Successful PV Site Evaluation: Page 3 of 3

Intermediate

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Successful PV Site Evaluation
Successful PV Site Evaluation
Solmetric’s Roof Azimuth Tool Screenshot
Solmetric’s Roof Azimuth Tool can determine orientation from aerial photos. Google Earth has a similar tool that can determine approximate roof area.
An inclinometer
An inclinometer is an inexpensive tool for quickly determining the a surface’s slope. The needle is pointing to the angle in degrees.
Smartphone app
An inexpensive smartphone app can measure the roof angles in degrees, percentage, rise-to-run ratio, and even radians.
Solmetric's free online tool
Solmetric offers a free online tool for determining annual insolation based on various combinations of azimuth and tilt. This example roof is within 5% of the ideal tilt and orientation.
Solmetric’s SunEye 210
The SunEye 210 is Solmetric’s latest solar siting tool, which displays an annual sunpath view, showing annual and seasonal solar access values.
Solmetric Screenshot
The SunEye 210's accompanying software includes additional displays, such as the obstruction elevation.
The Solar Pathfinder
The Solar Pathfinder uses a highly reflective dome to reveal obstructions, which can be outlined on a paper sun-path chart. It has a built-in level and compass, and the base can be adjusted for the site’s magnetic declination.
Solar Pathfinder Screenshot
Digital photos taken of the Pathfinder reading can be used with the Assistant PV software to generate detailed summary reports.
Capture readings from all four corners of the intended array area.
To properly evaluate a proposed PV array location, capture readings from all four corners of the intended array area.
A solar siting tool can be used to determine a “shade-free” distance from roof obstacles
A solar siting tool can be used to determine a “shade-free” distance from roof obstacles, such as this plumbing vent. This should be recorded on the site evaluation form.
Check the roof’s condition
Check the roof’s condition—repairs or reroofing should happen before installing a PV system.
Assess the roof’s structural condition
Inspecting the attic is another way to assess the roof’s structural condition, check for leaks, and map rafters for future array mounting.
Plan for wire and conduit runs in advance
Plan for wire and conduit runs in advance. The path between array and balance-of-system components needs to meet the Code as well as logistical requirements. This junction box makes a transition between PVC conduit coming from the pole-mounted array to EMT conduit running through the building interior to the inverter.
Check for obstacles
Check for obstacles—a propane tank in the yard indicates underground pipe runs that should be avoided when trenching for wire runs.
AC service entrance
Generally, a new grid-tied system will connect to the existing electrical infrastructure at the AC service entrance. Besides checking equipment condition, look for service amperage rating, main breaker rating, busbar ratings, and adequate breaker space. Incompatibility with any of these things may dictate upgrading the panel.
Balance-of-system components
Balance-of-system components take up space, and have Code and practical access requirements. Map their placement in advance.
Successful PV Site Evaluation
Solmetric’s Roof Azimuth Tool Screenshot
An inclinometer
Smartphone app
Solmetric's free online tool
Solmetric’s SunEye 210
Solmetric Screenshot
The Solar Pathfinder
Solar Pathfinder Screenshot
Capture readings from all four corners of the intended array area.
A solar siting tool can be used to determine a “shade-free” distance from roof obstacles
Check the roof’s condition
Assess the roof’s structural condition
Plan for wire and conduit runs in advance
Check for obstacles
AC service entrance
Balance-of-system components

The Rest of the System

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.

Additional Considerations

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.

Access

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

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