There is no shortage of monitoring features offered for your PV system, but what information is really important to collect and monitor?
“Understanding solar system performance is complicated because unlike fossil fuel plants, we don’t control the input: the sun. So it’s hard to know if the system is performing as expected. Moreover solar systems are designed to operate unattended, so problems may go unnoticed. That’s why we install monitoring systems.” - from a presentation by Saurabh Samdani, PE, Cupertino Electric, at Intersolar 2013
Selecting a Monitoring system is gaining more importance in the earlier stages of project development. It is no longer just about having a tool that allows you to brag about your PV system to your friends (or satisfying those with OCD tendencies), it’s about truly optimizing the performance of your investment and detecting irregularities before they result in significant lost energy and revenue.
Monitoring is a vital tool for managing, troubleshooting and maintaining the long-term performance and ROI of your system. The visibility that monitoring provides sheds light on opportunities for small improvements in performance, otherwise going unnoticed, that could have real effects on net profit or savings. When a deviation or underperformance occurs, monitoring provides the first indication to initiate the process of analysis and troubleshooting. But how does one know that something has happened to affect the system? Knowing the time will assuage any fears of low output if it’s simply nighttime – but in the case of low output during the day, is it electrical damage, dirt or clouds, or something else?
There are three essential functions of a monitoring system: Measuring, Modeling and Reporting.
Measuring
This is the sampling of actual power and energy delivered by the system, as well as possible codes produced by the equipment itself. It may also include local weather and irradiance data.
Inverter Direct – Simple Modbus output from the inverter itself to a web server or local display. This is the most basic way for an inverter to report on its own production.
Circuit Currents – Current Transducers (CTs) wrap around the input and output circuits of the system – then signal a datalogger with the measured current. This is essentially third party documentation of performance and can be accomplished at the module, string or zone (subcombiner) level depending on budget.
Revenue Grade Metering - really only necessary if your utility requires you to have revenue grade reporting. Using a revenue grade meter on it’s own as a monitoring approach, rarely provides sufficient data on the health of your system and not much insight into where a weak sub array or module may be if troubleshooting is required - but given the reliability of modern PV equipment, simple plug-in, networked metering may be a very cost effective approach.
Meteorological (meteo) - It is possible to measure available energy and weather locally, but due to required maintenance of the meteo equipment, this is probably not practical unless scheduled maintenance of the equipment is available
Modeling
This is the comparison of the power and energy produced to the power and energy for current or future available energy coming from the sun.
Simple output / state of health – PV array size, time of day and location are all that is needed to estimate what should be produced on any given day of the year. Adding weather data can fine tune that prediction.
Complex relative production - The latest new feature in the DECK Monitoring Software Platform is Relative Performance Analytics (RPA). Relative Performance Analytics is ideal for larger PV systems with granular generation data. RPA can be applied any time you have identical data types from two or more separate devices in one system. RPA represents a shift in the traditional approach to solar power diagnostics that can help you identify under-performing devices in your PV system. This ‘smart software’ surveys historical system data to map the deltas among reporting values for separate data points (or relative performance). It actually learns the relative performance patterns of the entire system, so users can identify a change in performance of a single (or group of) components relative to the others. System managers will be able identify outlier data points and detect changing performance patterns with greater accuracy and fewer ‘nuisance’ alarms.
Reporting
Dashboard - The Dashboard can be accessed locally or remotely online. Two examples of dashboards are the Deck Monitoring Dashboard and the Enphase Enlighten website and apps. The dashboard allows you to instantly view your system’s current energy consumption and generation in differing time increments, and real-time on site weather data - but a web connection and network must be available.
DECK Monitoring offers monitoring packages for either 5 or 10 years for both Residential and Commercial systems. These packages include the features mentioned previously (current weather data, and site specific satellite irradiance data with their ‘SolarAnywhere SystemCheck’) along with what would be considered the three most important features of any monitoring system: a Dashboard, Production Modeling, and Alarm capabilities.
When diving a bit deeper into these platforms, they also can provide you with Production Modeling and Alarm Notifications. Within the Admin Panel of your Deck Monitoring or Enphase website login you can manage multiple systems, troubleshoot onsite problems, view detailed information on each component of your system, review analytical tools including graphs, and download data onto your desktop. These platforms also allow their users to set up Alarm notifications to alert them when there is a system failure. Furthermore, you can compare performance of power production over user specified time intervals with historical collection of data to assess whether there are performance issues before a “failure” exists and you’re notified by an alarm.
These features provide us with a lot of information in multiple formats. As Saurabh Samdani explained in his presentation at Intersolar 2013, “most of these important monitoring features must be kept graphical, contextual, and focused. Graphs are much easier for us to understand than tables. Context is important because data is meaningless by itself. Focus because our brain cannot hold or process a lot of information at once”.
Draker labs has come up with a very nice implementation of a contextual presentation. The green bar is power, yellow is irradiance and index is shown as a percentage.
Most inverter companies and third-party monitoring providers, like Locus Energy, Deck or Draker, offer customizable features that, by appealing to our personal tastes, are extremely valuable. A simple and well designed monitoring system will be used more than a cluttered and confusing one. Simple and well designed monitoring systems provide the opportunity to fix problems before they get out of control - and sometimes before they even happen.