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)