Solar Repowering: What Owners Should Know Before Design Begins

By: Rob Greening, PE, National Structural Engineering Leader, and Evan Langran, PE, Electrical Engineering Manager 

As utility-scale solar assets age, owners and operators face an increasingly important question: Should they replace an existing facility, or can strategic upgrades extend its useful life and improve performance? 

Advances in solar technology, changing project economics, aging infrastructure, and severe-weather damage are prompting more owners and operators to evaluate repowering. But a repower is not a greenfield project with newer components substituted into an existing layout. Every facility carries the engineering decisions, construction practices, site conditions, and operating history of the period in which it was built. 

That history matters. Before owners can determine what to replace, they must understand what can be reused, what has changed, and how new technology will interact with legacy systems. The quality of those early decisions often determines whether a repower proceeds predictably or encounters costly surprises during design and construction. 

Why Are Owners Repowering Solar Assets? 

No two repowering projects begin for exactly the same reason, but several common drivers are shaping today's market. 

Some projects have experienced severe damage from hail, high winds, tornadoes, or other extreme weather events. Others have reached the point at which aging or underperforming equipment no longer delivers the expected performance or reliability. 

In many cases, owners and operators also want to take advantage of higher-efficiency modules, updated inverter technology, or other innovations that can increase energy production and improve long-term project economics. 

Rather than abandoning an existing asset, repowering gives owners and operators an opportunity to extend its useful life, improve performance, and capture its remaining operational value. 

A Repower Is Not a Greenfield Project 

One of the biggest misconceptions about utility-scale solar repowering is that it is simply another design project. 

Greenfield development starts with a blank slate. Site conditions are investigated before design begins, infrastructure is planned together, and the facility's systems are designed to function as an integrated whole. 

Repowering is fundamentally different. Instead of designing for future conditions, engineers must work with existing ones. That means every project begins with questions that generally do not exist on a greenfield site: 

• What infrastructure is already in place? 
• Does the existing facility match the available drawings? 
• How has the site changed over time? 
• Can existing foundations support new equipment? 
• How will updated technology interact with electrical systems designed years ago? 

Those questions must be answered before meaningful design work can begin. 

Reconstruct and Verify the Existing Asset 

Many existing facilities have changed owners or operators over time. Original construction documents may be incomplete, outdated, or lost, particularly when information from older projects was never digitized or consistently maintained. 

Field modifications may never have been documented. Redlines may exist only in paper archives, and existing conditions can differ significantly from the available drawings. Reconstructing that history requires careful investigation and an experienced understanding of past engineering and construction practices. 

We often describe this phase as engineering detective work. It involves reviewing historical documentation, validating field conditions, comparing existing infrastructure with original plans, and developing a clear understanding of how the site was actually constructed, not merely how it was intended to be built. 

In our experience, some of the greatest risks come from assumptions that appear reasonable on paper but have not been verified in the field. 

Verification is especially important when an owner plans to reuse foundations, steel piles, aboveground or underground collection systems, and other critical infrastructure. Assets that have supported the facility for years may still offer significant value, but their past performance alone does not confirm that they are suitable for the facility's next operating horizon. 

Structural evaluations may identify corrosion or deterioration that is not visible during routine inspections. Field investigations may reveal undocumented construction changes. Infrastructure that performed well under the original design may require additional analysis before it can support new equipment. 

The appropriate level of verification depends on the proposed upgrades, the quality of available records, the condition and age of the infrastructure, and the consequences if an assumption proves incorrect. Depending on those factors, verification may include document review, field measurements, visual assessments, material testing, subsurface investigation, or structural and electrical analysis. 

This work helps owners make informed decisions about where infrastructure can continue delivering value and where reinforcement, replacement, or redesign may provide the greatest long-term benefit. It also reduces the risk of discovering critical discrepancies after design or construction is underway. 

Current Technology Can Affect the Entire Facility 

Repowering projects are often driven by the opportunity to install newer, more efficient technology. Replacing equipment, however, is rarely a one-for-one exercise. 

Today's solar modules produce different outputs from those installed 10 or 15 years ago. Inverter technology continues to evolve, electrical configurations may change, and tracker systems may need to be updated or replaced. Each improvement can create ripple effects throughout the project. 

For example, changing module wattage can affect string layouts, electrical loading, cable sizing, and equipment spacing. Updated inverters may require modifications to collection systems. Different module dimensions or tracker configurations may alter structural loads and foundation requirements. Design assumptions that worked for the original project may no longer apply. 

What initially appears to be a straightforward equipment replacement can quickly become a multidisciplinary engineering effort involving structural, electrical, civil, environmental, geotechnical, water resources, surveying, and permitting considerations. 

That is why successful repowering projects evaluate the facility as an interconnected system, not merely as a collection of components being replaced. 

Manage Uncertainty Through Early Coordination 

Every repower combines known project requirements with conditions that may remain uncertain at the outset. Incomplete documentation, legacy equipment, undocumented construction changes, evolving design standards, and unexpected field conditions can influence project costs, schedules, and design decisions. 

The engineer's role is not simply to respond when surprises emerge. It is to identify and forecast potential risks as early as possible, test assumptions, and give owners and operators the information they need to make confident decisions before construction begins. 

That work requires coordination across disciplines. A structural modification may affect electrical layouts. Updated electrical equipment may require civil design changes. Existing site conditions may influence drainage, environmental permitting, access, or construction sequencing. 

When engineering teams work together from the beginning, they can identify dependencies and conflicts earlier, evaluate tradeoffs more effectively, and develop solutions that consider the project as a whole. The earlier risks are understood, the more opportunities owners have to avoid costly redesign, minimize delays, optimize investments, and support more predictable construction outcomes. 

Building the Next Chapter of Existing Solar Assets 

The most successful repowers begin with disciplined investigation, not equipment selection. By reconstructing the asset's history, verifying existing conditions, evaluating systemwide impacts, and coordinating disciplines early, owners can make more confident decisions about where to reuse, reinforce, replace, or redesign. 

Those early decisions shape every phase of the project that follows: 

• Understand the facility's history and current condition. 
• Validate existing infrastructure before incorporating it into the new design. 
• Evaluate how current technology will interact with legacy systems. 
• Identify risks before they become costly surprises. 
• Coordinate engineering disciplines from the outset. 

Westwood brings together the civil, structural, electrical, surveying, environmental, geotechnical, water resources, and permitting expertise required to evaluate a solar facility as an interconnected asset. That perspective helps owners reduce uncertainty and position existing projects for their next phase of operation. 

Considering a solar repower? Connect with our team to discuss the conditions, risks, and engineering requirements that should be evaluated before design begins. 

About the Authors 

Rob Greening, PE is a Principal Structural Engineer with more than 16 years of engineering experience. He specializes in renewable foundation design for utility-scale solar and battery energy storage projects. He has been with Westwood for more than 8 years. His experience spans EPC and consulting service environments for telecommunications, substation, transmission, distribution, and renewables projects across the United States. 

Evan Langran, PE is an electrical engineering manager and has more than 13 years of engineering experience. He specializes in electrical collection system design for utility-scale wind, solar, and battery energy storage projects. He has been with Westwood for more than 6 years. His experience spans EPC, utility, and consulting environments and includes leading renewable energy projects across the United States and Canada. 

Frequently Asked Questions 

What Is Solar Repowering? 

Solar repowering is the process of upgrading or replacing components within an existing solar energy facility to improve performance, extend its operational life, or address aging, damaged, or underperforming infrastructure. 

Depending on the project's goals, repowering may include replacing modules, inverters, trackers, transformers, combiner boxes, foundations, or other system components while reusing portions of the existing site. 

How Is a Solar Repower Different From a New Solar Development? 

Unlike a greenfield project, a solar repower begins with existing infrastructure. Owners and operators must evaluate current site conditions, verify available documentation, assess structural and electrical systems, and determine how new technology will integrate with assets that may have been designed more than a decade ago. 

This often requires more investigation, verification, and coordination before design work can begin. 

What Should Owners and Operators Evaluate Before Starting a Solar Repower Project? 

A successful solar repower starts with understanding the existing asset. Owners and operators should gather, digitize, and consolidate available drawings and documentation; inspect structural and electrical infrastructure; identify undocumented field conditions; and determine whether existing systems can support the proposed upgrades. 

Completing this work early can reduce project risk, inform design decisions, and streamline the engineering process. 

Why Is a Multidisciplinary Engineering Team Important for Solar Repowering? 

Repowering affects interconnected systems throughout a solar facility. Changes to modules, inverters, foundations, or collection systems can influence structural, civil, electrical, environmental, and permitting requirements. 

An experienced multidisciplinary engineering team can identify these dependencies early, improve coordination, reduce redesign, and support more informed project decisions.