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 Code Setbacks: The survey must account for local fire code setbacks. These requirements, often derived from the International Fire Code (IFC) and subject to the local authority having jurisdiction, typically mandate clear pathways for firefighter access in an emergency, which may include a 3-foot pathway from the eave to the ridge and specific setbacks from hips and valleys.

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, typically 100A, 125A, 150A, or 200A for residential properties. If the panel is undersized, an upgrade 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, where a new breaker is added to the main service panel, or a supply-side connection, which involves tapping the conductors between the meter and the main breaker. Understanding service entrance conductors per NEC rules is crucial here.
• Grounding and Bonding: The existing grounding electrode system is inspected to ensure it is up to code. A new grounding rod may be required for the solar array to meet NEC requirements for proper grounding and bonding.
• 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) is ideal. The optimal tilt angle is often close to the property’s latitude.
• 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 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, particularly the nec code book’s comprehensive NEC Article 690, which governs solar installations.

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: Per NEC 690.8, the maximum current is the sum of the parallel module short-circuit currents multiplied by 125%. This accounts for periods of enhanced irradiance.
2. Apply Continuous Load Factor: Because solar circuits are considered continuous loads, another 125% factor is applied for conductor sizing. The combined effect is a multiplier of 1.56 (1.25 x 1.25) on the Isc.
3. Select Conductor Size: Using the calculated required ampacity, select the appropriate wire gauge from NEC Table 310.15(B)(16), ensuring you account for temperature and conduit fill correction factors.
4. Design Overcurrent Protection: Size the overcurrent protection design (fuses or breakers) based on the calculated maximum current to protect the conductors.

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.

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. The site survey helps determine if MLPE is a cost-effective solution for a partially shaded roof.
• Rapid Shutdown Requirements: NEC 690.12 mandates rapid shutdown systems to de-energize rooftop conductors for firefighter safety. The survey must identify component locations and pathways for control circuits to ensure compliance.
• Series vs Parallel Circuit Design: The number of panels and their arrangement in a series vs parallel circuit will determine the system’s voltage and current. The survey data on available roof space and shading will dictate the optimal string design.

Staying current with these evolving standards is crucial. For any master electrician or journeyman electrician looking to specialize, formal electrician training is key, with many seeking to expand their career opportunities in solar. Master the first step of any solar project. Explore our NABCEP Associate courses.

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 code book, especially NEC Article 690 and local amendments, is non-negotiable.
• 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.
• 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) for the National Electrical Code (NEC)
• International Code Council (ICC) for the International Fire Code (IFC)

Frequently Asked Questions

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

While all components are important, the two 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 nearly every aspect of the PV system’s electrical design. The site surveyor must collect the necessary information to ensure the final design complies with its rules for conductor ampacity, PV source circuit sizing, overcurrent protection design, grounding and bonding, and rapid shutdown requirements.

Why is checking the main service panel capacity so important?

The main service panel capacity dictates the maximum size of the solar breaker that can be back-fed into it, which in turn limits the size of the PV system. Per NEC Article 705.12, the sum of the main breaker and the solar back-feed breaker cannot exceed 120% of the panel’s busbar rating. If the existing panel cannot accommodate the required solar breaker, a costly and time-consuming panel upgrade becomes necessary.