWAYS be matched to the
(Direct Current) to the quality voltaic modules and engineering iinverter.
required by the building equipment. * What other equipment will be a
plastics is toward Building part of the system? *Never run more than 4 para-llel
(120 volt Alternating current) Integrated PV (BIPV), that make strings of batteries. Since batteries
Batteries – The electricity storage the system a part of the building do not share loads equally, the life
system Additionally, there are application
structure, where the PV system is elements to be considered. of the battery bank will suffer.
Battery Cut Off Switch – Safety item both the roof, or wall, as well as the * Safety –
to isolate the battery bank power generator of the building. Keep in a ventlated area
Inverter.Safety Switch – So the MODULE MOUNTING Use insulated tools
Utility can shut system off in Module mounts are used to position
emergencies or work the collector relative to the sun.
There are fixed mounts and trackers
OTHER COMPONENTS
(which increase the amount of Charge Controllers –
power from an array). Where these (Solar Battery Charger) Conditions
are placed affects performance and the power from the solar module to
aesthetics. charge a battery.

3. Disconnects and Switches – How Do I Get More Information?
COMMON QUESTIONS
National Electric Code and local * Ask PV system owners .
Can run my air conditioner
codes require disconnects for * Call the utility company.
on solar?
safety of owners and workers. * Find a local PV dealer in the phone book.
In principle yes, but in
Remote Controls – practice it is not economically * Check Magazines – Solar Today and Home power magazines are
Many systems offer remote controls feasible. In a line tie system the most widely available sources of information on photovoltaic
for convenience and some offer the energy savings realized systems.
performance monitoring by by the solar power generated
computer.. will offset some of the power *Check the Internet
Meters and Data acquisition– needed to run an A/C unit * Arizona Solar Center www.azsolarcenter.com
Collect data about the system’s • * Az. Dept. of Commerce Energy Office
performance Useful for isolating How Much Does a Solar www.commerce.state.az.us/energy
performance problems Often linked System Cost?. * PV & systems manufacturers sites
to the Remote Control package. Currently installed cost is * National Renewable Energy Lab
about $8 to $9 per watt, www.NREL.gov *
before incentives. Incentives * U.S. Dept. of Energy www.doe.gov
include a State tax credit; a * California Energy Commission
State sales tax exemption www.energy.ca.gov
;and utility buy-down pro- * Florida Solar Center
grams which significantly www.fsec.ucf.edu
reduce the overall cost of a
photovoltaic system.
What is the Payback Time?
Wind Generators With a solar PV system you
Small wind generators can be a are buying power at a known
compliment to a solar system fixed cost of todays market.
installation, in providing for night- Payback can be calculated by
time power. Effectivenesss is a guessing future energy value
function of wind speed and the impacted by supply, inflation This information was prepared by the Arizona Solar Energy
minimum requirement is 5 to 7 miles rates, and other market Association & the Arizona Solar Center Inc. for the Arizona
per hour wind velocity. Like any factors. Department of Commerce Energy Office under a contract from the
U.S. Department of Energy Million Solar Roof Program
other equipment, a wind generator
requires regular maintenance and Can the Meter Spin
occasional replacement of parts. Backwards?
Yes, if more energy is NOTE: Financial support for this presentation has been provided by the
generated than used, it can Arizona Department of Commerce (Energy Office) and the U.S. Department
be put into the utility grid and of Energy through (DOE) Grant No. DE-FG51-01R021250. However, any
the Owner compensated. The opinions, findings, conclusions, or recommendations expressed herein are
compensation rate depends those of the author(s) and do not necessarily reflect the views of the Energy
on the utility company and Office or U.S. DOE. The State of Arizona and U.S. DOE assume no liability
State requirements and law. for damages arising from errors, omissions or representations contained in this
presentation