Calculation Methodology for Kindastuff Solar Analytics

Capacity Utilization Factor (CUF / PLF)

Purpose. Generation as a percentage of the theoretical maximum if the plant ran at rated capacity for every hour of the period.

Formula.

CUF (%) = [ E_AC / (P_ref × T) ] × 100

T = Days × 24   (hours in the analysis period)

Inputs / output. E_AC (kWh), P_ref (kWp or kW), period length (days) → CUF (%).

Reference. IEC 61724-1:2021 §3 (Terms and Definitions) and §7 (Performance Indices), Final Yield §7.3. Advisory basis; extended below.

Convention and caveats. IEC 61724-1 defines P_o as DC capacity, but many PPAs (SECI standard documents, CERC regulations) define CUF against contracted AC capacity. This calculator accepts both — label your report accordingly; the same plant produces different CUF values under each convention. CUF is a summary metric: a low value does not identify the cause, and it conflates irradiance variability with plant-side losses. Review alongside PR, irradiance, and availability. Solar CUF (typically ~15–25%) is not comparable to thermal PLF (70–90%) because operating hours differ fundamentally.

Open the CUF / PLF calculator · Detailed source (§1)

Degradation & Insolation Corrected CUF

Purpose. CUF normalised for module aging and for irradiance that deviates from design-year assumptions — for fair comparison of actual output against a degraded plant's expected output under actual irradiance.

Formula.

Step 1  P_DC_corrected = P_DC_nameplate × (1 − Da/100)^n

Step 2  SF = H_POA_actual / H_POA_design

Step 3  CUF_corrected (%) = [ E_AC / (P_DC_corrected × SF × T) ] × 100

Inputs / output. E_AC, P_DC_nameplate, uniform annual degradation rate (Da), years since commissioning (n), actual and design-year POA insolation → corrected CUF (%).

Reference. IEC 61724-1:2021 §4 and §7; degradation rates per IEC 61215-1:2021 long-term characterisation and Jordan & Kurtz (2013).

Convention and caveats. This corrected variant uses DC capacity only (kWp) — the conventional CUF tool accepts DC or AC to suit PPA conventions. Typical crystalline-silicon degradation is 0.4–0.7%/yr, applied uniformly here. Accumulated degradation reaches roughly 2–3.5% after five years, so comparing current CUF to the original design target without correction shows apparent underperformance that is simply expected aging.

Open the calculator · Detailed source (§2)

Specific Yield (Final Yield)

Purpose. Net AC energy per unit of installed DC capacity — normalises generation by plant size.

Formula.

Y_f      = E_AC / P_DC                (kWh/kWp)

Y_f_daily = E_AC / (P_DC × N)          (kWh/kWp/day)   N = days in period

Inputs / output. E_AC (kWh), P_DC (kWp), N (days) → yield (kWh/kWp; or per day).

Reference. IEC 61724-1:2021 §7.3. Standard-defined (system performance index, not a loss parameter).

Convention and caveats. Reflects both resource and system losses — it does not isolate plant-side efficiency from irradiance. When comparing two plants, confirm irradiance conditions are equivalent before concluding a performance difference. Typical Indian ground-mount fixed-tilt range: ~3.2–5.0 kWh/kWp/day, indicative only.

Open the calculator · Detailed source (§3)

Reference Yield

Purpose. In-plane energy available to the array, expressed as equivalent peak sun hours.

Formula.

Y_r       = H_POA / G_STC              (hours)
Y_r_daily = (H_POA / G_STC) / N        (hours/day)

G_STC = 1 kW/m²  (fixed constant)

Inputs / output. H_POA (kWh/m²), N (days) → reference yield (peak sun hours).

Reference. IEC 61724-1:2021 §7.1. Standard-defined (resource parameter).

Convention and caveats. This characterises what the sun provided, not plant performance. It is the denominator of Performance Ratio. POA must be measured at the array's actual tilt/azimuth — substituting GHI introduces a seasonal systematic error (see §5 Instrumentation).

Open the calculator · Detailed source (§4)

Performance Target Index (PTI)

Purpose. Compares actual daily Specific Yield against the expected yield implied by irradiance and an anticipated PR.

Formula.

PTI = Y_f_daily / (Y_r_daily × PR_expected)

PR_expected entered as a percentage (e.g. 55.78) and converted internally.

Inputs / output. Y_f_daily (kWh/kWp/day), Y_r_daily (h/day), PR_expected (%) → PTI (dimensionless).

Interpretation. <0.80 underperformance; 0.80–1.20 normal; >1.20 overperformance or unrealistic inputs (verify the PR assumption).

Caveats. The result is entirely dependent on the accuracy of PR_expected — an optimistic assumption will flag underperformance on a healthy plant. Internal diagnostic flag only; never for PPA compliance.

Open the calculator · Detailed source (§5)

Capacity-Based Performance Ratio (PR)

Purpose. The standard, most widely used plant performance index — actual output versus the reference yield from measured POA irradiance, normalised to DC capacity.

Formula.

PR = Y_f / Y_r

PR (%) = [ E_AC / (P_DC × H_POA / G_STC) ] × 100

G_STC = 1 kW/m² (fixed, non-adjustable)

Inputs / output. Energy generated (kWh), plant DC capacity (kWp), POA insolation (kWh/m²) → PR (%).

Reference. IEC 61724-1:2021 §7.5. Standard-defined.

Output flags. PR >96% → “Suspiciously high — verify data quality.” PR >100% → “Statistical error — physically impossible.”

Worked example. 450 kWh ÷ 100 kWp ÷ (5.5 kWh/m² ÷ 1 kW/m²) → (4.5 / 5.5) × 100 = 81.8%.

Caveats. Does not correct for temperature (use Temperature-Corrected PR for that). Highly sensitive to POA sensor accuracy. In DC-oversized plants, clipping suppresses PR even when the plant is working as designed. Best for trend analysis within one plant; cross-plant comparison requires identical capacity conventions, sensor placement, and time-alignment.

Open the calculator · Detailed source (§6)

Efficiency-Based Performance Ratio (PR)

Purpose. PR computed from module active area and rated efficiency instead of nameplate DC capacity — an independent check on the capacity-based figure.

Formula.

P_eff   = A_total × η_module × G_STC

PR (%)  = [ E_AC / (P_eff × H_POA / G_STC) ] × 100

which expands to:
PR (%)  = [ E_AC / (A_total × η_module × H_POA) ] × 100

Inputs / output. Energy generated (kWh), POA insolation (kWh/m²), total active module area (m²), rated module efficiency (%, validated 10–40) → PR (%).

Reference. IEC 61724-1:2021 §7.5 (algebraic rearrangement). Standard-informed.

Caveats. Total active area must represent generating surface only — including frame borders or spacing inflates it and suppresses PR. Useful where nameplate capacity is uncertain but module area and efficiency are known.

Open the calculator · Detailed source (§7)

Instantaneous Performance Ratio (PR)

Purpose. Real-time PR from SCADA power and irradiance readings — for dashboards and fault detection.

Formula.

PR_instantaneous (%) = (P_AC / P_DC) × (G_STC / G_POA) × 100

G_STC = 1000 W/m² (fixed, non-adjustable)

Inputs / output. AC power (kW), plant DC capacity (kWp), POA irradiance (W/m², hard-blocked outside 200–1361) → PR (%).

Reference. IEC 61724-1:2021 §7.5 (power form). Standard-defined.

Validation. Irradiance <200 W/m² is blocked (inverter efficiency is non-linear and SNR degrades). >1361 W/m² is blocked (above the solar constant). AC power > DC capacity is blocked. PR >95% flags suspicious; >100% flags error.

Caveats. Highly volatile — never use as a plant KPI; cloud transients, ramp delays, and sensor noise cause large, meaningless swings. Time-alignment of power and irradiance is critical (a 1-minute offset misleads during changing irradiance). DC-oversized plants clip at high irradiance, suppressing PR.

Open the calculator · Detailed source (§8)

Temperature-Corrected Performance Ratio (PR)

Purpose. PR normalised to 25°C module temperature — answers “what would PR have been at STC temperature?”, enabling fair seasonal comparison.

Formula.

Step 1  PR_raw = E_AC / (P_DC × H_POA / G_STC)

Step 2  temperatureCorrection = 1 + (γ / 100) × (T_module − T_STC)

Step 3  PR_tc = PR_raw / temperatureCorrection

γ = module power temp. coefficient (%/°C, negative)
T_STC = 25°C (fixed)

Inputs / output. Energy generated, DC capacity, avg module temperature (°C, validated −40 to 85), POA insolation, and γ (validated −0.65 to −0.15 %/°C) → corrected PR (%).

Reference. IEC 61724-1:2021 Annex B. Standard-defined method.

Directional behaviour. Above 25°C the correction denominator is <1, so PR_tc > PR_raw — it restores the thermal portion of apparent loss. Below 25°C it removes the cold-weather boost. If the denominator reaches ≤0, the calculation is blocked.

Output flags (applied to PR_tc). PR_tc ≥96% → “Suspicious PR — verify input data quality.” PR_tc >100% → “Statistical error — physically impossible; check inputs.”

Caveats. Uses average module temperature; because irradiance and temperature are correlated, precise work should correct interval-by-interval (15-min/hourly) before aggregating. The linear γ model is standard practice but approximate. Using the wrong module's γ biases the result. This removes the aggregate thermal effect only — it does not isolate inverter thermal derating or inter-row gradients. Always source γ from the installed module's datasheet.

Open the calculator · Detailed source (§9)

Soiling Analysis

Purpose. Quantifies the efficiency penalty from soiling using paired pre-clean / post-clean power and irradiance readings.

Formula.

Per-sample efficiency:
η_sample (%) = (P × 1000) / (G × A) × 100

Soiling ratio (literature form):
SR = P_soiled / P_clean

Overall efficiency (arithmetic mean):
Overall (%) = Σ η_sample / n

Derived soiling loss (percentage points):
Loss (pp) = Post-Clean Efficiency − Pre-Clean Efficiency

Derived relative soiling loss:
Relative loss (%) = (Post-Clean − Pre-Clean) / Post-Clean × 100

The calculator reports the pre-clean and post-clean efficiency figures; the loss values above are derived from them. Percentage points and relative percentages are not interchangeable — state which one you are quoting.

Inputs / output. Plant active area (m²), rated module efficiency (%), and up to 20 pre-/post-clean power–irradiance pairs → pre-clean and post-clean efficiency (%), per-sample bar chart. Power readings <0.3 kW are rejected.

Reference. IEC 61724-1:2021 (soiling as a loss category) and Micheli et al. (2021), DOI 10.1002/pip.3441.

Caveats. Measures soiling only at the cleaning event — it is not a continuous soiling rate. Irradiance normalisation mitigates, but does not eliminate, temperature differences between readings. Sample efficiencies are cross-validated against rated module efficiency to catch impossible results. For reliable data, take pre/post readings close in time, above ~400 W/m², avoiding cloud transients, with the same instrument and connection points.

Open the calculator · Detailed source (§10)

Solar Inverter Efficiency Dashboard

Purpose. DC-to-AC conversion efficiency per inverter from time-stamped field data, with statistics, charts, and a record explorer. Isolates the inverter stage only.

Formula.

η (%) = (P_AC / P_DC) × 100

Energy (trapezoidal integration):
Eᵢ = ((Pᵢ + Pᵢ₊₁) / 2) × Δt

Inputs / output. CSV/Excel with Timestamp, Inverter, DC Power, AC Power (≤5 MB, ≤1,000 rows, ≤5 inverters) → per-inverter mean/median/std-dev/min/max η, integrated DC/AC energy, plant summary, diagnostic charts.

Reference. IEC 61683:1999 (efficiency measurement principle; the basis for Euro-eta / CEC-weighted figures). Field efficiency is complementary to — not the same as — datasheet weighted efficiency.

Caveats. DC and AC columns must share the same unit (no auto-conversion; a unit mismatch is the most common cause of impossible results). Energy accuracy depends on evenly spaced timestamps — logger gaps silently understate energy (treat as a lower bound). A high standard deviation signals inconsistent conversion (intermittent string faults, loose DC connections, thermal derating cycling), not uniform degradation. Below 80% at rated load suggests a fault; below 50% is almost always a data problem; low efficiency in the morning/evening is normal.

Open the calculator · Detailed source (§11)

Solar Panel Efficiency Calculator

Purpose. Module-level STC, operating, and temperature-corrected efficiency, expected output, and a Module PR health index — for single modules, up to 10 in comparison, or a SCADA CSV batch.

Formulas.

A       = Length × Width                                  (module area, m²)
η_STC   = [ P_rated / (A × G_STC) ] × 100                 (%, G_STC = 1000 W/m²)

Cell temperature — NOCT model:
  T_cell = T_amb + G_total × ((NOCT − 20) / 800)

Cell temperature — Faiman model:
  T_cell = T_amb + G_total / (U0 + U1 × WS)               U0=29.0, U1=6.9

Cell temperature — back-of-module RTD:
  T_cell = T_mod + (G_total / 1000) × ΔT_cond             ΔT_cond=3°C default

Effective irradiance (bifacial):
  G_total = G_front × (1 + BG/100)
  G_total = G_front + (G_rear × φ)                        φ default 0.70

Operating efficiency:
  η_op = [ P_measured / (A × G_total) ] × 100

Temperature-corrected efficiency:
  η_tc = η_op / [ 1 + (γ/100) × (T_cell − 25) ]

Thermal loss:
  Thermal Loss (%) = −γ × (T_cell − 25)

Expected output:
  P_expected = P_rated × (G_total/1000) × [ 1 + (γ/100) × (T_cell − 25) ]

Module PR:
  Module PR (%) = (P_measured / P_expected) × 100

Inputs / output. Module dimensions/area, rated power, NOCT, γ, irradiance, ambient/module temperature, wind speed, measured DC power, optional bifacial parameters → η_STC, η_op, η_tc, thermal loss, P_expected, Module PR.

Reference. IEC 61215-1:2021 (STC, NOCT procedure) and IEC 61730 (operating limits). Faiman (2008) cell-temperature model; defaults consistent with pvlib open-rack glass-polymer values.

Validation highlights. STC efficiency >40% is hard-blocked (almost always millimetres entered instead of metres) and <10% is warned. Measured power >1.5× nameplate is blocked (cloud-edge spikes only justify ~1.15×, which is a warning). Operating efficiency >1.3× the module's own η_STC is blocked. γ magnitude must be 0 < |γ| ≤ 0.60 %/°C; magnitudes below 0.10 or above 0.45 warn. Wind speed <0 or >50 m/s is blocked (>20 m/s warns). Module temperature outside −40–100 °C warns and the row is retained; irradiance >1500 W/m² warns. Irradiance <50 W/m² is excluded (night filtering); SCADA rows with negative irradiance/power are set to 0 with a warning.

Caveats. Module-level, not plant-level — Module PR is not IEC 61724-1 plant PR. Not a substitute for IEC 61215/61730 certification testing or for yield-simulation software.

Open the calculator · Detailed source (§12)

Solar String Current Deviation Calculator

Purpose. Peer-group screening of DC string currents within the same combiner box / MPPT channel, flagging strings that warrant field inspection. A screening tool, not a diagnostic instrument.

Formulas.

Group reference (choose one):
  I_ref = median(I_active)          (Active Median, default)
  I_ref = mean(I_active)            (Active Mean)
  I_active = strings with current > 0.05 A

Spread:
  σ  = √[ Σ(Iᵢ − Ī)² / (n_active − 1) ]     (Bessel correction)
  CV = (σ / Ī) × 100

Method A — fixed percentage band (default ±5%):
  ΔI (%) = ((Iᵢ − I_ref) / I_ref) × 100

Method B — Modified Z-Score via MAD:
  MAD = median(|Iᵢ − activeMedian|)
  M   = 0.6745 × (Iᵢ − activeMedian) / MAD

  MAD fallback (when MAD collapses to 0):
  MAD_fallback = 0.8453 × MeanAbsoluteDeviation

Energy loss estimate:
  δᵢ = max(0, (I_ref − Iᵢ)/I_ref)      (0-current strings → δ = 1.0)
  E_healthy = P_string_STC × PSH × PR  (PR fixed 0.80)
  E_daily_loss = Σ δᵢ × E_healthy
  E_annual_loss = E_daily_loss × 365
  Revenue_loss = E_annual_loss × tariff

Inputs / output. Group ID, String ID, current (required); voltage, timestamp (optional). Manual entry or CSV/TSV. Outputs reference current, CV, confidence rating, per-string deviation and Modified Z-Score, status badges, recommended field action, energy/revenue impact, and CSV/JSON export.

Reference. IEC 62446-1 (string current verification); robust statistics per Iglewicz & Hoaglin (1993). Kindastuff screening thresholds.

Validation / thresholds. Current >45 A hard-blocked; >25 A warned (Y-harness/bifacial?). ≤0.05 A treated as inactive (“check fuse”), excluded from the baseline; negatives flagged as polarity issues. Duplicate String IDs in a group are rejected. Default ±5% band (watch begins at ±3%); MAD method default threshold 3.5 (watch at |M|=2.1).

Caveats. Comparisons are valid only between strings of the same module model, series count, tilt/azimuth, and tracker position. Readings at low irradiance (<~200 W/m²), during cloud transients, or with tracker movement are unreliable. Equal current does not prove equal energy (voltage and temperature matter). Uses a fixed PR of 0.80 for loss estimation. The PSH normalisation deliberately avoids overstating losses (noon-deficit × 10 h would overstate by 40–70%) — it remains an operational estimate, not a PVsyst-equivalent simulation. Confirming any fault requires physical testing (clamp meter, Voc, I-V trace, thermal imaging, insulation resistance).

Open the calculator · Detailed source (§13)

Solar Insolation — POA Back-Calculator

Purpose. Back-calculates plane-of-array (POA) insolation from measured plant energy output, using two independent back-calculations that are cross-validated against each other. Intended for cases where a direct POA sensor reading is unavailable or suspect.

This is an estimation tool, not a measurement. The result is derived from energy output and inherits every assumption embedded in the PR and module efficiency inputs. It is directional, not auditable, and is not a substitute for calibrated pyranometer or reference-cell data.

Standard reference. Both methods are algebraic rearrangements of IEC 61724-1:2021 relationships — the capacity method inverts the Performance Ratio definition (§7.5); the area method inverts the efficiency-normalised PR form (§7.5). No new formulas are introduced.

Formulas.

G_STC = 1 kW/m²   (= 1000 W/m², fixed physical constant)

Method 1 — Capacity basis:
    H_POA_capacity = (E_AC / P_DC) × (G_STC / PR)

Method 2 — Area basis:
    H_POA_area     = E_AC / (A_total × η_module × PR)

Cross-validation:
    difference (%) = |H_POA_area − H_POA_capacity| / H_POA_area × 100

Accepted result (difference ≤ 25%):
    H_POA = (H_POA_capacity + H_POA_area) / 2

Inputs.

Both PR and η_module are entered as percentages and converted to decimals internally. G_STC is fixed at 1 kW/m², consistent with IEC 61724-1 and every other PR calculator on this site.

Method. The two methods reach the same quantity from different inputs. Method 1 uses P_DC, a nameplate value from commissioning documents. Method 2 uses module area and efficiency, physical and datasheet values. If both agree, the capacity, area, and efficiency inputs are mutually consistent with the reported energy; if they diverge beyond 25%, at least one input is inconsistent and no result is returned.

Cross-validation.

Worked example

E_AC = 48,000 kWh   P_DC = 1,000 kWp   A = 5,000 m²
η_module = 19%      PR = 80%          G_STC = 1 kW/m² (fixed)

Method 1: H_POA_capacity = (48,000 / 1,000) × (1 / 0.80)
                         = 48 × 1.25 = 60.00 kWh/m²

Method 2: H_POA_area     = 48,000 / (5,000 × 0.19 × 0.80)
                         = 48,000 / 760 = 63.16 kWh/m²

Difference = |63.16 − 60.00| / 63.16 × 100 = 5.0%  → within tolerance

Result: H_POA = (60.00 + 63.16) / 2 = 61.58 kWh/m²
        Insolation POA = 61.58 kWh/m²

Convention and caveats.

• Capacity basis must match PR. If PR is defined on DC capacity, P_DC must be DC capacity; mixing a DC capacity with an AC-based PR gives a wrong result.
• Period alignment. The energy and the assumed PR must cover the same period — do not pair a monthly energy figure with an annual PR.
• Within-tolerance disagreement is not surfaced. Inside the 25% band the two values are silently averaged; a 15% disagreement already signals meaningful input inconsistency but is not flagged. Verify inputs independently.
• Agreement is not proof of accuracy. Two methods can agree within 25% while both are wrong — for example if capacity, area, and efficiency are scaled incorrectly relative to each other.
• Not a substitute for measurement. Do not use the back-calculated value in place of measured POA insolation for PR calculations, performance audits, or contractual reporting.
• No physical upper bound. The tool does not cap the output. Back-calculated daily values well beyond a site's plausible range (typically 3.0–7.5 kWh/m²/day) indicate input errors.
• Use in-field efficiency. Nameplate module efficiency overstates the area basis for a degraded array and suppresses the area-method result.

Open the calculator · Detailed source

Documentation in progress

The following calculators are live but their full methodologies are not yet published. No formula is documented here until it is verified.

• Plant & Grid Generation Loss
• Plant & Grid Availability
• NMGG Calculator