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Pro Tips for Repowering Legacy Solar + Storage Systems

Repowering legacy solar and storage systems can present a range of complexities, but with the right strategy and an experienced engineering partner, these challenges can be effectively addressed. By carefully evaluating the existing infrastructure, incorporating modern technology, and optimizing system performance, the repowering process becomes more streamlined and efficient, extending the system’s lifespan while enhancing energy production and reliability. Partnering with a knowledgeable team like Pure Power Engineering ensures that every step, from initial assessment to final commissioning, is managed with precision and expertise.

 

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Never trust the as-builts, verify the existing conditions, industry standards, best practices and contract requirements have come a long way in the past decade. This fact is particularly noticeable when we compare the As-Built drawings for legacy systems to the field conditions. In the Wild West days of solar, some feel that systems were deployed without accurate as-built drawings. In addition, all the system repairs and modifications that have taken place over the previous decade or so are often not captured in the records.

As a result, the first step in repowering any project is to survey and document the existing conditions thoroughly. In addition to accounting for major equipment, it is crucial to document conductor, gauge and type, as well as conduits, sizes, quantities and routes. Coordinate closely with the AHJ and pull permits as required. Unlike routine O&M activities, full scale system repowering activities are generally subject to state review and approval as part of the engineering process.

Pure power will flag any existing conditions that may align with current code requirements. One typical example is that legacy systems often use color coding conventions that are different from those in the most recent editions of the National Electric Code. Some AHJs may approve the reuse of these circuits, provided that conductors are re-identified using electrical tape. Others may require you to remove and replace the existing conductors and roof-mounted systems.

Repowering activities may proactively trigger rapid shutdown requirements. If so, these considerations will drive the design process. Have these types of conversations with AHJs early and often to ensure that repowering projects are scoped and engineer properly from the beginning.

 

 

Structural modifications require engineering supervision. The benefit of removing and replacing existing modules is that project stakeholders can increase system capacity in the process, whereas legacy systems might be built with 200-watt modules that are 15% efficient. Modern systems might integrate 400-plus watt modules that are 20% plus efficient. In this scenario, repowering activities include deciding how best to repurpose an existing ground mount or carport structure.

Given the new module dimensions, this process invariably involves new sheet studies and strategic structural modifications, perhaps changing Perlin orientation or extending structural numbers. This may also require trenching adjacent to existing foundations. These structural changes or foundation disturbances must be reviewed and supervised by a professional engineer. Additionally, the original equipment manufacturer may need to sign off on certain types of structural mods, such as plans to install a new string converter on the ground.

Mount piles in place of legacy Combiner boxes. Listed equipment modifications require field evaluation and certification. Certain types of product modifications also trigger field value and certification requirements. For example, today's C&I string inverters are designed for use with 1000-volt nominal PV source circuits, whereas legacy systems integrate 600-volt rated modules. Consult with equipment vendors early during the design phase to ensure that modern inverters will work with legacy system components to improve maximum PowerPoint track and efficiencies.

An OEM may be able to make a one off adjustment to the DC operating parameters for listed inverter in some cases by reducing the native AC output voltage. While these types of parameter changes solve operational problems, a field evaluation service will then need to certify that the modified equipment meets relevant product safety standards. Similarly, field modification is to legacy.

Mounting systems may trigger field evaluation and certification to ensure that the installation meets current product safety standards. Engineering Experience and Expertise Mitigate Project Risk. Legacy systems are a reminder that solar technologies have come a long way in a relatively short amount of time. A repowering approach that works for PV system fielded with SATCOM inverters will not work for bipolar PV array integrated with advanced energy inverters.

Ultimately, the best way to avoid the pitfalls associated with repowering projects is to choose a qualified and competent engineering partner who will ask the right questions on the front end to deliver a repowering solution that meets projects specific goals. As a full service engineering company specializing in solar and ESS projects, Pure Power is uniquely qualified to work with stakeholders to give legacy systems a second lease on life.

With more than a decade of industry specific expertise as an organization and nearly 400 years of combined experience as a team, there is nothing in C&I and utility scale solar as well as solar plus storage applications that we have not seen.