Solar PV Performance
What is Solar PV Performance?
Solar PV performance is a percentage showing how much of the expected solar generation was actually generated by the solar PV system.
How is Solar PV Performance Is Calculated?
The actual solar generation is retrieved via the equipment on site. The expected solar generation is calculated by combining the physical characteristics of the solar PV system and hyper-specific satellite weather data. The actual generation is then divided by the expected generation and expressed as a percentage. Alerts are generated when the cumulative actual solar generation is less than 80% of the cumulative expected solar generation over the last 7 days. Alerts are resolved when this calculation returns to 80% or greater.
Solar PV Performance Last 7 Days Formula:
Cumulative Actual Solar Generation Over Last 7 Days / Cumulative Expected Solar Generation Over Last 7 Days
Solar PV Performance Last 7 Days Example:
Over the last 7 days, 100kWh of solar generation was reported by the meter on site.
Over the last 7 days, 200kWh of solar generation was expected.
Solar PV Performance Last 7 Days is 50%.
Where can I see more details?
This data is available in more detail by clicking into the site view and going to the Solar PV tab.
In the Solar PV Analytics chart, the actual generation, expected generation, and actual / expected metrics are shown. By toggling the zoom, the scale of the time changes. For example, in the 1-week zoom, these metrics are shown on a day-by-day basis, but clicking the 1-year zoom shows these metrics on a month-by-month basis.
The Solar Generation During Billing Period chart shows the actual generation and expected generation on a 15-minute interval basis.
The Solar PV Performance at my site is below 80%. Is that an issue?
Although performance can vary site-by-site, and daily discrepancies can occur due to imperfect weather data, if the 7-day solar performance goes below 80% there is a very high likelihood of an issue at the site. This can be due to a number of issues, such as an inverter going offline. ETB Monitor will trigger an alert when a site’s solar PV performance dips below the 80% threshold and will resolve the alert when the site’s solar PV performance returns to 80% or greater.
How do I troubleshoot my site’s solar PV performance?
Step 1. Make sure that ETB Monitor has the correct site location.
In the Site Overview tab, you can see the site location. This location is partially used to determine weather conditions at the site, which is then used as part of the formula for determining the expected solar PV generation. If this location is inaccurate, then inaccurate weather data may be being used to calculate the expected solar PV generation. If this is the case, you can update it via the user interface if you have the necessary permissions, or you can contact your ETB account manager with the correct data.
Step 2. Make sure that ETB Monitor has the solar equipment information.
In the Solar PV tab, you can see the specification of the solar equipment on site. This data is also used when calculating the expected solar PV generation. If the equipment here is incorrect, then the expected solar PV generation data being calculated may be inaccurate as a result. If this is the case, you can click the solar array information and edit the details or contact your ETB account manager with the correct data.
Step 3. Determine if lower than expected performance is weather-related.
For a day or two the solar performance percentage and interval charts may decrease due to imperfect weather readings as opposed to issues at the site. Luckily, if this is the case it is easy to determine by looking at the charts provided in ETB Monitor. The way to do this is to look at the recent data and analyze the shape of the actual solar generation and expected solar generation curves. If they are spikey, like the example image below, then this the issue may be weather related, and it may be best to wait for a good solar day.
Step 4: Compare actual generation to expected generation on a recent good solar day.
To find a good solar day, look for when the actual solar generation and expected solar generation curves have a typical solar PV generation shape like the image below. If the shape of each curve is the same on good solar days, but the scale of the actual generation is significantly lower than expected, then there is a high likelihood that there is an issue with the solar equipment on site. If you have entered detailed solar equipment information into ETB Monitor, this can be utilized as well during this comparison. For example, if the peak power output of the actual solar generation on site is consistently 62kW lower than the expected peak power output, and the inverters on site are rated at 62kW, then there is a high likelihood an inverter is offline.