Solar Panel Efficiency and the Factors that Affect it | Act On Solar Power
25th November 2010
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Solar panels efficiency and the factors that affect it

What’s a typical solar panel efficiency rating?

Most solar panels are around 11-15% efficient (check out this handy comparison table ofsolar panel efficiency to see the differences between brands). The efficiency rating measures what percentage of sunlight hitting a panel gets turned into electricity that you can use. The higher the efficiency, the less surface area you’ll need in your solar panels. Although the average percentage may sound a little low, you can easily outfit a typical roof with enough power to cover your energy needs.

What are the most efficient solar panels?

In the lab, scientists have developed solar panels that are 40% efficient, or even slightly more than that. But there’s a big difference between the lab and the real world. Manufacturers haven’t figured out how to take these experiments and produce economically viable products yet. Waiting for new whiz-bang technology is one of the Top 5 Solar Myths.
Out of the solar panels on the market, SunPower makes some of the most efficient–one of their models is 19% efficient. They’ve managed to reach that number by using several techniques, including a reflective coating that can capture more light from an angle. They also offer a line of panels that’s 18% efficient. Sanyo, another solar panel manufacturer, offers efficient models as well.

Should I choose the most efficient solar panels available?

High efficiency doesn’t mean better, it just means you use less space for the solar array on your roof. Efficiency isn’t usually a critical concern unless you have an unusually small space for your solar panels. In that case, you’ll probably choose to spend a little more for higher efficient panels.
The installers we work with usually offer a choice of different recommended panels, including a more efficient type of panel for people concerned about space. If you have a normal amount of roof space to work with, you can focus more on the price and annual expected kilowatt production of your panels. Your installer will be experienced in choosing the best solar panels for your particular conditions; for example, if you live in a hot climate, some solar panels will be better for you.

Getting the best power performance

In addition to efficiency and size, there are other factors that affect how much power your solar panels will create. It’s important to make sure that the panels are installed in the optimal position, which is why you want to find a skilled, experienced installer . Your installer will decide on the correct orientation for your panels based on the direction and angle of your roof and issues with shading. They’ll also make sure the panels are installed with the proper amount of airflow so they can stay cool– solar panels don’t like it hot, and will produce more power if they’re the right temperature. To learn more, check out this article on how solar panels work.
If you just go to the Big Box store and slap on a bunch of panels, you could waste a lot of money. A quality installer designs a system and considers many factors in order to get the most electricity out of every inch of your solar panels.

Factors that affect solar array efficiency include:

  • Panel Orientation

    In the U.K., your roof ideally should face South, but designers can compensate for most other directions.
  • Roof and Panel Pitch

    The “pitch” or tilt of your roof can affect the number of hours of sunlight you receive in an average day throughout the year. Large commercial systems have solar tracking systemsthat automatically follow the sun’s tilt through the day. These are expensive, however, and not typically used for residential solar installs.
  • Temperature

    Some panels like it hot, but most don’t. So, panels need to be installed a few inches above the roof with enough air flow to cool them down. Some PV panels are designed to be more efficient in hotter climates.
  • Shade

    Shade is the enemy of solar. With poor solar design, even a little shade on one panel can shut down solar production on all of your other panels. Installers use special gadgets to instantly reveal any shady spots on your roof, no matter what time of year. Remember: Shade bad. So, trim those nearby trees. Did I mention shade is evil for solar panels? Beware the shade.
For more on solar cell efficiency, go back to the Different Types of Solar Panels. Want to know more about what goes into a solar PV system? See our next page.

Harish Dabasia UKs most connected person in the PV Solar Power/Energy sector Advocate, Ambassador, Introducer, Influencer, Facilitator and Deal maker. Through Act On Solar compiling the UKs First PV Solar installation Map.


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Harish D

Member since: 9th May 2011

UK s most connected person in the Solar Energy Bisnesses. and provide a complete done-for-you social media Marketing and Internet service for Solar...

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