Is Your Factory Solar Producing What You Paid For? — Performance Ratio (IEC 61724) & the O&M That Keeps It

A solar system isn't "install and forget" — studies in Thailand find many systems quietly producing 10–20% less than they should, without the owner noticing, due to soiling, inverter faults, or module degradation (PID). Every lost percent is savings you paid for but aren't getting. This guide shows how to measure system health with the Performance Ratio (PR) per IEC 61724, and the O&M needed to protect your output.

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What is the Performance Ratio (PR)?

PR measures how "well" a system converts light into electricity relative to its potential — with weather effects removed (unlike raw kWh, which depends on that day's sun).

PR = actual energy yield (kWh) ÷ the yield expected from the incident light and installed capacity

Per IEC 61724-1, PR runs from 0 to 1:

PR	Meaning
0.80–0.85	Healthy system (a good benchmark for a new install)
0.75–0.80	Normal–fair, room to improve
< 0.75	Abnormal, investigate the cause
< 0.70	Clear problem (heavy soiling / inverter / wiring)

The global average for operating systems is ~0.80 — a good PR in a tropical climate like Thailand is around 0.78–0.85 (high temperatures pull it down somewhat).

Benchmark: Thailand's specific yield

An easier-to-read metric is specific yield = annual energy per installed capacity (kWh/kWp/year).

• Typical Thailand: ~1,400–1,600 kWh/kWp/year (Bangkok ~1,386, Rayong ~1,589 in real studies)
• If your system is clearly below ~1,300, that's a sign something is eating your output.

A quick check: divide your full-year energy by the kWp installed, then compare against the 1,400–1,600 band.

Why output drops — the main causes

Cause	Typical impact	Fix with
Soiling (dust)	3–5%+ (worse in Thai dry season / near factories-farms)	Scheduled cleaning
Shading	Location-dependent, can be large	Layout / trim trees / optimizers
Inverter fault / clipping	High (cuts a whole string)	Monitoring + alerts
PID / LID (module degradation)	1–3%+ cumulative	EL imaging, anti-PID
Hot spot / cell failure	Localized but can spread	IR thermography
High module temperature	~0.3–0.4%/°C above 25°C	Under-panel ventilation
Loose wiring/connectors (DC loss)	Continuous + fire risk	Inspect + retighten

For a deep dive on PID/LID degradation + EL imaging, see PV module degradation PID/LID and EL inspection.

The O&M you need to do

Preventive:

• Clean the panels on a schedule (see the next section)
• IR thermography to find hot spots / dead cells — recommended yearly (drone for large roofs)
• IV-curve testing per IEC 62446-1, compared with the as-installed values
• Inspect inverters + strings — error logs, heat, fans
• Check DC connectors/wiring for loose/burnt points
• A monitoring system tracking PR + alerting when output drops abnormally

Corrective: replace faulty panels/inverters, fix wiring, claim warranty.

How often to clean (and when it pays)

Simple rule: clean when the value of energy lost to dust exceeds the cleaning cost.

• Thailand's rainy season helps wash dust off, but the dry season (Nov–Apr) builds dust fast, especially near industrial estates / roads / farmland.
• A typical factory cleans 2–4 times/year, adjusted to the real soiling rate.
• Use monitoring to catch "PR dropping after no rain" = time to clean (more accurate than a fixed schedule).
• ⚠️ Never use high-pressure water / stiff brushes — microcrack risk; use clean (low-TDS) water + a soft brush.

Monitoring: set a baseline, then watch

Per IEC 61724-1, monitoring systems are graded Class A/B/C by precision (measuring POA irradiance, temperature, energy). What you should have:

• A baseline — expected PR/yield (from a PVsyst model or the first-year result) to compare against
• Track PR monthly — see the downward trend before damage compounds
• Allow for degradation ~0.5%/year as natural decline (separate from a fault)
• Automatic alerts when output falls below expected by X%

Diagnosing a low PR

flowchart TD
  A["PR below expected"] --> B{"Whole system
or some strings?"}
  B -->|"Whole system"| C{"Just after rain stopped
+ not cleaned for a while?"}
  B -->|"Some strings/panels"| D["IR thermography
find hot spots / dead cells"]
  C -->|"Yes"| E["Soiling →
clean the array"]
  C -->|"No"| F{"Inverter showing
errors/clipping?"}
  F -->|"Yes"| G["Repair/reconfigure
the inverter"]
  F -->|"No"| H["IV-curve + check DC wiring
for PID/loss"]
  D --> I["Replace/claim
faulty panels"]

Let Sahawatthanakit keep your system producing

We provide system health checks (PR audits) + O&M contracts for factory solar — PR measured against benchmark, IR thermography, IV-curve, scheduled cleaning, monitoring + alerts — so the system you already paid for delivers its full return (systems we installed and those installed by others).

• Phone: 02-096-2118 / 061-541-6939 / 096-109-4244 (Khun Mam)
• LINE: @406rrgvm
• Email: info@sahawatthanakit1988.com
• Free quote / consultation: click here

Frequently Asked Questions

What Performance Ratio counts as good? A healthy system in Thailand should reach a PR of about 0.78–0.85. Below 0.75, investigate the cause (soiling/inverter/wiring/module degradation). The global average for operating systems is ~0.80.

How do I know my system is underproducing? Compare specific yield (annual kWh ÷ kWp) against Thailand's 1,400–1,600 kWh/kWp/year band, or track PR from monitoring against a baseline. Persistently below expected = something is eating output.

How often should I clean the panels? Typically 2–4 times/year, adjusted to actual dust — more often near industrial estates / roads / farmland. The most accurate approach is to clean when PR drops after a dry spell.

How fast does solar degrade? Quality panels degrade naturally at ~0.5%/year (warranties usually cover ~80–90% at year 25). Much faster decline is abnormal — possibly PID/LID or hot spots.

I already have solar installed by someone else — will you maintain it? Yes — we start with a PR audit to find where output is being lost, then propose a cost-effective O&M plan. It doesn't have to be a system we installed.