I. Solar Panel Parameters
The main performance parameters of solar panels include: short-circuit current, open-circuit voltage, peak current, peak voltage, peak power, fill factor, and conversion efficiency.
1. Short-circuit current (isc): When the positive and negative terminals of a solar cell are short-circuited, making u=0, the current at this time is the short-circuit current of the cell. The unit of short-circuit current is ampere (A). The short-circuit current changes with the light intensity.
2. Open-circuit voltage (uoc): When the positive and negative terminals of a solar cell are disconnected from a load, making i=0, the voltage between the positive and negative terminals of the solar cell is the open-circuit voltage. The unit of open-circuit voltage is volt (V). The open-circuit voltage of a single solar cell does not change with the increase or decrease of the cell area, and is generally 0.5 to 0.7V.
3. Peak Current (im): Peak current is also called maximum operating current or optimal operating current. Peak current refers to the operating current when the solar cell outputs maximum power, and the unit of peak current is ampere (A).
4. Peak Voltage (µm): Peak voltage, also called maximum operating voltage or optimal operating voltage, refers to the operating voltage at which the solar cell outputs maximum power. The unit of peak voltage is V. Peak voltage does not change with the increase or decrease of the cell area, and is generally 0.45 to 0.5 V, with a typical value of 0.48 V.
5. Peak Power (pm): Peak power, also called maximum output power or optimal output power, refers to the maximum output power of a solar cell under normal operating or testing conditions. It is the product of peak current and peak voltage: pm = im × um. The unit of peak power is W (watts). The peak power of a solar cell depends on solar irradiance, solar spectral distribution, and the cell's operating temperature. Therefore, solar cell measurements must be performed under standard conditions, using the European Commission's Standard 101, which specifies the following conditions: irradiance 1 kW/m², spectral density 1 μm.5, and test temperature 25°C.
6. Fill Factor (ff): The fill factor, also called the curve factor, is the ratio of the maximum output power of a solar cell to the product of its open-circuit voltage and short-circuit current. The formula is ff = pm/(isc × uoc). The fill factor is an important parameter for evaluating the output characteristics of a solar cell. A higher fill factor indicates that the solar cell's output characteristics are more rectangular, and the cell's photoelectric conversion efficiency is higher.
Series and parallel resistances have a significant impact on the fill factor. The smaller the series resistance and the larger the parallel resistance of a solar cell, the larger the fill factor coefficient. The fill factor coefficient is generally between 0.5 and 0.8, and can also be expressed as a percentage.
7. Conversion efficiency (η): Conversion efficiency refers to the ratio of the maximum output power of a solar cell when it is illuminated to the solar energy power irradiated onto the cell. That is: η = pm (peak efficiency of the cell) / a (area of the cell) × pin (incident light power per unit area), where pin = 1kw/㎡ = 100mw/cm2.
II. Types of Solar Panels
1. Monocrystalline silicon photovoltaic cells
Monocrystalline silicon solar cells have a photoelectric conversion efficiency of around 15%, with the highest reaching 24%, which is currently the highest among all types of solar cells. However, their manufacturing cost is very high, preventing their widespread and common use. Because monocrystalline silicon is typically encapsulated with tempered glass and waterproof resin, it is robust and durable, with a lifespan generally reaching 15 years, and sometimes up to 25 years.
2. Polycrystalline silicon photovoltaic cells
The manufacturing process of polycrystalline silicon solar cells is similar to that of monocrystalline silicon solar cells, but the photoelectric conversion efficiency of polycrystalline silicon solar cells is significantly lower, around 12%. In terms of manufacturing cost, they are cheaper than monocrystalline silicon solar cells due to simpler material manufacturing, lower energy consumption, and lower overall production costs, thus leading to their widespread adoption. However, polycrystalline silicon solar cells also have a shorter lifespan than monocrystalline silicon solar cells. In terms of performance-price ratio, monocrystalline silicon solar cells are slightly better.
3. Amorphous silicon photovoltaic cells
Amorphous silicon solar cells, a new type of thin-film solar cell that emerged in 1976, are manufactured using methods completely different from those of monocrystalline and polycrystalline silicon solar cells. The process is greatly simplified, requiring very little silicon material and resulting in lower power consumption. Its main advantage is its ability to generate electricity even in low-light conditions. However, the main problem with amorphous silicon solar cells is their relatively low photoelectric conversion efficiency, which is around 10% at the international advanced level, and it is also not very stable, with its conversion efficiency decreasing over time.
4. Multi-component compound photovoltaic cells
Multi-component compound solar cells refer to solar cells that are not made of a single-element semiconductor material. Many different types are being researched in various countries, but most have not yet been industrialized. The main types include:
1) Cadmium sulfide solar cells;
2) Gallium arsenide solar cells;
3) Copper indium selenide solar cells (novel multi-element bandgap gradient Cu(In, Ga)Se2 thin-film solar cells).
The above is an introduction to the performance parameters and types of solar panels. Furthermore, encapsulation is a crucial step in solar cell production. Without a good encapsulation process, even the best cells cannot produce good solar panels. Encapsulation not only ensures the lifespan of the cells but also enhances their impact resistance; therefore, the quality of solar panel encapsulation is extremely important.
