2 Nov

Does solar panel efficiency really matter?

Read 119 times Tagged under Does solar panel efficiency really matter?


If paying a lot of extra money to install higher efficiency solar panels makes you feel better, well then maybe. The truth is that unless you live in an area that gets very little annual sunshine or your roof is not large enough to accommodate enough lower efficiency solar panels to meet your needs, then you're probably throwing your money away by paying a higher price for higher efficiency solar panels.

Unlike inverter efficiency which is absolutely critical to your system's performance, under full illumination, a higher efficiency solar has very little bearing on performance. A 300 watt high efficiency solar panel produces the same 300 watts as a 300 watt low efficiency solar panel. The only real difference between the two is the physical size of each solar panel.

High efficiency versus low efficiency

You'll save a few square feet on your roof but you'll typicall pay
several thousand dollars more for the same amount of power
production. That's some expensive real estate on your roof.

Some higher efficiency solar panels are priced so much higher than lower efficiency panels that it begs the question of why consumers are paying so much more for these systems. I won't mention brand names but a high efficiency 6 kW solar panel system, built by a very popular manufacturer, currently sells for about $4.50 per watt or $27,000 installed before incentives. The same size 6 kW lower efficiency solar system sells for about $3.00 per watt or $18,000 before incentives. That's a savings of $9,000 if you choose the lower efficiency 6 kW system that will produce the same amount of power in sunny areas of the country.

Here's another way to look at it. If you took that $9,000 that you saved by purchasing the lower efficiency solar panel system and used that money to upgrade your lower efficiency system, at $3.00 per watt you could increase your 6kW system's size by another 3kW for a total of 9 kW!

So a 6 kW high efficiency system or a 9 kW lower efficiency system for the same price, which one would you choose? It throws the whole "pro high efficiency" argument out the window.

Instead of efficiency, which as you can see is practically meaningless, a far more important metric to measure performance by is the solar panel's PTC to STC ratio. PTC stands for PVUSA Test Conditions and STC stands for Standard Test Conditions.  PVUSA is an independent laboratory that was chosen by the state of California's Energy Commision to evaluate the real world performance of solar panels that being considered for use in Californi's Solar Energy Incentive Program.

A solar panel's PTC rating represents a more real world performance rating than does the manufacturer's STC or Standard Test Condition. You can compare the real world performance rating of thousands of solar panels on the following California government website. http://www.gosolarcalifornia.ca.gov/equipment/pv_modules.php

As you can see on this website, the PTC Watt rating is always lower than the manufacturers STC or name plate Watt rating. By dividing the manufacturer's STC name plate rating by the panels PTC rating, you can compare the purformance of different brands and size solar panels. For example, on this list you will find the SolarWorld SW 310 XL Mono solar module has a 271.1 Watt PTC rating. Divide this module's 271.1 Watt PTC rating by its 310 Watt STC rating and you get a PTC to STC ratio of 87.45%

Now lets compare this 87.45% performance ratio to that of another solar module on the state's list. For example, the Renesola JC310M-24/Ax-b solar module has a 284 PTC Watt PTC rating. Divide this module's 284 Watt PTC rating by its 310 Watt STC rating and you get a PTC to STC ratio of 91.61%  The higher the PTC to STC ratio, the higher the performance. The irony of this is that this SolarWorld mono crystalline solar module has a higher efficiency rating than ReneSola's poly crystalline solar module , yet according to the government's website, the Renesola modules offer better real world PTC performance

Another far more important performance metric than efficiency, especially for those of you who live in warm/hot climates is a solar panel's temperature coefficient rating. A popular misconception is that solar panels perform better in hot climates but nothing could be futher from the truth. The fact is that the hotter it gets, the poorer any solar panel will perform and a measure of that performance is the solar panel's temperature coefficient. The lower that number, the better the solar panel's performance. So even though your solar panel may offer higher efficiency, that efficiency can be lost if your solar panel possesses a poorer temperature coefficient rating.




Solarland® SLP180


SolarWorld® SW275


 Astronergy® CHSM6612P 305


Kyocera® KD325GXLFP


Suniva® OPT270


SunPower® E20-327


Bifacial Bifacial 300


As you can see from the chart above, various solar panel models offer differing temperature coefficient ratings. For example, the Solarland model offers a temperature coefficient rating of  negative 0.50% per degree C. I other words, for every degree C above 25 degrees C (or 77 degrees fahrenheit), this panel will lose a half percent of its power rating. So at 32.22 degrees C or (90 degrees fahrenheit), this panel would lose 7.22% of its rated power output.

Don't get me wrong, solar module efficiency is not a bad thing as long as you're not paying a lot more for it than what you would have paid by buying a lower efficiency solar module and you have adequate roof or ground mount space. Well shopping for solar modules for your home or place of business, remember, there are far more important considerations than efficiency if you want the best value for your investment.
Read b>408 times Last modified on Monday, 2 November 2015 11:03


If you live in a warm climate then your solar panel's temperature coefficient is far more important than its efficiency.