---
title: "Inverter low-performance detection"
url: "https://ensights.productfruits.help/en/article/inverter-low-performance-detection"
language: "en"
last_updated: "2026-10-01T08:34:18.507Z"
---

# Inverter low-performance detection

The **Inverter Performance** alert flags an inverter that produces less than it should. This page explains how enSights decides that, why a healthy inverter used to be flagged, and how to make the alert trustworthy on your sites. It is for O&M teams and asset managers who act on inverter alerts or need to explain one.

## The problem it solves

Inverters on the same site often share an AC rating but have different amounts of DC behind them. Take a site with 16 inverters, all rated 125 kW AC: six have 11 strings, nine have 10, and one has 9. On a raw AC power graph, a healthy inverter with fewer strings and a genuinely faulty one both run below the pack, and nothing on the graph tells you which is which.

![Raw AC power of 16 inverters over one day: a healthy 9-string inverter and a faulty inverter both run below the pack](https://cdn-assets.productfruits.com/1f533750-5e80-4dfc-af1c-8e9b700eaad3)

## How detection works

1.  Each inverter's output is **normalized**: divided by its capacity, so inverters of different sizes can be compared.
2.  The **peer reference** is the average normalized value across the site's inverters.
3.  Each inverter's **deviation** = (its normalized value ÷ peer reference − 1) × 100.
4.  The alert opens when the deviation is below the threshold set on the alert rule (for example −10%).

The steps are the same at every level. Only what the output is divided by changes, and that is what decides whether the alert can be trusted.

## DC capacity vs AC capacity

| Basis | Output is divided by | Used when |
| --- | --- | --- |
| **DC capacity** | Each inverter's DC capacity (kWp) | Every inverter on the site has a DC capacity entered. |
| **AC capacity**<br>(fallback) | Each inverter's AC capacity | Even one inverter on the site has no DC capacity. Marked as lower confidence. |

The choice is **all-or-nothing per site**: a site never compares one inverter on DC and its neighbour on AC. Each system shows the basis it is using, so any alert can be explained.

### Divided by AC capacity: two flags, one wrong

The 9-string inverter (7) has about 10% less DC behind the same 125 kW rating, so on an AC basis it looks like a fault. It is healthy, and this false alert arrives every day for the life of the site.

![Inverters normalized by AC capacity: two inverters flagged below the threshold, one of them healthy](https://cdn-assets.productfruits.com/cf401291-5c2b-4bc1-a042-bd71f445d9a6)

### Divided by DC capacity: one flag, the real one

Output and DC capacity scale together, so dividing one by the other cancels out the difference in string count. Every healthy inverter lands on the same value, inverter 7 drops out of the alert, and inverter 12 stays flagged because its problem is real.

![Inverters normalized by DC capacity: only the faulty inverter is flagged](https://cdn-assets.productfruits.com/0a26a80e-b5a5-4cca-89db-022ad9eb1dc2)

## Simple and Advanced detection

| Method | Each inverter is compared with | Best for |
| --- | --- | --- |
| **Simple** | The other inverters on the site, after normalizing each by DC capacity. | Any site with DC capacities entered. No weather inputs needed. |
| **Advanced** | Its own share of the site's expected weather-adjusted curve, shared out by DC capacity, after clipped energy has been added back. | Sites with irradiance and a weather-adjusted calculation. Also catches the whole site sagging together, which a peer comparison can't see. |

An inverter's share of the site curve is: site Expected WA Power × (inverter DC capacity ÷ total DC capacity). See **Weather-adjusted calculation: Simple and Advanced** for how the site curve is built.

### Clipping

When the panels can produce more than the inverter's AC limit, output pins flat at the ceiling around midday. Energy is lost, but the inverter is healthy. Compared on raw energy, it would look like the worst performer on the site.

![Clipping day: measured AC power flat at the inverter limit while the expected curve continues above it, with the clipping loss shaded](https://cdn-assets.productfruits.com/55507f68-146a-49e7-a085-917630cdd29d)

Advanced detection adds the clipped energy back before comparing:

-   **Clipping loss** = the sum, over the clipped intervals, of how far measured power fell below expected.
-   **Potential energy** = measured energy + clipping loss.
-   The inverter is judged on potential energy ÷ DC capacity.

Clipping can only be found in the 15-minute data, not in daily totals: over a whole day, intervals above and below expected cancel out and the clipping disappears.

## The alert rule

The threshold, severity, delay, SLA and recipients are set on the **Inverter Performance** (`INVERTER_LOW_PERFORMANCE`) code in the system's **Edit → Alerts Management**.

![Alerts Management with the Inverter Performance alert rule: threshold, severity, alert delay, SLA and recipients](https://cdn-assets.productfruits.com/2dc304a6-cf6e-4507-9fe4-5ce2599b38fd)

## How to

### Stop a healthy inverter being flagged every day

1.  Open the system's inverter settings and check that every inverter has a DC capacity.
2.  Fill in any that are missing. From then on the site is compared on DC capacity, and a difference in string count no longer triggers the alert.

### Explain why an inverter was flagged

1.  Check which basis the site is on. On AC capacity, a structural DC difference can still look like a fault.
2.  On a hot, sunny day, check whether the inverter was clipping. Advanced detection allows for this; Simple doesn't.
3.  Open the inverter on the Analysis graph and compare it with its neighbours for the alert's date.

## Notes

-   **Night is not underperformance.** Zero irradiance never counts against an inverter.
-   **Single-inverter sites** can't be compared with peers. The screen says so instead of showing an empty result.
-   **The basis can change between periods**, for example after you fill in missing DC capacities. The change is shown, not applied silently.
-   **The method is never switched for you.** If a system's inputs change later, enSights asks before re-evaluating.
-   The detection method is being rolled out account by account. If you don't see it, contact your enSights representative.