Guides · Faisalabad, Lahore, Punjab
How to Read a Solar Panel Datasheet
Short answer
A solar panel datasheet tells you the panel's power (Pmax), its voltages and currents (Voc, Vmp, Isc, Imp), its efficiency, how it behaves in heat (temperature coefficients and NMOT), its size and weight, and the tests it has passed. Most of these figures are measured under Standard Test Conditions, so they are best used to compare panels with each other, not to predict exact output on your roof. This guide explains each line in plain words.
Whether you call it a solar panel or a solar plate, every genuine module has a datasheet from the manufacturer. Ask for the datasheet of the exact model in any quotation.
First, the test conditions
Datasheet figures are measured under agreed laboratory conditions so that panels from different makers can be compared.
| Condition | What it means | Used for |
|---|---|---|
| STC (Standard Test Conditions) | Sunlight of 1,000 W/m², cell temperature 25°C, air mass 1.5 | The headline wattage and electrical figures |
| NMOT (Nominal Module Operating Temperature), older sheets say NOCT | Sunlight of 800 W/m², air temperature 20°C, wind 1 m/s | A more realistic "outdoor" set of figures |
A Punjab roof at noon in June is far hotter than 25°C at the cell, so real output is usually below the STC figure. That is normal, not a fault.
Reading a panel datasheet
Electrical
Pmax, Voc, Isc at STC
Temperature
Coefficients and NMOT
Certificates
IEC 61215 and 61730
An example datasheet, line by line
The numbers below are round illustrative figures for a made-up 620 W panel. They are not the specs of any real model.
| Datasheet line | Example value | What it means |
|---|---|---|
| Maximum power (Pmax) | 620 W | The rated wattage at STC |
| Power tolerance | 0 to +5 W | The panel will test at or above 620 W, never below |
| Open-circuit voltage (Voc) | 50 V | Voltage with nothing connected |
| Max power voltage (Vmp) | 42 V | Voltage at the point of maximum power |
| Short-circuit current (Isc) | 15.6 A | Current if the terminals are shorted |
| Max power current (Imp) | 14.8 A | Current at the point of maximum power |
| Module efficiency | 22% | Share of sunlight on the panel turned into electricity |
| Temperature coefficient of Pmax | −0.30%/°C | Power lost per degree above 25°C |
| Temperature coefficient of Voc | −0.25%/°C | Voltage change per degree |
| Temperature coefficient of Isc | +0.05%/°C | Current change per degree |
| NMOT | 42°C | Typical cell temperature at NMOT conditions |
| Max system voltage | 1,500 V DC | Highest string voltage the panel is rated for |
| Max series fuse rating | 30 A | Largest fuse allowed in series with the panel |
Note that Vmp × Imp = Pmax (42 × 14.8 ≈ 620 W). This is a quick check that the datasheet figures are consistent.
The electrical figures explained
Pmax and power tolerance
Pmax is the wattage on the label: 615 W, 650 W, 720 W and so on. A positive-only tolerance (such as 0 to +5 W) means every panel should test at or above its label. A sheet that allows a negative tolerance means some panels may test slightly below. Compare price per watt on Pmax; see our solar panel price page.
Voc and Isc
These are the "limit" values. Voc is the highest voltage the panel produces when not connected; it rises on cold mornings. Isc is the highest current it can deliver. Engineers use Voc to make sure a string never exceeds the inverter's maximum DC voltage, and Isc to size cables, fuses and the inverter's current per input.
Vmp and Imp
These are the working values. The inverter's MPPT holds the panel near Vmp and Imp to draw maximum power. The string's Vmp must stay inside the inverter's MPPT voltage window in both summer and winter. Our series vs parallel guide shows how Voc and Vmp decide how many panels go in a string.
Efficiency
Efficiency tells you how much power you get per square metre. A higher-efficiency panel gives more watts from the same roof. It matters most when roof space is tight; on a large factory roof, price per watt may matter more. Efficiency ranges by cell type (N-type, P-type, back-contact) are covered in N-type vs P-type and bifacial panels.
The heat figures: important in Punjab
Temperature coefficients
The coefficient of Pmax is the most useful number for Punjab. It tells you how much power the panel loses for each degree its cells run above 25°C. A figure closer to zero is better in heat. For example, at −0.30%/°C, a panel whose cells reach 65°C (40°C above 25°C) loses about 12 percent of its rated power at that moment.
The coefficient of Voc is negative, so voltage falls in heat and rises in cold. This is why string design checks the coldest winter morning. Our guide to solar panels in Punjab summer heat has a worked example comparing cell types.
NMOT (or NOCT)
NMOT is the cell temperature the panel reaches under the NMOT conditions. A lower NMOT means the panel runs a little cooler outdoors. Many datasheets also list Pmax at NMOT, which is lower than the STC figure and closer to typical outdoor output.
Physical and mechanical figures
| Line | Why it matters |
|---|---|
| Dimensions | Decides how many panels fit and the structure layout. See solar panel size in feet. |
| Weight | Adds to roof load, especially with double-glass panels. See will my roof hold solar panels? |
| Glass and frame | Single or double glass; frame thickness. Affects strength and weight. |
| Mechanical load (front/back, in Pa) | How much wind and pressure the panel is tested to withstand. Structure design must respect it. |
| Junction box and connectors | Protection rating of the box and the connector type. Mixing connector brands is a common fault point. |
| Cable length | Affects how panels are linked in a string. |
| Bifaciality (bifacial panels only) | How much the rear side can add, as a percentage of the front. |
Certifications listed on the datasheet
Most datasheets list the tests and standards the model has passed. The two you will see most often are:
- IEC 61215: tests for performance and long-term reliability, such as heat cycles, humidity, mechanical load and hail.
- IEC 61730: tests for electrical and fire safety of the module.
Datasheets may also list factory management standards (such as ISO 9001) and tests for salt mist, ammonia or PID (potential-induced degradation). These certifications belong to the panel manufacturer and model, not to the company selling or installing it. A listed certificate is only meaningful for a genuine panel, so always check the serial number with the maker; see how to check genuine solar panels.
Warranty and degradation lines
The datasheet usually shows a product warranty and a performance warranty curve: a first-year degradation figure and a yearly figure after that. Read the actual terms in writing for the model you buy; we give the manufacturer's warranty per product in writing with every quote. Our solar warranty guide and solar panel lifespan explain these in full.
How to compare two datasheets
- Check the panels are the same type (for example, both N-type TOPCon) and similar size.
- Compare efficiency and Pmax for your roof space.
- Compare the Pmax temperature coefficient; closer to zero is better for Punjab summers.
- Check the tolerance is positive-only.
- Check weight and dimensions against your structure.
- Confirm the model code matches the quote exactly. Different versions of the same family can differ.
Use these checks alongside our quotation comparison checklist.
How Solar Works Pakistan uses datasheets
Our in-house engineers design every string from the actual panel and inverter datasheets, using your site's summer and winter temperatures. Each quotation lists the exact panel 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.
Get today's price or a free site survey
Send us any datasheet or quote you have, and we will explain what it means for your roof.
- 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. See our Faisalabad and Lahore pages, or contact us.
Frequently asked questions
What is the most important number on a solar panel datasheet?
Pmax tells you the panel's size, but for Punjab the Pmax temperature coefficient is just as important because it shows how much power is lost in heat. Efficiency matters when roof space is limited.
What is the difference between Voc and Vmp?
Voc is the voltage with nothing connected, the panel's maximum. Vmp is the voltage at which the panel delivers maximum power while working. Engineers use Voc for safety limits and Vmp for the inverter's working range.
Why does my panel produce less than its rated wattage?
The rating is measured at 25°C cell temperature and 1,000 W/m² sunlight. On a real roof, cells run hotter, sunlight varies and dust, wiring and inverter losses apply. Output below the label is normal.
What do NOCT and NMOT mean?
Both describe the cell temperature under milder outdoor-like conditions: 800 W/m² sunlight, 20°C air and 1 m/s wind. NMOT is the newer term. A lower value means the panel runs slightly cooler.
What do IEC 61215 and IEC 61730 mean on a datasheet?
IEC 61215 covers performance and reliability testing; IEC 61730 covers electrical and fire safety. They apply to the panel model, and only to genuine panels, so verify the serial number too.
Is a higher efficiency panel always better?
Not always. It gives more power per square metre, which helps on small roofs. On large roofs, a slightly lower efficiency panel may give better value per watt. Compare efficiency, price per watt and heat performance together.
Sources
- DualSun FAQ, NMOT (formerly NOCT) test conditions
- Portlandia Electric Supply, solar panel specifications guide (STC, tolerance, max system voltage, series fuse)
- Fraunhofer ISE, module certification (IEC 61215 performance and reliability; IEC 61730 safety)