Solar panel efficiency

The average cell efficiency of a solar panel is between 17 - 24%. The level of efficiency varies between manufacturers and the type of panel.

The higher the efficiency of a solar panel, the more solar power it will produce per square metre.

Higher panel efficiency has been recorded in laboratories; scientists at the National Renewable Energy Laboratory (NREL) have a developed a six-junction solar cell that converts sunlight to electricity at 39.2% under one-sun illumination and 47.1% under concentrated illumination.

Solar panel efficiency formula

Solar panel efficiency is calculated by dividing the power output of the panel over its surface area.

The formula is shown in the image below:

For example, a 440W panel with dimensions of 1.05m x 1.80m is 23.28% efficient.

Most efficient solar panels

The best quality solar panels tend to be the most efficient. The most efficient residential solar panel available in Australia is SunPower’s Maxeon 7 445W module, it boasts 24.1% efficiency.

The panel efficiency of many popular brands is above 22%. The table below shows the most efficient solar panels in Australia:

Most efficient solar panels in Australia

*The solar panels in this table are all panels suitable for residential installation.

Solar panel efficiency is one indicator to the level of quality of the panel, but not the only one. It's important to consider warranty information, in particular the length of the product warranty.

The system inverter is important too. It's best to pair a good panel with an inverter of similar quality.

Solar panels power rating

Solar panels are given a power rating in Watts, based on the amount of electricity they can produce in one hour of peak sunlight. However, these ratings are classified under ideal conditions in a laboratory, and therefore don’t represent the amount of power that could be expected of that panel on a day-to-day basis. So a 440W panel installed on a household rooftop, is not going to produce 440 Watts of electricity, even in peak sun.

Factors that affect the efficiency and output of a solar panel

There are several factors that affect the efficiency of a solar panel and ultimately how much electricity it produces. All of these factors must be considered when calculating solar power at any given location.

Manufacturer’s output tolerance

Most solar panels have an output tolerance +/- 3%, which means that the manufacturers panel will perform within 3% of its Watts rating.

The effect of dirt on solar panels

Dirt and grime also affect the efficiency of a solar panel. This varies from panel to panel, however, it’s best to factor in a loss of performance. In all of our calculations, we equate the loss of efficiency due to dirt and grime to be 5%. If you were to clean your panels regularly, they would perform better.

Temperature derating

Solar panels are affected by temperature. The hotter the panels get, the less efficient they become. In short, the temperature coefficient, ambient temperature, as well as the type of installation all impact the efficiency of the panel and therefore solar panel output.

Roof tilt and orientation

The orientation of solar panels, and their angle, also have an affect on the output of the panel. If they are not positioned at the optimum angle and direction, then the panels will not produce their expected output for that location. Measuring these inefficiencies is important when calculating solar output.

Inverter efficiency

The inverter converts Direct Current (DC) into Alternate Current (AC), so that electricity produced by solar panels can be used in your home. This process is not 100% efficient. Whilst inverter efficiency technology is improving, it can still account for as much as an 8% loss in efficiency. We allow for an average of 5% in all of our calculations.

Battery inverter efficiency

If you have a hybrid system with a solar battery, your battery will not operate at its full storage capacity. Inverter efficiency for batteries is in the realm of 92%, representing an 8% loss.

DC cable loss

There may be a small voltage drop between the solar panel system and the inverter, this can account for efficiency losses of around 1-2%.

AC cable loss

Similarly, the connection between the inverter and the electricity switchboard can result in a drop in voltage leading to a small loss in the efficiency of the system.

When accurately calculating solar panel output for a given location, all of these factors should be accounted for. All of our calculators that ask for your postcode factor in the affect of tilt and orientation, and all of the solar panel efficiency factors.

Solar panel efficiency over time

The efficiency of a solar panel decreases slowly over time. The best solar panel brands have a lower rate of degradation or, a higher performance ratio. The performance ratio for most panels is around 80% after 25 years, the most efficient panels have a ratio of above 90%. This level of performance falls under the solar panel warranty.