Solar Panel Performance: Peak Power, Cell Types, and Efficiency Factors

Fundamentals of Photovoltaic Module Performance

What is Peak Power of a Photovoltaic Module?

Peak power is the maximum output power, measured in Watts (Wp), that a photovoltaic panel produces under standard test conditions (STC). STC requires maximum solar illumination, defined as approximately 1 kW/m² radiation, which typically occurs around solar noon on a sunny day.

Monocrystalline vs. Polycrystalline Solar Cells

Photovoltaic modules are composed of either monocrystalline or polycrystalline silicon solar cells. The primary difference between these types lies in their manufacturing process.

Manufacturing Monocrystalline Cells

Monocrystalline silicon cells are obtained from very pure silicon. The manufacturing process involves:

1. Melting the silicon in a crucible along with a small proportion of boron (doping).
2. Introducing a "seed crystal" into the liquid material. New atoms from the liquid re-grow onto the seed, sorting themselves according to the crystal structure. This results in a single, doped crystal.
3. Cutting the crystal into wafers, typically approximately 0.3 millimeters thick.
4. Feeding the wafers into special ovens where diffuse phosphorus atoms are deposited on one side, reaching a certain depth in the surface.
5. Coating the surface with an anti-reflective treatment (such as titanium dioxide or zirconium) before screening the surface for interconnections.

Manufacturing Polycrystalline Cells

Unlike the single-crystal process, polycrystalline cells are manufactured by allowing a pulp mold of silicon to solidify slowly. This process results in a solid formed by many small silicon crystals, which are then cut into thin multicrystalline wafers.

Do PV Modules Work on Cloudy Days?

Yes, photovoltaic modules produce electricity even on cloudy days, although their efficiency decreases significantly. The production of electricity varies linearly with the light incident on the panel.

A completely cloudy day is equivalent to approximately 10% of the total intensity of direct sunlight, and panel performance decreases proportionally to this value.

Key Factors Affecting Solar Panel Performance

The performance of a photovoltaic panel is fundamentally affected by two main factors:

• Intensity of Light Radiation: The current intensity generated by the panel increases directly with radiation, while the voltage remains approximately constant.
• Temperature of the Solar Cell: A rise in cell temperature causes a slight increase in current but a much larger proportional decrease in voltage. The overall effect is that the module power decreases significantly as its working temperature increases.

Importance of Module Placement

The placement of the modules (orientation and angle to the horizontal) is crucial because radiation values vary throughout the day depending on the sun's angle on the horizon.

Note on Temperature: An irradiation of 1,000 W/m² is capable of heating a panel about 30 degrees Celsius above the ambient air temperature.