This is a question that we hear over and over again: “…how much additional revenue can retrofitting BM optimisers really give? Is it worth it at all?”
We then normally take a deep breath and start explaining all over again. it’s a bit of a long story, and we do tend to loose a few listeners along the way. However, Ii you have anything to do with photovoltaics and if you live it in the real world (see below), your attention will be rewarded.
The current that cannot flow through the string is therefore dissipated as heat, causing some panels to warm up more than others. Thanks to a simple set of electronic processes, BM optimisers manage even very mild levels of panel mismatch. They enable conventional inverters to harvest the output of each panel.
So…how much more energy can we harvest using BM technology? BM optimisers will recover up to 99.5% of the energy that is normally dispersed due to panel mismatch. Optimisation is carried out in three stages, to ensure it is always efficient and energy positive.
At low levels of mismatch only the first stage of optimisation, known as “Energy Spring”, is active: the energy that cannot flow through the string due to the bottleneck effect is briefly stored by the BM units, enabling the inverter to harvest it using its conventional MPPT (Maximum Power Point Tracking) processes.
The Energy Spring mode delivers tangible benefits even at very mild levels of panel mismatch. Keep these numbers in mind:
• Most modern crystalline PV panels are supplied with a -0+3% power tolerance. Older panels may feature up to +-5% from factory.
• Panel degradation, which based on recent studies accounts for 0.2-2% per year, affects panels unevenly across the string. This means that we can safely estimate that there will be at least a 4% difference in performance between the best and the worst panels within a string by the time the plant is 20 years old.
• Cell microcracks, that affect panels during transport and installation and increase during the first few episodes of thermal stress following installation. Studies show that on average 6% of cells are affected. Although the effect on efficiency is negligible, this contributes to real-world panel mismatch
• Uneven installation surfaces: in the case of ground mounts especially, panels are rarely lucky enough to be facing exactly the same direction. Most ground mounts will feature panel mismatch of at least 2-3% due to uneven ground.
As the mismatch increases, a DC/DC conversion process steps in, gently adjusting the current and voltage in order to improve the quality of the curve and bring it within a range that PV inverters can best manage. Based on the incidence of soiling and partial shading, this stage of optimisation will deliver benefits of up to 25%.
Finally, if a panel is underperforming to an extent that power optimisation is no longer viable, BM optimisers switch it to a “cool bypass” mode. The affected panel is virtually sectioned from the rest of the string whilst staying cool and protected from the hotspot effect and overheating that would normally feature heavily shaded or damaged modules. If you are lucky enough to know what a panel with extensive transversal shading can do to the performance of your PV string, you don’t need any numbers. You just want that panel to keep quiet in a corner until the cause of underperformance has been eliminated, letting the other units operate unaffected.
So, do you wish to find out how much more revenue your plant could generate with optimisation? Any other questions? Send us the plant details and we’ll reply with numbers!