Performance Ratio (PR) is one of the core health metrics shown in the PV Systems table. This article explains what PR measures, how it is calculated, and how to read the three PR-related columns — Ensights PR, Expected PR, and Actual vs. Expected PR — so you can judge at a glance whether a system is performing as it should.

Performance Ratio expresses how effectively a system converts the sunlight it actually receives into electricity. Rather than measuring raw output — which naturally rises and falls with the weather — PR compares actual production against the production that was theoretically possible given the irradiance the site received over the same period.

Because it accounts for available sunlight, PR isolates true system health from environmental variation. It lets you compare a cloudy month against a sunny one, or a small rooftop against a large ground-mount, on equal footing.

PR is expressed as a percentage. A value of 100% would represent a system with zero losses. In practice, healthy systems typically fall between 75% and 85%, with the shortfall reflecting unavoidable real-world losses such as temperature derating, soiling, inverter and wiring losses, module mismatch, and downtime. A PR that drifts well below this range is an early signal that a system needs attention.

PR is the ratio of a system’s actual energy yield to its reference (ideal) yield. The reference yield is derived from the plane-of-array irradiation the system received and the reference irradiance that defines standard test conditions.

Where:

EAC — actual AC energy produced over the period (kWh)

PSTC — installed system capacity at standard test conditions (kWp)

HPOA — plane-of-array (in-plane) irradiation over the period (kWh/m²)

GSTC — reference irradiance at standard test conditions (1 kW/m²)

Because GSTC equals 1 kW/m², the formula is often written in its simplified working form:

The reference irradiance term is what keeps PR a true, dimensionless ratio. Dividing the plane-of-array irradiation by 1 kW/m² converts it into equivalent peak-sun-hours, which then matches the units of specific yield (energy per kWp) — hours divided by hours — producing a clean percentage.

The PV Systems table surfaces performance at a glance through three related columns. Together they show measured performance, the target it is being held to, and the gap between the two.

The PV Systems table, showing the Ensights PR, Expected PR, and Actual vs. Expected PR columns.

Step 1: Open PV Systems from the left navigation menu. The portfolio table appears with one row per system.

Step 2: Read the Ensights PR column. This is the system’s measured Performance Ratio for the selected period, calculated as described above. The value reflects actual, weather-normalized performance.

Step 3: Compare it against the Expected PR column, which is the modeled target the system should achieve under normal conditions.

Step 4: Check the Actual vs. Expected PR column for the gap between the two. A green upward figure means the system is meeting or beating its target; a red downward figure means it is underperforming and may warrant investigation.

Note: If a PR column is not visible, use the column controls in the table toolbar to show, hide, or reorder columns.

Close-up of the three PR columns alongside the period selector.

PR is always calculated over a defined time window. Use the period controls in the table toolbar to change the window the PR columns reflect.

The Period selector and date navigation controls in the table toolbar.

Step 1: Open the Period selector and choose a resolution, such as Daily.

Step 2: Use the arrows or the calendar picker to move to the period you want to review. The PR columns recalculate to reflect the selected period.

Use this table as a quick guide to what each PR column shows and how to interpret it.