What does ‘efficient’ mean in terms of solar?

Efficiency in electricity production is how much of the power source’s energy is converted into electrical energy.

For example coal has an efficiency of 33%, whereas oil carries an efficiency of 37% meaning 37% percent of the heat energy contained in coal is converted into electricity.

Combined-cycle gas-fired plants fare better by being able to convert 56% – 60% of their energy to electricity.

Of course, this doesn’t even look at the terrible effect fossil fuels have on the environment, with pollutants and greenhouse gases contributing to climate change and mining destroying natural habitats.

Solar panels have an efficiency between 19%24%, with monocrystalline PERC panels giving higher rates when it comes to the residential solar market.

The boffins in the labs around the world are trying to get those efficiencies a lot higher; they’ve managed to more than double efficiencies in the last decade.

The lower efficiency panels are polycrystalline panels, which are considered old tech now and rarely used in domestic installations, so this blog is largely about monocrystalline panels.

solar efficiency in comparison to other sources

Getting the most from your solar panels

There are many factors that affect the amount of energy solar panels can generate, some at the manufacturing stage and some during the lifetime of the panels itself.

The efficiency of the cells degrades over 25 – 40 years, but if the cells get damaged or overheat it can happen faster.

How manufacturing affects the efficiency of a solar panel.

Solar Cell Construction

How the solar cell is constructed is very important to the efficiency of your solar panel.

Silicon crystals are what create the electrical magic in ‘crystalline’ panels.

Silicon is a semiconductor and can be found in quartz and sand, among other things.We extract it by heating the base material up to melt the silicon and extract it. After that, the silicon is purified using Boron – the purer the silicon the more efficient it is.

The silicon is then further treated to create the crystals – either single crystals which are very efficient, or clusters of crystals which are still very useful but less efficient.

This silicon is then cut into thin layers to make photovoltaic cells.

Cell splitting

One way the solar boffins have found of increasing efficiency in using the current technology is to split the single crystals in two, creating a smaller, less resistive cell.

This also means that there can be twice as many cells in a smaller space – which we see in 104 Half Cell Monocrystalline panels – whose efficiency is 24%.


The construction of a panel is very important.

Materials that heat up will affect the silicon inside the cells.

The hotter silicon gets, the more resistive it becomes, which increases the barriers to electricity flow.

Monocrystalline cells are black, so black on black panels have become popular. It’s not just aesthetic though; black materials absorb heat, so it is kept away from the crystals.

Some panel constructions utilise a reflective base and double-sided cells to collect the light that is reflected by the panel’s casing.

What affects the efficiency of an installed solar panel?


Once installed the panels will perform best if they are in direct daylight with nothing in between the panel and the sun.

While clouds offer a little shading, most of the ‘important’ light makes it through them and onto your panels, but the thicker the cloud cover the more it will affect the efficiency.

shading explained for solar

Other shading will come from roof furniture, like ariels and chimneys, and also trees and other fauna reaching over the roof.

Dust and dirt also don’t help your panels, but a good rainstorm will usually clean them enough to make sure they are operating at maximum efficiency.

One problem with shading and damage is that string inverters only work at the same rate as the lowest performing panels in the array.

This means that, say you have 12 panels on your roof and they are all working at full efficiency, the sting inverter will function at full efficiency as well.However, if one of those panels is in the shade of a tree and its efficiency drops, the inverter will then only work at the same efficiency of that panel.

Shaded panels can be boosted using optimisers.


Yes, solar panels do not like the heat!

The common misconception is that hotter countries are better for solar panels, but this isn’t strictly speaking true.

While hotter countries have stronger sunlight, and more of it, that sunlight can also heat up the silicon, creating high resistance and restricting the flow of electricity, reducing the panels efficiency. 

Northern Europe actually has the best climate for fully utilising solar, but only Germany is really harnessing that power – with France coming in a close second.

Keep them clean

Luckily, due to the angle they are fitted, most rooftop panels self clean using the rain and snow. 

But, if the local wildlife is clambering all over your roof, or you live by the sea and suffer from a lot of salt in the air, you may need to invest in having your panels cleaned properly a couple of times a year. 

Obviously, any dirt and dust covering the glass case of the panel will reduce the amount of light getting to the cells and reduce your yield.

Get the panels facing as close to the South as possible. 

A South facing roof in the UK will get direct light from the sun throughout the day, which means the panels will be producing electricity from sunrise ‘til sundown. 

As you angle away from the south the light hitting the panels will be slightly less intense.

That said, an East West split can be a great way to get power all day but you may need to optimise some of the panels. 

Get the right angle 

To work out the best angle for a solar panel you would 15 degrees to your latitude during winter, and subtract 15 degrees from your latitude during summer.

So, here in the UK the latitude is around 51 degrees – so, in a perfect world, your panels will be at 34 degrees and in winter 66 degrees.

But, we can’t be moving panels every few months, so somewhere in the range of 50 – 30 degrees is best.

Get them installed by a reputable installer!

Anyone registered with MCS is going to know what they’re doing in terms of angles, shading and panel placement. 

If they don’t, your system is not going to yield anywhere near its potential, and it could actually be dangerous.

Types of solar panels and their efficiency

efficiency of different types of solar panels

Monocrystalline Solar Panels

First off, we’ll tell you how panels work.

Panels are made of photovoltaic cells that contain silicon.

Silicon is the material that creates the magic as when it is hit by light, the molecules inside jiggle about to create electricity. The purer and more crystalline the silicon, the more electricity is created.

Monocrystalline panels are the industry standard these days, and they are by far the most efficient, as the photovoltaic cells are created using 100% pure, single crystal silicon.

The latest monocrystalline panels take the process a step further by splitting the crystals in two – this reduces resistance inside the crystals and allows more electricity to flow.

These are called Half Cell Monocrystalline panels and they can have an efficiency of up to 24%.

This makes them perfect for installations that have limited space but need more yield, which is why they are the ‘go to’ panel for domestic, and even commercial, instals. Learn more about Monocrystalline Solar Panels.

Polycrystalline Solar Panels

Polycrystalline panels are cheaper to make as the process of making the silicon wafers is much easier.

Polycrystalline means ‘many crystals’, which in this case relates to the fact that silicon is not split into single crystals and is instead a mass of crystals all squished together.

That sounds like it should be better but the amount of electrical resistance it creates slows the flow of electricity.

This is why polycrystalline panels are usually 16% – 19% efficient.

Polycrystalline panels are generally used where there is lots of space, like on solar farms or in DIY projects in people’s backyards.

Learn more about Polycrystalline Solar Panels

Thin Film Solar Panels

Thin film solar panels are slightly different to their crystalline cousins as they can be made from different materials:

  • Amorphous silicon
  • Cadmium telluride
  • Copper indium gallium selenide
  • Organic PV cells

The materials are layered over the top of one another to create the ‘film’ – this makes the panel flexible and able to be fitted to almost any surface.

So, while they are still in development they are starting to appear as helpful camping tools, to charge phones etc, as well as on some buildings where they can replace cladding or tiles.

The downside is they are not as efficient as crystalline panels – coming in at between 7 – 13%.

Testing the efficiency of solar panels

Solar Panels are tested incredibly vigorously and, as they are guaranteed for 25 years and can last twice as long, that seems like a good idea. (We offer 30 years..)

When they are subjected to testing the idea is not only to find out if they are robust or not, but also that they can maintain their efficiency no matter what the conditions.

Most important is the Irradiation Test.

This is how the panel performs with full solar noon sunshine (irradiance).

Standard test conditions for a solar panel are 1000 W/m2 (1 kW/m2) when the panel and cells are at a standard ambient temperature of 25 degrees C with a sea level air mass (AM) of 1.5 (1 sun)- no, we don’t understand it either!

At those levels the panel will perform at its absolute best, giving you its full efficiency. 
Panels are then tested to be hurricane, hail, water, and extreme low temperature safe.

Solar panel’s natural loss of efficiency

Silicon is a very robust material but unfortunately it does degrade over time.

Electricity is created by daylight, or photons, jiggling the atoms inside the silicon – the more they jiggle the more electricity you get.

But, also, they will start to lose their jiggle as the years go by, at a rate 0.5% every 12 months. 

Not something that’s going to worry you too much as, after 25 years the efficiency is still around 80% of what it was when the panel came off the production line.

solar panels loss of efficiency

Learn more about how long solar panels last.

Looking to the future and increased Solar Panel efficiency.

As we mentioned earlier, the materials that are used in solar panels do restrict the people in labs trying to up everyone’s efficiency. 

But that doesn’t mean we can’t start experimenting with some different materials – mostly replacing silicon with much more attractive superconductors.

Organisations like NREL, National Renewable Energy Laboratory, are experimenting with unique construction, advanced technology and new materials – with some prototype panels showing an efficiency of 47.7%, which is incredible. 

That kicks coal and oil into a cocked hat – and no emissions! 

Graphene is a super conductor that is revolutionising the world of electricity and may take us past the 50% efficiency mark – though tests at the moment concentrate on combining it with silicon.

It’s used in batteries already and the solar panel aspects are being investigated right now.

Unfortunately, graphene is currently around $180 a square inch and the price goes up, exponentially, the more you want – so it’s far from being a solution just yet.

Perovskites are another collection of materials that are starting to make their way into the solar market but are currently so expensive that they won’t be commercially viable for a good few years. 

These new technologies mean that Solar Power is still very much in its infancy when it comes to development and we can only look forward to more efficiency, meaning more power per square metre and much more affordable electricity.

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