Let’s discuss solar panel efficiency

Solar panel efficiency varies from brand to brand, but it’s often a key selling point for many of our customers. Today, we’re going to focus on how efficient solar panels are, whether they lose efficiency over time and what you can do to make them as efficient as possible.

What is the definition of solar panel efficiency?

Solar panel efficiency refers to the amount of sunlight solar panels convert into usable energy.

How is solar panel efficiency measured?

The efficiency is in a percentage which is the result of dividing the electrical power output (in watts) by the solar energy input (sunlight) which is received over the surface area of the panels.

How efficient are solar panels?

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% 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. However, This doesn’t account for the terrible effect the burning of fossil fuels has on the environment, with pollutants and greenhouse gases contributing to climate change, and mining destroying natural habitats every single day.

On the other hand, solar panels have an efficiency of between 19%-24%, with monocrystalline PERC panels offering higher rates in the residential solar market. And with efficiencies doubling in the last decade, this is only the beginning for solar efficiency.

The lower efficiency panels are polycrystalline panels, which are considered old tech now and rarely used in domestic installations, so let’s focus on monocrystalline versions instead.

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 themselves. The efficiency of the cells degrades over time, but if the cells get damaged or overheat, it can happen even sooner.

Can solar panels be 100% efficient?

No, it’s impossible for solar panels to be 100% efficient due to inherent material limits which cap efficiency levels.

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 panels. Silicon crystals are what create the electrical surge in 'crystalline' panels, a semiconductor which can be found in quartz and sand, among other materials.

We extract it by heating the base material up to melt the silicon and extract it. After that, the silicon is purified using Boron, and 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.

On the other hand, the hotter silicon gets, the more resistive it becomes, which increases the barriers against electricity flow. Monocrystalline cells are black, so black on black panels have become popular. It’s not just for aesthetics though; black materials absorb heat, so it’s kept away from the crystals.

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

Cell splitting

One way scientists have increased solar efficiency is by using current technology and splitting 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 which have an efficiency of 24%.

What affects the efficiency of an installed solar panel?

Here are some issues that can reduce solar panel efficiency, as well as how you can increase solar panel efficiency.

Shading

Once installed, the panels will perform best if they’re in direct daylight with nothing blocking the sun from reaching them. 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’ll affect the efficiency of the panels.

Other shading may come from roof furniture, like aerials and chimneys, and trees and other fauna reaching over the roof. 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 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. However, shaded panels can be boosted using optimisers.

Are dirty solar panels less efficient?

They can be. Dust and dirt won’t help your panels, but a good rainstorm will usually clean them enough to make sure they’re operating at maximum efficiency. Learn how to clean solar panels to improve efficiency.

Heat

Yes, solar panels don’t like the heat. The common misconception is that hotter countries are more suitable for solar panels, but this isn’t factually correct. 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.

Keep them clean

Luckily, due to the angle they’re fitted at, 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 there’s 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 reaching 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. However, an east west split may still benefit your power generating, but you’ll likely need to optimise some of the panels.

Get the right angle

To work out the best angle for a solar panel, you’d add 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.

Therefore, your panels should be at 34 degrees in the summer and 66 degrees in winter. However, we understand this isn’t always achievable, especially as you don’t want to be moving your panels each season, so somewhere in the range of 50-30 degrees is recommended.

Get them installed by a reputable installer

You should always source an installer that’s registered with MCS as they'll be fully knowledgeable in angles, shading and panel placement. Without this knowledge, your system is not going to yield its full potential, and it could actually be dangerous.

Types of solar panels and their efficiency

Efficiency can also be determined by the type of solar panel. Let’s take a look at how efficient each type is.

Are more efficient solar panels worth the extra cost?

Whether more efficient solar panels are worth it will depend on your position. We recommend opting for the most efficient if you have limited roof space, you plan to stay in your home long-term, you want to generate more energy from less sunlight or you live in an area with high energy prices. On the other hand, it’s not always viable if you don’t have the budget, savings don’t outweigh the initial investment or if you’re planning on moving soon.

Testing the efficiency of solar panels

Solar panels are tested vigorously to ensure they reach their lifespan of 25 years. When they’re subjected to testing, it's not only to identify their robustness, but to ensure they’ll maintain their efficiency, no matter the conditions.

The most important test is the Irradiation Test, which is designed to identify how the panel performs against 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).

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.

Do solar panels lose efficiency over time?

Yes, 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, and the more they jiggle, the more electricity you get. But they also start to lose their jiggle as the years go by, at a rate of 0.5% every 12 months.

Are solar panels becoming more efficient?

As mentioned above, the materials that are used in solar panels restrict how efficient they can be. But that doesn’t mean we can’t start experimenting with other materials, mostly replacing silicon with much more attractive semiconductors.

For instance, organisations like NREL, The National Renewable Energy Laboratory, are experimenting with unique construction, advanced technology and new materials, with some prototype panels showing an efficiency of an incredible 47.7%.

Graphene is a semiconductor that is revolutionising the world of electricity, with a potential vision to take us past the 50% efficiency mark, but tests at the moment concentrate on combining it with silicon still. Unfortunately, graphene is currently around $180 a square inch and this will continue to rise, meaning it’s not a solution as of yet.

As another future trend in solar panel efficiency, 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 several 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 most importantly, affordable electricity.

The efficiency of solar panels comes down to various factors, including the type and angle. If you’re considering starting your solar journey, get a free, non-obligation quote from Wickes Solar and we’ll answer any questions and concerns you may have.