Solar Panel Efficiency: A Quick Guide

When you purchase solar panels, you may have a long list of questions, including whether your house is right for solar, total system cost, warranties on installation and equipment and how long panels will last. Another main talking point with your solar installer may include solar panel efficiency.

It's a good idea to understand the basics of solar panel efficiency before you take the plunge on paying for solar panels, because the fact of the matter is that they're not cheap. In this piece, we'll walk through solar panel efficiency, how materials compare for efficiency, whether the efficiency of solar panels changes over time and whether future technology can make solar panels more efficient.

By the time you're finished reading, you'll understand the basics about solar panel efficiency. You might even be able to zero in on the right type of solar panels for your home, which can put you ahead of the game when you start shopping for your own solar panel system.

How Efficient Are Solar Panels?

First of all, when we say "efficiency," what do we mean? Solar efficiency refers to the exact amount of sunlight reflected on photovoltaic (PV) panels and the amount that gets converted into usable electricity.

The type of solar panel and its construction, along with location and weather conditions, impact efficiency. Irradiance level, the rate at which sunlight hits the panels, also affects efficiency. Surprisingly, solar panels generate more power at cooler temperatures.

And, if you choose higher-efficiency panels, you usually won’t need as many solar panels to power your home.

Most solar panels range from 15 – 20% efficiency, though some outliers can claim nearly 23% efficiency (these tend to cost more). This means that if a solar panel has a 20% efficiency rating, a total of 20% of the sunlight that hits a solar panel will be converted into electricity.

Understanding Solar Panel Efficiency

Why is solar panel efficiency such an important topic? The fact is that not all of the sunlight that goes into a photovoltaic (PV) cell becomes converted into electricity – believe it or not, you end up losing most of it.

Two numbers drive efficiency rating: photovoltaic (PV) cell efficiency and total panel efficiency. To get the total panel efficiency, you take the maximum power rating under test conditions divided by the total panel area.

The amount of irradiance (aka sunlight) each solar cell can convert into energy is expressed as a percentage. This is also called conversion efficiency.

To get a handle on the loopholes of where efficiency "escapes" a solar system, let's go over exactly how solar panels work. When sunlight reaches the earth's surface, it is made up of photons. Your panels capture the photons from sunlight and generate direct current (DC). Solar panels have inverters that convert DC to alternating current (AC), which homes can actually use.

However, when light strikes the surface of a solar cell, some photons are reflected and others pass through the solar cell to produce electricity.

Reflection means that light reflects immediately off a cell's surface. Anti-reflection coatings can help minimize the issue, such as using untreated silicon and textured surfaces. In addition, high-efficiency cells are usually dark blue or black.

Recombination is also another factor that prevents maximum efficiency in a solar cell. What does "recombination" mean? While there are a few types of recombination that can occur in solar panels, one example happens when a negatively-charged electron called a "charge carrier" combines with a hole, another charge carrier, and limits efficiency.

Another efficiency loophole occurs due to high temperatures. While you might think that solar panels work best under high temperatures, the reverse is actually true. Solar cells work best under low temperatures because high temperatures cause decreases in voltage and damage to the cell and other materials that make up your solar panels. Extreme high temperatures can lead to a rapid lowering of the cell's lifespan.

How Do Solar Panel Materials Compare For Efficiency?

The material used for a solar system can also affect efficiency, and home solar installations typically feature monocrystalline, polycrystalline or amorphous (aka thin-film) solar panel materials.

So, what are the most efficient solar panels?

Let's go over the definition of each type, keeping in mind that monocrystalline installations are usually the most efficient (and the most expensive).

• Monocrystalline: Monocrystalline solar panels have a one-crystal structure and were among the first types of solar panels to be created.
• Polycrystalline: Just as the name sounds, polycrystalline solar panels contain several silicon crystals. They're usually less efficient than monocrystalline structures. It's very possible that you'll have to have more polycrystalline panels to equal the amount of energy produced by monocrystalline panels.
• Amorphous: Amorphous solar panels are usually made of thin sheets of silicon attached to the metal, glass or plastic of a solar panel. The cheapest option, they also offer the least efficiency of the three.

Does The Efficiency Of Solar Panels Change Over Time?

Solar panels do become less efficient over time. The industry puts the average lifespan of solar panels at 25 – 30 years. The National Renewable Energy Laboratory (NREL) research shows that solar panels have a median degradation rate of about 0.5% per year, though degradation could end up being higher in hotter climates and for rooftop systems. 

Homeowners can rest assured, however, that the warranty period for home solar panels often matches or exceeds their expected lifespan. That being said,  even after their expected lifespan, panels will continue producing solar power, just at a lower rate.

Other Aspects Of Solar Efficiency

While age and condition impact the efficiency of solar systems, updates in solar cell technology make newer panels more efficient than older ones. There are also things you can do to impact and maintain your solar panel efficiency.

Regular cleaning can help your solar energy system produce power at its maximum capability. Dust and dirt, bird droppings, salt spray (if you live by the ocean), leaves and other types of debris can reduce the efficiency of your panels.

Solar installers often suggest cleaning your solar system up to four times per year to keep them working throughout their typical lifespan of 15 – 20 years. Depending on your location, you may be able to stretch this to every six months, particularly if you don't have a lot of issues with dirt and dust. Unfortunately, if you notice debris on your solar panels regularly due to any one of the above types of obstructions, you might have to clean your solar panels more regularly.

Make sure your panels are installed correctly, whether you hire an installer or install them yourself. If they aren't installed on the right part of your roof, you could experience a decrease in efficiency. It's also a good idea to avoid installing solar panels in shaded areas. If you live the shade of gigantic pine trees, your home might not be a good candidate for a solar panel system. It's a good idea to ask an installer for a detailed explanation of how well your solar panels will function based on your living area and particular situation.

You may also want to consider using a solar concentrator, which is an additional piece of equipment that concentrates radiation to a certain focal point to produce electricity. They intensify the amount of sunlight that hits solar cells.

Will Technology Make Solar Panels More Efficient?

Advancements in technology have improved solar panel efficiency. However, will emerging technology continue making panels more and more efficient? The answer is yes. It's important to remember that the first solar modules were only about 6% efficient. Solar panel manufacturers have succeeded in making panels that have increased in efficiency approaching 50%, with most commercial panels usually getting up to 20% at maximum efficiency.

In the future, panels using perovskite could result in solar panel efficiencies in the range of 33 – 40%. Many semiconductor materials can be used for PVs besides perovskites, including silicon, copper indium gallium diselenide (CIGS), cadmium telluride (CdTe) and other types of semiconductor materials that can lend themselves to more efficiency. Bifacial models can also collect light on both sides of solar system panels and concentrator PV (CPV) technology may also contribute to high efficiency solar panels. CPV technology uses low-cost optics to put light onto a smaller solar cell, and PERC solar cells are becoming a popular high-efficiency option. 

However, cost efficiency must also be a determining balancing factor in the materials chosen. This is why perovskite technology looks so promising, because they have a low production cost. Improving the materials used could also improve the current low rate of recycling for PV panels.

The Bottom Line

Solar efficiency is an important concept because it takes into consideration the amount of light that gets converted into electricity through solar panels. Solar panel construction, location, climate and the rate at which sunlight hits the panels affects your efficiency level. Most solar panels range from 15 – 20% efficiency – which means not all of the sunlight that goes into a photovoltaic (PV) cell becomes converted into electricity. However, we’ve made great strides to improve efficiency. The first panels were only about 6% efficient and now most commercially sold panels usually only go up to 20% at this point in history.

Monocrystalline installations are usually the most efficient (and the most expensive) types of solar panels on the market, though rapidly booming technological innovations will also continue to produce more efficient solar panels, hopefully at a more affordable price.

Do your research into the types of solar panels you should get for peak efficiency. Don't forget to ask as many questions as you can about solar efficiency rating before you install your solar system. Conversion efficiency is a major concern, because you want to get the best bang for your buck when installing your solar panels.

Still wondering if a home solar array is right for you? Check to see whether your home is a good fit for producing solar energy.