## How much do you know about solar cell efficiency and electrical basis

**Solar cell efficiency**Efficiency is a unitless quantity used to indicate the effect of a device converting one form of energy (ie, heat, kinetic energy, electrical energy, etc.) into another form of energy. When talking about solar cells, efficiency is often mentioned, so it is very important to understand what it means and what it means for battery operation. There are many ways to describe the efficiency of solar cells:

●Battery efficiency: the amount of electric power generated by the unit of light energy incident on the solar cell. Usually measured under standard test conditions (STC): ambient temperature 25°C and irradiance 1000W/m

^{2}. Solar cells are rarely in STC in the field, so they rarely work at rated efficiency. The relationship between efficiency and power output is as follows:

Efficiency = output power / input power

The standard value of irradiance is 1000W/m

^{2}, if the battery efficiency is 22% and the area is 0.2m2, then

Output power = efficiency x input power

Output power=0.22 x 1000W/m

^{2}x 0.2m

^{2}=44W

●Module efficiency: The photovoltaic module efficiency measured by the same method of cell efficiency, the difference is that it includes reflection loss, glass shading, and other minor losses.

Be vigilant when considering efficiency graphs. Check the test conditions to understand how the array performance will change after installation. The environment will not be the standard test conditions. Changes in temperature, wind speed and solar radiation will seriously affect the array performance. The rated efficiency under STC is generally the best indicator for comparing the performance of cells and modules. The system output is not suitable for comparison, because the battery temperature in the field changes throughout the day and may not reach 25°C. The photovoltaic cell efficiency obtained in the laboratory Generally, the efficiency is significantly higher than that of existing photovoltaic modules, because the multi-counting technology in the laboratory is not economically feasible for large-scale production.

**Electrical basics**Basic knowledge of electrical terminology is important to understand the workings of photovoltaic cells.

Current: It is represented by the symbol I, and the unit of measurement is ampere (A). The current is formed by the flow of electrons. The greater the current, the higher the flow rate of the electron flow. There are two types of current:

Alternating Current (AC): Electrons first flow in one direction, and then flow in the other direction, continuously changing directions at a constant frequency, which is called alternating current due to the change in the direction of electron flow. AC power is used for grid power supply.

Direct current (DC): Direct current does not change the direction of electron flow, but flows steadily in one direction. The output of photovoltaic cells is direct current

Voltage: Usually measured between two points, it is the potential energy change of a unit charge between these two points. It is represented by the symbol V, and the unit of measurement is volts (V).

Energy: The unit of measurement of energy is watt-hour (Wh) or joule (J), which is a measure of functional power. When a person eats a biscuit, the energy obtained from the food can be used to do work, such as going up stairs. The electrical energy output by a photovoltaic system is usually described in kilowatt-hours (kWh)

Power: The unit of measurement of power is watts (W) or joules per second (J/s), which is the speed of energy supply. 1W is equal to 1J/s. Power is the product of current (I) and voltage (V):

P=IV

Circuit: A circuit is a system composed of wires and electrical components (including photovoltaic modules) through which current flows. Current can only flow through a closed circuit.

Series connection: When two elements in the circuit are connected end to end, it is called series connection. The two flow through the same current, and the voltage is distributed between the two (the greater the resistance, the higher the voltage).

Parallel connection: When two elements in the circuit are connected by the same potential difference (ie the same voltage), it is called parallel connection, and the current is distributed between the two.