Fast read
Solar panels can lose their performance for several reasons, known as derate factors.
These include the thermal coefficient or the effect of heat on the panels' efficiency; inverter losses, or the loss of power in the process of converting DC to AC electricity.
The panel age, or the natural degradation of the panels over time.
The accumulation of dirt or other substances on the panels. As well as shading, or the reduction of sunlight reaching the panels. Finally, a loss of power in the cables connecting the panels to the inverter.
Understanding and minimising these factors is important to maximise a solar system's performance.
Will the derate factor affect my energy output?
Understanding how much power your household requires now and in the future when you might seek to charge an electric car is crucial to sizing the solar panel system to the correct size. A correct size design helps you properly design your system and determine the system’s financial payback. However, a recent development has arisen where the system seems to produce less electricity compared to its previous output. Many factors can cause a reduction in the performance of a system. We call them solar panel derate factors.
Sometimes people will ring me up and say, “Look, I’ve had my solar system for a year or two. It worked well in the first year; it worked well in the second year, so what has happened to it?
Understanding and minimising the derate factors can ensure a higher solar system output over the years.
- The derate factor isn’t something you’ll find on the datasheet for a solar panel; it is unique to your system.
- Based on the entire solar energy system’s performance.
To get the precise derate factor, you need to know all the details of your solar system, which is nearly impossible.
To reduce losses, analyse and minimise each factor that could lower your panel’s performance. Instead of trying to tackle them all at once, focus on one factor at a time.
The key reasons for a solar system’s reduced performance aside from the derate factor
Thermal coefficient
Thermal Coefficient is a term often used in solar. This means that the hotter the air and panels, the less electricity solar panels produce.
As this derate factor depends on temperature, its effect on your solar system will vary throughout the year.
Inverter losses
A solar inverter changes the electricity from solar panels into energy that your house can use. Solar inverter solutions have high energy efficiency, be they micro inverters, optimisers, or string inverters.
However, they lose a few % of the initial panel output in the DC to AC conversion. This conversion is also what creates heat in inverters. The product datasheet usually indicates the efficiency rating of your inverter technology.
The inverter in the described case could reduce the system output.
Some string inverters have two in-points called MPPs for two strings of solar panels to enter the inverter. If one of these strings has an issue, for example, with a faulty cable or input plug, then one could lose the output of 50% or more of the system.
Panel age
Even quality solar panels lose the capacity to create electricity as they age. Your solar panel’s power warranty will provide you with an estimate of the annual power degradation loss. Many performance warranties say that the loss from ageing would be larger in the first year, e.g. 3%, then level off from year two onward to a consistent degradation of 0.7, 0.5 or 0.3% each year for the panel’s life.
To find the specific derate factor of a panel, you need to know its age, wattage, and performance warranty.
Soiling
The panels on the roof angle to allow the dust to wash off, especially in heavy rain. This makes them self-cleaning to an extent.
If you have a flat panel or birds nesting and pooping on it, it will obviously cause problems. From that perspective, you might have to book a regular system cleaning regime to remove this degrading factor.
You will lose about 2% of output because of minor to medium soiling. However, if your environment has low rainfall and is dusty, and if you don’t have your panels frequently cleaned, this loss percentage of potential output might be substantially higher.
Look at the solar panels if they are safely accessible to check if they have become dusty or soiled. You might consider hiring a professional to clean your solar panels, especially if it hasn’t rained. We recommend using plain or warm water with a little glass cleaner and a bucket.
PLEASE NEVER climb onto a sloping roof or a two-storey roof yourself. Cleaning panels is a professional job. For tips and tricks on this issue, see our article about solar panel cleaning here.
Shading
Another factor could be shading. The best guess is that your solar panels will produce electricity until the sun goes down in the evening. Shade panels may lower solar system output if there are nearby trees or buildings obstructing sunlight on the roof.
If your solar array is not performing well, check for nearby palm trees or other plants that may be blocking the amount of sunlight. Shade can significantly affect the performance of a solar panel. It can cause reductions of over 50% even if it is only on one part of the system.
Snow
The final factor that can affect solar panel efficiency is snow. Snow can also be a situation that causes degradation in solar panel efficiency. While a thin coating of snow can blow off solar panels, any significant snowfall will linger and build up. Flatter roofs are more prone to this issue, although inclined roofs can still accumulate snow.
It just takes roughly 2 to 3cm of snow to shut down solar electricity production. However, snow is only an issue in a few parts of Australia and NZ. The number of days you lose in power production because of snow will vary depending on where you reside.
So what is the derate factor?
Understanding solar panel derate factors is crucial for maximising the performance and energy output of your solar system. These factors encompass various elements that can impact the efficiency of solar panels, ultimately affecting the amount of electricity generated.
Things like high temperature, inverter issues, panel age, dirt, shade, and snow can lower solar panel efficiency. Combating these issues entails a mix of preventive actions and regular upkeep.
