Solar Panel Efficiency: Key Things for Home Solar

By Hannah Glenn
July 17, 2018
Efficiency of solar panels

You may hear the term “efficiency” thrown around a lot when reading up on solar panels. It sure sounds like a good thing, but what exactly is solar panel efficiency? How is it measured?

We’ll go over some of the major factors contributing to the efficiency of solar panels, and environmental factors that detract from it. We'll be specifically covering the silicon-based solar cell efficiency, as that's by far the most common material on the residential solar market today.

What is the efficiency of solar panels?

Solar panel efficiency is a measurement of how much of the sun’s energy a certain panel can convert into usable electricity. This is done by capturing the electrical current generated when sunshine interacts with silicon or thin film cells inside a solar panel.

These solar cells are tightly packed alongside each other inside glass rectangles designed to attract sunlight. You can read more about how solar panels are manufactured in this post. Then the energy is converted, sent to your circuit breaker box and distributed throughout the house.

It’s measured fairly simply. If a solar panel has 20 percent efficiency, that means it’s capable of converting 20 percent of the sunshine hitting it into electricity. The highest efficiency solar panels can reach almost 23 percent efficiency. But the average efficiency of solar panels falls between the 15 to 18 percent efficiency range.

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SunPower panels hold the highest silicon panel efficiency today at 22.8%. Get SunPower system quotes on Pick My Solar's marketplace.

Factors that affect solar panel efficiency

Many internal and scientific factors play into the solar cell efficiency equation. But two major components are

  • Reflectance efficiency
  • Thermodynamic efficiency

Reflectance efficiency is determined by how much sunlight is reflected back instead of absorbed and put to use. The less reflection in solar cells, the better. Silicon reflectance can be as much as 38 percent, though most solar cells have a slight micro-pyramid shape. This reduces reflectance to about 11 percent.

SKEL_PYRMicro-pyramids on textured surface of solar cells reduce solar reflectance (source)

There are ways to reduce reflectance, such as anti-reflective coatings. Really advanced solar cell construction or, “stacking micro- and nano-sized arrays on top of the larger structures” can bring reflectance down to just 1 or 2 percent.

Thermodynamic efficiency is the maximum efficiency possible. It’s the height at which the sun’s energy could be converted into electricity. This number is right around 86 percent, the thermodynamic efficiency limit.

The way photons interact with solar cells, they can only generate electricity from the sun’s energy up to a certain point. After that point (86 percent) thermal energy, or heat, is created.

One way to improve thermodynamic efficiency is to construct multi-junction or tandem solar cells. This improves efficiency by dividing the solar spectrum into smaller areas, which raises the efficiency limit for each section.

Environmental Factors Affecting Solar Cell Efficiency

Shade from nearby buildings, trees, or heavy cloud coverage are the nemeses of efficiency. After all, how can your expertly engineered solar panels produce electricity without sunlight? Though, some light does make it through the clouds.

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Shading from nearby trees will impact your solar array's electricity production

Significant amounts of dirt and dust can also reduce efficiency. For the most part, solar panels are self-cleaning. A rain shower can reset you panel efficiency in just a few minutes. If you live in a particularly arid region and heavy dust-storms are a problem, you might want to clean the panels off yourself. Here’s how to know if your panels need cleaning and how to go about it.

A common misconception is that winter weather will mean lower efficiency. The opposite is often true. Though solar panels are designed to withstand average temperatures, they’re more inclined to function better when they’re cooler. This is true with most electronic equipment. And since solar panels need light (not heat) from the sun, bright winter days might be some of the most productive.

Snow is another area of confusion with solar panel efficiency. A thin layer of snow won’t hinder solar efficiency much. Read more about snow with solar, and solutions for heavy snowfall with solar here.

Efficiency's Importance in Home Solar Solutions

Of course, efficiency isn’t the only determining factor in which solar panels are right for your home. You may not need the most efficient solar panels if you have enough roof space for less efficient, but more cost effective, panels.

The direction your roof is facing, the slant, style, and area of your roof all weigh in on which panels might work best for you. If you’re curious about how solar-friendly your property is, find out here.

Hannah Glenn

Written By

Hannah Glenn

Hannah Glenn is a writer specializing in renewable energy and healthcare. When not 10 inches from a computer screen, Hannah loves hiking in the Santa Monica Mountains and reading National Geographic.

More articles by Hannah Glenn

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