Browser-based calculators for monthly O&M reporting — PV plant performance, generation shortfalls, and losses from soiling, downtime, and grid curtailment. No login required. Calculations run in your browser and your inputs are not sent to a server.
Methodology for the core calculators is published on GitHub — formulas, variable definitions, and standards references.
Pick the task you are working on. Each calculator page explains its inputs, how to read the result, and its limitations.
CUF, Specific Yield and Performance Ratio answer different questions. Using the wrong one is a common cause of misleading monthly reports.
| Metric | Formula | What it answers | What it does not tell you |
|---|---|---|---|
| CUF | EAC / (Pref × hours) | How much of the plant's capacity-hours was delivered | Whether a low value is a fault or just a cloudy month |
| Specific Yield (Yf) | EAC / PDC (kWh/kWp) | Output per kWp, so plants of different sizes can be compared | Plant-side efficiency separate from the solar resource |
| Performance Ratio | Yf / Yr | Output relative to the POA insolation actually received | Temperature effects; it is sensitive to sensor accuracy |
| Temperature-Corrected PR | PR adjusted for module temperature | PR comparable across hot and cool months | Other losses such as soiling or clipping |
← Swipe table to see all columns →
Illustrative single-day example: 450 kWh from a 100 kWp plant with 5.5 kWh/m² of POA insolation gives Yf = 4.5 kWh/kWp, Yr = 5.5 h, and PR = 81.8%.
Free calculators that run in your browser, with the formulas published so you can check them.
Open any tool and calculate immediately — no registration or email.
PPAs define CUF against either DC or AC capacity. The CUF calculator accepts both — confirm which one your contract requires before reporting.
Calculations run locally. For the inverter and panel tools, the files you select are read in your browser, not stored on a server.
Built by Aman Yadav — B.Tech Electronics & Instrumentation engineer with 8+ years in solar O&M, including performance monitoring on a 30 MW ground-mounted plant.
Practical guides and analysis for solar plant performance and O&M engineering.
Which loads make up auxiliary power consumption in a utility-scale solar plant, where to meter it, and how it changes net energy, PR and CUF — with field photos, formulas and monthly reconciliation checks.
Read Full ArticleCommon questions about solar plant performance metrics and our calculators.
CUF measures how much energy a solar plant actually generates relative to its rated capacity over a given period, so it is strongly influenced by the solar resource available at the site. PR compares actual generation with the expected generation based on measured plane-of-array irradiance and the installed PV capacity, making it more suitable for assessing plant performance under the solar resource actually received.
A good Performance Ratio (PR) depends on the plant design, location, operating conditions, and calculation methodology. As a general indication, a PR above 80% often indicates strong performance with losses within expected limits. A PR between 70% and 80% can be normal for many commercial solar plants, depending on site conditions and system losses. A PR below 70% may indicate significant performance losses and should trigger a structured loss analysis to identify the cause.
Performance Ratio (PR) naturally drops in summer because module temperatures rise significantly above the 25°C Standard Test Conditions (STC) reference. Crystalline silicon modules typically lose about 0.29–0.45% of power per °C above 25°C depending on technology (TOPCon and HJT at the low end, older polycrystalline at the high end), so a cell temperature of 55°C can reduce output by roughly 9–13%. This is expected thermal behavior — not a fault. Use Temperature Corrected PR for a fairer comparison across seasons.
Always use POA (Plane of Array) insolation for accurate PR calculation. GHI (Global Horizontal Irradiance) measures sunlight on a flat horizontal surface, but your PV modules are tilted. POA represents the actual irradiance hitting the module surface and is the standard required by IEC 61724-1. Using GHI changes the result. For tilted arrays GHI is usually lower than POA, which gives a higher PR; the difference depends on tilt, latitude, tracking and season, and it can reverse in some seasons.
Soiling analysis quantifies how much module efficiency improves after cleaning, using paired power and irradiance readings taken before and after a cleaning event. That measured loss can inform cleaning decisions, but the appropriate threshold depends on local conditions, cleaning costs, and electricity revenue.
NMGG (Net Minimum Guaranteed Generation) is the minimum annual AC energy output a plant is contractually obligated to deliver under its PPA, typically measured at the grid interconnection point after auxiliary consumption. Falling below this threshold triggers financial penalties or deemed generation adjustments depending on the contract structure. In some contracts, monthly NMGG targets are derived by distributing the annual figure proportionally across months based on expected POA insolation — so months with higher irradiance carry higher targets, reflecting the plant's actual generation potential through the year.
The calculators implement the formulas published in our methodology document on GitHub. Results are limited by input quality: calibrated sensors, correct POA measurement, and clean inverter data. Metrics that are not defined in IEC 61724-1 are labeled as custom on their calculator pages.