Solar Panel Efficiency Over Time: When To Replace (& Why Degradation Matters)

Georgette Kilgore headshot, wearing 8 Billion Trees shirt with forest in the background.Written by Georgette Kilgore

Solar Panels | April 1, 2024

Man carrying a replacement solar panel to another person’s house that has seen a drop in solar panel efficiency over time and the solar panel lifespan impacted by solar panel degradation, leaving the homeowner asking why do solar panels degrade and how long do solar panels last?

Understanding solar panel efficiency over time helps you know when to replace your panels and how to maximize their lifespan.

If you have a solar energy system in place or you are considering installing a photovoltaic system, solar panel degradation is an important consideration because it impacts the real return on your investment you’ll receive, as well as how ‘green’ the panels turn out to be.

When solar panel cells are tested for efficiency in a laboratory setting, their output rating is at its premium. However, in a real-world situation, the performance isn’t always optimal.

However, solar panel efficiency over time can diminish, and what you may not know is that how you care for your solar panels can either help ensure that maximum lifespan or contribute to an early demise.

This guide outlines ways to enhance the efficiency of your solar panels to get the most power generation for the longest possible time.

Most Efficient Solar Panels (Types Solar Panel)

For a few years now there have been only 3 main types of solar panels available on the residential market.

They were Monocrystalline, Polycrystalline, and Thin-film all with varying levels of efficiency and power outputs.

However, recent innovations have introduced a new type of solar panel called PERC (Passivated Emitter and Rear Cell panels), and the developers have evolved the efficiency rating beyond that of traditional solar panels.

Types of solar panels Description
Monocrystalline panels Each cell comprises wafer-thin silicon crystals cut from a pure single ingot. They have better energy production for the space used and are the most expensive.
They counter that high price tag by retaining their level of proficiency for longer
Polycrystalline panels Manufactured from fragmented silicon crystals, have a reduced energy coefficient, and will require a larger surface area to match the output of Mono panels.
On balance, they are somewhat cheaper.
In states with high temperatures, surprisingly, the performance is affected
Thin-film panels The main benefits of thin-film photovoltaics1 are flexibility, lightness, ease of installation, and the lack of a rigid frame.
They can be used in numerous situations and in a wide range of sizes.
Prices are low, but the energy output is the lowest on the market
PERC panels On the rear of the cells, a reflective passivation layer has been added to reflect light that normally is not captured, back into the cell.
It also absorbs light wavelengths that the other photovoltaic cells cannot detect, increasing efficiency and output.
The advantage of a PERC system is space. It has a slightly higher price tag but if space is limited and a high kWh solar panel watts per square foot is required, a PERC panel may be the way to go

How Long Do Solar Panels Last (Solar Panel Lifespan)

Solar panels do not last forever. This is one of the reasons that the carbon footprint of solar panels is higher than that of nuclear energy.

A loss in solar panel production over time is one key indicator that the lifespan of your solar panel is nearing that endpoint.

Photo of several solar panels on a grassy field.

(Image: Michael Förtsch8)

This generally occurs with solar panels that are between 25 to 30 years old.

That is not to say that when your panels reach these milestones they are ready to be thrown onto the scrap heap, just that they may not be as spry at energy conversion as they used to be.

Solar Panel Degradation: Solar Panel Efficiency Expectations

So what are your options when the gradual degradation and reduction of your solar panels do become noticeable?

The solar panel efficiency over time will begin to become more pronounced after about 25 years of use, but that’s not to say that it hasn’t started beforehand. This reduction in power efficiency begins from the first year of installation when that impressive factory level of proficiency meets the real-world environment.

From the very first moment of installation and every year thereafter, there will be a degradation of 0.5% to 0.8%, and this phenomenon is known as the solar panel degradation rate.

The reasons for this gradual decline and premature failure2 start from the very first intensive bombardment of photons from the sun, high winds, rain, snow, and also from birds leaving their mark on the surface of the panels.

Even though there are relatively few moving parts, simple wear and tear will also take its toll.

It has been estimated that after 5 years the official output rating will have declined to about 95%, and after 10 years that will drop further to 92%.

By year 25, their original output capacity will be reduced to about  82%.

Line graph of Solar Panel Degradation After-Time showing the solar panel age in years on x-axis and efficiency on the y-axis.

This decrease in energy output may or may not be noticeable as most homeowners at the point of purchase are advised to install more panels than needed. Because of this excess energy produced, a minute decrease can easily go unnoticed.

Until it doesn’t.

Extra appliances, a bigger refrigerator, a new EV vehicle, or an extension, will put a greater strain on the household energy requirements, and then even a small drop in power will become noticeable.

At that point, recycling the used panels is the next step.

Solar Panel Degradation Curve (Solar Cell Efficiency and How To Create an Energy Graph)

The rate at which degradation occurs will vary depending on various outside factors.

Hail, dust, sand, and corrosion of the frame itself can lead to cell contamination that can accelerate the degradation and quickly decrease the solar panel efficiency over time.

Year 1 2-3% loss 97%
Year 2 0.7% 96.30%
Year 3 0.7% 95.63%
Year 4 0.7% 94.93%
Year 5 0.7% 94.27%
Year 6 0.7% 93.61%
Year 7 0.7% 92.96%
Year 8 0.7% 92.31%
Year 9 0.7% 91.66%
Year 10 0.7% 91.02%

You can keep your solar panels ‘healthier’ by understanding how to clean solar panels and performing the task each month.

Solar panels installed on a trailer.

(Image: Steven Lawler9)

If the seal becomes damaged, water or dust particles can cause microcracks which will determine how long do solar panel last.

Repowering involves replacing less productive solar panels with newer ones to maintain the same level or even increase the level of energy production.

Year 11 0.7% 90.38%
Year 12 0.7% 89.75%
Year 13 0.7% 89.12%
Year 14 0.7% 88.50%
Year 15 0.7% 87.88%
Year 16 0.7% 87.27%
Year 17 0.7% 86.66%
Year 18 0.7% 86.05%
Year 19 0.7% 85.45%
Year 20 0.7% 84.85%

By year 20, the production efficiency has decreased.

Solar panels are tilted for better angle.

(Image: Gellerj10)

Not all panels would have to be replaced and understanding how to test a solar panel will help to identify the original cells that have been in place since the first day of the manufacturing3 process, but are now letting the team down.

If you wanted to create a chart that would demonstrate the degradation curvature for curiosities sake, the data to input would look like this.

Year 21 0.7% 84.26%
Year 22 0.7% 83.67%
Year 23 0.7% 83.08%
Year 24 0.7% 82.50%
Year 25 0.7% 81.95%

Depending on the age of the panel, the output will be diminished.

Close up image of solar panels with rain droplets.

(Image: Les Chatfield11)

Some solar panel manufacturers guarantee the level of output that their products will have at the end of 25 years. A few give a guarantee of 90%, but most of them offer a power guarantee output of 80%.

Solar Company Guarantees and High-efficiency Solar Panels

When nearing the end of its useful life or when the power output is significantly reduced, the comparison of solar panels manufactured to different levels of quality can become quite apparent.

After 25 years of continuous use, the difference between a high-quality panel and a lower-grade one can be a power output of 90% instead of 80%.

For a solar panel with a rating of 350 watts, a 10% reduction would mean it would then produce 315 kWh instead of 350 watts.

Compare that to a lower-grade solar panel that would have an output as low as 280 kWh at the end of that period.

An average household with a standard-size of solar panel system comprised of 15 to 25 panels, would experience an overall energy reduction of solar panel efficiency4 over time that would be hard to ignore.

Proficient vs Efficient Photovoltaic Systems

Photovoltaic systems are not purchased for their looks, but for how efficient they are and their power output.

This method of distinguishing one high-quality and highly proficient solar panel from another demonstrates that they have the same power rating, but when tested side by side, one clearly has the advantage over the other.

It is this ability to deliver an accurate power output that is important to homeowners.

Investing in solar panels is not something they are going to be doing every year so the importance of installing a system that is going to encompass all of their energy requirements for decades is going to be of paramount importance.

Zoomed in image of a broken solar panel.

(Image: Kiran Jonnalagadda12)

Barring unforeseen damages (from hail or other issues) or a solar panel failure from a fault that has gone undetected since the point of manufacture, or damage during transportation, solar panels will only need upgrading decades down the road.

If there is any doubt, it is possible to create an energy graph to highlight the rate of energy reduction to be aware of when the level of electricity becomes insufficient for your household or business requirements.

It is at that point, regardless of whether you are in year 25 or year 10 when it might be prudent to change your aging solar panels for the latest models.

In the last 5 years, the technology5 and efficiency of solar panels have improved immensely.

In the next 10 years, they are certain to be even smaller, more powerful, and deliver a greater output of electricity.

Solar Panel Size Chart

Solar panels have different cell configurations to provide different power applications for an ever-increasing variety of premises.

Space is often the biggest consideration before purchasing a solar system kit.

Limited space can mean limited power because cells can only convert so much sunlight into electricity, even as the solar panel efficiency over time decreases.

If you know the available space on your roof, by using a solar panel size chart, it would be possible to calculate how many panels can be installed.

Standard size of solar panels are:

Solar Panel Size Configuration Quantity of Cells
3.25 feet x 5.5 feet 6×10 grid 60 cells
3.25 feet x 6.42 feet 6 x 12 grid 72 cells
3.45 feet x 5.22 feet 8 x 12 grid 96 cells

After calculating the monthly or yearly energy consumption of your household from your utility bills, it’s possible to ascertain the number of solar panels that you will need.

From that information, the correct solar panel system can be determined based on your power needs and the space available.

With these 3 standard sizes to choose from, it shouldn’t be too difficult to select the right configuration and a professional installer would advise the appropriate panel sizes to select, that will not only fit onto your roof but also into your budget.

Emerging Photovoltaics

Over the last decade, solar panels have gone from a power rating of 295 Wp to 600 Wp, with the implementation of silicon-based cells, actually doubling their power output.

Researchers are well aware that solar panel efficiency over time will continue to decline and have been experimenting with new materials inspired by the insect eyes6 to reduce that degradation, increase everyday efficiency, and make the solar panels thinner and lighter.

Solar panel being held by a man with gloves for check up.

(Image: United Solar Ovonic13)

Perovskite cells have the potential to exceed the proficiency of silicon cells once the technology has been refined.

Cheaper, lighter, and even more flexible photovoltaic systems that are supported by improved battery storage methods will attract more consumers to this form of cleaner energy that is quickly evolving to offset the effects of climate change.

Understanding solar panel efficiency over time can help you know when to replace them, and how to determine the real value of the solar energy system you’ve installed.

Frequently Asked Questions About Solar Panel Efficiency Over Time

What Is Solar Panel Efficiency?

The overall efficiency of a solar panel is not measured solely by the amount of sunlight it can absorb, but by how much it can convert into usable electricity.

What Impacts the Efficiency of Photovoltaic Cells? Why Do Solar Panels Degrade?

Solar irradiation, variations in temperature, voltage fluctuations, and natural wear and tear will affect solar panel efficiency over time.

What Is the Nrel Efficiency Chart?

The National Renewable Energy Laboratory efficiency chart illustrates the reasons for the degradation of solar panels over their life cycle.

What Is Cell Max? (Best Solar Panels)

The best solar7 panels have a high cell maximum capability, meaning that they convert a larger portion of irradiation into electricity than their slightly inferior counterparts.

What Time Is Better for Using Solar Panels?

The hours between 11 to 4 are the best time as the sun’s rays are more intense at this time of day.

Are Some Months Better Than Others for Solar Panels?

Between March and September, there are more daylight hours and irradiation for the photovoltaic systems to capture.

What Is the Size of Standard Solar Panel?

The standard solar panel size varies, depending on type of panel and brand.

Learn More About Solar Panel Efficiency Over Time


1Solar Photovoltaic Technology Basics. (2023). NREL. Retrieved 04 05, 2023, from: <>

2NIST Study Uncovers a Potential Driver of Premature Solar Panel Failures. (2020, 03 10). NIST. Retrieved 04 05, 2023, from: <>

3Solar Manufacturing. (2023). Energy Efficiency & Renewable Energy. Retrieved 04 05, 2023, from: <>

4Solar Performance and Efficiency. (2023). Energy Efficiency & Renewable Energy. Retrieved 04 05, 2023, from: <>

5Solar photovoltaic. (2023). Lafayette College. Retrieved 04 05, 2023, from <>

6Stanford News. (2017, 08 21). Insect eyes inspire new solar cell design by Stanford researchers. Retrieved 04 05, 2023, from: <>

7Researchers improve efficiency of next-generation solar cell material. (2021, 02 24). MIT News. Retrieved 04 05, 2023, from: <>

8Michael Förtsch. Unsplash, Retrieved from: <>

9Old solar panel shed. – panoramio Photo by Steven Lawler / Attribution-Share Alike 3.0 Unported (CC BY-SA 3.0). Resized and Changed Format. From Wikimedia Commons <>

10Ecological Farm Solar Panel Photo by Gellerj / Attribution 4.0 International (CC BY 4.0). Resized and Changed Format. From Wikimedia Commons <>

11Solar panel on meter Photo by Les Chatfield / Attribution-ShareAlike 2.0 Generic (CC BY 2.0). Resized and Changed Format. From Flickr <>

12Cracked solar panel near Leh Photo by Kiran Jonnalagadda / Attribution-ShareAlike 2.0 Generic (CC BY 2.0). Resized and Changed Format. From Flickr <>

13UNI-Solar’s thin-film laminate product Photo by United Solar Ovonic / Public Domain. From Wikimedia <>