Solar Panels

Solar panel efficiency is a measurement of a solar panel’s ability to convert sunlight into useable electricity.  Solar panel efficiency is determined by the production of electricity by solar cells, which is in turn influenced by the cells’ composition, electrical configuration, surrounding components, and more.

In other words:
If you have two solar panels that have a the same wattage output (350w panel vs. 350w panel) the panel with the higher efficiency will wake up earlier in the day, and go to bed later in the evening, thus producing significantly more kilowatt hours (kWh).  Since solar is all about producing kWh to offset electric bills, the better the efficiency rating, the less panels you need to produce the same amount of power.

The above describes two panels with the exact same wattage output!  However, their production over time would be VASTLY different.

The difference of 16.7% and 19.3% may seem small, but in the course of 25 years, the LG panel would produce much more power than the CanadianSolar panel… even though they are the same wattage per panel.

Few home owners actually realize that every panel actually has 2 warranties.

1. Lineal Power Output Warranty:
A lineal power output warranty is what most salespeople point to.  It basically says that if over 25 years the panels degrade too quickly, there is a limited warranty to have it replaced.  Most panels do not cover labor, although the higher quality panels typically do.

2. Product Warranty:
This is the more important warranty, as it pertains to the panel actually working for a certain amount of time.  Many panels have a 10, 12, 15, or even 25 year manufacturers warranty.  Your lineal power warranty is virtually worthless if the panel is not working!

Sales point to the lineal warranty and say “It’s covered for 25 years,” which couldn’t be farther from the truth!  The most important warranty is the product warranty!

When it comes to installing solar panels in hot areas (such as Arizona or California Desert areas), solar panel efficeincy is even MORE important. Solar panels start to lose efficiency when their temperature reaches approximately 80 degrees. How much efficiency they lose is determined by the panels Temperature Co-efficient. The lower the temperature coefficient, the less efficiency the panel will lose in areas of extreme heat. This doesn’t matter as much in temperate climates like Los Angeles or San Diego, but it is very important in areas where temperatures are normally higher than 110 degrees. If you live in the desert, pay extra attention to the graph below, and understand the temperature coefficiency and its affects on the overall panel efficiency and its expected performance in heat.

What is solar panel degradation?

NREL research has shown that solar panels have a median degradation point rate of about 0.5% per year, but the rate could be higher in hotter climates and for rooftop systems.  A degradation rate of 0.5% implies that production from the solar panel will decrease at a rate of 0.5% per year.
If a panel degrades at 0.5% each year, a solar panels efficiency will drop to 80% of it’s original efficiency after 25 years.

In contrast, Sunpower Panels come with a degradation guarantee of no more than 0.25%, which means you will be getting 92% of the power on year 25.

If you take the degradation and efficiency ratings from a higher quality panel, and compare them to a lower quality panel, the better panel can produce 25% MORE kWH over a 25 year period.  This does not take into account inverters or other system component quality, which can push that to over 45%

Most solar panels you will see are called “60-cell” and are close to the same size.  Some panels simply add cells to be larger, like a 72 panels cell.  Most of what you will see in residential solar is 60-cell.

As a rule of thumb, if you purchase a  panel that produces less than 350w, it should much cheaper than a panel producing more than 350w.  All panels producing 400w or higher (that we know of) are physically larger than those producing 280-350w.

If you are constrained for space, a higher wattage panel will make more sense for you.  If you have a lot of space on your roof, you can save a little money by going with a panel that puts out lower wattage per panel.

Weight:  The average panel weighs around 40lbs.  On your roof, that is not much weight spread out amongst 15+ square feet.