If you read the specs or data sheets of a solar panel, you may have asked yourself: what is the difference between Watts (W) and Watts-peak (Wp)? Without too much technical jargon, here is a brief explanation.

What is electrical power?

Every electrical appliance we use today requires power. The power requirement is higher or lower based on the use in question. For example, a blender needs less power than a toaster since the blender only needs to rotate its blades while the toaster needs to heat up and maintain a high temperature. This is reflected by their power ratings: for example about 200W for the blender and 800W for the toaster. This clearly shows that the toaster uses more power than the blender.

Lightbulbs, motors, etc… are often chosen based on their power and the use we will make of them. For example, the choice between two lightbulbs often hinges on their power, since generally the less powerful the bulb, the less light it will emit. That being said, due to the technology used, an LED lamp may emit as much light as a 100W incandescent lightbulb while using less power.

For a more detailed explanation, including details on the difference between power and energy, check out our article.

What about solar panels?

Solar panels are different. They produce energy using the Sun as their primary source of power, but its lighting is variable.
How can we then compare two solar panels if the power they produce is variable based on the light they receive from the Sun?
An engineer working in Africa could, in theory, find that his solar panel has a higher performance than another being tested in Iceland. How can we avoid this situation?
This is where peak power steps in. It describes the power that a solar panel produces in controlled, standard conditions. This means that two solar panels can be compared, since the power of each has been tested in these standard conditions.
A panel with a peak power of one watt peak (Wp) can deliver one watt of power for the standard conditions below:

  • Solar irradiation (amount of light) of 1000 W/m2
  • Solar panel temperature of 25°C
  • Conditions that simulate the solar irradiation going through an air mass 1.5 times that of the atmosphere, with a cloudless sky and at an angle 45°.

In practice, the power delivered by a solar panel is not equivalent to its peak power, and will depend on the light it receives from the Sun. This will depend on the day, time, weather and geographic location. In addition, the panel’s angle, temperature and efficiency also influence its production.

For example: a solar panel of one square metre receives an illumination of 1000W, and its output electrical power is 200W. A large part of the energy therefore hasn’t been used. We can then say that the panel has an efficiency of 20% (based on the ratio, 200W/1000W). In these standard conditions, the panel will produce 200W, but in reality, the irradiation will not necessarily be equivalent to 1000W. Therefore, the panel will produce more or less energy.

The watt-peak is therefore a unit which allows us to compare solar panels among them, but does not necessarily describe how much power the panel will produce once in use.

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Autor : TALEBMOUSTAPH Cheikhna
Credit icons : flaticon – freepik