Growing popularity of PV systems and many support mechanisms have large influence on shape of residential PV market. Multiple manufactures joining the market and number of technologies can confused not only many investors but also dealers.
Most dealers are focused on price of PV modules which is not always the best way to measure quality of PV modules. We have to remember that they need to work for at least 20-25 years so when it comes to choosing right panels we need to check also other parameters like:
Durability, shade and temperature tolerance are only few examples of parameters that impact on failure frequency which is a key value that can decide about cost-effectiveness of whole investment.
If you want to learn how to calculate PV system payback time and cost-effectiveness check our previous article.
Because of that, before we buy our PV modules we always need to check their data sheet, warranty conditions and opinions of other dealers. What is more because of many new companies on the market with poor quality products we should always choose products of experienced manufacturers.
Temperature Coefficient of Power
It is one of the most important parameter of PV modules. It informs us how high temperature change efficiency of our PV modules. Usually that coefficient is about -0.24%/°C in case of thin film panels and even -0.45%/°C in case of mono- and polycrystalline modules.
Decreasing power output over time
Unfortunate all PV modules suffer lose of their efficiency over time. It is a normal process but its scale depends on quality of our PV panels. In most cases it is about 1% of our maximal efficiency per year.
Efficiency in bad conditions
Power of our PV modules (described in Wp) is always measured in STC (Standard Test Conditions). That test take place in almost best possible conditions with irradiation equal to 1000 W/m2 and temperature around 25°C. In practice those conditions are almost impossible to achieve. Because of that before we should also check power of our PV modules in bad conditions with lower irradiation.
When we want to choose less popular technologies like thin-film panels we should be sure that our others devices will work well with them. That technology requires for example special mounting systems and inverter with galvanic isolation.
EVA (Ethylene-vinyl acetate) layer is a thin and transparent layer on the surface of PV modules.
Many cheap panels provide low quality EVA layer that lose its transparency over time. This process is one of the main reason of sliding efficiency of those panels.
Like you can see, before you choose proper panels you need to analyze many of their parameters. Nevertheless, that effort will guarantee you that your systems will work for years.