Guides · Faisalabad, Lahore, Punjab
Solar Panel Efficiency: What the Percentage Means
Short answer
Solar panel efficiency is the share of sunlight falling on the panel that it turns into electricity under standard test conditions. A 22% panel converts about 22% of the 1,000 watts of sunlight per square metre used in the test into electrical power, so it gives about 220 watts per square metre of panel. Efficiency tells you how much power fits on your roof. It does not mean a higher-efficiency panel produces more units per kW installed: a 600 W panel at 21% and a 600 W panel at 23% make similar energy, and the more efficient one is simply smaller.
Whether you call it a solar panel or a solar plate, the efficiency figure is printed on its datasheet. Here is how to read it and when it should change your choice.
How the percentage is calculated
Every datasheet efficiency figure comes from the same simple formula:
Efficiency = rated power (Pmax) ÷ (panel area × 1,000 W/m²)
The 1,000 W/m² is the sunlight level used in the Standard Test Conditions (STC), along with a cell temperature of 25°C.
You can check any datasheet yourself. Using round illustrative numbers for a made-up 600 W panel measuring 2.38 m by 1.134 m:
- Area = 2.38 × 1.134 ≈ 2.70 m²
- Sunlight on that area in the test = 2.70 × 1,000 = 2,700 W
- Efficiency = 600 ÷ 2,700 ≈ 22.2%
If your own calculation is far from the datasheet figure, check that you have the right dimensions and model code. Our guide on how to read a solar panel datasheet explains the other lines on the sheet.
Panel efficiency
Higher efficiency
More watts per square metre
Same watts
Same output, whatever the efficiency
Cell efficiency vs module efficiency
You may see two different numbers in brochures and news:
- Cell efficiency is measured on a single solar cell. Record laboratory cells and the best production cells reach high figures, and these are what headlines usually quote.
- Module efficiency is measured on the finished panel, over its whole outside area. That area includes gaps between cells, the frame and the edges, which make no power.
Module efficiency is therefore lower than the cell figure behind it. When you buy, compare module efficiency only. A brochure quoting cell efficiency is not wrong, but it is not comparable with another maker's module figure.
Typical efficiency by panel type
These are broad, generic ranges for commercial modules, for orientation only.
| Panel type | Typical module efficiency | Status in Pakistan |
|---|---|---|
| Polycrystalline | About 15 to 18% | Old technology, largely phased out |
| P-type mono PERC | About 20 to 21.5% | Older stock still found |
| N-type TOPCon | About 22 to 24% | Mainstream today |
| N-type back-contact (BC) | About 23 to 25% | Premium, high-efficiency end |
What these cell types are is covered in N-type vs P-type and bifacial panels, and how the newer designs compare in TOPCon vs HJT vs back-contact panels.
The common misunderstanding: efficiency and units
Many buyers assume a 23% panel will produce more electricity than a 21% panel. Per kW installed, it mostly will not.
A 10 kW array is 10 kW whether it is built from 21% or 23% panels. Its daily output depends mainly on:
- sunlight at your location and season;
- panel temperature, set by heat and airflow (the temperature coefficient matters here; see solar panels in Punjab summer heat);
- tilt, direction and shading;
- dust, wiring and inverter losses.
The higher-efficiency array just takes up less roof. Small differences in output between panel types usually come from temperature behaviour, low-light behaviour or bifacial gain, not from the efficiency percentage itself. For realistic output figures, see how many units a 5, 10 or 15 kW system produces in Punjab.
When panel efficiency really matters
Small or crowded roofs
On a 5 or 10 marla house with water tanks, a stair tower and parapet shade, roof space is often the limit. Here a higher-efficiency panel lets you fit more kW in the usable area.
For example, if you want 10 kW and your panels are 20% efficient, you need about 50 m² of panel surface (10,000 W ÷ 200 W/m²). At 22%, you need about 45 m². That difference of roughly 5 m² (about 54 sq ft) can be the space between two more panels or none, before walkways and gaps are added. See solar panel size in feet and solar system size for 5 marla, 10 marla and 1 kanal houses.
Large roofs and factory sheds
On a large, open factory roof, space is rarely the limit. There, price per watt usually matters more than efficiency, and a mainstream N-type panel may give more kW for the same budget. See solar panel prices per watt and today's solar panel price in Pakistan.
Structure and handling
A more efficient panel of the same wattage is smaller and often lighter, so it needs fewer structure members per kW. Very large high-wattage panels need more care on the roof and a structure designed for their size.
Efficiency changes with heat and age
The datasheet figure is measured at 25°C cell temperature. On a Punjab roof in June, cells run far hotter, so every panel works below its rated efficiency at midday. A panel with a temperature coefficient closer to zero loses less.
Efficiency also falls slowly over the years as panels degrade. Manufacturers state the expected decline in their performance warranty. Some panels also lose power early through effects such as LID and PID, explained in PID and LID degradation, and long-term ageing is covered in solar panel lifespan.
Panel efficiency vs system efficiency
Panel efficiency is only one link in the chain. The energy reaching your appliances also depends on cable losses, dust, temperature and the inverter. Inverter figures are a separate topic, covered in inverter efficiency ratings explained. A well-designed system with mainstream panels often outperforms a poorly designed one with premium panels.
How Solar Works Pakistan chooses panels
Our in-house engineers start from your roof layout, structure, budget and load, then compare panels on efficiency, price per watt and heat performance together. Each quotation names the exact brand, model and wattage, with the datasheet on request. We supply panels from LONGi, JinkoSolar, Canadian Solar, JA Solar, AIKO, Cora Dawn and Jasco; see our brands page. Panels carry their manufacturer's warranty per product, and our structures carry a 3-year structure warranty.
Get today's price or a free site survey
Not sure whether a high-efficiency panel is worth it on your roof? Send us roof photos and your bills, or book a site survey.
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM daily
We serve customers throughout Punjab, with site surveys normally free. See our Faisalabad and Lahore pages, or contact us.
Frequently asked questions
What is a good solar panel efficiency today?
Mainstream N-type TOPCon panels typically state module efficiencies in the low twenties, and back-contact panels a little higher. Check the exact model's datasheet and compare module efficiency, not cell efficiency.
Does a higher-efficiency panel produce more units?
Per kW installed, not much. A higher-efficiency panel gives more watts per square metre, so you fit more kW on the same roof. Units per kW depend mainly on sunlight, heat, direction, shading and dust.
How do I calculate solar panel efficiency?
Divide the panel's rated power by its area in square metres multiplied by 1,000. For example, a 600 W panel with an area of 2.7 m² gives 600 ÷ 2,700, or about 22%.
Why is cell efficiency higher than panel efficiency?
Cell efficiency is measured on a single cell. Module efficiency covers the whole panel, including gaps between cells, the frame and edges, which produce no power, so it is lower.
Is a high-efficiency panel worth it for a factory roof?
Usually only if roof space is limited. On a large open roof, price per watt often matters more, and a mainstream N-type panel may give more kW for the same budget.
Does solar panel efficiency drop in summer?
Yes, temporarily. Panels lose some output as their cells heat up, which is why the temperature coefficient matters in Punjab. Efficiency also declines slowly over the years with normal degradation.
Sources
- SurgePV glossary, cell efficiency vs module efficiency (definitions and area-based calculation)
- SurgePV, TOPCon vs other solar technologies (typical commercial module efficiency ranges)