Your quote lists a 450 W panel, while another option reaches 500 W. Is that enough to make a decision? The technical brochure, often called a datasheet, helps you understand what you are comparing: power, dimensions, efficiency and measurement conditions.
You don’t need to become an engineer. You need to recognize a few key details and ask the designer to explain how they relate to your roof. A brochure describes the panel; the system design assesses how the entire installation will work.
Start with the full model code and the correct column
Ask for the manufacturer’s official brochure for the exact model code in your quote. A product range may include several power ratings and different variants. In the table, find the column that corresponds to the specific product, rather than looking only at the largest number on the cover.
Also check the document version and the market it refers to. If the proposed model changes before the order is placed, ask for a new brochure and an explanation of what changes in the layout or system design. This process complements the comparison of solar quotes.
What Wp and STC conditions mean
The Wp rating describes nominal power under specific test conditions, known as STC. In technical brochures, these are defined as irradiance of 1.000 W/m², a cell temperature of 25°C and a specific solar spectrum, AM 1,5. Using the same conditions makes it possible to compare products.
The 25°C refers to the cell, not the air temperature shown in your weather forecast. So a 450 Wp panel is not expected to continuously deliver 450 W on your roof. Nor does this rating, on its own, tell you how many kilowatt-hours it will produce in a year.
Estimating annual energy production requires information about location, orientation, shading and losses. The PVGIS documentation explains why production depends on irradiance and panel temperature, along with the system’s other parameters.
Compare power together with dimensions
A panel’s efficiency, expressed as a percentage, indicates how effectively it converts incoming solar energy into electricity under the reference conditions. It is not the percentage by which your bill will be reduced. The basic concept of efficiency is also explained by the U.S. Department of Energy.
A more powerful panel may simply be larger. Ask for the external dimensions and efficiency to be compared, and, most importantly, for it to be shown how many panels of each option will actually fit on your roof, with the necessary clearances and access.
For illustration, let’s assume panel A is 450 W with an area of 2 m², and panel B is 500 W with an area of 2,5 m². Their power per unit area is 225 and 200 W/m², respectively. Panel B has more watts per panel, but panel A has more watts per square meter. This is a hypothetical numerical example only, not a reference to specific products or a production forecast.
Check the power temperature coefficient
Look for “temperature coefficient of Pmax,” usually expressed in %/°C. It describes the relative change in power as temperature changes. In typical silicon panels, an increase in temperature reduces power, so the coefficient is negative. Under comparable conditions, a value closer to zero means a smaller reduction due to heat.
Let’s assume a 450 W panel with a coefficient of −0,30%/°C. If the cell temperature rises from 25°C to 65°C, a simple linear approximation gives a reduction of 12%, or about 396 W, with all other conditions held constant. This is an educational example illustrating only the effect of temperature, not an operating forecast or an estimate of annual losses.
Don’t choose a panel based only on this figure. Ask whether the difference has a meaningful effect on the estimated production of your own installation.
How to read NOCT or NMOT ratings
Some brochures provide additional operating data labelled NOCT or NMOT. Always read the conditions stated alongside these ratings and compare like-for-like values across products. For example, don’t compare one panel’s STC power with another panel’s NOCT power.
The absence of these ratings is not enough to conclude that a panel is inferior. JinkoSolar explains in its technical FAQs that it does not include them in its current brochures and refers users to additional simulation data when needed. Ask the designer for the appropriate information, without assuming that all brochures must follow the same format.
Which details need a technical review
Vmp and Imp refer to voltage and current at the maximum power point. Voc and Isc refer to open-circuit voltage and short-circuit current. These values are used to check the electrical layout and compatibility with the inverter; they are not connection instructions.
Also check the dimensions, weight and mounting requirements. Ask the qualified professional responsible to confirm that the panels are suitable for your roof and mounting system. A load rating listed in the brochure does not replace an assessment of the building and installation.
What to ask before you decide
- Full model code and official technical datasheet.
- Comparison of power and efficiency under the same measurement conditions.
- Actual layout for each alternative panel size.
- Explanation of the temperature assumptions used in the energy production estimate.
- Confirmation of equipment compatibility and suitable mounting.
- Separate warranty documents, as explained in our photovoltaic warranty guide.
At Solar Home, we assess your space and needs alongside the equipment. You can request a system study and quote, so your panel choice is based on the complete installation and clear assumptions.
Sources and technical references
- Trinasolar — sample technical datasheet with STC definitions and electrical and mechanical specifications. Used to interpret the fields, not as a recommendation for a specific product version or warranty in Greece.
- U.S. Department of Energy — performance and the effect of temperature.
- European Commission, JRC — PVGIS data and methods.
- JinkoSolar EU — technical FAQs on NOCT/NMOT fields.
