The asset management of solar plants has come under increasing focus in recent years as installations age and maintenance activities are needed, especially for plants that were not designed with long-term operation in mind. Asset owners can find themselves faced with growing operational expenses, which may not have been considered in the original project cash-flow, either because of lack of experience or due to poor equipment selection. However, as more solar projects are installed, asset owners are gaining new insights into the importance of making the right decisions during the design phase to help ensure maintenance is cost-effective throughout the lifetime of projects.
The main goal for every asset manager is to maximize generation revenue while controlling O&M expenses. Ways to accomplish this goal are to detect any underperformance quickly, keep site visits to a minimum, and, on the occasions when a site visit is required, ensure problems can be resolved quickly. To achieve this, the asset manager must have a clear overview of the problem – what is it, where is it located, and how much energy production is being lost as a result? With this information, a decision can be made quickly on whether field personnel really need to be dispatched, and, if so, what the scope of work is in order to avoid a second visit. And, by knowing the lost production, it can be decided if the visit can wait until the next day or the next scheduled visit.
An even more important aspect in asset management is risk management and personnel safety. The safety of field crew needs to be on the top of list in terms of importance and every step that can be taken to make the system more resilient to error while maintenance is being performed should be considered and adopted.
However, when it comes to maintaining solar plants, the fact is that the two sides of the system – AC and DC – are not created equal. Inverters, transformers, and other equipment on the AC side of the plant have alarms, warnings and monitored variables which provide valuable insights into system performance and health. In comparison, equipment on the DC side of the system, such as panels and combiner boxes, offer very little in the way of performance data, effectively creating a blind spot for maintenance staff.
Improving solar safety at the string level
At first, the industry began to adopt string-level monitoring to provide greater visibility of the DC technology. This consisted of installing current sensors in the combiner box or in the inverter re-combiner for each string. This level of monitoring warns the asset manager when a string has an issue or is not performing at the expected level. While it was a good step, it requires the installation of additional communication infrastructure for the data flow from the combiner box to the monitoring system, and it can only provide insights at the string level. This means that when a concern or issue is detected, a field visit is likely required to understand what the issue is, and a second visit may be required to remedy the issue.
Since then, other methods to monitor DC arrays have also come to the fore. For example, I-V curve tracing became popular due to its ability to detect panel issues such as burnt diodes and broken glass. However, it can be costly as it requires a site visit by a specialized crew to gather data and the use of specialized software or personnel to analyze that data.
For larger installation, aerial inspection, either via airplane or drone, and post-processing data analysis is deemed to be an effective way of detecting the panel issues which would otherwise only be possible via site inspection. This practice provides the asset manager with a one-time picture of the array’s status and health and is usually performed once or twice a year. However, should a potential issue be identified, once again it will be necessary to deploy a field team to the site – first to confirm the problem, and then to fix it.
Harnessing DC Optimization to provide 360° plant visibility
As the industry continues to gain a greater understanding about the role that maintenance costs play in the long-term profitability of solar plants, there has been a significant movement to adopt module-level monitoring, enabled by DC Optimization which includes module-level power electronics (MLPE). As the name implies, this form of enhanced monitoring provides highly granular and robust performance data at the module, rather than string level, in real time. As a result, asset managers are provided with complete visibility on system performance and health 24-7.
With such highly granular data at their fingertips, O&M personnel can remotely perform diagnostics on both the AC and DC systems, and only dispatch field personnel when it is most economical to do so, resulting in more efficient fleet management and lower O&M costs. For example, with module-level monitoring, if a module has a failed diode, then an automatic alert will notify the O&M provider. The module can be easily identified, and a screenshot can be provided to the module manufacturer for a warranty claim. This means that during the next scheduled site visit, the O&M provider can bring a module to replace the failed one, saving a field trip, positively impacting the O&M budget, and contributing to a lower LCOE. More so, this type of monitoring solution also provides reports on array performance, such as panel degradation, which is often required by investors, banks, or utilities.
By enabling asset managers to transition to selective maintenance, module-level monitoring provides a powerful tool to optimize maintenance schedules, as maintenance activity is only performed when it is actually needed. While preventive maintenance will still be required, waiting to uncover issues during preventive maintenance activities may lead to extended production losses and peaks in maintenance workload, potentially requiring labor costs increases to cover surge labor or overtime to remedy latent issues uncovered during these visits.
It is not simply the operational efficiencies that are achievable with DC Optimization enabled monitoring that has made the technology so appealing to asset managers, however. An even more important aspect in asset management is risk management and personnel safety.
Systems equipped with DC Optimization provide an extra layer of safety during maintenance as the array DC voltage is lowered to safe DC levels (typically 30VDC) avoiding potential electrical shocks if a mistake should happen. Another advantage is that should a DC ground or arc fault occur, the array is de-energized and will remain at this state until the issue is remedied. This will significantly reduce the likelihood of further issues, such as secondary arcs, which can occur if issues are not treated in a timely manner upon a warning.
By harnessing the power of DC Optimization to provide continuous and highly granular module-level monitoring to enable selective maintenance, solar plant O&M activities are streamlined and much more efficient. This allows for less time onsite, fewer truck rolls, and means that, when a site visit is required, it can be done during regular working hours, helping to keep labor costs under control. This is especially pertinent right now in the current climate of rising labor costs and a tightening labor market.
Kleber Facchini is Director of Commercial Product Management, SolarEdge Technologies; and Frank Kelly is Head of Value at NovaSource.
