When selecting modules, it is important to perform a cost-benefit analysis on whether a high-efficiency module makes financial sense. Higher efficiency solar panels will cost more per watt and per unit, but there are several advantages to using these modules with high power density:
- Assuming we are designing for a target system wattage, higher efficiency modules = lower module count overall, which in turn means reduced racking/BOS costs.
- Higher efficiency modules are generally more modern and may come with better features, such as more bypass diodes, split-cell technology, bifacial technology, etc.
- Higher efficiency modules are beneficial for systems where space is constrained.
Not all high-efficiency modules are the same; premium solar modules are the cream of the crop. These high-efficiency modules often feature superior aesthetics, excellent warranties, and most importantly higher power output and efficiency.
Some of the premium solar power modules include LG, Panasonic/Tesla, Sunpower, and Solaria. While they are not the cheapest option on the market, their value can be quantified in more than just dollars per watt.
For example, there are many reasons why Solaria modules are considered to be the best in class, combining curb appeal with maximum performance and efficiency.
How is efficiency defined and measured?
Solar panel efficiency is a measure of the ability of a PV module to convert incoming solar radiation to usable electricity. It is usally measured under Standard Testing Conditions (STC), where the irradiance is 1000 W/m2, the temperature is 25 degrees Celsius (or 77 degrees Fahrenheit) and the air mass coefficient is 1.5.
Another word for irradiance is “incident radiation flux,” and both are measured in watts per meter squared [W/m2].
Other Testing Conditions
There are other testing conditions that are commonly used in the industry, which will result in different efficiency ratings.
The most notable and recognizable one is the PVUSA Test Conditions (PTC) rating, which is derived from the STC rating, the STC efficiency, and the nominal operating cell temperature (NOCT).
The PTC rating is generally thought to be closer to the real-life rating of the module because it uses lower irradiance and accounts for temperature losses.
The PTC ratings are calculated and posted by the California Energy Commission (CEC) in a list that’s updated two to three times per month.
It is important to note that there are several factors that reduce system efficiency, and many of them are environmental.
Accumulation of snow, dirt, and detritus can cause significant losses on the surfaces of each collector. Within the array, temperature, module mismatch, wiring losses, and connector losses can also decrease overall system efficiency.
Lastly, modules degrade over time as they age, with most being warranted to produce 80%+ of their nameplate power after 25 years.
If your system is producing less than expected, any or all of these factors could play a role! To do your part in reducing soiling and detritus losses, panels should be cleaned a couple of times a year with mild soap and warm water.