fourtytwo
New Member
Hi all, I have a completely DIY setup (excluding the bought panels) that has been running since 2015. We moved house this year and the new location is definitely sub-optimal, ground mount with bad shading from buildings and trees especially now in winter. I have looked at many options like optimisers etc but such things can be expensive to construct for a DIY person, magnetics being particularly difficult and of course the whole enclosed in a waterproof case.
I have decided instead to have a go at the inverter software instead to change the control algorithm from a simple hill climb MPPT to do a periodic full scan of panel voltages to see if the hill climb has found the wrong peak! An example simulation is enclosed that shows a hill climb starting from maximum voltage will arrive at ~24W/118V output whilst a full scan shows a much better peak of ~110W/28V. You might think that simply reversing the direction of hill climb would solve the problem (start from lowest voltage) but peaks will appear in different places depending on the nature of shading that varies a lot.
As a large input capacitor is used to reduce 100hZ ripple if the load happens to be AC a target voltage change takes a while to come into effect at low insolations so the steps of the scan cannot be very fast, in this case I have chosen 1.28 seconds giving a scan time of about 30 seconds for 5V steps across the range. If a scan is performed every 10 minutes about 5% of generating capacity is lost however the gain from using the right peak is huge. 5V steps are adequate as the new target voltage would be passed to the existing hill climber as a new starting point that it will then fine tune.
So that's my story of what I will be working on this winter and hopefully produce a result soon enough to get more use out of the winter sun.
Sorry plot only downloadable pdf as png was no good!
Edit : Pic showing partial shading added.
I have decided instead to have a go at the inverter software instead to change the control algorithm from a simple hill climb MPPT to do a periodic full scan of panel voltages to see if the hill climb has found the wrong peak! An example simulation is enclosed that shows a hill climb starting from maximum voltage will arrive at ~24W/118V output whilst a full scan shows a much better peak of ~110W/28V. You might think that simply reversing the direction of hill climb would solve the problem (start from lowest voltage) but peaks will appear in different places depending on the nature of shading that varies a lot.
As a large input capacitor is used to reduce 100hZ ripple if the load happens to be AC a target voltage change takes a while to come into effect at low insolations so the steps of the scan cannot be very fast, in this case I have chosen 1.28 seconds giving a scan time of about 30 seconds for 5V steps across the range. If a scan is performed every 10 minutes about 5% of generating capacity is lost however the gain from using the right peak is huge. 5V steps are adequate as the new target voltage would be passed to the existing hill climber as a new starting point that it will then fine tune.
So that's my story of what I will be working on this winter and hopefully produce a result soon enough to get more use out of the winter sun.
Sorry plot only downloadable pdf as png was no good!
Edit : Pic showing partial shading added.
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