After completing the solar window analysis, you still need to plan for routing conduit, grounding conductors, and placing the balance-of-system components (inverters, disconnects, and combiner boxes). A thorough inspection of the existing electrical panel includes documenting the enclosure make and model, as well as verifying additional breaker space, and checking the main breaker size and bus bar ratings. The service equipment ratings will be used in system design calculations to determine allowable PV backfeed capacity and the associated breakers needed for interconnection. Ensuring adequate breaker space avoids expensive surprises later, like needing to upgrade the service panel.
Planning for Code-compliant conduit routing requires considering equipment placement, the mechanical integrity of equipment mounting and conductor runs, aesthetics, local regulations, and climate. Part IV: Wiring Methods, Article 690.31 of the 2011 National Electrical Code (NEC) dictates the type, placement, routing, and marking of conduit. Because of the higher temperatures commonly encountered on roofs, the details of conduit routing can affect system design due to required derating of conductor ampacity.
Identifying grounding components of the existing AC electrical system is another important step of the site survey. The location of the existing grounding electrode conductor (GEC) and grounding electrode (often a ground rod) will inform decisions for routing the PV system grounding conductor(s) to interconnect the two systems. In some cases, the inverter will have a GEC that must be connected to the building’s existing grounding electrode or GEC. Depending on the system, the PV array may also have a GEC that must be connected to the grounding system. Planning these routes will help ensure Code-compliant installation.
Inverter and disconnect placement involves satisfying Code regulations that apply to the working space around the equipment, weather considerations, and aesthetics. Disconnect locations must be accessible and installed within height limitations. In cold climates, some inverter models need to be installed indoors to keep them within their operating temperature range. Inverters placed outdoors should avoid south or west orientations as the intense sun may cause the inverter to derate its power output to protect internal components from excessive heat damage. Direct solar exposure can also burn out the LCD screen, which includes state of operation information, energy production values, and potential error messages.
Analyzing the building’s loads—and researching measures for improving the overall efficiency—is another important part of the site evaluation. Shrinking a building’s loads can often result in a smaller PV system, resulting in PV system savings that are greater than the efficiency investments. Lighting and refrigeration are two of the easier places to start with efficiency upgrades—incandescent bulbs and old refrigerators are prime candidates for replacement. Insulation and other weatherization measures can also make a significant impact on electricity usage in homes with electricity-based space heating.
Jeff Tobe is a PV curriculum developer and instructor at Solar Energy International (SEI). He has been instrumental in the development of SEI’s state-of-the-art PV lab training facility in Paonia, Colorado, and spearheads renewable projects for indigenous communities in the United States. He is an ISPQ-certified PV Instructor, has a NABCEP certification in Technical Sales, and is a NABCEP-certified PV Installation Professional.
Magnetic declination finder • bit.ly/CalcDeclination
PV-ready home checklist • bit.ly/PVHomeChecklist
PV system production estimator (PVWatts) • bit.ly/PVWattsV1
Solmetric roof azimuth tool • bit.ly/SolmTools
Solar Site Evaluation Training & Certification:
Solmetric • bit.ly/SolmTraining
MREA • midwestrenew.org