In this early stage of marketing solar electric power systems to the residential market, it is advisable for an
installer to work with well established firms that have complete, pre-engineered packaged solutions that
accommodate variations in models, rather than custom designing custom systems. Once a system design
has been chosen, attention to installation detail is critically important. Recent studies have found that 10-20%
of new PV installations have serious installation problems that will result in significantly decreased
performance. In many of these cases, the performance shortfalls could have been eliminated with proper
attention to the details of the installation.
1.1. Basic Principles to Follow When Designing a Quality PV System
1. Select a packaged system that meets the owner's needs. Customer criteria for a system may include
reduction in monthly electricity bill, environmental benefits, desire for backup power, initial budget
constraints, etc. Size and orient the PV array to provide the expected electrical power and energy.
2. Ensure the roof area or other installation site is capable of handling the desired system size.
3. Specify sunlight and weather resistant materials for all outdoor equipment.
4. Locate the array to minimize shading from foliage, vent pipes, and adjacent structures.
5. Design the system in compliance with all applicable building and electrical codes.
6. Design the system with a minimum of electrical losses due to wiring, fuses, switches, and inverters.
7. Properly house and manage the battery system, should batteries be required.
8. Ensure the design meets local utility interconnection requirements.
1.2. Basic Steps to Follow When Installing a PV System
1. Ensure the roof area or other installation site is capable of handling the desired system size.
2. If roof mounted, verify that the roof is capable of handling additional weight of PV system. Augment roof
structure as necessary.
3. Properly seal any roof penetrations with roofing industry approved sealing methods.
4. Install equipment according to manufacturers specifications, using installation requirements and
procedures from the manufacturers' specifications.
5. Properly ground the system parts to reduce the threat of shock hazards and induced surges.
6. Check for proper PV system operation by following the checkout procedures on the PV System
Installation Checklist.
7. Ensure the design meets local utility interconnection requirements
8. Have final inspections completed by the Authority Having Jurisdiction (AHJ) and the utility (if required).
PV Installation Guide
June 2001 Page 5
SECTION 2: SYSTEM DESIGN CONSIDERATIONS
2.1 Typical System Designs and Options
PV Electrical System Types
There are two general types of electrical designs for PV power systems for homes; systems that interact with
the utility power grid and have no battery backup capability; and systems that interact and include
battery backup as well.
2.1.1. Grid-Interactive Only (No Battery Backup)
This type of system only operates when the utility is available. Since utility outages are rare, this system will
normally provide the greatest amount of bill savings to the customer per dollar of investment.
However, in the event of an outage, the system is designed to shut down until utility power is
restored.
Typical System Components:
PV Array: A PV Array is made up of PV modules, which are environmentally-sealed collections of PV Cells—
the devices that convert sunlight to electricity. The most common PV module that is 5-to-25 square
feet in size and weighs about 3-4 lbs./ft2. Often sets of four or more smaller modules are framed or
attached together by struts in what is called a panel. This panel is typically around 20-35 square feet
in area for ease of handling on a roof. This allows some assembly and wiring functions to be done
on the ground if called for by the installation instructions.
balance of system equipment (BOS): BOS includes mounting systems and wiring systems used to integrate
the solar modules into the structural and electrical systems of the home. The wiring systems include
disconnects for the dc and ac sides of the inverter, ground-fault protection, and overcurrent
protection for the solar modules. Most systems include a combiner board of some kind since most
modules require fusing for each module source circuit. Some inverters include this fusing and
combining function within the inverter enclosure.
dc-ac inverter: This is the device that takes the dc power from the PV array and converts it into standard ac
power used by the house appliances.
metering: This includes meters to provide indication of system performance. Some meters can indicate home
energy usage.
other components: utility switch (depending on local utility)

2.1.2. Grid-Interactive With Battery Backup
This type of system incorporates energy storage in the form of a battery to keep “critical load” circuits in the
house operating during a utility outage. When an outage occurs the unit disconnects from the
utility and powers specific circuits in the home. These critical load circuits are wired from a
PV Array DC/AC
PV Array Inverter
Circuit
Combiner
Main Service
Panel
Utility
Utility
Ground-Fault Switch
Protector
AC
Fused
Switch
DC
Fused
Switch
Grid-Interactive PV System w/o Battery Backup
PV Installation Guide
June 2001 Page 6
subpanel that is separate from the rest of the electrical circuits. If the outage occurs during daylight
hours, the PV array is able to assist the battery in supplying the house loads. If the outage occurs
at night, the battery supplies the load. The amount of time critical loads can operate depends on
the amount of power they consume and the energy stored in the battery system. A typical backup
battery system may provide about 8kWh of energy storage at an 8-hour discharge rate, which
means that the battery will operate a 1-kW load for 8 hours. A 1-kW load is the average usage for
a home when not running an air conditioner.
Typical System Components:
In addition to components listed in 2.1.1., a battery backup system may include some or all of the
following:
1. batteries and battery enclosures
2. Battery charge controller
3. separate subpanel(s) for critical load circuits
2.2. Mounting Options
There are several ways to install a PV array at a residence.
Most PV systems produce 5-to-10 Watts per square foot of
array area. This is based on a variety of different technologies
and the varying efficiency of different PV products. A typical 2-
kW PV system will need 200-400 square feet of unobstructed
area to site the system. Consideration should also be given for
access to the system. This access space can add up to 20% of
needed area to the mounting area required.
2.2.1. Roof mount
Often the most convenient and appropriate place to
put the PV array is on the roof of the building. The
PV array may be mounted above and parallel to
the roof surface with a standoff of several inches for
cooling purposes. Sometimes, such as with flat roofs,
Figure 1 Roof Mounted PV System
PV Array
PV Array
Circuit
Combiner
Ground-Fault
PV Array Protector
Switch
Backup
Power
System,
DC/AC
Inverter,
and
Battery
Charge
Controller
Main Service
Panel
Utility
Utility
Switch
AC
Fused
Switch
Backup
Battery
Charge
Controller
Battery
System
Critical Load
Sub-Panel
PV Installation Guide
June 2001 Page 7
a separate structure with a more optimal tilt angle is mounted on the roof.
Proper roof mounting can be labor intensive. Particular attention must be paid to the roof
structure and the weather sealing of roof penetrations. It is typical to have one support bracket
for every 100 Watts of PV modules. For new construction, support brackets are usually mounted
after the roof decking is applied and before the roofing materials is installed. The crew in charge
of laying out the array mounting system normally installs the brackets. The roofing contractor
can then flash around the brackets as they install the roof. A simple installation detail and a
sample of the support bracket is often all that is needed for a roofing contractor to estimate the
flashing cost.
Masonry roofs are often structurally designed near the limit of their weight-bearing capacity. In
this case, the roof structure must either be enhanced to handle the additional weight of the PV
system or the masonry roof transitioned to composition shingles in the area where the PV array
is to be mounted. By transitioning to a lighter roofing product, there is no need to reinforce the
roof structure since the combined weight of composite shingles and PV array is usually less than
the displaced masonry product.

2.2.2. Shade Structure
An alternative to roof mounting is to mount the system as a
shade structure. A shade structure may be a patio cover or
deck shade trellis where the PV array becomes the shade.
These shade systems can support small to large PV
systems.
The construction cost with a PV system is a little different
than for a standard patio cover, especially if the PV array is
acts as part or the entire shade roof. If the PV array is
mounted at a steeper angle than a typical shade structure,
additional structural enhancements may be necessary to
handle the additional wind loads. The weight of the PV array
is 3-to-5 lbs./ft2, which is well within structural limits of most
shade support structures. The avoided cost of installing roof
brackets and the associated labor could be counted toward
the cost of a fully constructed patio cover. The overall cost of
this option will likely be higher than roof mounting, but the
value of the shade often offsets the additional costs. Other
issues to consider include
• Simplified array access for
maintenance
• Module wiring, if visible from
underneath, must be carefully
concealed to keep the installation
aesthetically pleasing
• Cannot grow vines, or must be
diligent about keeping it trimmed
back from modules and wiring
2.2.3. Building-Integrated PV Array (BIPV)
Another type of system displaces some of the
conventional roofing product with buildingintegrated
PV modules. Commercially available products currently include roof slates (similar to
masonry roofing) and standing seam metal roofing products. Special attention must be paid to
ensure that these products are installed properly and carry the necessary fire ratings.
Figure 2 Patio Cover or Deck Shade
Figure 3 Building-Integrated Installation
PV Installation Guide
June 2001 Page 8
Dimensional tolerances are critical and installation requirements must followed precisely to avoid
roof leaks.
2.3 Estimating System Output
PV systems produce power in proportion to the intensity of sunlight striking the solar array surface. The
intensity of light on a surface varies throughout a day, as well as day to day, so the actual output of a solar
power system can vary substantial. There are other factors that affect the output of a solar power system.
These factors need to be understood so that the customer has realistic expectations of overall system output
and economic benefits under variable weather conditions over time.
2.3.1. Factors Affecting Output
Standard Test Conditions
Solar modules produce dc electricity. The dc output of solar modules is rated by manufacturers under
Standard Test Conditions (STC). These conditions are easily recreated in a factory, and allow for consistent
comparisons of products, but need to be modified to estimate output under common outdoor operating
conditions. STC conditions are: solar cell temperature = 25 oC; solar irradiance (intensity) = 1000 W/m2
(often referred to as peak sunlight intensity, comparable to clear summer noon time intensity); and solar
spectrum as filtered by passing through 1.5 thickness of atmosphere (ASTM Standard Spectrum). A
manufacturer may rate a particular solar module output at 100 Watts of power under STC, and call the
product a “100-watt solar module.” This module will often have a production tolerance of +/-5% of the rating,
which means that the module can produce 95 Watts and still be called a “100-watt module.” To be
conservative, it is best to use the low end of the power output spectrum as a starting point (95 Watts for a
100-watt module).
Temperature
Module output power reduces as module temperature increases. When operating on a roof, a solar module
will heat up substantially, reaching inner temperatures of 50-75 oC. For crystalline modules, a typical
temperature reduction factor recommended by the CEC is 89% or 0.89. So the “100-watt” module will
typically operate at about 85 Watts (95 Watts x 0.89 = 85 Watts) in the middle of a spring or fall day, under
full sunlight conditions.
Dirt and dust
Dirt and dust can accumulate on the solar module surface, blocking some of the sunlight and reducing
output. Much of California has a rainy season and a dry season. Although typical dirt and dust is cleaned off
during every rainy season, it is more realistic to estimate system output taking into account the reduction due
to dust buildup in the dry season. A typical annual dust reduction factor to use is 93% or 0.93. So the “100-
watt module,” operating with some accumulated dust may operate on average at about 79 Watts (85 Watts x
0.93 = 79 Watts).
Mismatch and wiring losses
The maximum power output of the total PV array is always less than the sum of the maximum output of the
individual modules. This difference is a result of slight inconsistencies in performance from one module to
the next and is called module mismatch and amounts to at least a 2% loss in system power. Power is also
lost to resistance in the system wiring. These losses should be kept to a minimum but it is difficult to keep
these losses below 3% for the system. A reasonable reduction factor for these losses is 95% or 0.95.
Dc to ac conversion losses
The dc power generated by the solar module must be converted into common household ac power using an
inverter. Some power is lost in the conversion process, and there are additional losses in the wires from the
rooftop array down to the inverter and out to the house panel. Modern inverters commonly used in residential
PV power systems have peak efficiencies of 92-94% indicated by their manufacturers, but these again are
PV Installation Guide
June 2001 Page 9
measured under well-controlled factory conditions. Actual field conditions usually result in overall dc-to-ac
conversion efficiencies of about 88-92%, with 90% or 0.90 a reasonable compromise.
So the “100-watt module” output, reduced by production tolerance, heat, dust, wiring, ac conversion, and
other losses will translate into about 68 Watts of AC power delivered to the house panel during the middle of
a clear day (100 Watts x 0.95 x 0.89 x 0.93 x 0.95 x 0.90 = 67 Watts).
2.3.2. Estimating System Energy Output
Sun angle and house orientation
During the course of a day, the angle of sunlight
striking the solar module will change, which will affect
the power output. The output from the “100-watt
module” will rise from zero gradually during dawn
hours, and increase with the sun angle to its peak
output at midday, and then gradually decrease into
the afternoon and back down to zero at night. While
this variation is due in part to the changing intensity of the sun, the changing sun angle (relative to the
modules) also has an effect
The pitch of the roof will affect the sun angle on the module surface, as will the East-West orientation of the
roof. These effects are summarized in Table 1, which shows that an array on a 7:12-pitch roof facing due
South in Southern California gives, for example, the greatest output (correction factor of 1.00), while an East
facing roof at that same pitch would yield about 84% of the annual energy of the South facing roof (a
correction factor of 0.84 from Table 1).
Table 2 is intended to give a conservative estimate of the
annual energy expected from a typical PV system, taking
into account the various factors discussed above.
These values are for annual kWh produced from a 1-kilowatt
(1kW) STC DC array, as a simple and easy guide. If the
system includes battery backup the output may be reduced
further by 6-10% due to battery effects.
Example: A 4 kWSTC solar array (as specified under STC
conditions) located in the Los Angeles area at a 4:12 pitch
and facing southeast should produce at least 5343 kWh of
electric energy annually (1406 kWh/kW x 0.95 x 4 kW =
5343 kWh). The typical residential customer in that area
uses about 7300 kWh annually1, meaning such a PV system
could produce at least 75% of the total energy needed by such a
typical home. And if energy efficiency measures were taken by the owner to reduce the overall electrical
consumption of the home, the percentage could approach 100%. Note that the low end of the range was
used to calculate the actual savings. It is wise to be conservative when making performance claims.
Net metering has recently been extended to time-of-use customers yielding a potential additional value of
20-30% for the PV electricity generated by the system. With this net time-of-use metering, the homeowner
would cover almost their entire electric bill and only have to pay the monthly metering charge.
1 Actual residential electrical energy usage varies dramatically from one home to the next. It is best to use the previous
two years of energy bills to determine actual energy consumption for a particular home. Energy consumption in California
can vary from 3,000 kWh/year for a very minimal user to 25,000 kWh/year for a large home with heavy electrical usage.
Table 1: Orientation Factors for Various
Roof Pitches and Directions
Flat 4:12 7:12 12:12 21:12 Vertical
South 0.89 0.97 1.00 0.97 0.89 0.58
SSE,SSW 0.89 0.97 0.99 0.96 0.88 0.59
SE, SW 0.89 0.95 0.96 0.93 0.85 0.60
ESE,WSW 0.89 0.92 0.91 0.87 0.79 0.57
E, W 0.89 0.88 0.84 0.78 0.70 0.52
Table 2: Annual Energy Production
by City per kWSTC array rating
CITY kWh/kWstc (range)
Arcata 1092 - 1365
Shasta 1345 - 1681
San Francisco 1379 - 1724
Sacramento 1455 - 1819
Fresno 1505 - 1881
Santa Maria 1422 - 1778
Barstow 1646 - 2058
Los Angeles 1406 - 1758
San Diego 1406 - 1758
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June 2001 Page 10
2.4. Installation Labor Effort
Installation effort is very sensitive to specific house layouts and roofing type. An experienced crew can
install a 2 kW non-battery PV system in two-to-four person-days. Systems with large solar arrays are
relatively less effort per watt of power and kWh of energy than smaller systems because the installation of
the inverter and other hardware required by all PV systems is spread over more solar modules. Systems
with battery backup are more labor intensive than non-battery systems because of the additional wiring
required for wiring the critical load subpanel. A battery system can add 50-100% to the time required for the
installation.

2.5. Incentives to Reduce Costs
Financial incentives are available from the Energy Commission, the CPUC, and several local utilities and
municipalities throughout California to reduce these system costs. The CEC buydowns are calculated by
multiplying $4.50 times the adjusted peak dc power from the system in Watts (up to a maximum of 50% of
the system cost). This buydown is available for all Pacific Gas & Electric (PG&E), Southern California Edison
(SCE), and San Diego Gas & Electric (SDG&E) customers. Some municipal utilities in cities such as
Sacramento, Los Angeles, Palo Alto, and Roseville provide the same or even higher incentives.
This level of rebate can reduce the cost of systems by 30 to 50 percent or more and result in much more
favorable economics for the owner. An owner can incorporate a basic 1 kW solar power system for as little
as $3,000-$5,000. If the system is included in the mortgage of the home, this small increment in house
payment may be offset by an equivalent reduction in the monthly utility bill.
2.6. Estimating Electrical Energy Savings
One of the key benefits of residential solar power systems is a lower electric utility bill resulting from the
energy that the solar system produces. The energy savings to a homeowner can be estimated by simply
multiplying the annual energy in kWh that a PV system might produce times the utility electric energy rate.
These rates vary by local utility, and are likely to increase from their current values. Estimated energy
savings from small and large PV systems in Southern California are presented below to illustrate the kinds of
savings that can be achieves.
Sample Annual Electric Utility Bill Savings
Solar Utility Electric Energy Rate
Array
(STC)
Estimated
Annual
Energy
$0.10 /kWh $0.15 /kWh $0.20 /kWh $0.25 /kWh
1.2 kW 1687 kWh $168.70 $224.93 $337.40 $421.75
4.0 kW 5624 kWh $562.40 $843.60 $1,124.80 $1406.00
2.7. Supplier and System Qualifications
When choosing a supplier and specifying a PV system, the following are a series of general guidelines to help
guide the decision-making process.
2.7.1. Pre-Engineered Systems
When a owner considers an HVAC system for a home, they do not buy a compressor from one manufacturer
and a cooling coil from another company, and a fan from a third company and then put these pieces together.
The equipment manufacturers have engineered a packaged system that is designed to work together. Each
model of a home may need a slightly different unit based on the size and layout, but those variations have been
PV Installation Guide
June 2001 Page 11
designed into the product. In the same way, the components of a PV system should be engineered to work
together as a unit accounting for variations in system size for different homes.
Since the PV industry is in the early stages of development, there is a wide range of competency levels among
PV system integrators. Unless the installer is familiar enough with the technology to recognize whether the
system integrator is competent, it is much safer to stay with a firm that provides pre-engineered systems. Preengineering
may not guarantee a flawless system, but the concerns over product compatibility and specification
of individual components have been addressed in the system design.
2.7.2. Warranties
There are several types of warranties that come with a system or can be purchased in addition to a standard
warranty. These include (1) product warranties covering defects in manufacture; (2) system warranties covering
proper operation of equipment for a specific time period (5 or 10 years); and, (3) annual energy performance
warranties covering the guaranteed output of the PV system. The installer, to guarantee proper system
installation, often covers the system and annual energy performance warranties.
Product warranties:
It is common these days to see warranties on PV modules of 20 or more years. Although this is impressive and
indicates the level of confidence manufacturers place in the longevity of their products, there are many other
components in these systems that may not have the same life expectancy. Inverters may have 10-year, fiveyear,
or even one-year warranties. This must be considered when reviewing the cost of inverters and other
system components.
System warranties:
It is equally important to look for entire system-level warranties of five years or more. This indicates that the
manufacturer has taken many other operational issues into account. Since these systems generate electrical
power, it is helpful to have system performance included as part of the warranty. For instance, a typical systemlevel
warranty might state that the system is guaranteed to produce two kilowatts (2 kW) of AC power at PVUSA
Test Conditions (PTC) (PTC is 1kW/m2 irradiance, 1 m/s wind speed, 20oC ambient temperature) in the fifth year
of operation. The equipment to perform this test is expensive, but the fact that a company would know enough
to specify this type of warranty is an indication that they are confident in their system design. Currently, the
California Energy Commission Buydown program requires installing contractor to provide these warranties. The
intent of this requirement is to improve customer acceptance of PV systems.
Annual energy performance warranties:
Although there are very few companies selling systems with this type of warranty, an energy performance
warranty guaranties that the system will perform consistently over a period of time. This is particularly helpful in
ensuring that the customer receives the bill savings that they expect. This type of warranty is more common with
energy efficiency retrofit projects for commercial and industrial clients. Adequate metering to verify the system
power output and energy generation is necessary to help the system owner understand whether the system is
operating properly, or has warranty-related performance issues. With an adequate meter, the customer can
readily identify when the system is malfunctioning.
2.7.3. Company Reputation (years in business, previous projects)
The reputation of the PV manufacturer is a critical piece of the decision-making process. The size of the
company, number of years in business, number of previous projects completed, are all important issues that
need to be reviewed before choosing a company’s products. Although price is often the strongest single
consideration in reviewing proposals, the other less tangible considerations often add up to a similar level of
importance with cost. Fortunately, there are several companies with very strong financial and historical records
in this field. It is recommended that you research the background and history of the prospective vendor
thoroughly.

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June 2001 Page 12
2.8. Overall Project Coordination
Once the decision is made to install a PV system, several issues must then be addressed.
2.8.1. Utility Considerations
The electric utility company providing service to the residence plays a very important role in this process.
Interconnecting a PV system to the utility grid is not a trivial undertaking. Fortunately, PV has a welldeveloped
set of utility interconnection standards making the process fairly straightforward. However, utilities
are generally cautious since most have little experience interconnecting PV systems. The key point is to
involve the utility as early as possible in the installation. Most knowledgeable utilities have adopted IEEE
929-2000 Recommended Practice for Utility Interface of Photovoltaic (PV) Systems. If the utility is unfamiliar
with this document, make sure that they obtain a copy and thoroughly review it.. An inverter listed to UL 1741
(with the words "Utility-Interactive" printed on the listing mark) indicates that the unit is fully compliant with
IEEE 929-2000.
The other major utility-related consideration is metering requirements. In California, as in many other states,
there is legislation mandating utility companies to “net-meter” a certain amount of PV systems. Net metering
refers to a standard house utility meter that measures the flow of electricity in and out of the home2. California
law allows customers to carry-over excess energy from month-to-month with an annual true-up and payment of
the electrical bill for any net consumption over the whole year. The net metering law does not require the utility
to compensate the customer for excess electricity at the end of that 12-month period. For more information
about this and other consumer-related PV issues, download the document, Buying a Photovoltaic Solar Electric
System: A Consumers Guide, from the California Energy Commission’s website at
http://www.energy.ca.gov/reports/500-99-008.PDF or call 1-800-555-7794 (Renewable Energy Call Center) to
receive a copy by mail.
2.8.2. Acceptance of Systems (performance evaluation)
Typically, the installer verifies that the system has been installed according to the manufacturer’s
procedures. A checkout procedure should be developed, such as the one provided in section 4 of this guide,
to ensure an efficient and complete installation. Obtaining extremely accurate performance is difficult and
requires expensive test equipment. Fortunately, it is not necessary to define the performance with extreme
accuracy. A system can be checked with some common test equipment to verify proper installation and
performance. A key to keeping the system testing simple is to do the tests on cloudless days. Clouds can
cause fluctuations that confound evaluation of the results. The PV System Installation Checklist that
accompanies this guide has a detailed System Acceptance Test.
2.8.3. System Documentation
Up to this point, selection, installation, and performance of PV systems have been discussed. Of similar
importance are operation and ongoing maintenance of the equipment. As with other major systems in a
home, it is essential that the owner have complete documentation on the system. System documentation
should include an owner’s manual and copies of relevant drawings for whatever system maintenance might
be required in the future.
2.8.4. System Monitoring
The key component of the system providing feedback to the customer is the power and energy metering.
Without proper metering the customer will never know whether the system is operating properly or not. A
simple meter, registering the power output of the PV system and recording the energy delivered to the
house, can provide the owner with the satisfaction that they can monitor the performance of the system.
2 Yes, out! Even a 500-Watt PV system on a sunny day may generate more electricity than the home
consumes at any given time.
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June 2001 Page 13
Maximum power output of most properly installed PV systems occurs near midday on sunny days in the
spring and fall. If the owner fully understands this characteristic they will not be disappointed with
unavoidable low output in the middle of the winter. The meter is also a way of proving to the owner that the
equipment is properly installed. Often, the owner’s primary indication of whether they feel the system is
operating properly on not is their monthly electric bill. If the owner suddenly begins using more electricity,
they may not see much decrease in their bill and assume the PV system is under-performing. A meter can
help avoid disputes between the installer and the owner by showing that the system performs as advertised.
One of the attractive attributes of PV system is low maintenance. However, even electrical systems need to
be maintained from time to time. With proper metering, an informed owner can easily determine if their
system is operating properly or not. It is important that the owner have contact information for contractors
that can perform system maintenance in their area. Although many areas do not have full-time PV
contractors, it is always helpful to provide a list of two or three local contractors that offer PV maintenance
services. Along with the information on local contractors, the system warranty information should be provided
so that the customer clearly understands what is and is not covered by their warranty.
2.9. References
1999 National Electrical Code (NEC) Article 690 and Article 702.
Emerging Renewables Buy-Down Program Information: http://www.energy.ca.gov/greengrid
Buying a Photovoltaic Solar Electric System: A Consumers Guide:
http://www.energy.ca.gov/reports/500-99-008.PDF
Clean Power Estimator: http://www.energy.ca.gov/cleanpower/index.html
List of Certified PV Modules: http://www.energy.ca.gov/greengrid/certified_pv_modules.html
List of Certified Inverters: http://www.energy.ca.gov/greengrid/certified_inverters.html
California Energy Commission, 1516 9th Street, Sacramento, CA 95814-5512, 800-555-7794
(Renewable Energy Call Center)
UL Standard 1703, Standard for Flat-plate Photovoltaic Modules and Panels
UL Standard 1741, Inverters, Converters, and Controllers for Independent Power Systems
IEEE Standard 929-2000, Recommended Practice for Utility Interface of Photovoltaic (PV) Systems
IEEE Standard 1262-1995, Recommended Practice for Qualification of Photovoltaic (PV) Modules
Environmental benefits of PV systems can be found at the following USEPA website:
http://199.223.18.230/epa/rew/rew.nsf/solar/index.html

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June 2001 Page 14
SECTION 3: SYSTEM INSTALLATION
3.1. General Recommendations
The following is a list of general recommendations to help the installer choose the right materials, equipment,
and installation methods that will help ensure that the system will provide many years of reliable service.
These recommendations can be used to evaluate pre-engineered system designs and compare system
features from one supplier to another.
3.1.1. Materials recommendations
• Materials used outdoors should be sunlight/UV resistant
• Urethane sealants should be used for all non-flashed roof penetrations.
• Materials should be designed to withstand the temperatures to which they are exposed.
• Dissimilar metals (such as steel and aluminum) should be isolated from one another using non-conductive
shims, washers, or other methods.
• Aluminum should not be placed in direct contact with concrete materials.
• Only high quality fasteners should be used (stainless steel is preferred).
• Structural members should be either:
o corrosion resistant aluminum, 6061 or 6063
o hot dip galvanized steel per ASTM A 123
o coated or painted steel (only in low corrosive environments such as deserts)
o stainless steel (particularly for corrosive marine environments)
3.1.2. Equipment recommendations and installation methods
• All electrical equipment should be listed for the voltage and current ratings necessary for the application.
• PV modules should be listed to UL 1703 and warranted for a minimum of 5 years (20-25 year warranties are
available).
• Inverters should be listed to UL 1741 and warranted for a minimum of 5 years (outside CA these may not be
available).
• All exposed cables or conduits should be sunlight resistant.
• All required overcurrent protection should be included in the system and should be accessible for
maintenance
• All electrical terminations should be fully tightened, secured, and strain relieved as appropriate.
• All mounting equipment should be installed according to manufacturers’ specifications
• All roof penetrations should be sealed with an acceptable sealing method that does not adversely impact
the roof warranty
• Integral roofing products should be properly rated (e.g., class A roofing materials)
• All cables, conduit, exposed conductors and electrical boxes should be secured and supported according to
code requirements.
• PV Array should be free of shade between 9:00 a.m. and 4:00 p.m. This requirement includes even small
obstructions such as vent pipes and
chimneys. A small amount of shade can have
a disproportionately high impact on system
performance
3.2. PV System Design And Installation
3.2.1. Preparation Phase
1. Contact the California Energy Commission 1-800-555-7794 (Renewable Energy Call Center) to
receive a copy of the guide for the Buydown program or download the guide from the Buydown
Website at www.energy.ca.gov/greengrid.
Figure 4 Simple PV System Diagram
PV Array
DC/AC
Inverter
Combiner
Box
Main
Service
Panel
Utility Utility
Switch
PV Installation Guide
June 2001 Page 15
2. Obtain past electric bills for the home if available and audit home to determine what can be done to
reduce electricity usage.
3. Determine the size of the PV system based on budget, energy cost reduction, and available
mounting area for the system. The PV system supplier typically provides the customer with sizing
and performance information. The method in section 2 of this document is intended to provide a
basis to identify those suppliers who are thorough in their sizing estimates.
4. Determine the physical size and dimensions of the PV array and its primary components. This is
critically important in determining where the PV array and ancillary equipment is to be mounted.
3.2.2. Design Phase
1. Examine location options for mounting the PV array (i.e. roof, patio cover, other structure).
2. Review available pre-engineered system packages that contain the desired options. Compare the
various product and system warranties available from each supplier.
3. Confirm that the PV equipment has the necessary listings required by building officials (e.g. UL
1703, UL 1741, and any applicable evaluation reports from National Evaluation Services (NES) or
International Conference of Building Officials (ICBO) Evaluation Services)
4. Select system options making sure the equipment meets the guidelines of local incentive programs.
For the California Buydown Program check that the PV modules and inverter are listed on the
Buydown Website at www.energy.ca.gov/greengrid
5. Contact local utility company (PG&E, SCE, or SDG&E) to obtain the required documents for
interconnection and net metering.
6. Review documents to ensure system meets local interconnection requirements
7. Purchase the equipment.
8. Send completed Buydown Reservation package to the California Energy Commission.
9. Lay out PV array on roof plan or other structure. If roof mounted, determine required location of PV
modules on roof and any potential roof penetrations due to plumbing or combustion appliance vents
that could affect array placement or shade the array. Some obstructions can be relocated to another
portion of the roof should the penetration dramatically impact the location of the array. Attempt to
provide for an aesthetically pleasing layout by attempting to follow the dimensional shape of the roof
section (example: if the roof is rectangular, try to maintain the same shape rectangle in the array
layout). If modules are to be grouped in panels of several modules for ease of wiring and mounting,
try to arrange the panels in symmetrical arrangements.
10. Calculate the impact of shading on the PV array layout with the assistance of a Solar Pathfinder
(http://www.solarpathfinder.com/). Consider other locations to mount the PV array if the
proposed location receives too much shade. Review the mounting options discussed in section two
of this guide for alternatives.
11. Measure the distance between the estimated locations of all system components and develop site
drawing and one-line diagram of PV system installation for the permit package. (See example
drawing).
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June 2001 Page 16
12. Assemble the permit package for the local authority having jurisdiction (AHJ). This package should
include the following:
a. Site drawing showing the location of the main system components--PV Array, conduit runs,
electrical boxes, inverter enclosure, critical load subpanel, utility disconnect, main service
panel, and utility service entrance. (see drawing EX-1 in Appendix)
b. One-line diagram showing all significant electrical system components. (see drawings EX-2
and EX-3 in Appendix)
c. Cut sheets for all significant electrical system components (PV modules, inverter, combiner,
dc-rated switches and fuses, etc…).
d. Copy of filled out utility contract.
e. Structural drawing if the system is incorporated into a separate structure.
f. Structural calculations as necessary
3.2.3. Installation Phase
1. Submit required permit materials to the AHJ and pay for permit to begin construction.
2. Receive equipment and prepare for installation. Examine all equipment to be sure that all equipment
was shipped and that none was damaged in shipping.
3. Review installation instructions for each component to become familiar with the installation process.
4. Estimate length of wire runs from PV modules to combiner and inverter.
5. Check ampacity of PV array circuits to determine the minimum wire size for current flow. Size wire
for the run based on maximum short circuit current for each circuit and the length of the wire run.
Example using drawing EX-1 in the appendix:
Check ampacity of PV array circuits:
a. Minimum wire ampacity for the wire run from modules to combiner is based on module
maximum series fuse rating printed on the listing label (i.e. 15-amps on 100-Watt module).
From Table A-1 in the appendix, use the column for 90C in an open rack, use at least #14
AWG USE-2 wire. This is the minimum wire size and may need to be enlarged to reduce
voltage drop.
b. Minimum wire ampacity for the wire run from combiner to inverter is based on the number of
module series strings times the maximum series fuse rating (5 series strings = 5 x 15 amps
= 75 amps). From Table A-1 in the appendix, use the column titled “Ampacity of 75C wet
rated conductors (45C)”, for a minimum of #3 AWG THWN wire in conduit. This is the
minimum wire size and may need to be enlarged due to voltage drop.
6. Size PV array wiring such that the maximum voltage drop at full power from the PV modules to the
inverter is 3% or less (6-amps for a 100-Watt module). If array combiner box is located remote from
the inverter, spread the voltage drop accordingly between the PV array-to-combiner wiring and the
combiner-to-inverter wiring (example from EX-1 in the appendix: with a 100-foot wire run from PV
modules to inverter (3% total) comprised of a 25-foot wire run from PV modules to combiner box and
a 75-foot wire run from combiner box to inverter—use a maximum of 1% for the 25-foot run and 2%
loss for the 75-foot section for a total of 3%)
a. wire run from modules to combiner is 25 feet. From the 48-Volt Table A-3 in the appendix,
1% voltage drop for 25 feet and 6 amps (to use table for 1% voltage drop, find D-Factor for
3% voltage drop for 6-amps at 25 feet (1.1), then multiply this value by 3 (3.3) to obtain
proper size of wire on Table A-1in the appendix), use #10 AWG wire.
b. wire run from combiner to inverter is 75 feet. From the 48-Volt Table A-3 in the appendix,
2% voltage drop for 75 feet and 30 amps (to use table for 2% voltage drop, find D-Factor for
3% voltage drop for 30 amps at 120 feet (16) then multiply this value by 1.5 (24) to obtain
proper size of wire on Table A-1in the appendix), use #2 AWG wire.
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June 2001 Page 17

7. Estimate length of wire run from inverter to main service panel (Example drawing EX-1 in the
appendix: wire run from inverter to panel is 25 feet).
Example using sample drawing EX-1 in the appendix:
Goal is 1% voltage drop for ac-side of system (3% absolute maximum)
From 120-Volt table A-4, 1% voltage drop for 30 feet and 35 amps (to use table for 1% voltage
drop, find D-Factor for 3% voltage drop for 30-amps at 30 feet (2.5), then multiply this value by 3
(7.5) to obtain proper size of wire on Table A-1), use #6 AWG wire.
8. Examine main service panel to determine if the panel is adequately sized to receive the PV breaker
or whether the panel must be upgraded.
Many homes in California are fed by a 100-amp service panel. For residential applications, the NEC
690-64 allows the total supply (utility plus PV) to the busbar of the service panel to equal 120% of
the busbar rating (100-amps x 1.2 = 120-amps). This means that a 100-amp service panel can have
a 100-amp main breaker and a 20-amp PV breaker. If our example system can supply 45-amps of
continuous power, we need room for a 60-amp circuit breaker (45-amps x 1.25 = 56.25 amps). A
system that size will require either replacing the 100-amp main breaker with a 75-amp unit (not
usually recommended) or replacing the existing 100-amp service panel with a 200-amp service
panel. The 200-amp service panel is allowed 240-amps of supply (200-amps x 1.2= 240-amps) so if
the PV breaker is rated at 60-amps, the main breaker can be up to 180 amps (240 amps – 60 amps
= 180 amps)
9. If system includes a critical load subpanel (battery standby system), determine which circuits are
critical. These circuits must be adequately designed to handle the anticipated electrical loads. The
standby portion of the system is considered by the NEC to be an Optional Standby System covered
by Article 702.
a. Warning: Multi-wire branch circuits in a home must be closely evaluated to allow them to be
wired to a 120VAC optional standby system. There are four main ways to deal with these
types of circuits:
i. Install an autotransformer on the output of the inverter to step up the supplied
voltage from 120Vac to 240Vac if necessary. The critical load subpanel can then be
powered without concern of neutral overload.
ii. Rerun one new branch circuit with each multiwire circuit so that one of the supply
conductors of the multiwire circuit can be eliminated and the two circuits no longer
share the neutral.
iii. Avoid multiwire branch circuits in the home. This is often unacceptable since
refrigerators and other key loads are normally found on multiwire branch circuits.
iv. Derate the supply breaker to match the ampacity of the neutral wire. This is done by
first determining that the maximum load on the two circuits is less than 80% of the
rating of one pole of the double-pole supply breaker. For instance, if the supply
breaker is a 20-amp double-pole breaker, the maximum allowable load on both
circuits is a total of 16-amps at 120-Vac. To confirm this load, turn on all the loads
intended to be operated at the same time and measure the load current with a
clamp-on ammeter. If the total from the two circuits is less than 16-amps, the circuit
may be supplied by a single-pole 20-amp circuit breaker, which protects the neutral
from overload.
b. All loads to be connected to the optional standby system must be carefully evaluated to
determine if the actual power consumption and daily usage for each load can be met by the
system in standby mode.
c. All standby loads must be wired into a separate sub-panel for connection to the standby
output of the inverter.
d. Average power consumption for the standby power system loads must be calculated to
determine how long the storage battery will provide uninterrupted power for typical electric
usage.
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June 2001 Page 18
e. Article 702--Optional Standby Systems allows sizing based on supply of all equipment
intended to be operated at one time (NEC 702-5). This means that all the 120-Volt loads
could be run off of a single-pole 60-amp breaker from an optional standby system as long as
the actual continuous load is below the 80% limit for continuous operation of a breaker (48
amps).
f. It is recommended that the storage battery system consist of maintenance-free valveregulated
lead-acid (VRLA) batteries with absorbed glass mat (AGM) construction since
these require no maintenance by the homeowner. Other types of batteries may become
available in the future that are equally suited to this application, but do not attempt to use
any battery that has not been thoroughly tested in Uninterruptible Power System (UPS)
applications.
g. Battery storage cabinet must be kept out of the sun and in as cool a place as practical.
h. Every battery storage system, whether it includes flooded lead-acid, or valve-regulated leadacid
batteries, requires ventilation. Battery storage cabinet must be ventilated to the
outdoors; vents need to be at the high and low points in the cabinet. For battery systems in
utility rooms in a living space, follow the same ventilation requirements as needed for gasfired
service water heaters.
10. Determine location of critical load subpanel, install subpanel and prepare to move circuits
11. Install PV array. Packaged systems should include detailed instructions on each phase of the
installation process. Some basic guidelines that may help in reviewing installation procedures are:
a. Prepare structure for mounting of PV array. If roof-mounted, hire roofing contractor to install
roof mounts according to manufacturer’s directions.
b. Check modules visually and check the open circuit voltage and short circuit current of each
module before hauling onto the structure to verify proper operation—see checklist.
c. Use plug connectors to connect panels together where listed products are available. This
reduces installation time.
d. Use only as many attachment points and roof penetrations as necessary for structural
loading concerns. The number of attachment points and structural requirements of the roof
must be specifically identified in the drawings.
e. Mount PV array to support structure.
12. Install PV combiner, inverter, and associated equipment to prepare for system wiring.
13. Connect properly sized wire (determined in step 6 of installation phase) to each circuit of modules
and run wire for each circuit to the circuit combiner(s). (WARNING: It is advisable to terminate the
circuits in the circuit combiner prior to completing the final connection for each string at the PV array
end of the circuit.)
14. Run properly sized wire (determined in step 6 of installation phase) from circuit combiner to inverter
overcurrent/disconnect switch (if available--follow installation procedure supplied by manufacturer).
15. Run properly sized wire (determined in step 7 of installation phase) from inverter to utility disconnect
switch (WARNING: Make sure the neutral wire does not get routed through one of the switch poles
in the disconnect box.)
16. Run properly sized wire (determined in step 7 of installation phase) from utility disconnect switch to
main service panel and connect circuit to the main utility service.
17. Use the checklist in section 4 to ensure proper installation throughout the system.
18. Verify that all PV circuits are operating properly and the system is performing as expected. The PV
System Installation Checklist in section 4 of this guide has a detailed performance testing procedure
entitled System Acceptance Test.
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June 2001 Page 19
19. Shut system down and call for final inspections (AHJ first then utility--if necessary).
20. Once approval to parallel is received from the utility, begin system operation.
21. Mail completed Buydown Request Form, with all necessary attachments, to the California Energy
Commission to receive Buydown payment.
22. Enjoy watching your meter spin backward. (note: Time-Of-Use net meters do not have a meter disk
to watch run backward—it has a digital readout instead).
3.2.4. Maintenance and Operation Phase
1. Wash PV array, during the cool of the day, when there is a noticeable buildup of soiling deposits.
2. Periodically inspect the system to make sure all wiring and supports stay intact.
3. On a sunny day near noon on March 21 and September 21 of each year, review the output of the
system (assuming the array is clean) to see if the performance of the system is close to the previous
year's reading. Maintain a log of these readings so you can identify if the system is performance is
staying consistent, or declining too rapidly, signifying a system problem.
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June 2001 Page 20
SECTION 4: SOLAR ELECTRIC (PV) SYSTEM INSTALLATION CHECKLIST
Following the completion of each item on the checklist below, check the box to the left of the item
and insert the date and initials of the person completing the item whether that is the installing
contractor or owner-installer. Remember to follow the proper safety procedures while performing the
system installation. The appropriate safety equipment for each section of the checklist is listed above
each section of the checklist.
Before starting any PV system testing: (hard hat and eye protection recommended)