The operations and maintenance (O&M) of a utility-scale solar project is largely obvious — keep solar panels clean, monitor inverter health, maintain the grounds and check tracker mechanisms for wear. Maintaining large-scale lithium battery energy storage system (BESS) installations takes a different skill set, although they’re largely hands-off and don’t require any weather-related upkeep. But that doesn’t mean there isn’t anything to monitor, since BESS projects actually generate an enormous amount of data. Asset managers can help portfolio owners sift through the mountains of data to ensure batteries are working at their full ability.
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 yield. Solar Power World talked with Robert Johnson, global VP of sales solutions at Power Factors, about the asset manager’s work in the BESS space.
SPW: What kind of maintenance is regularly performed or monitored on large-scale lithium BESS?
Credit: NextEra Energy
Johnson: Maintenance activities fall under two broad categories: corrective maintenance and preventive maintenance.
Corrective maintenance involves activities like replacing faulty BESS modules (the components that encompass a set of cells), BESS racks (the components that encompass a set of modules), inverters or inverter components, balance of system (BOS) components like HVAC systems and distribution panel breakers, or fire and safety-related components.
Preventive maintenance involves activities like replacing filters, refilling liquid-cooling systems, calibrating sensors, replacing modules that indicate excessive degradation, checking fire suppressant systems, recalibrating state of charge (SOC) estimations and much more.
However, the ability to perform these activities effectively rests on having a solid O&M strategy and the underlying data and tools to execute the strategy.
What are some recommendations you have for O&M strategies for these systems?
Acquiring the data is key, and it’s not always easy. BESS systems involve a lot of data, and in some cases can represent a step-change in the volume of data from more familiar asset classes like solar and wind. It’s critical for owners, operators and O&M providers to understand the importance of this data and to develop a strategy for securing access to it. That means understanding your network capacity for continuously transmitting it, having the right communication gateways to collect it and the right upstream systems to process, store and retrieve it.
Once you have your data under control, the next best strategy is to develop a capacity to foresee system failures so you can proactively address them before they occur. This helps avoid costly truck rolls and downtime incidents, which reduce revenues and may incur liquidated damages depending on the underlying contractual agreements. The key to foreseeing system failures is predictive alerting. Power Factors provides a growing library of early fault detection (EFD) alerts and events.
For example, we detect imminent cooling system failures, which allows operators to intervene well in advance of 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 the liquid-cooling system had not been returned to service after a recent maintenance activity. Luckily, they were able to return the system to service before any damage was done and avoid the expensive headache of having to litigate who was responsible for the mishap.
How does Power Factors acquire the data needed to support these strategies?
We get data from the battery management system (BMS) provided by the BESS integrators, as well as from power plant controllers (PPC) and supervisory control and data acquisition (SCADA) systems. We acquire data from systems using communication gateways, which are typically deployed onsite. However, we can also acquire data from sites remotely over a secured network. We can also acquire and exchange data with other central data aggregators via APIs (access 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 acquire string-level sensor measurements of temperature, voltage and current, as well as any digital error and fault codes. We can also read this data directly from equipment like inverters, meters and relays. We then use all this data to determine if systems are operating within their nominal parameters. If they are not, our event management system generates important information that helps to answer questions like: Which device is impacted? What is the severity level (how urgently do I need to act)? What is the ongoing revenue impact? Am I nearing any compliance or warranty thresholds? Who is responsible for fixing this issue?
It’s easy to see how important this type of information is. If you’re operating just one large BESS or if you have just a couple sites with the same OEM, you can probably get by using the BMS or energy management system (EMS) for your monitoring needs. But as soon as you have a few systems or more, and especially if they involve different OEMs and integrators, managing the torrent of information is daunting, let alone trying to build and sustain 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 on a battery’s health. The more analog readings and digital codes we have related to 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 manufacturing quality or temperature impacts from thermal management system design flaws, which lead to unbalanced power distribution on the shared DC bus and can quickly pull down the performance of adjacent strings. String-level sensor-based measurements from the BMS are necessary for these diagnostics.
State of charge also warrants special mention. SOC indicates a battery’s capacity to discharge, and for lithium-iron phosphate (LFP) chemistries, which are predominant today, they can be notoriously difficult to estimate. Power Factors provides advanced diagnostics that help operators understand the accuracy of the native BMS SOC estimations, and we’re hoping to soon to have the capability of providing SOC estimations that are more accurate than those provided by the BMS itself.
Other important system indicators include state of health, round trip efficiency, cycle counts and depth of discharge.
How does O&M monitoring differ for BESS installed in New York vs. Arizona?
The most significant difference is probably their differing weather profiles. Arizona is generally hotter most of the year, while New York sees a lot more snow and cold weather.
For sites in Arizona, operators might focus more on failure signatures related to high temperature conditions and then tune their alarming thresholds accordingly. They might 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 with dust, so they may have a more frequent filter replacement regimen. In New York, they’re likely planning for severe cold weather and perhaps even hurricane or flooding conditions. They may be especially interested in telemetry and forecasts from specialized weather data providers.
It’s important to note here that many BESS have service obligations, such as reserve capacity agreements, that require them to support the grid precisely when these extreme weather events are happening, so owners and operators need to be especially prepared. This is also another reason why it’s so important to have confidence in your SOC levels.
On top of that, most revenue for BESS assets comes from just a fraction of the days in a year. It’s critical for an owner/operator to know which days those are likely to be and then plan maintenance accordingly. This will look different between Arizona and New York due to their contrasting market and weather dynamics.
