Locus Energy’s Virtual Irradiance (VI) Performance Waterfall is a tool that analyzes power generation data from a meter to determine whether the panel(s) and inverter(s) behind the meter are working as expected.
VI Performance Waterfall Overview
Locus Energy’s Virtual Irradiance (VI) Performance Waterfall is a tool that analyzes power generation data from a meter to determine whether the panel(s) and inverter(s) behind the meter are working as expected. For systems that are not performing to expectations, the VI Performance Waterfall helps determine why discrepancies arise between measured and modeled performance of a system.
The VI Performance Waterfall first calibrates a PV model based on measured energy data from the site, to create an accurate as-built estimation. Leveraging VI as the source of irradiance, the Performance Waterfall then analyzes the differences between the modeled and measured data series to estimate the following kWh losses on a daily basis:
Snow cover loss
Partial capacity losses / string outage loss
Other losses (i.e., something other than the above)
These loss buckets are available in the charting tool, reporting interface, and our external API with daily or higher granularity
Requirements for the VI Waterfall
In order for the VI Performance Waterfall to run, the meter needs to meet the following requirements:
VI data available
Located in the Continental US or Hawaii
Meter component is a LGate (50, 100, 101, 120, or 320, using the .1 meter device), Enphase, Itron, SolarEdge, Solar Log, Veris, Elkor or Solar City device
Component has 1 year or more of data. The component’s data is used to infer a configuration and calibrate a PV model.
Note: Degradation analysis requires two years of data.
Meter is monitoring arrays with roughly a single fixed (non-tracking) orientation. Multiple orientations may work if they are similar, though there will be some accuracy loss.
Consistent data quality with no major midlife system changes. E.g., the following are examples of issues that can break the analysis:Significant timestamping or power data issues.Capacity added or removed (e.g., new arrays, removed shading obstructions, etc.)Data merges from different meters types (e.g., if third-party meter data has been merged into an LGate
Frequency of Analysis
The waterfall analysis may take up to 4 weeks to update. This process runs on a 3-4 week cycle across the entire Locus fleet, so the results for a supported site may lag behind the current date by up to 3-4 weeks.
Note: If a site’s location is updated or the site uploads historical data, the waterfall can also take up to 4 weeks to account for the new information.
Explanation of Loss fields
Downtime losses are attributed to times when the system is not producing, but the model predicts an output based on incoming irradiance, and there is not significant snow.
Partial capacity losses
Partial capacity losses identify events such as string outage losses, or when a single inverter goes down on a site with multiple inverters. These losses occur when the system is still producing, but at a reduced capacity. Based on the productivity of the site, the Waterfall identifies step-function losses in site capacity and estimates the associated lost energy.
This bucket attributes losses when objects obstruct incoming radiation from reaching the panels. Using information on sun positioning, array positioning, and site productivity, the Waterfall is able to identify shading objects and estimate the associated lost energy.
Snow cover loss
These losses are attributed to the loss of production due to snow on the arrays. These losses are distinguished from downtime when snow is present and the system is not producing.
This bucket captures losses as a result of dirt, dust, and other environmental particles accumulating on the arrays. Losses of this type are reversible and tend to accumulate slowly. Using changes in the site's productivity and rainfall data, the Waterfall estimates the amount of energy lost to the array being dirty.
Degradation accounts for losses in panel efficiency as a PV system ages. This analysis requires over two years of data in order to accurately quantify degradation losses. Degradation losses occur at a relatively constant pace over the lifetime of the system and are irreversible without equipment replacement. Currently, the Performance Waterfall assumes a loss of 0.5% a year and displays losses in the Degradation bucket when the system deviates from this assumption. Degradation losses will be positive if the system degrades faster than 0.5% and negative if the system degrades slower than 0.5% a year.
Losses that occur when inverter DC input exceeds the inverter AC capacity. The Waterfall uses historical data to infer DC size, AC capacity, and effective tilt & azimuth (blending multiple array orientations if present). It then calculates clipping wherever the AC capacity limits output.
When the differences between measured and modeled energy cannot be completely accounted for by the existing buckets, the remaining losses are labeled “other.” These losses can be attributed to data collections issues (data spikes, comms loss, etc) and small modeling inaccuracies.
VI Waterfall data in the data API
When the VI Waterfall is enabled, if a site has results available, the following data fields will populate in dataavailable:
All of the above fields will be available at daily, monthly and yearly granularities. These data fields will populate in the charting and reporting tools as available data and will also be available in the Locus External API.
Q: How do I gain access to the VI waterfall?
A: Contact your Locus Sales Rep in order to make sure your account has VI enabled and that your sites qualify for the waterfall analysis.
Q: Why is my site not showing degradation losses?
A: Degradation requires two years of clean data to populate.
Q: The sum of all the losses on site do not match the difference between measured and modeled energy.
A: The model used in the VI waterfall is different than the model generated by an on site sensor and available through the API. Currently, we do not display the VI waterfall model through the API or on the platform.
Q: How can some losses be negative?
A: The "Other" and "Degradation" buckets can both be negative.
If the waterfall over-assigns losses to the named buckets, the “Other” bucket can be negative to correct for the difference between measured and modeled energy.
The Performance Waterfall assumes a loss of 0.5% a year and displays losses in the Degradation bucket when the system deviates from this assumption. Degradation losses will be negative if the system degrades slower than 0.5% a year.