As solar and storage facilities approach midlife, many owners are facing critical decisions on maintaining or replacing equipment. Repowering a solar facility refers to the process of upgrading or replacing key components of an existing solar power system. These may include inverters, PV modules, and even supporting structures or electrical infrastructure.
Repowering will extend the life of the facility, restore or improve performance, and align the facility with newer technology standards. It can be a partial retrofit or a near-complete overhaul, depending on the condition of the facility, its age (typically five to 15 years) and the goals of the asset owner. It typically requires multidisciplinary engineering coordination and is not a simple replace-in-kind process.
Inverters Are Pivot Point
The most common or noticeable trigger for repowering projects centers around the inverter as it provides a single point of failure between the output of the PV array and the grid. Unlike a lithium battery, where energy levels slowly diminish over time, an inverter failure is analogous to a computer crash where the system shuts down and can’t be turned back on.
Inverters typically have design life of 20-30-years, though they may have failures prior to the end of design life. For premature failures, a number of factors are to blame:
- As individual components within the inverter wear out, it eventually becomes more efficient to replace the entire inverter unit rather than individual parts on the original equipment, especially if those original parts are no longer supported by the manufacturer.
- Manufacturers have integrated proprietary components within their designs, creating challenges for sourcing original replacement parts.
- Solar plant design and inverter architecture have evolved. Whether due to changes to the National Electrical Code (NEC), improved equipment technology, or the result of innovation over the years, the market has produced new ways of combining and converting the DC output of the solar modules into consumable AC power.
When all of these factors are combined, it becomes a complex challenge to find a suitable replacement for aging inverters.
A Constantly Changing Industry
Due to an ever-evolving trend in new technology and manufacturing, the solar industry has seen manufacturers move in and out of the solar market. As changes affect the pool of manufacturers, repowering projects have become far more complex, due to the inability to purchase compatible parts for repairs or replacement. It is often technically infeasible to replace individual components that have been sourced from a manufacturer that no longer offers certain equipment.
Standardized design of equipment has not taken place in the solar industry, so most equipment installed in the field has differing designs. Unique product designs from each manufacturer require creative workarounds when retrofitting new equipment on existing solar plants.
Additionally, the NEC has changed over the years to allow for higher DC voltages, going from 600 volts to 1,500 volts now. This is leading to a cascade of further work to change cables and other balance-of-plant equipment.
Assessing the Impacts of Repowering
Because it is cost prohibitive to rip and replace an entire solar plant, a progressive replacement program may be a suitable option. This will typically result in a bottom-up approach to determine portions of the system that are still suitable.
An evaluation of the existing modules can determine feasible options for matching an inverter to repower. As the NEC code permitted higher system voltages, the string sizes have gotten longer. Often, this means existing module strings do not produce high enough voltage to operate the newer 1,500-volt inverters. While stringing together more modules to achieve higher voltages may be an option, spatial limitations on existing trackers or structures likely prohibit longer string sizes. In addition, routing string cables between structures can be prohibitively expensive. There may also be limitations to the voltage rating of older balance-of-plant equipment that may prohibit the installation of longer strings.
Inverter manufacturers offer solutions to modify the operating voltages of their 1,500-volt inverters to retrofit existing 1,000-volt systems and operate at voltages of 1,000-volt inverters. Changing the inverter will inevitably result in different connection points between the AC and DC portion, so reconfiguring the cabling and additional equipment may be required to reconnect the inverter. Shifting the operating voltages will also result in a reduction in the capacity of the inverter, so careful consideration needs to be given when selecting the best replacement.
Every structure within a solar plant has been designed to accommodate wind and structural loading expected within a specific location. Changes to both the weight and footprint of the equipment will require a careful structural evaluation. This can affect all parts of the system, including modules, trackers and inverters.
EPC Advantage
As the solar industry continues to mature, manufacturers have begun to transition toward finding suitable solutions for older equipment that may be compatible with modern equipment. Manufacturers that work to backfill the need for now-defunct inverters often benefit from a relationship with an engineer-procure-construct (EPC) contractor with experience in navigating the unique repowering challenges each project may encounter.
The current state of industry transition reduces the likelihood of a plug-and-play approach for repowering projects. When an inverter or module must be replaced, it creates a cascade effect with related equipment also needing to be modified. The custom engineering this requires creates demand for custom designs to anticipate the often-unique elements of these increasingly complex projects.
Every system we analyze currently requires an engineered solution, due to the differences in site characteristics and previously designed conditions. Engaging early with an EPC partner with an extensive track record of experience in the nuances of repowering aging solar plants is a proactive step that will help owners navigate unexpected challenges.
Planning for future augmentation of battery energy storage systems is a prudent strategy.
