Asset managers, performance engineers, owners and investors alike are looking for ways to optimize the performance of their large-scale utility, commercial and industrial solar PV projects. The latest advances in performance monitoring and reporting can provide rich, timely and actionable information to help each stakeholder make smarter decisions.
Gavin Boggs
Bob Szymanski
What is performance monitoring?
Performance monitoring puts critical actionable data in front of asset managers, site personnel and other decision-makers to maximize the production output and revenue of the site. Performance monitoring can be applied over short time frames for prompt response to ongoing issues or over longer periods of weeks, months or years to understand systemic causes of lost energy and to develop strategies to mitigate them in the future.
At the heart of performance monitoring is a comparison of actual inverter power output to an expected power model, based on irradiance and panel temperature. With an accurate expected power model, even very small deviations between actual and expected power can be flagged as potential problems. Potential problems can then be ranked by impact and addressed in a systematic way until all inverters are performing to their expected (full-production) potential.
Recording special weather conditions, curtailment events and other external factors at the site is important to explain losses that are otherwise unaccounted for. Was there a dust or snow storm that fouled panels, or a rain storm that washed them clean, or high winds and debris that damaged sensors? Generally, these events need to be captured manually, but including issue tracking in parallel to automated performance monitoring helps remove uncertainty about the causes of lost production.
Performance monitoring is generally composed of three stages:
1. Data Collection and Transformation: Critical site data is loaded from a SCADA system or operational historian and loaded into the performance monitoring database in the appropriate format. At a minimum, site data should include irradiance, panel temperature, inverter AC power output, and combiner box DC current output.
2. Background Calculations: Expected energy and other values are calculated using the raw site data on a regular basis or as data is loaded.
3. Visualizations, Alerting and Reporting: Data and calculations are presented to decision-makers in a way that is easy to interpret and act upon.
How does EDF Renewable Services use performance monitoring?
EDF Renewable Services’ performance monitoring initiatives and resulting development projects have quickly led to improvement of EDF Renewable Energy-owned plant performance and improved service offerings to third-party customers. The system requirements were developed from the point of view of asset managers, who tend to focus on performance percentages and profitability as they relate to both operations and maintenance work in the field, as well as monitoring in the control center. This led to the development of an improved data acquisition technology stack with plant performance as a priority.
With improved data acquisition, the availability of raw data from different levels of the site asset infrastructure allows for cohesive asset mapping and data normalization. With data available from the combiner boxes, there is visibility to issues with individual strings, and this allows field and site crew to address issues that wouldn’t be noticed as easily in higher-level site data from the feeders or main meters.
Asset managers, site managers, performance engineers and control center operators regularly review daily performance dashboards to identify potential performance issues. Some of the common issues that are captured include inverter faults, late start-ups, combiner box open protection circuits, underperforming strings, and failed solar tracking systems. Without attentive operators and an effective performance monitoring system, a small issue such as a blown combiner box fuse could go unnoticed for months, quietly costing hundreds of dollars per day in lost revenue.
This inverter-level to combiner-level monitoring also enables the site to use pinpointed condition-based maintenance strategies as opposed to scatter-shot or interval-based strategies, greatly improving the effectiveness of each man-hour. Prioritizing maintenance on inverters or combiner boxes with lower performance makes it more likely that a spot check will identify an actual correctable issue.
Performance issues aren’t always easily identifiable in an OEM SCADA system, which may only provide inverter production in real time. For example, utilizing performance dashboards to compare inverters against each other through an entire day allows asset managers to easily identify tracker issues or performance issues that only appear at certain times of the day. These issues can be easily missed if operators only monitor individual inverter generation in real time without graphical representation (graphs, trend lines, etc.).
To further reduce the time and effort required to find and correct potential issues, a notification system sends alerts when an inverter’s capacity-weighted daily production is significantly lower than that of the other inverters at the same site. This makes it unlikely that any major issue will slip through the cracks.
Over longer periods, production, irradiation and availability are compared to monthly budgeted numbers in automated monthly reports. By eliminating the need for asset managers to manually compile data from multiple sources, their workload is reduced by several hours per month, freeing up more time to work on performance optimization while, at the same time, improving the accuracy and repeatability of the final reports.
How performance reporting can help owners make smarter decisions
For asset managers who are seeking actionable information to maximize the return on investment of their PV project investment, performance monitoring is a valuable tool that can put some of the most important metrics right at their fingertips. It allows them to stay connected to their assets so they can make smarter economic decisions. When an issue arises, a response plan is built on all of the available information, and the better the information, the better the plan. Is the problem significant enough and specific enough to mobilize a crew? It is possible for the corrective action to end up costing more than the original problem if it’s not well planned. Is there an issue that could be addressed proactively? An inverter with an intermittent fault could be identified and fixed before it causes a longer downtime incident. If the work is scheduled at a convenient time, such as after sundown or along with scheduled maintenance on a nearby inverter, it further minimizes the adverse economic impact. Is panel soiling significant enough to consider washing the panels? Are the string-level production losses great enough to justify infrared (IR) aerial photography? Performance monitoring can take the guesswork out of these strategic decisions.
With drill-down performance information, owners can transition from asking whether their site is performing according to a rough budget to asking whether each inverter or each combiner is producing the exact amount of energy it should be based on the sun and weather conditions. Armed with precise information, owners can be confident that their site is running at its full potential, or if not, they know exactly where the problem lies.
Opportunities for system improvements
While the capabilities of performance monitoring and reporting systems have advanced greatly over the past several years, opportunities for innovation and improvement still exist. Areas that limit current performance monitoring systems include the following:
•Accuracy, resolution and availability of raw data measurements;
• Accuracy of expected energy model; and
• Spatial resolution of measurements.
The accuracy of data measurements and the expected energy model combined determine what failures can be identified. If the system error is larger than the energy lost, the failure won’t be detected. Sensors that are improperly calibrated or incorrectly installed, especially at the combiner level, will limit operators’ ability to find the causes of plant underperformance. While current weather-adjusted expected energy models are quite accurate, more advanced models that correct for air mass and spectral response, solar incident angle, shading, and other factors could flag smaller and smaller issues.
Today’s systems that measure at the combiner level can still only limit the location of a failure to hundreds of possible modules. Although that may represent a significant improvement over inverter-level monitoring, it doesn’t match the spatial resolution of aerial IR scans. Installing current sensors at the string or module level could improve performance monitoring, but for now, there is still a place for occasional IR fly-overs to find module or sub-module failures. At the same time, there are clear advantages in using frequent performance monitoring to catch performance issues much more quickly than aerial scans might allow.
A good performance monitoring and reporting system provides asset managers with actionable data that empowers them to make better, quicker decisions that will result in the optimum operation of their PV asset. Accurate data combined with an accurate expected energy model that automatically feed into timely and flexible reporting systems with drill-down and trending capabilities save time and money for the owners and operators of large PV installations. Systems today are better than ever, and future advancements will only improve the ability to catch and fix performance issues.
Bob Szymanski, director of operational technologies for EDF Renewable Services, is responsible for the Operations Control Center and SCADA Integration groups. Gavin Boggs, renewable energy analytics engineer for EDF Renewable Energy, is the lead fleet engineer for solar assets in the Performance and Reliability Engineering group.
