Solar panel efficiency

Solar cell efficiency is the rate at which a solar panel transfers the sunlight via photovoltaics into electricity. The average cell efficiency of a solar panel is between 11 – 22%. It varies between manufacturers. 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; Australian scientists are setting the pace in this regard having a developed a cell that converts sunlight to electricity at 34.5%.

graphic explaining cell efficiency and variance of manufacturer performance

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 250W panel installed on a household rooftop, is not going to produce 250 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 panel output and efficiency of a solar panel. All of these factors must be considered when calculating solar power at any given location.

infographic showing solar panel efficiency factors by percentage

Manfacturer’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. We cover this topic in great detail here, but the short of it is: the temperature coefficient, ambient temperature, as well as the type of installation all affect the efficiency of the panel and therefore solar panel output.

Roof tilt and orientation

The direction that solar panels face, and the angle that they are mounted, 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 rated output for that location. This is a must when accurately calculating solar output.

Inverter efficiency

The inverter converts Direct Current (DC) into Alternate Current (AC), so that the energy produced by solar panels can be used to power your home’s electricity. 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 rated Wattage. 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

Likewise, connection between the inverter and the electricity switchboard of the property, may experience 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.

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