Why is my solar system not performing?

Fast read

The number of panels installed may exceed the inverter's capacity since solar panel systems are sometimes created to optimise the rebates offered to clients. This is a standard industrial procedure, and there shouldn't be any issues if the inverter is sized correctly. However, if it is sized incorrectly, your solar system may not perform at its best.

Solar panels are evaluated based on how much energy they can produce under ideal circumstances. Still, in practice, their output may be lower due to things like solar intensity and cell efficiency. Therefore, when sizing the inverter, it is taken into mind that the production of a solar panel system would typically be lower than the rated capacity of the panels.

Working with a qualified local supplier or installer is important to ensure that your solar panel system is sized and installed correctly.

Why is my solar system not performing at its best ability?

Many solar customers come across the same issue of asking why their solar system is not performing. In many cases in Australia when solar companies sell you a system, they try to sell a solar system that maximises the rebate and the rebate is currently linked with the solar panels.

So solar companies want to sell you as many panels as possible because that also means there’s a maximum rebate coming towards the sale price, benefiting you and the company, as the purchase price will be lower.

In many cases, you might get 6.4 kilowatts worth of panels, being 16x 400W, but the inverter they have added to the solar system is only a 5-kilowatt inverter.

Regularly, customers are a little concerned when they find out that more kW of panels have been added to the inverter solution, which is called in the industry “oversizing”.

They wonder if that means the inverter has to handle too much electricity and might overheat or other compatibility issues might arise, meaning your solar system doesn’t perform at its best.

Let me reassure you – a design like this is acceptable and is typical industry practice.

installer working on solar panel which was not performing
Each panel varies in output, so “oversizing” kW of panels is acceptable

Why is this not an issue? 

Every solar panel is slightly different in output as they are made out of many other cells, and the efficiency of each cell varies somewhat. Therefore the overall production of solar panels differs slightly.

When a solar panel, let’s make it a 400W rated panel gets flash tested to tell you it’s really at least a 400W panel, the manufacturer uses a thousand Watts of light intensity per square meter and flashes it for a fraction of a second onto the panel. Then they measure the output, and in this sample, let’s say it measures 401.6W.

If it only measures 399.4W, it could not be called a 400W panel but would be sold as a 395W model.

In many parts of Australia and New Zealand, even though our light intensity is excellent compared to many parts of the world, it does not reach 1000W per m2.

In many cases in many parts of Australia, we only get a light level of maybe 700, 800 or 850 Watts per square meter. This is actually not a bad number because in Southern Germany, for example, you might only have 450 to 500 Watts of light intensity per square meter.

So even if the panel is flash tested at 401.6W, that 400W rated panel in an actual generation will only reach more on a sunny day in Australia at 325W and NZ maybe 300W output and in Germany only a bit more 200W.

Therefore if a customer purchased 16 x 400 W panels, it creates a solar system size of 6.4 kW. The actual output of these panels is more likely to be around 5000 to 5100 Watts in the middle of a sunny day when the solar system’s production is the highest.

What capacity inverter do I require so my solar system performs at its best?

Therefore a 5kW capacity inverter is the correct size for such a system and will not influence your solar system’s ability to perform. However, one is allowed by solar design regulations to oversize the inverter by one-third of capacity. This means a 5 kW inverter can have a maximum of 6.6 kW of panels installed, or a 10 kW inverter can see up to 13.33 kW s of solar panels added.

If, for whatever reason, the solar system in our sample on a clear, cool sunny day with a low level of dust in the air generates 5.2 kW for 20 min in the middle of the day, the extra 200W will be lost as it exceeds the inverter capacity. Such a loss is called “clipping”. It happens rarely and will not damage the inverter.

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