Time and again, solar has proven to be an effective way to reduce utility costs. Even with weather-driven variability, the benefits far outweigh the drawbacks. However, photovoltaic (PV) systems must perform as expected over the long term for the full savings to materialize. What happens when your best energy asset suddenly isn’t there for you? How can you tell when you should be getting even more from solar?
Like other systems, solar requires maintenance and periodically runs into issues like soiled panels, a failed inverter, or a tripped disconnect. PV systems can also run for years without a hiccup, which makes it easy to forget they need attention at all. Nothing obvious stands out like it would when a chiller malfunctions. In addition, solar production is naturally variable day-to-day because of weather, which makes it hard to tell a system issue from an ordinary cloudy day.
When solar malfunctions, the system just quietly produces less than it should, and the only signs may be higher grid consumption and a higher utility bill a month or two later. Often no one notices, and the savings leak away for months. For example, a Gridium client recently had outages over multiple months which cost them $175,000 in higher utility charges for a single building. They are not alone. This is a common story with on-site solar.
Gridium’s latest solar release now makes production losses more apparent. Chief engineers and property managers can see exactly how their solar is performing, get an early signal when something is off, and know when it’s time to investigate before a small loss becomes much bigger.
Here’s what you should be tracking with your solar, how the Gridium platform shows it to you, and what to do when the numbers say something’s wrong.
The Performance Metrics That Matter for Solar
Solar performance monitoring has a handful of useful metrics and measures that cut through the noise of “is my system doing okay?” The Gridium platform is built around these:
- Expected vs. actual production. A direct view of system performance. Every PV system has an expected output based on factors such as system capacity, orientation, and the solar and weather conditions it actually experiences. Comparing what a system should have produced against what it did produce separates a normal weather dip from a real issue, and it’s the foundation for everything else on this list.
- Performance Index. For a quick read on system performance, the ratio of actual production to expected production tells you how closely a PV system is performing to expectations. The IEC 61724-1 standard for PV monitoring defines this model-based metric as the Energy Performance Index. Gridium’s Performance Index (PI) is built on that definition. The value of PI is that it takes those expected factors off the table. A cloudy week, a hot afternoon, a system in its eighth year, typical panel soiling: Gridium’s model accounts for these factors, so they do not affect PI. What does move PI are the things you can take action on, like excessive soiling, new shading, or a fault. A Performance Index near 1.0 means the system is producing what conditions allow. When it drops and stays down, something has changed that is not expected, and that is worth a look.
- Estimated production losses. Rather than just flagging that a system underperformed, this quantifies how much was lost, in kWh, over a given period. This is what turns “performance is a little low” into a number a property owner or asset manager can act on.
- Downtime and outage events. For how many daylight hours was the system not producing power? Increased downtime can point to an outage, such as an inverter fault, tripped breaker, or grid-side issue, rather than gradual degradation. How many times did outages occur? Frequent outages can point to recurring issues that are easy to overlook, whereas a sustained outage is more apparent.
- Historical trends. Any single day’s numbers can be noisy: clouds roll through, curtailment happens, a cleaning crew disconnects a string for an hour. What matters is whether performance metrics are holding steady, trending down (a flag that maintenance could be needed), or recovering after an intervention.
How the Gridium Platform Shows You Solar Performance
The Gridium platform now calculates these metrics automatically for every solar meter, using a physics-based model that accounts for solar irradiance, temperature, system capacity, panel orientation, soiling, and age-related degradation.
Expected production on the load chart. Every solar meter shows an expected production line alongside actual production, so you can see at a glance, interval by interval, whether the system tracked its expected output or fell short.
Solar production shown on the load chart including actual and expected production (Energy page on Usage tab)
Estimated losses. When actual production falls short of expected, the platform calculates the gap in kWh for the selected timespan to quantify the shortfall. The losses are categorized into soiling (beyond expected for the PV system), outages, and other losses.
Summary of actual and expected production along with estimated losses in production (Energy page on Usage tab)
Performance metric summary and historical trends. A dedicated solar performance view on the Insights tab rolls up performance index, soiling and outage losses, outage events, downtime, and age-related degradation into a summary, alongside historical trends so you can see whether performance is stable, declining, or recovering after maintenance.
Solar metrics summary (Solar Performance page on Insights tab)
Automated outage detection. The platform automatically flags production outages directly on the load chart and surfaces them in your weekly email, so you find out about a downed inverter or a tripped breaker shortly after it happens, rather than when the next utility bill arrives.
Solar production outage note (Energy page on Usage tab)
Together, these views answer the question chief engineers and property managers actually care about: is solar delivering like it should for my building?
What to Do When Solar Underperforms
Whether you own the system or buy solar power through a third-party power purchase agreement (PPA), underperformance costs you money. If you own the asset, every lost kWh is a kWh you buy from the utility instead. You also miss out on potential savings from demand charges and have greater exposure to expensive time-of-use (TOU) periods. Under a PPA, you generally stop paying for kWh you never receive, but you still have to replace it at the utility’s rate, which means higher energy costs and less opportunity to reduce demand charges or avoid TOU periods. Either way, a quiet failure shows up on your bill.
If you own the solar asset:
- Check the outage notes and load chart first. A sudden drop can indicate an inverter fault, a tripped breaker, a grid issue, or an issue with the monitoring system. Some of these issues can be resolved quickly once identified.
- See if there is a gradual decline in Performance Index, rather than a sudden drop. This can point to excessive soiling or new shading of panels and is a signal to schedule a panel cleaning or physically inspect before the next billing cycle.
- Loop in your operations and maintenance (O&M) provider with the specific date range and estimated loss. A concrete number and timeframe gets a faster response than “the system seems off.”
If your solar is under a third-party PPA:
- You’re generally not responsible for fixing the system, but you still depend on it performing as expected.
- Use the estimated losses and outage history as documentation when you contact your PPA provider. Depending on the terms of the PPA, the contract may include production guarantees. A clear record of when and how much the system underperformed can be useful when discussing performance with the provider.
- If underperformance is recurring rather than a one-off event, historical trends make the case for an equipment inspection.
Either way, the goal is the same: know quickly when solar isn’t delivering, know how much it is underperforming, and have the data on hand to justify a fix.
Ready to see how your solar is performing? Find these views on any solar meter under the Usage and Insights tabs in the Gridium platform. If you have solar that isn’t yet set up in Gridium, or a building that could benefit from these capabilities, reach out to our team.
