Solar Panel Output & Efficiency: Everything You Need to Know

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For many Australians, installing a solar PV system in their home is a major step in adopting renewable and solar technology. However, getting maximum performance from your rooftop solar depends on far more than the number or size of solar panels you install.

Solar panel output and efficiency are the two solar panel specifications that you need to take into consideration when purchasing a PV system. These will determine how much usable electricity can be generated for your household.

In this article, we will explain what solar panel efficiency is, how it affects the electricity generation of your solar PV system, and how it is affected by different factors. We will also highlight what you can do to keep your solar panel output at optimal performance.

If you’re interested in learning more about solar panel efficiency and output, keep on reading.

Table of Contents

What is Solar Panel Efficiency?

Solar panel efficiency is the rate at which panels convert sunlight into usable electricity through photovoltaics. This refers to the ratio of the solar panel’s energy output to the solar energy input and is the most common measure of performance.

Although solar panel efficiency degrades over time, it usually stabilises over the first year of use.

This conversion efficiency is affected by several factors, including:

Wavelength – Since photons are the main components of light, they come in various wavelengths and energy forms. The sun’s light that reaches the Earth’s surface includes wavelengths such as ultraviolet and infrared. Not all these pass through solar cells as a portion of the light is reflected, bouncing back onto the environment.

Among those that pass through, some photons turn their energies into heat. Only those with just the right amount of energy to separate electrons from their atomic bonds can produce charge carriers and usable electricity (electric current).

Recombination – A ‘charge carrier’ is one-way electricity flows in a semiconductor. This carrier, usually in the form of a negative electron, will flow across the material. Other carriers will behave as a positive charge carrier. They can recombine whenever the two meet, effectively cancelling their contributions to the electrical current.

When direct recombination occurs, light-generated electrons and holes meet, recombine, and produce a photon — a reversal of the process of generating usable electricity from light in a solar cell. This is one of the fundamental factors limiting commercial solar panels’ efficiency.

Temperature – Since solar cells work best at relatively low temperatures, an increase or rise in their ambient temperatures creates a shift in the properties of the semiconductors, which results in a small increase in current, but a much larger decrease in voltage.

In addition, any extreme temperature increase will damage the solar cells and other panel components, leading to much shorter operating lifetimes. This is why proper thermal management is important in solar panels to improve efficiency.

Reflection – The efficiency of a solar cell increases when the amount of light reflected away from the cell is minimised, thereby placing importance on material selection for the solar panels.

For instance, untreated silicon reflects more than 30% of incident light. So, adding anti-reflection coatings or textured surfaces will help decrease this and increase efficiency. High-efficiency cells usually appear black or dark blue.

How Efficient are Home Solar Panels?

The cell efficiency of solar panels ranges from 15% to 22%, with variances occurring largely between manufacturers rather than between models from the same manufacturer.

Despite a large difference in efficiency ratings between solar panels at times, Australia is one of the best places to use home solar panels, as it is one of the sunniest continents on the planet.

In fact, according to data from the Clean Energy Regulator, in 2020, one in four households in Australia were equipped with solar PV systems. Since solar panel efficiency is one of the continually improving aspects of solar panels, it’s safe to assume that the number of houses using solar PV systems has increased dramatically.

What Determines Solar Panel Efficiency Ratings?

The top three components that impact and determine the efficiency rating of a solar panel are the type of solar cell, how the cells are wired together, and the panel’s back sheet.

How solar panels are constructed can be likened to a layer cake; there are multiple layers, each serving a specific purpose. The materials used to manufacture these layers are critical in determining a solar panel’s efficiency rating.

Solar Cell Type – This is the largest determinant of efficiency ratings. A solar panel’s solar cells are what take solar energy and turn it into usable power. There are three primary types of silicon solar cells: polycrystalline, monocrystalline, and thin film.

Despite this, we will only tackle the monocrystalline panels since they are used in almost every solar installation in Australia. Every high-efficiency solar panel on the market uses some variation or form of this cell technology. The most common high-efficiency monocrystalline cell types are:

a. PERC Solar Cells – These are called ‘Passivated Emitter and Rear Contact Cells’. PERC cells usually provide about a percent more in added efficiency due to having a reflective back layer that reflects any light that could pass through the cell.

b. HJT Solar Cells – Heterojunction with Intrinsic Thin Layer Cells are essentially Monocrystalline cells that have been placed in between layers of a different type of silicon that can absorb various wavelengths of light. This increases their energy production. Panasonic and the REC Group are known to use HJT technology.

c. Half-cut or Split Cells – These cells are exactly what they sound like — solar cells cut in half using a high-precision laser that reduces heat and resistance, increasing overall solar efficiency.

Busbars and Wiring – How solar cells are wired together can also impact the solar panel’s efficiency. The face of a solar panel has thin lines running across it — these are a series of copper or aluminium wires responsible for conducting electricity, moving it from the solar cells onto the solar inverter.

Some solar companies have started using multi-busbar technology, wherein multiple ultra-thin busbars are used instead of fewer but thicker ones. Thinner busbars reduce the shading on the solar cells, allowing them to absorb much more sunlight, and increasing their efficiency.
Backing – You might have noticed that black solar cells are surrounded by white space — that is the panel’s back sheet. All-black solar panels are most likely using a black back sheet. Black backing has gained popularity among residential solar users because of its sleek and uniform look. However, this preferred look trades off efficiency as the black backing makes the panel hotter. And as discussed earlier, a hot solar panel produces less electricity.

What Type of Solar Panels are the Most Efficient?

Solar panel efficiency largely depends on the type of solar cells it uses. The most efficient solar panels on the market right now have Monocrystalline Cells, averaging 15% to 20% efficiency.

The solar cells in solar panels contain silicon, which is responsible for converting sunlight to Direct Current (DC) electricity through the photovoltaic process. Different types of cells are commonly used for household solar panels:

Monocrystalline Cells – These are sliced from one large silicon crystal (an ingot) and run at 15% to 20% efficiency.

Polycrystalline Cells – These are manufactured by pouring silicon into moulds known as cast ingots. Solar panels that use these cells have a slightly lower efficiency rating than monocrystalline-using panels at 13% to 17%. However, this is usually offset by using larger installations or more solar panels.

Thin Film Cells – These are created by spraying silicon onto a surface and are less efficient than monocrystalline and polycrystalline cells, despite being more expensive to manufacture than the latter. The most widely used thin-film technology used to be Amorphous silicon. However, recent advancements have led to the wider use of Cadmium Telluride and Copper Indium Gallium Selenide.

Building-integrated Photovoltaic Modules (BIPV) – These are much less common in Australia. BIPV is an application of thin-film technology that integrates PVs with building materials such as roofs (shingles or solar tiles), skylights, facades, and awnings. Facade systems are better suited to regions where the sun’s angle is lower, such as northern Europe.

What Solar Panel Brands are Most Efficient in Australia?

The most efficient residential solar panel currently available in Australia right now is the Maxeon 3 400W module of SunPower. It has a 22.6% efficiency. LG and REC are also two manufacturers known to produce high-efficiency solar panels above 21%.

Solar panels widely considered to be of the best quality are also among the most efficient. However, the most efficient solar panels are also the most expensive, and therefore may not offer the best value for money. Other factors such as longevity and cost per kWh need to be considered when choosing the best solar panels for your scenario.

Much higher solar panel efficiencies have been recorded within laboratory environments. Case in point, scientists at the National Renewable Energy Laboratory (NREL) in Colorado, United States, have developed a six-junction solar cell that converts sunlight to electricity at an incredibly high-efficiency rate of 39.2% under one-sun illumination.

The table below shows the most efficient solar panels commercially available in the Australian market at time of publication.

Most efficient residential solar panels in Australia

BRAND	POWER	MODULE	EFFICIENCY
SunPower	400 W	Maxeon 3	22.6%
LG	380 W	Neon R	22.0%
REC	380 W	Alpha	21.7%
Trina Solar	375 W	Honey M DEO8M	20.7%
Longi Solar	375 W	Hi-Mo 4	20.6%
Solaria	370 W	Power XT	20.5%
Jinko Solar	390 W	Tiger Mono-facial	20.4%
Q Cells	340 W	Q Maxx – G2	20.4%

Source: SolarQuotes

What Factors Affect Solar Panel Output?

Various factors affect a solar panel’s output, including the output tolerance, dirt and grime on the solar panels, temperature derating, roof tilt and orientation, and the inverter efficiency.

Below we explain each one:

Output Tolerance – Most solar panels on the market today have a +/-3% output tolerance set by the manufacturer. This means the panel will perform within 3% of its indicated rating.

Dirt or Grime on Solar Panels – Dirt and grime also affect the output of a solar panel. Although how badly a panel is affected depends on the specific solar panel model, it will always cause some performance loss. Some have equated the decrease in output to a 5% loss in efficiency. Remember that light has to pass through the panels, so if there is too much dirt, some amount of light will not pass through and undergo the photovoltaic process.

Temperature Derating – The hotter a solar panel is, the less efficient it becomes. The temperature coefficient, ambient temperature, and the exact type of installation affect the efficiency and, thereby, the solar panel’s output. A climate that is too hot will cause this, but this does not mean that a frigid storm is ideal either, as there will be no sun to deliver photons despite the panel’s low temperature. Extreme weather will, therefore, negatively affect the output.

Roof Tilt and Orientation – Most people overlook the roof tilt and orientation when it comes to solar panels. Since solar panels have to face the sun to maximise electricity generation, poor positioning will limit the light that can reach or pass through them, decreasing output. You need to ensure the panels have an uninterrupted view of the sun, and that you understand the best angle for solar panels in your location.
Inverter Efficiency – Solar inverters convert Direct Current (DC) into Alternate Current (AC). This conversion is required so that the energy produced by the solar panels may be used by the appliances and other electrical components in your house. Unfortunately, the conversion process is not 100% efficient, so some energy is lost. Although solar inverter technology has made progress, it can still be responsible for about an 8% loss in efficiency or an average 5% decrease in output.

How to Maximise Solar Panel Efficiency?

As with most electrical devices, there are things that you can do to maximise the efficiency of your solar panel. Among these are purchasing more efficient solar panels, considering installation location, and ensuring the installation is properly done.

We will discuss these factors below:

Purchase a More Efficient Solar Panel Model – Although the initial cost of purchasing a higher-end model will be more expensive, purchasing one is arguably the most important thing you can do for the best results. Solar panel efficiencies do not increase; they only go down from the moment they are used, so think of it as a long-term investment or future-proofing.

Avoid Installing near Shaded Areas – It only takes one photovoltaic cell out of the many to be shaded to cause a noticeable impact on its energy generation because it acts as a resistor. Nearby buildings and tall trees are usually the most common culprits. Make sure to consider these things during the installation’s planning stage.

Hire an professional to Install the Solar Panels – Incorrect or improper solar panel installation may prevent you from receiving your solar panels’ optimal performance. There are a lot of technical details to take into account, so while it may sound appealing to install one yourself, it’s best to call an expert.

Keep the Solar Panels Clean – The absence of moving parts in solar panels means little to no maintenance is required. However, this does not mean you should neglect your solar panels. Make sure to periodically check your solar panels for any dirt or grime that may be interfering with their efficiency. This is especially important during extreme weather conditions such as storms with strong winds where a lot of debris tends to fly out.

Monitor the Solar Panel Output via Energy Management Software – Although it is possible and safe to have a solar PV system installed and forego any additional components or modifications, it may be a problem if you do not use some type of energy management software. This is because you will never get an actual idea of the solar panels’ energy output, and thus, you will never know when there is a problem in the electricity generation of your panels.

How to Calculate Solar Panel Output?

Due to the numerous factors involved, the largest of which is the uniqueness of each solar PV system, it is difficult to determine exactly how much electricity a PV system would generate. You can, however, get benchmarks through your daily and monthly panel output.

Solar Panel Output Per Day – Determine how much electricity measured in kilowatt-hours (kWh) is produced by your solar panels each day using this formula:

a. Size of the solar panel (in square metres) x1,000
b. That figure x efficiency of one solar panel (percentage as a decimal)
c. That figure x number of sun hours in your area each day
d. Divide by 1,000

Solar Panel Output Per Month – For the monthly solar panel output, calculate the daily figure, then multiply by 30.

Solar Panel Output Per Square Metre – The most popular domestic solar panel system in Australia is 6kW, anywhere from 16 to 18 solar panels. If each is 1.6sqm in size, multiply it by the rated capacity in W (in ideal conditions). So the formula is:

a. Number of solar panels x capacity of the solar panel system
b. Capacity ÷ total size of the system (number of panels x size of one panel)

To estimate solar panel output, you can also use the SolarQuotes Solar & Battery Calculator.