With the growing popularity of solar energy, there has been an upsurge of system installers and manufacturers in the market. You get to hear a new name every day which, more often than not, causes confusion in the minds of buyers. Majority of buyers are not well-versed with the industry and end up basing their decision on either cost or presentation of the sellers. To address this problem, SunKalp brings to you a guide to choose your solar modules wisely- this is a technical guide for Solar EPCs. Listed below are the factors you should consider apart from cost:.
1. Rated Power:
If you take a look at module datasheet of a manufacturer, almost always you will see more than 1 module with same number of cells. Have you ever wondered the reason behind it? On a manufacturing line, cells are arranged in a pre-defined pattern. After modules are manufactured, they are tested for their rated power which lies in a range based on the quality of cells used for manufacturing. These manufacturing lines follow a bell-curve as shown below. Maximum modules are concentrated around a power rating which lies somewhere in the middle of the range.Rated power at expected value of bell curve helps one easily judge the quality of solar modules one is purchasing without going into technical details of cell grading.
2. Module Efficiency:
A lot of buyers go by the module efficiency. For them, a higher efficiency means higher generation, which is true to a very small extent. Module efficiency is not defined by the quality of cells, but by rated power per unit area. So, this only means that with a higher efficiency module, you would only be able to produce more power using the same area. This detail is rendered useless when available area is not a constraint.Example: Dimensions of 250Wp module of ABC solar are 1650mm x 990mm x 42mm.
3. Temperature Coefficients:
Temperature coefficient, by definition, refers to the change in a quantity per unit change in temperature. Temperature coefficients for voltage, current and power listed on datasheets of solar modules. Open circuit voltage and power tend to decrease with increase in temperature and therefore, have negative temperature coefficients, whereas, short circuit current tends to increase with increase in temperature and therefore, has a positive coefficient. One should prefer a smaller temperature coefficient to avoid any large deviations from rated values.
Example: 250Wp module of ABC solar has -0.4%/degree C power temperature coefficient. For every 1 degree increase in temperature over standard temperature (25oC), 0.4% of 250W, i.e. 1W, will drop.
4. Power Tolerance:
It refers to the expected deviation in the output of a solar module at STC. It determines the extent to which the module is expected to over-perform or under-perform from the rated power. Most solar modules work in the range of +-3%. Try to avoid a high negative power tolerance.
Example: 250Wp module of ABC solar has power tolerance of +-3%. What it means is that at STC, power could be anywhere between 242.5Wp and 257.5Wp
Generation of solar modules degrade over time. Degradation is predicted based on light test that the modules go through before being launched into the market. Below are the 2 kinds of degradation that are claimed by the manufacturers:
a) Step degradation: Modules are expected to lose a part of their generation capacity within the first few years.
b) Linear degradation: Modules are expected to lose their generation capacity gradually over time.
Linear degradation is always preferred over step degradation for the obvious reason that overall guaranteed generation (area under the curve) is more.