Most PV system owners can be frustrated and confused when their, say, 5kW system only ever kicks out 4kW. There may be the occasional spike, and the occasional dip, but most days the inverter will show 4kW at best. Is this a problem? Should you be worried if your system never delivers on its promise?
Not at all! Most Australian solar panels peak at 80% of their manufacturer’s peak performance spec. It’s not widely-known, but not hidden either. And there’s definitely nothing wrong.
Any industry that sells hardware with performance specs uses the absolute optimum conditions and usage to get the best numbers possible. These conditions and usages hardly ever exist in the real world; plus, the real world throws its own challenges in the way…
The five challenges every PV system must face
The manufacturer’s own power tolerance – a 1% loss
All PV panels have a power tolerance, mainly from -1% to +3%, so you may see your panels losing 1%, just because…
Ambient temperature loss – 10%
When solar panels get hot, their output drops. Once it goes over 25C, panels lose 10% of their rated power output; they lose more if it’s hotter.
Dirt – a 5% loss
As soon as your panels go up, airborne particulates of all stripes start to gather and settle on them. These pollutants stop some of the sunlight from getting to the cells behind the glass. This loss can be anything from 5% to 15%, but around 5% is more usual, especially if you clean your panels once a year at least.
Voltage losses – 2%
Your panels are all interconnected with wires, then finally to your inverter by DC wires. Each wire presents some resistance, so the electricity passing through them will see some voltage drop, typically around 2%.
Your inverter’s efficiency – a 4% loss
All your electricity goes through your inverter and no inverter is 100% efficient, with the best ones achieving around 95-96% efficiency. This means a 4% loss.
If you add all these losses together you’re looking at an overall drop of around 20%. Your panels are operating at around 80% of their spec, which, as we don’t live in a perfect world, is as good as it gets!