How much energy does a solar panel produce?

The factors affecting the efficiency of solar panels: power, solar irradiance, orientation, weather conditions

The power of a panel is crucial as it indicates the amount of energy it can produce. It’s vital for calculating the total number of modules needed to achieve a certain output.

Panels are the core of any photovoltaic system, responsible for converting captured solar energy into electricity. Inclination, orientation, and weather conditions are all factors that can influence the overall system performance and significantly affect energy production.

To accurately assess these factors, a photovoltaic software can be helpful in estimating solar PV production based on precise solar irradiance data, optimizing the overall system performance.

Solar Panel Power

The measure of a photovoltaic panel’s maximum possible production is its power, measured in watt peak (Wp) or kilowatts peak (kWp).

Watt Peak is used to denote the power of a single panel, while kilowatts peak (kWp) quantify larger solar power, typically referring to the size of an entire photovoltaic system.

Solar Panel Power and Efficiency

The power of a photovoltaic panel is a significant parameter for calculating its efficiency. It is deduced under Standard Test Conditions (STC) with an irradiance of 1000 W/m², temperature of 25 °C, and spectral distribution = 1.5.

The efficiency of a photovoltaic panel is the amount of solar energy it can convert into electricity per unit area and is always the maximum efficiency under STC.

The efficiency of a photovoltaic panel is calculated knowing the peak power and dimensions:

Calculating the efficiency of photovoltaic panels

Calculating the efficiency of photovoltaic panels Calculating the efficiency of photovoltaic panels


  • W is the peak power;
  • is the panel’s surface area;
  • 1000 is the irradiance of 1000 W/m²;
  • 100 is the percentage factor.

For example, for a 250 Wp panel with dimensions of 1.65 m x 1 m (surface area of 1.65 m²), we get:

Efficiency = (250 / 1.65 / 1000) * 100 = 15.15%

The dimensions and peak power are available on the panels’ technical data sheets or labels.

What is the Power of a Solar Panel?

A standard photovoltaic panel produces approximately 330 Wp of energy. However, efficiency can vary depending on the panel type and manufacturer. High-efficiency panels can even reach a peak power of 450 Wp under optimal conditions.

However, the amount of energy actually produced by a solar system over a year is influenced not only by the panel’s characteristics but also by several other factors as discussed below.

Factors Affecting the Energy Production of a Solar Panel

The factors influencing the amount of energy a panel can produce are:

  • solar irradiance;
  • seasons;
  • weather conditions;
  • orientation and inclination;
  • component quality.

Solar Irradiance

The main factor for assessing whether a site is suitable for installing a photovoltaic system is estimating the solar energy reaching that location. Solar radiation reaching the Earth’s surface varies throughout the year due to the sun’s changing paths.

To understand the average solar radiation value of a specific location, solar paths are reported within a solar diagram, allowing you to determine the solar path concerning a specific site. Thanks to photovoltaic software, shading analysis can be studied directly on the solar diagram to verify the amount of solar energy in a particular period.

Solarius-pv solar diagram

Solarius-pv solar diagram Solarius-pv solar diagram


The energy generated by a photovoltaic system can vary with seasons. With autumn and winter, solar irradiance decreases significantly, along with overall daylight hours.

However, during spring and especially summer months, abundant solar irradiation allows photovoltaic panels to produce more energy than needed for the standard daily requirements.

Weather Conditions

Optimal conditions for photovoltaic system operation occur during sunny, cloudless days. Obviously, such circumstances are not constant, especially during autumn and winter.

Orientation and Inclination

To capture maximum solar radiation, solar panels should be oriented towards south. However, modules exposed to Southeast and Southwest directions can also perform well.

The inclination (tilt) varies and depends on the latitude. Rough values at our latitudes are 20-40°.

To determine the best value accurately based on the installation area, a photovoltaic software can be useful again to estimate solar PV production from concrete solar irradiance data, available for many locations extracted from major reference climatic databases.

Component Quality

An essential element for optimal system performance is the high quality of its components. For example, high-quality inverters and photovoltaic panels are crucial to ensure long-term efficiency, considering the progressive wear and tear that inevitably affects panels over the years.

It should be noted that photovoltaic panels experience a gradual efficiency loss every year due to wear. Therefore, it’s essential to invest in systems composed of quality components with proven certifications ensuring high efficiency in the long run. This choice maximizes system performance and ensures reliable performance over the years.

Photovoltaic Panels: Dimensions and Power

The relationship between the dimensions and peak power of photovoltaic panels is particularly complex, depending on various variable factors. It’s not always true that a larger photovoltaic module is also more powerful; conversely, the opposite could occur.

Currently, standard monocrystalline photovoltaic panels have an average power ranging from 300 to 400 Wp (peak power), but there are also models reaching 500 Wp. For example, conventional 300 Wp photovoltaic panels have dimensions of approximately 165 cm in height by 100 cm in width, with a thickness of about 4 cm and a total area of 1.65 m². Therefore, to achieve a total power of 3 kW from the photovoltaic system, 8-10 modules will be needed, with a required space of at least 14-17 m².

Based on the efficiency and performance of photovoltaic panels, it’s possible to calculate the area occupied by the modules per installed kWp to better understand the differences between various types of panels in terms of occupied space.

In particular, considering a standard module measuring 165 x 100 cm, the dimensions per kW of photovoltaic panels are approximately:

  • 4.7 square meters per installed kWp with monocrystalline panels (average peak power of 350 Wp);
  • 6.1 square meters per installed kWp with polycrystalline panels (average peak power of 270 Wp);
  • 13.75 square meters per installed kWp with thin-film panels (average peak power of 120 Wp).

It’s evident how dimensions and power significantly impact photovoltaic system sizing; therefore, during design, the best compromise between costs, dimensions, and energy efficiency must always be found, carefully assessing the photovoltaic kW/m² ratio.



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