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)