FAQS

The power rating (Pmax) of solar panels is based on cell temperature of 25°C. During operation, the output power drops with rise in cell temperature. Temperature coefficient is the factor at which the output power derates with each degree rise in cell temperature. For example, if the temperature coefficient of a module is -0.5%/°C, then when the cell temperature is 65°C, the output power will be derated by (65-25) x 0.5 = 20%.

Cell efficiency refers to the conversion efficiency of the output power of one cell (typically 125 x 125 mm) whereas module efficiency refers to the conversion efficiency of an entire module (typically 60 cells or 72 cells).

Due to the spacing between cells and the module frame, module efficiency is lower than cell efficiency.

Solar panel efficiency refers to the efficiency of conversion of sunlight to electricity. It is defined as the ratio of DC power output from the solar panel to input power (irradiance) from the sun.

The efficiency depends on the spectrum and intensity of the incident sunlight and the temperature of the solar cell. The standard test condition to measure efficiency is an irradiance of 1000W/m2, air mass of 1.5 and a cell temperature of 25°C.

A solar panel of say 17% module efficiency means that 17% of sunlight intensity (irradiance)  of 1000W/m2 is converted to DC electricity. Hence DC output = 17% x 1000 = 170 W/m2. If the solar panel dimension is 2 x 1 m  = 2 m2, it's rated DC output = 170 x 2  = 340 Wp. 

Solar PV panels are made up of many solar cells. Solar cells are made of silicon, like semiconductors. They are constructed with a positive layer and a negative layer, which together create an electric field, just like in a battery. When photons from sunlight hit a solar cell, they knock electrons loose from their atoms. If conductors are attached to the positive and negative sides of a cell, it forms an electrical circuit. When electrons flow through such a circuit, they generate electricity. Multiple cells make up a solar panel, and multiple panels (modules) can be wired together to form a solar array. The more panels you can deploy, the more energy you can expect to generate. 

Solar panels typically carry a product warranty of 10 years and a power warranty of up to 25 or even 30 years. The power warranty may be step or linear. For step warranty, typical guaranteed figures are 90% output power for first 10 years and 80% for next 15 years. For linear power warranty, typical figures are 2.5 to 3% power degradation at year one and not more than 0.7% power degradation per year from year 2 to 25.