2
Nov
Does solar panel efficiency really matter?
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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.
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.
LOWER PERCENTAGE IS BETTER
|
MODEL
|
TEMPERATURE COEFFICIENT
|
|
Solarland® SLP180
|
-0.50%
|
|
SolarWorld® SW275
|
-0.45%
|
|
Astronergy® CHSM6612P
305
|
-0.45%
|
|
Kyocera® KD325GXLFP
|
-0.45%
|
|
Suniva® OPT270
|
-0.42%
|
|
SunPower® E20-327
|
-0.38%
|
|
Bifacial Bifacial
300
|
-0.28%
|
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.
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Last modified on
Monday,
2 November 2015 11:03
