In utility-scale solar projects, thorough planning is critical to ensure the most reliable, efficient, and safe operations. Beyond standard design documents, several pre-construction studies play a crucial role in optimizing solar project efficiency and preventing costly setbacks. In this article, we explore three essential studies—System Advisor Model (SAM) simulations, ampacity studies, and coordination studies—that should be conducted before breaking ground to streamline project execution and minimize future risks.
1. System Advisor Model (SAM) Simulations for Optimized Sizing
One key preconstruction study is the System Advisor Model (SAM) analysis, developed by the National Renewable Energy Laboratory (NREL). This free software allows for preliminary simulations of photovoltaic (PV) systems, calculating maximum short-circuit current and open-circuit voltage. Conducting SAM simulations before construction enables precise system sizing by helping to determine the most efficient number of PV modules per string. Additionally, it allows engineers to optimize cable and equipment sizing, avoiding issues like undersized or oversized components that can affect project efficiency and costs.
Unlike standard design codes, such as the National Electric Code (NEC), which can be conservative or overestimate requirements, SAM provides real-time, site-specific data. For example, in one of Castillo Engineering’s projects in Illinois, SAM analysis revealed that the sizing factor could be adjusted from NEC’s 1.25 to 1.36, significantly impacting DC wire sizing. This minor adjustment prevented the team from undersizing the cables, which could have led to overheating or operational inefficiencies. By using SAM to refine these values, companies can avoid such issues and reduce project costs through optimized equipment selection and reduced voltage drops.
2. Ampacity Studies for Accurate Conductor Sizing
Ampacity studies are another critical component in utility-scale solar development, providing insight into proper conductor sizing under site-specific conditions. These studies assess the carrying capacity of underground conductors, considering soil temperature, thermal resistance, and other environmental factors that can impact current capacity. Standard NEC sizing is often conservative but still may not account for unique site conditions, such as dry or hot soil, which can reduce conductor efficiency.
For instance, on a recent project that Castillo worked on, the customer rejected pursuing an ampacity study, but an Independent Engineer later insisted on the ampacity study for this project. Once complete, the ampacity study then revealed that NEC sizing would have been insufficient due to dry soil conditions, which heightened the risk of overheating. The customer had initially procured wires based on standard NEC calculations, only to discover the need to upsize after conducting the ampacity study. This situation highlights the financial risks associated with reordering and reinstalling wires, which can amount to tens of thousands of dollars—an outcome that could have been avoided with a preliminary ampacity analysis.
3. Coordination Studies for Reliable System Protection
Coordination studies ensure that the protective devices within a solar PV system operate in the correct sequence, safeguarding the system against faults and minimizing disruptions. Each protective device—from auxiliary circuit breakers to main breakers—requires precise calibration to maintain the integrity of the system. Without proper coordination, a minor fault in an auxiliary circuit could trigger the main breaker, leading to a complete system shutdown and interrupting power generation unnecessarily.
Through coordination studies, engineers evaluate the interplay between various protective devices to avoid these issues. For example, in a project with 16 inverters, each protected by individual breakers, required a main breaker that would only trip if a fault affected the entire system, not just one inverter. By conducting a coordination study, engineers ensured that only the faulty circuit would shut down, preserving the functionality of the remaining inverters. These studies are essential for meeting utility requirements, which often mandate protective coordination for operational safety and reliability. Without it, equipment damage and increased project downtime could occur, resulting in lost revenue and expensive repairs.
While the initial design phase of a utility-scale solar project includes basic engineering and planning, the value of in-depth preconstruction studies—such as SAM simulations, ampacity analyses, and coordination studies—cannot be overstated. These studies allow for customized equipment sizing, maximum solar production, accurate conductor selection, and reliable system protection, ultimately reducing costs and enhancing long-term project efficiency. If you have any questions about these preliminary assessments, get in touch with a technical expert at Castillo.