How to understand the significance of the electrical ratings?

As you have decided to go for the solar energy, you must understand the electrical parameters of the most important component of the solar system that is the SOLAR PANEL. When you go to purchase solar panels you are encountered by so many electrical jargon which can confuse you and put you in dilemma and you hesitate to go ahead for the solar power.

You feel that solar is something which is not my cup of tea. But don’t worry here we will learn and understand the few basics that will make you to step ahead with confidence. You will find electrical parameters written on the sticker at the back of the panel

The electrical parameters under STC (Standard Test Conditions)

The Standard test conditions are:

• \(\color{navy}{Cell\ temperature=25^oC}\)  &
• \(\color{navy}{Solar\ Irradiance=1000W/m^2}\) (Amount of the solar energy received on the surface per unit time per unit area.)

The parameters which are evaluated under above-mentioned conditions are:

• \(P_m\) = Power in watts is the maximum power which a panel can produce under standard test conditions (STC)
• \(V_{mp}\) = Voltage at maximum power
  
• \(I_{mp}\) = current at the maximum power.
  
• \(V_{oc}\) = This is called the open circuit voltage. This is the voltage across the terminals of the solar panel when no load is connected and the flow of the current is zero.
  
• \(I_{sc}\) = This is called short circuit current. This is the closed circuit current when wires are connected but there is no load.
  

Example

Let us understand with an example:

• Pm =12 watts.
  
• Vmp=17 volts
  
• Imp =0.71 amp
  
• Power=V*I =17 volts X 0.71 amp. =12 watts

Where 12 watts is the maximum power under standard conditions. However, the temperature affects the output power of the panels. The more is the temperature, the hotter the solar cells get and in turn the energy is lost as heat and less power is received at the output.

• So for every increase in degree of temperature above \(25^oC\) the amount of electricity produced is reduced by about 0.5 percent. In this case the output power is less than the rated power. So it is advised to leave some gap between two panels so that air can pass through to cool the panels.
• Whereas, on sunny day in the spring when the temperature is lower than \(25^oC\) the output power produced is more than the rated power.
• The output power is also the function of the irradiance. The slight haze due to cloud, dust and humidity, in the atmosphere can affect the efficiency of the solar panels.
• The electricity produced from the solar panels is directly proportional to the amount of irradiance. With 10 percent increase in the irradiance levels will increase the output from the solar panels by 10 percent.

In a clear whether which is free of dust, cloud or humidity, the output power can be greater than the rated power.
So, in concise the output power is the function of the temperature and the amount of irradiance.

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