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How effective are solar panels?

We’re all aware of the increasingly pressing need to switch to renewable energy for our homes and businesses. With a climate crisis upon us, it’s never been a better, or more important, time to look to replace our existing energy sources with a more environmentally-friendly alternative.

It is estimated that there is at least four to five billion years of sunlight left on the planet, and with the sun rising each day, using the sun’s energy to create electricity for our use seems like a no brainer.

In the past, seeking cleaner energy sources has been confined to those wanting to live off-grid, or with an abundance of spare cash to spend on changing their traditional source of energy.

As solar panel technology has continued to develop over the last two decades, installing a solar system to your home or business has never been easier to achieve or more affordable.

Cutting down on your monthly energy bills, and reducing your carbon footprint is a very appealing prospect, but one of the questions you may have before taking the plunge and investing in solar is how effective are solar panels for a home or business.

To better understand how you can benefit from installing solar panels, it’s a good idea to first learn about the efficiency levels of different solar systems. Considering the effectiveness of the panel will help you decide which system is best for your economic and environmental needs.

A variety of factors will impact how effective solar panels are; including panel placement on your roof, geographic location of your home, temperature, roof design and the sunlight to shade ratio your roof receives each day. Each of these must be considered ahead of purchase to ensure you get the best from any system you choose to install. 

Determining how effective are solar panels is simply the measurement of energy output across the surface area. The higher the efficiency of a panel, the less space it will take up. It’s important to remember that the most efficient panel may not be the cheapest.

For example, if you have a smaller roof with limited space, a more efficient solar panel is the right choice for you. The increased efficiency may mean a higher cost but they will meet your energy needs.

If you have a larger roof space, you have the option to choose cheaper and larger panels to reduce costs, as you’ll be able to install more solar panels for the space you have. Or, you might still optimise the space you have with the highest efficiency panels, and increase the size of your system, rather than having to compromise.  

How effective are solar panels: everything you need to know

Solar panel system efficiency is the measure of the amount of sunlight that falls on to a solar panel and is converted into useable electricity.

There have been many advances in photovoltaic technology in the last decade, meaning that solar panel efficiency has increased from 15% to over 20%. This huge jump in efficiency levels has resulted in a power increase in an average-sized solar panel to increase to 370W.

As we explained earlier, the efficiency of a solar panel is determined by several factors, but the two most important are the photovoltaic (PV) cell efficiency, which is based on the cell’s design and silicon type, and the panel’s total efficiency, which is made up of the cell layout and panel size.

What is cell efficiency?

Solar panel systems are made from photovoltaic cells, which is why another name for solar panels is solar PV. These cells are what helps the conversion of the sun’s energy into electricity.

The efficiency of a solar panel cell is determined by the structure of the cell and the base material, usually silicon. Cell efficiency is calculated by what is known across the industry as fill factor, which is the maximum conversion rate of a photovoltaic cell running at optimum operating conditions (voltage and current).

The design of each cell plays an important role in determining how effective solar panels are. 

What is panel efficiency?

Testing panel efficiency is measured based on a standard cell temperature of 25 degrees, solar irradiance of 1000W/m2, and air mass of 1.5. From this calculation, the percentage efficiency of a panel is calculated by the maximum power rating, divided between the total square meter area of the panels.

Panel efficiency can be influenced by several factors, such a temperature, cell type and the way the cells are connected to each other. It may surprise you to learn even the protective back sheet on a solar system can affect efficiency. Black back sheets absorb more heat, resulting in a higher cell temperature and increased resistance, which can rescue total conversion efficiency.

As well as standard test conditions, testing to determine how effective solar panels are is undertaken in extreme conditions such as snow, chemical exposure and humidity too.

What determines how effective solar panels are?

The efficiency of solar panels is dependent on several factors including installation and assessment of the roof structure. Ahead of any install, a solar professional will assess the design and location of where your panels will be fitted, to determine the best type of installation for your needs. 

Some factors that can impact efficiency:

Panel design

The majority of solar panels are designed with a layer of glass to protect the cells, which sunlight must be able to pass through. The amount of energy converted depends on the angle in which the light passes through, and reduction in reflectivity of the glass must be taken into account too.

Panel installation and position

The correct installation of a solar system is particularly important in order to capture the maximum amount of sunlight available. How effective your solar panels are will be determined by the amount of sunlight converted into energy.

The slope of your roof

The angle of your roof will impact how much sunlight the solar panel system receives throughout the day. While residential solar panels are often static, larger businesses can benefit from commercial solar tracking systems, which compensate for the movement of the earth.


Whether your roof is surrounded by trees, or there are other buildings blocking sunlight, the amount of shade your roof is exposed to can have an impact on the efficiency of your panels. In an ideal world, panels will be fitted to avoid any shade throughout daylight hours.


Considering the nature of a solar panel system, the temperature can have an impact on the efficiency of the system. Very high temperatures can reduce efficiency and output, so depending on where you live, you may need a solar system designed for warmer climates.

What are the most efficient types of solar panels?

There are three most common types of solar panels:

  • Monocrystalline solar panels
  • Polycrystalline solar panels
  • Thin-film solar panels

It’s very important to remember that the efficiency of the individual solar cells does not determine how effective solar panels are as a system overall.

Monocrystalline solar panels

Also called single-crystalline cells, monocrystalline solar panels are derived from the purest silicon. Monocrystalline cells are created in a complex process, which includes wafering molten silicon to form a shell, then cooled to become solar cells. 

These types of cells are the original material for solar panels and are still widely considered to be the best and most efficient. 

Currently, monocrystalline solar cell efficiency stands at 22-27%. These cells are easily identified as they have a rounded edge and are black to the naked eye.

Polycrystalline solar panels

Growing in popularity, this type of panel is a more recent introduction to the solar panel market. Just like monocrystalline cells, these cells are made from silicon, but the main difference is the way they are produced. 

During the manufacturing process, the silicon crystal is given time to fragment and cool. The cells of a polycrystalline solar panel are blue, as sunlight reflects on the fragmented crystals. 

The current efficiency of polycrystalline panels stands at 15-22%, these panels can be determined by the square cut and blue speckled shade.

Thin-film solar panels

Designed to be flexible and low in weight, the production of thin-film panels is slightly less complex, so the panels are known to degrade slightly faster than the other two types of panel. 

They are made by covering a section of glass, metal or plastic with one or several layers of photovoltaic material to create a panel. 

The efficiency of thin-film panels is currently 15-22%, but thin-film technology is quickly closing the efficiency gap with more expensive types of solar panel, and thin-film panels are often installed on large scale projects and industrial-sized solar power plants.

What to look for when choosing a solar panel system

Hiring a professional solar installation company, such as Project Solar UK, to assess your building and infrastructure will help you to determine the most effective solar system for your needs.

Good quality solar panels should last at least 20 years, and with Project Solar you’ll receive a lifetime warranty guarantee when purchasing a system.

If you’re ready to start your solar installation journey, get in touch with our team today.