Glossary · Basics · Intermediate · Pakistan 2026
Nameplate watts are a laboratory. Derate is the roof.
Derating is the haircut from STC watts to annual AC kWh. Heat raises cell temperature and drops voltage. Dust sits on glass. Strings mismatch. Cables drop volts. The inverter is 97%, not 100%.
People also search derate factor system losses heat loss solar
Key takeaways
- We fold that into 0.78 unless the site is a washed, windy, high-albedo ground mount.
- Our house derate: 0.78 — Default in calculators.
- Clean high mount: 0.80–0.82 — Only if wash is real.
- Dirty + hot + PVC: 0.70 — The Facebook plant.
- If a lender or an engineer wants a site file, we can split derate into temperature, soiling, mismatch, wiring, availability.
What it is
We fold that into 0.78 unless the site is a washed, windy, high-albedo ground mount. A shop that sizes 10 × 645 W × 5 PSH × 1.0 is promising 32 kWh that will not arrive.
In Pakistan 2026
Lahore smog, Multan dust, Karachi film, and Peshawar winter sun each steal differently. The number 0.78 is one honest average so the calculator does not lie in May.
How we spec it
If a lender or an engineer wants a site file, we can split derate into temperature, soiling, mismatch, wiring, availability. For a house quote, one 0.78 is clearer than five fake decimals.
Numbers you can actually use
Street ranges, not a quotation. Confirm the carton the week you book.
| Thing | 2026 number | How to use it |
|---|---|---|
| Our house derate | 0.78 | Default in calculators |
| Clean high mount | 0.80–0.82 | Only if wash is real |
| Dirty + hot + PVC | 0.70 | The Facebook plant |
Temperature in the haircut
Module temp coefficient of power is about −0.29 to −0.34 %/°C for N-type, worse for leftover PERC. Cell temperature of 65 °C is 40 °C above STC. That alone is ~12% down before dust. This is why “latest 650 W” still needs derate, and why PERC leftover is a worse May plant.
Worked example — Lahore
Take a 3.6 kW-class hybrid in Lahore (LESCO, ~5.1 PSH). 6 × 645 W is 3.87 kW DC. Derated yield ≈ 3.87 × 5.1 × 0.78 ≈ 15.4 kWh on a clean day — then smog film and a 6–12 week file. This page (Derating) is the piece of that plant people skip on WhatsApp. If your quote cannot survive this Lahore sentence, it will not survive May. Open the calculator with city set to Lahore, and the lookup map for a stocking dealer — not a green-meter SKU.
Keywords this lesson actually answers
People land here asking derate factor, system losses, heat loss solar. The honest 2026 answers still collapse to: N-type plates with flash, IP65 hybrid with GRID vs LOAD, 51.2 V LFP on CAN, 14 SWG, XLPO, derate 0.78, and net-billing at ~Rs 11 export if you file with LESCO. Everything else on this page is how not to get robbed while buying those things.
Internal links worth clicking before you pay
Size: system sizing · Policy: net-billing · Battery: LFP · Buy: checklist · Shops: near you · City climate: Lahore · Numbers: calculators.
How shops fail this
Yield using STC × PSH × 1
Yield using STC × PSH × 1
No soiling in south Punjab
No soiling in south Punjab
Inverter 99% used as system 99%
Inverter 99% used as system 99%
FAQ — Derating
Is 0.78 too harsh?
Look at your May app vs the quote. Harsh is cheaper than a lawsuit.
Does washing change derate?
A dawn wash in dusty months is the highest-ROI labour on the plant.
Where do I enter derate?
The yield path in the calculator. Do not hide it in a bigger PSH.
Read next
Peak sun hours (PSH)
Peak sun hours are not clock hours of daylight.
glossarySTC (standard test conditions)
STC is a laboratory noon that your roof will never be.
guideTemperature coefficient of power
Hot cells make fewer watts. N-type better than PERC. HJT best-in-class.
guideHow often to wash panels
Dusty belts: more. After smog and after storms.
glossarykW (kilowatt)
kW is how fat the pipe is — not how much you used today.
glossarykWh (kilowatt-hour)
kWh is the unit on your bill — the bucket, not the tap.
Open the calculators Shops near you All lessons
Educational page, September 2026. Not a DISCO filing, not a live quotation, not medical or bank advice. SRO 251(I)/2026 net-billing for new files after 9 Feb 2026.