Solar panels work by converting sunlight into electricity. But there are no panels available which convert 100% of the light they receive into power. The measure of how much sunlight is converted into electricity by solar PV panels is known as their efficiency.

Solar technology has come a long way in recent years, and one way that is readily apparent is in the improvement in the efficiency of solar panels. The highest grade of panels which are commonly used can now reach efficiencies of up to 23%.

There are many factors which affect the efficiency of solar panels such as the type of materials they are made from, your local climate, and the location of your home or business.

Depending on a number of factors, the efficiency of solar panels used in most homes and businesses will tend to range in efficiency somewhere between 15% – 23%.

On a pitched roof solar panels can only be placed in the direction any given side is facing

Why Solar Panel Efficiency is Important

There are a number of reasons why you might opt for more or less efficient solar panels depending on financial and environmental factors.

As a rule of thumb, the more efficient solar panels are, the more expensive they are going to be. Being made of higher quality materials and design will push up the cost, so consider your budget when selecting panels.

You also need to take into consideration the amount of space you have available for your solar PV panels. Not all rooftops have a lot of space to install solar panels. If there is limited space on your roof, then high-efficiency panels could be your best option to maximise your electricity output.

Get a Quote for Rooftop Solar

Take our 90-second online assessment and we’ll determine if your home is well suited to solar. It only takes 90 seconds and it’s 100% cost and commitment free.

Do Solar Panels Degrade

Solar panels also degrade and lose efficiency over time, usually at a rate of approximately 0.5% each year. If your solar panels are starting from a higher efficiency, then you will get much longer out of them before the loss becomes noticeable.

If you have an extremely high quality solar panel, with an annual degradation of just 0.25% efficiency, then after a 25 year period the solar efficiency will have fallen by just 6.25%.

lifespan of solar panels is 25 - 30 years

Types of Solar Panels

There are three main types of solar panels using different materials and construction methods, which deliver different levels of efficiency.

The three main varieties of solar panel technology are:

  • Monocrystalline
  • Polycrystalline
  • Thin-Film
three main types of solar panels

Monocrystalline Panels

The most efficient, and thus most expensive type of solar panel, mono-crystalline panels are made from a single silicon crystal. They produce the most electricity per square metre, with an efficiency of around 17% – 23%, and thus will take up less roof space overall.

Polycrystalline Panels

Made from multiple silicon crystal fragments  which are melted together, These have a cheaper manufacturing process, making them more affordable. However this comes at the cost of lower efficiency, which usually ranges from 13% – 17%.

Thin-Film Panels

Easy to produce, and flexible unlike other varieties of solar panel, Thin-Film panels are made by layering a film of photovoltaic material over a substrate, or several layers of film. Most of these used in home installations will have an efficiency of around 6% – 15%.

There will always be examples of the cutting-edge industry leading models of each of these types of solar panel which will exceed these efficiencies. But the figures above give an approximation of most models on the market.

8 Years

A typical solar installation is fully paid back within 8 years. All our panels are under warranty for 25 years, so you will enjoy 17 years of free energy generation.

0% VAT

As of May 10th 2023, the government has removed all VAT on Solar installation and solar panel supply. Solar has never been more affordable. 

Government Grants

There is are a number of government grants available for all new solar installations. Our team will guide you through the application process. 

External Factors Affecting Solar Panel Efficiency

There are multiple other factors outside of the manufacturing specifications of your solar panels which will affect their real world efficiency. These can be broadly split up into environmental factors, and installation factors.

External Factors Affecting Solar Panel Efficiency-39

Solar Panel Installation

The location and installation of your solar panels and other elements in your solar PV system will affect how efficient they are at producing electricity.


Solar panels should be orientated to take maximum advantage of the sun in your local environment. In Ireland, a south facing solar PV array will deliver the greatest amount of electricity overall, while east and west facing panels might also be considered depending on when you use the most electricity.


Having your solar panels installed at the correct angle is important to ensure that they absorb the most sunlight. Ideally, solar panels in Ireland should be angled at 30 – 40 degrees for the optimum absorption or sunlight.


Having your solar panels in areas where they are in shade can significantly reduce the efficiency of solar panels, or the entire array depending on your specific setup. If all of the solar panels in your PV system are connected on a string to a single inverter, then they can only operate at the level of the least efficient solar panel. 

This means partial shading on just one or two panels can affect all of them. Having microinverters which are installed on each individual solar panel can help to address this issue.

Environmental Factors

Along with how your solar panels are installed, you must also take into consideration the natural elements of your area.

Hours of Sunlight

How much sunlight is received in your local area will have a profound effect on the amount of power produced by your solar panel. In Ireland, the south-east of the country receives the greatest amount of sunlight per year, while the south-west receives the least.


Solar panel efficiency is affected by the temperature of the environment. But not in the way you might expect. The Standard Test Conditions for solar panels in the lab measure their efficiency at a cell temperature of 25 degrees Celsius. When the panel temperature rises above that level, they begin to lose efficiency. 

Because the real world rarely mimics lab conditions, most solar panels specifications will include how much power they will produce under a Nominal Operating Cell Temperature (NOCT), usually around 44 degrees.


The buildup of dirt  or ice on your solar panels can severely reduce the efficiency of solar panels by blocking sunlight from getting through.


Rain itself does not affect the efficiency of your solar panels, and may actually improve their performance by keeping them clean of dirt, or cooling them off if their temperature has gotten too hot. However, rain clouds can reduce their efficiency by blocking the sunlight.

Technical Specifications Affecting Efficiency

Power Temperature Coefficient

The amount which electricity generation increases or decreases as the cell temperature rises above or below 25 degrees Celsius is known as the power temperature coefficient. The temperature coefficient is measured as a % / ℃. 

The lower the temperature coefficient is, the more efficient the panel is at dealing with higher temperatures. High-end Monocrystalline N-Type solar cell panels have a temperature coefficient 0.26%, meaning that for a 10 degree increase in cell temperature over 25 degrees, their efficiency will fall by 2.6%.

Inverter Efficiency

The power inverter is what converts the DC electricity produced by your solar PV array into AC electricity which is usable in your household. Your solar panels might be connected on a string to a single inverter, or in some cases might have microinverters connected to each panel.

Get a Quote for Rooftop Solar

Take our 90-second online assessment and we’ll determine if your home is well suited to solar. It only takes 90 seconds and it’s 100% cost and commitment free.


Solar panels typically come with a 25 year warranty, but they can last even longer than that, just at reduced efficiency. They will still produce a considerable amount of electricity after that time. However, you will likely have to replace the inverter at least once in that 25 year period.

The number of solar panels you need for your home and business depends on the amount of electricity you consume, how much of that electricity bill you want to offset, the type of panels you pick, and many other factors. Typically, domestic solar PV arrays will range in size from 1kWp to 6kWp in size.

Regular maintenance of your solar panels can help ensure that they are operating at their maximum efficiency for as long as possible. Investing in a solar monitoring system can also provide real-time information on the performance of your solar panels, and let you know if it’s dropping for any reason.

Learn more about solar panels today

Take the energy efficiency online assessment today to get the best quote for your home solar panels today.

Find out how much you can save on your home energy bills with solar panels.

consider getting solar panels installed on your home or business

Solar Energy Saves Households Thousands in Electricity Costs

Take our 2-minute questionnaire and find affordable solar options to suit your budget and lifestyle