How to Read a Solar Site Survey for Effective PV Array Layout

A successful and efficient photovoltaic (PV) installation begins long before the first panel is mounted. For any journeyman electrician or master electrician entering the solar industry, mastering the solar site survey is the critical first step. A thorough solar site survey is a detailed on-site assessment that gathers all necessary structural, electrical, and environmental data to design a safe, compliant, and high-performing solar array. This process involves more than just measuring a roof; it requires a deep dive into the building’s electrical system, a precise shading analysis, and a clear understanding of the customer’s energy goals to ensure the final design is both effective and code-compliant. Ultimately, interpreting the data from a site survey correctly is what separates a problematic installation from a profitable, long-lasting energy asset.

What is a Solar Site Survey?

A solar site survey is a comprehensive engineering evaluation of a property to determine its suitability for a solar PV system. It’s the foundational data-gathering phase that informs every subsequent step, from system design and equipment selection to permitting and installation. The goal is to collect precise information about the physical site, the existing electrical infrastructure, and any environmental factors that could impact system performance. This process ensures the proposed system is optimized for energy production, structurally sound, and compliant with all relevant codes and regulations. For professionals seeking advanced electrician training in this field, understanding the nuances of a site survey is non-negotiable.

The Core Components of a Comprehensive Solar Site Survey

A detailed site survey can be broken down into three critical areas of evaluation: structural, electrical, and environmental. Each provides a piece of the puzzle needed to design an optimal PV system.

Structural Assessment: Roof and Mounting Planes

The first physical inspection involves the roof or ground area where the array will be located. Key data points include:

• Roof Condition and Age: An inspector will check the roofing material (asphalt shingle, metal, tile), its age, and its overall condition, looking for signs of wear or damage. Installing a 25-year solar array on a 15-year-old roof that needs replacement is a costly mistake.
• Structural Load Considerations: The roof must be able to support the added weight of the solar panels, racking, and potentially snow. This involves inspecting the framing, trusses, and sheathing from the attic or crawlspace to determine rafter size and spacing. A structural engineer may be required to sign off on the plans.
• Roof Dimensions and Obstructions: Precise measurements of all roof planes are taken, along with the location of vents, skylights, chimneys, and other obstructions that the array must be built around.
• Fire and Access Requirements: The survey must account for local fire and building code setbacks and firefighter access requirements. These requirements vary by jurisdiction (often coming from the International Fire Code or local amendments) and commonly require designated access pathways across the roof and setback areas. Check the local authority having jurisdiction (AHJ) for exact dimensions and access-path requirements — they are not uniform nationwide.
• Rapid-Shutdown Array Boundary: In addition to fire access concerns, NEC rapid-shutdown rules define an “array boundary” used to determine reduced-voltage requirements in an emergency (the NEC defines this array boundary at roughly 305 mm / 1 ft from the array edge). Treat rapid-shutdown planning and firefighter access planning as complementary but distinct requirements.

Electrical System Evaluation

For a licensed master electrician or journeyman electrician, this is the most familiar territory. This part of the survey ensures the existing electrical system can safely integrate the new power source.

• Main Service Panel Capacity: The survey must determine the busbar rating and main breaker size of the existing electrical panel (common residential ratings include 100 A, 125 A, 150 A, 200 A, and larger). If the panel cannot safely accommodate the proposed inverter backfeed or the required overcurrent devices, an upgrade or alternative connection path may be necessary before solar can be installed.
• Interconnection Methods: The electrician will identify the most viable method for connecting the solar system to the grid. This can be a load-side connection (a new breaker in the main service panel) or a supply-side connection that taps the conductors between meter and main. Understanding service entrance and interconnection implications in the NEC and local utility requirements is critical when selecting the method.
• Grounding and Bonding: The existing grounding electrode system is inspected to ensure it is compliant. PV systems require proper grounding and bonding per the NEC; the survey identifies whether additional grounding electrodes or connections are needed.
• Inverter Location: A suitable location for the inverter (or inverters) must be identified. This spot should be out of direct sunlight, well-ventilated, and reasonably close to both the array and the main panel to minimize voltage drop.

Shading Analysis and Optimal Array Placement

Even small amounts of shade can drastically reduce a solar panel’s output, making shading analysis one of the most critical parts of the survey. A shadow on just one part of a panel can impact the production of the entire string of panels.

• Azimuth and Tilt Angle: The survey identifies the roof planes with the best orientation (azimuth) and pitch (tilt). In the Northern Hemisphere, a true south orientation (180 degrees) generally produces the highest annual output. The optimal tilt angle is often close to the property’s latitude, though project goals (year-round vs. seasonal optimization) can change the recommendation.
• Identifying Shading Obstacles: The surveyor will identify all potential sources of shade—trees, neighboring buildings, chimneys, and even utility poles—and map their impact throughout the day and year.
• Solar Irradiance Data: Using tools like a Solar Pathfinder, fisheye imaging, or specialized software, the surveyor measures the available “solar window” for each roof plane, quantifying the solar irradiance (sunlight intensity) available. This data directly translates into energy production estimates.

PV System Design and NEC Compliance

Once the site data is collected, it’s used to design a system that complies with the National Electrical Code (NFPA 70), particularly NEC Article 690, which governs photovoltaic (PV) system installations and includes requirements for circuit sizing, grounding and bonding, rapid shutdown, and other PV-specific provisions.

Step-by-Step: PV Source Circuit Sizing

Properly sizing the conductors for a PV source circuit is a fundamental skill. It involves a multi-step calculation based on the module’s short-circuit current (Isc) rating to ensure conductor ampacity is sufficient for worst-case scenarios, like high irradiance and cold temperatures.

1. Determine Maximum Circuit Current: NEC guidance starts with the module short-circuit current (Isc). For PV string circuits the code requires accounting for module conditions, and NEC describes using a 125% factor on the sum of parallel Isc values when establishing the circuit maximum current.
2. Apply NEC Ampacity Factors: NEC then requires sizing the conductors so that their ampacity is not less than the calculated maximum circuit current times another 125% (unless the equipment assembly is listed for operation at 100% of rating). Because of those two steps in the NEC sizing approach, the combined effect is commonly about 1.56 times the summed Isc unless an exception for listed 100% operation applies. Always confirm whether listed equipment or exceptions apply to avoid unnecessary upsizing.
3. Select Conductor Size: Using the calculated required ampacity, select the appropriate wire gauge from the ampacity tables in NEC Article 310 (use the Article 310 ampacity tables that match conductor insulation and installation conditions) and apply the required temperature- and bundling/conduit-fill correction factors per Article 310.
4. Design Overcurrent Protection: Size the overcurrent protection (fuses or breakers) so conductors are adequately protected for the calculated currents, NEC requirements, and any applicable local or utility rules.

Installers often use a voltage-drop calculator to ensure the selected wire size doesn’t lead to excessive power loss over the length of the run; Article 310 guidance and wiring practices should be used when calculating voltage drop and choosing conductor routing.

Advanced Considerations for the Modern Electrician

The solar industry evolves rapidly, and today’s site surveys must account for modern technologies and updated safety requirements.

• Module-Level Power Electronics (MLPE): Systems using MLPE, such as microinverters or DC optimizers, can mitigate the impact of shading because each module operates independently. The site survey helps determine if MLPE is a cost-effective solution for a partially shaded roof and whether it affects wiring and rapid-shutdown strategies.
• Rapid Shutdown Requirements: NEC requires rapid-shutdown capability for rooftop PV conductors on buildings to reduce hazards for first responders. The survey must identify component locations and control circuits to ensure the installed system meets rapid-shutdown rules and the AHJ’s expectations.
• Series vs Parallel Circuit Design: The number of panels and their arrangement in series vs parallel will determine the system’s voltage and current. The survey data on available roof space and shading will dictate the optimal string design and whether higher-voltage string architectures are suitable and code-compliant.

Staying current with these evolving standards is crucial. For any master electrician or journeyman electrician looking to specialize, formal electrician training is key, and certifications help demonstrate competency in PV installations.

From Survey to Success: Tools and Best Practices

While traditional tools like a compass, inclinometer, and tape measure are still used, modern installers leverage technology for greater accuracy and efficiency. Drones can quickly capture high-resolution imagery for roof measurements and 3D modeling, while software platforms can perform highly accurate shading analysis and production modeling.

Key Takeaways for an Effective Survey:

• Accuracy is Paramount: Double-check all measurements, from roof dimensions to electrical readings. A small error in the survey can lead to major design flaws and costly change orders.
• Document Everything: Take clear photos of the roof, attic, electrical panel (inside and out), and any potential obstructions. Detailed notes and labeled pictures are invaluable during the design phase.
• Know the Code: A deep understanding of the NEC (especially Article 690 and Article 250 for grounding and bonding) and applicable Article 310 ampacity requirements is non-negotiable. Also coordinate with the AHJ and the utility for interconnection policies.
• Safety First: Adhere to all safety protocols when accessing roofs and working near live electrical equipment. A professional should always handle the installation of components like a service mast riser or any supply-side interconnection work.
• Communicate with the Client: Use the survey to understand the client’s energy goals and set realistic expectations about system size and performance.

Primary Sources

• National Fire Protection Association (NFPA) — NFPA 70, the National Electrical Code (NEC)
• International Code Council (ICC) — the International Fire Code (IFC) for local fire-access requirements; consult the AHJ for local amendments

Frequently Asked Questions

What is the most critical part of a solar site survey?

While all components are important, two of the most critical parts are the electrical system evaluation and the shading analysis. An inadequate main service panel capacity can halt a project or add significant unexpected costs, while an inaccurate shading analysis can lead to a system that dramatically underperforms, causing customer dissatisfaction.

How does NEC Article 690 impact the solar site survey process?

NEC Article 690 governs many aspects of the PV system’s electrical design. The site surveyor must collect the necessary information to ensure the final design complies with rules for conductor ampacity, PV source circuit sizing, overcurrent protection design, grounding and bonding, and rapid-shutdown requirements, among other provisions.

Why is checking the main service panel capacity so important?

The main service panel capacity helps determine allowable interconnection options and the size of a solar breaker that can be safely introduced to the panel. Many interconnection approaches restrict the sum of certain overcurrent device ratings or otherwise limit the backfeed current to preserve safe operation of the existing equipment and clearances. If the existing panel cannot safely accommodate the required interconnection, a panel upgrade or alternate connection method is often necessary.