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

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.

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%.

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.

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.

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