How Efficient Are Solar Panels?

The efficiency of solar panels is a prime consideration when it comes to how much electricity a system will actually generate. This has a direct effect on how much money you make from it and how long it takes to break even on the investment.

Efficiency is a buzzword that is often used yet rarely understood in depth. To understand solar panel efficiency, you need to understand the many components that affect system performance, output, and longevity.

Let’s take a closer look at solar panel efficiency so you can better determine whether a system is right for your home. We’ll also explore factors that affect efficiency and how this metric impacts other system variables.

How Efficient Are Solar Panels

What is solar panel efficiency?

Solar panel efficiency denotes the level of efficiency with which a photovoltaic (PV) cell converts sunlight into usable electricity. Solar panel efficiency can also be described as thermal or conversion efficiency.

A cluster of cells make up a panel, and a cluster of panels make up a solar array or solar power system. All of these elements work together to create usable energy in the form of alternating current (AC) as opposed to direct current (DC).

So, how efficient are solar panels? The highest solar panel efficiency ratings are 23%. This means that even the best system only converts 23% of the actual sunlight that hits the panels into alternating current. Most of the top panels will range somewhere between 19% – 22% in practice.

The reason that so much efficiency is lost is due to various factors, outlined in more detail below. But flaws in the crystal, high temperature, or light reflection/deflection are the main considerations in terms of the loss of output.

It is important to know the solar efficiency of a given solar panel. Lower efficiency will mean you need more panels, which is a big problem if you don’t have a lot of rooftop space.

Factors that affect solar panel efficiency

There are four core factors that affect the efficiency of solar panels. It’s useful to know these, but the end figure is what you should be most concerned with. If a solar panel array has 22% efficiency, then you know what it will generate compared to how much sunshine they receive each year. This allows you to focus on costs and the financials without getting overly technical.

Thermodynamic efficiency

Solar cells can only absorb 86% of the sun’s light before it turns into heat energy. This is the maximum percentage possible of the conversion of sunlight to usable electricity.

This is a scientific principle that holds true for all thermal devices that use the sun’s rays. It is also known as the Chambadal-Novikov efficiency. The bottom line is that 86% is actually the highest conceivable level of efficiency possible, and 14% will always be lost.

Reflection

When the sun’s rays hit a solar panel, much of it is actually reflected back out. So the less that is reflected, the higher the efficiency.

Practically all solar panels have an anti-reflective coating of some kind. Untreated silicon (the material solar panels are made from) will deflect 30% of light, which is an unacceptable number. This is why the highest efficiency solar panels are either black or blue. They absorb the light rather than reflecting it like a white solar panel would.

Material

The majority of residential solar panels are monocrystalline, with a smaller number being polycrystalline. Monocrystalline is made of a single silicon crystal while polycrystalline is made of numerous silicon crystals melted together. The result is that monocrystalline solar panels are more uniform and transfer the energy more smoothly. Polycrystalline tends to have more resistance due to its design, making it inferior in terms of efficiency.

Temperature

Solar panels do less well in high temperatures, which might sound counterintuitive. With higher temperatures, the properties of the semiconductor shift, and the result is a decrease in voltage.

A key theme here is that the energy that is ’lost’ in a solar panel is usually transformed to heat energy. You want to avoid this. Another factor is that extreme heat could shorten the longevity of the solar panels.

How important is the efficiency of solar panels?

This is important but is actually not the dominant criteria in terms of how much money you save or how much energy you generate. The efficiency of solar panels is determined by how much usable energy is produced when sunlight hits a solar panel. It assumes that sunlight is already available.

So the most important component is sunlight which will be determined by your location and the weather. Even if you broke the laws of physics with a 100% thermally efficient panel, you would have no energy if there was no sunlight. And there can be a large variance in the number of annual hours of sunshine between a city like Perth as opposed to Hobart.

Your location will also determine the feed-in-tariff rates as well as the price of electricity. In the wider solar power ecosystem, thermal efficiency is of relevance but must be viewed in light of all other factors.

Can solar panels be 100% efficient?

The maximum efficiency of any thermal device seeking to transform sunlight to usable electricity is 86%. There is no way to achieve 100% efficiency with the technology available (or the laws of physics as we understand them).

What is the average solar panel efficiency?

The average solar panel efficiency tends to be between 19-22%. You can get high-quality solar panels with 23-24%, but no system will go beyond this. There are low-end systems that will be less efficient, but the upfront cost savings will not benefit you in the long term on a system that gets between 16-19% efficiency.

The increased thermal efficiency will nearly always offset any increased cost in the initial investment. Of course, this holds true for the common brand of monocrystalline solar panels. Niche panels used for industrial and government research purposes will have higher efficiency levels.

Which type of solar panel is the most efficient?

Monocrystalline solar panels are more efficient than polycrystalline. But there are other kinds of solar panels less common in residential applications that have varying efficiencies.

Bifacial solar panels

It is unknown exactly how efficient these panels really are, but there are claims around 30-40%. These panels absorb light on both sides, and the majority of those have been made from monocrystalline silicon. Though they could well be the future of solar power, they are currently difficult to install, costly, and need to be near reflective surfaces to work well.

Thin-film solar panels

The efficiency of these solar panels is only 7-12%. However, they still have an application in the residential market. They are far cheaper, and you can put them on most surfaces. They are very flexible and perfect if you have the space available.

Concentrated PV cells

While this is almost hands down the most efficient type of solar panel at 46%, it is not suitable for residential purposes. It is simply too expensive and requires significant maintenance.

What brands have the best levels of solar efficiency

The following table outlines what brands have the highest levels of solar efficiency. This is for residential purposes only. Only specialised kinds of solar panels, such as concentrated PV, will have higher levels of efficiency, but they are not commercially viable for residential installation.

What time of day are solar panels most efficient?

Solar panels are most efficient during the hours of 11 a.m. to 4 p.m. when the sun’s rays tend to be strongest. The amount of sunlight your panels get is the number one consideration in terms of how much electricity is generated.

For the purposes of the overall ROI of your solar array, the total hours of sunshine per year is more relevant than the efficiency of your solar panels. You can simply look up the typical hours of sunshine your location gets in a given year to work out how much you should expect to save.

Solar panels will work in the rain and on cloudy days, but their output will be reduced. In terms of the lifespan of your solar array, rain will have pretty much no effect. They are designed to be waterproof, and the water can touch any of the internal components. The rain might even serve to clean the panels from dust, which can also reduce total output.

How does the angle of the sun affect the efficiency of solar panels?

You will typically lose 15-17% of total available output if you face your solar panels east or west instead of true north. A panel with 22% thermal efficiency might be reduced to 19% if you face it west.

But this might be worth it in certain instances. For instance, if your family uses more energy in the evening, you might want to have north-west facing panels instead of true north to take advantage.

Getting the angle right can be tricky, and it’s best to consult a CEC-licensed professional to make the right decision. The table below demonstrates the output ratio for various angles of solar panel arrays in Sydney.

As you can observe, it is often best to face the panels in a true north direction. The angle or tilt of the array is less important. You might lose 3-4% if it is tilted, but you will lose 20% if it is perpendicular to true north.

How many solar panels would it take to run a house?

It’s not really a question of how many solar panels, though people often ask this. It’s a question of how much energy your solar system needs to generate to meet your typical energy requirements.

For example, you might need a 6kWh system to meet your current energy consumption levels. A solar array able to produce this will typically have around 16-20 solar panels. Panels can be of variable sizes (though they are somewhat standardised into three primary sizes) and varying levels of efficiency. So the number of panels in itself is something of a meaningless metric.

In general, it takes between a 5kWh – 7kWh system to run most houses in Australia. If you’re wondering whether you can run your home on solar power alone, the answer is that it is possible but implausible. You would need a solar battery to help power the home at night or on cloudy days, and this is often not worth the high expense. Let solar power take care of most of your energy needs and use the grid as necessary.

How efficient are solar panels: the bottom line

To make the most in terms of the efficiency of solar panels, you’ll want to get a solar design consultation from a licensed and experienced professional. Roland Lawrence Electrical has over 40 years of combined experience in Sydney and knows the solar industry inside and out.

As a qualified team of electricians, we can give you insights into your solar installation to generate maximum output and maximum ROI for your unique circumstances. The bottom line is that we’re going to save you time and money with minimal fuss. We’re five-star rated by clients for a reason.

Talk to us now for a fast and free quote on 02 9567 5886.