The operation and maintenance (O&M) of a utility-scale solar project is largely self-explanatory: keep the solar panels clean, monitor the health of the inverter, maintain the grounds, and check the tracker mechanisms for wear and tear. Maintaining large-scale lithium battery energy storage system (BESS) installations requires different skills, although they are largely hands-off and do not require weather-related maintenance. But that doesn’t mean there’s nothing to monitor, as BESS projects actually generate a huge amount of data. Asset managers can help portfolio owners sort through the mountains of data to ensure batteries are operating optimally.
Software company Power factors optimizes its customers’ project portfolios through data-driven products. The company’s Unity Performance Management product helps BESS project owners and operators with O&M tasks, improving uptime and returns. World of solar energy spoke with Robert Johnson, Global VP of Sales Solutions at Power Factors, about the asset manager’s work in the BESS space.
SPW: What maintenance is regularly performed or monitored on large-scale lithium BESS?
Credit: NextEra Energy
Johnson: Maintenance activities fall into two broad categories: corrective maintenance and preventive maintenance.
Corrective maintenance includes activities such as replacing defective BESS modules (the components comprising a set of cells), BESS racks (the components comprising a set of modules), inverters or inverter components, Balance of System (BOS) components such as HVAC systems and distribution panel breakers or fire and safety related components.
Preventive maintenance includes activities such as replacing filters, refilling liquid cooling systems, calibrating sensors, replacing modules that indicate excessive degradation, checking fire suppression systems, recalibrating state of charge (SOC) estimates and more.
However, the ability to execute these activities effectively relies on having a solid O&M strategy and the underlying data and tools to execute the strategy.
What are some recommendations you make for O&M strategies for these systems?
Credit: NextEra Energy
Getting the data is essential, and it’s not always easy. BESS systems are data-heavy and in some cases can represent a step change in the amount of data from more familiar asset classes such as solar and wind. It is critical that owners, operators and O&M providers understand the importance of this data and develop a strategy to secure access to it. That means understanding your network capacity to transmit it continuously, having the right communications gateways to collect it, and having the right upstream systems to process, store and retrieve it.
Once you have your data under control, the next best strategy is to develop an ability to foresee system failures so you can proactively address them before they happen. This helps prevent costly truck rolls and downtime incidents, which reduce revenues and may result in damages depending on the underlying contractual agreements. The key to predicting system failures is predictive alerts. Power Factors offers a growing library of early fault detection (EFD) alerts and events.
For example, we detect impending failures in the cooling system, allowing operators to intervene well before significant degradation or damage. On a recent occasion, one of our customers dispatched a field technician after receiving a cooling failure EFD event. When they arrived on site, they discovered that the liquid cooling system had not been returned to service following a recent maintenance activity. Fortunately, they were able to put the system back into service before any damage was done and avoided the expensive headache of having to litigate over who was responsible for the accident.
How does Power Factors obtain the data needed to support these strategies?
We get data from the BESS integrators’ battery management system (BMS), as well as from power plant controllers (PPC) and supervisory control and data acquisition systems (SCADA). We collect data from systems using communications gateways, which are typically deployed on-site. However, we can also obtain data from locations remotely via a secure network. We can also acquire and exchange data with other central data aggregators through APIs (application programming interfaces). In many cases, Power Factors is the provider of the PPC and SCADA, which greatly simplifies the data integration process.
From BMS we obtain string-level sensor measurements of temperature, voltage and current, as well as any digital fault and error codes. We can also read this data directly from equipment such as inverters, meters and relays. We then use all this data to determine whether systems are operating within their nominal parameters. If not, our event management system generates important information that helps answer questions such as: Which device is affected? What is the severity level (how urgently do I need to act)? What is the ongoing impact on revenue? Am I near compliance or warranty thresholds? Who is responsible for solving this problem?
It’s easy to see how important this kind of information is. If you operate only one large BESS or have only a few locations with the same OEM, you can probably leverage the BMS or energy management system (EMS) for your monitoring needs. But once you have a few systems or more, and especially if several OEMs and integrators are involved, managing the deluge of information is difficult, let alone trying to build and maintain a coherent operations and maintenance strategy .
Which data is most important for BESS O&M?
Let’s start with the cooling system. Knowing the status and health of the cooling system is critical because temperature is such an important factor in the health of a battery. The more analog measurements and digital codes we have regarding temperature, the better.
Cell imbalance is also particularly important due to its negative impact on system performance. These imbalances are generally the result of variations in production quality or temperature effects due to design flaws in the thermal management system, which lead to unbalanced power distribution on the shared DC bus and can quickly degrade the performance of adjacent strings. This diagnostic requires sensor-based measurements at string level from the building management system.
The indictment also deserves special mention. The SOC indicates a battery’s discharge capacity, and the composition of lithium iron phosphate (LFP), which predominates today, can be notoriously difficult to estimate. Power Factors provides advanced diagnostics that help operators understand the accuracy of their own BMS SOC estimates, and we hope to soon have the ability to provide SOC estimates that are more accurate than those of the BMS itself.
Other important system indicators include health status, round trip efficiency, number of cycles and depth of discharge.
How does O&M monitoring differ for BESS installed in New York versus Arizona?
The main difference is probably their different weather profiles. Arizona is generally hotter most of the year, while New York experiences much more snow and cold weather.
For locations in Arizona, operators could focus more on fault signatures associated with high temperatures and then adjust their alert thresholds accordingly. They may have more liquid than air cooled systems because they are more efficient, so they will have telemetry specific to those systems. And they may be more concerned about dust, which means they need to replace their filters more often. In New York they are probably planning for extremely cold weather and maybe even hurricane or flooding. They may be particularly interested in telemetry and forecasts from specialist weather data providers.
It is important to note that many BESS have service obligations, such as reserve capacity agreements, that require them to properly support the grid when these extreme weather events occur. So owners and operators must be specially prepared. This is also another reason why it is so important to have confidence in your SOC levels.
Furthermore, most of the income for BESS assets comes from just a fraction of the days in a year. It is critical that an owner/operator knows what days those are likely to be and can plan maintenance accordingly. This will look different between Arizona and New York due to their contrasting market and weather dynamics.