And therefore, if we extrapolate this out, can we use two completely different strings of panels (within reason) , connected in parallel (via blocking diodes) and still get a satisfactory result?
My question is why do you want to do it this way?
just create a second string that is near enough to the OCV of the existing string of 11, add a couple of dollars worth of blocking diodes and BAM, I will have string #2 (east west) producing ~2kWh for nearly the whole day, instead of peaking at 11am and then tapering off to not much by mid-arvo.
Hope that makes sense.
Should be fine, SMA calls it "polystring", I don't know if they're using blocking diodes but they probably do.
http://www.smainverted.com/files/2012/12/Article_Polystring_East-West-Orientation-TEN122510.pdf
I would like to drive the inverter a bit harder and flatten out my daily production bell curve. (and increase my daily output)
My daily production is biased to late-morning due to the east facing string. Power production generally peaks around 11am and then tapers off as the east facing string gets less and less direct sunlight.
So the obvious solution is to add panels onto the west facing roof, and parallel them onto the second MPPT ( with the east string = 11 panels )
The current "advice" is that this can be done is using the exact same panels and number of panels. (( i.e. 11 panels the same as what I have (suntech 195W ))
The issue is that these panels are not available any more, and I still think that blocking diodes will be required to prevent reverse biasing the cells if there was any shadowing.
So, my options are to replace ALL of the panels, so that the 2 paralleled east and west facing strings are exactly the same
OR
just create a second string that is near enough to the OCV of the existing string of 11, add a couple of dollars worth of blocking diodes and BAM, I will have string #2 (east west) producing ~2kWh for nearly the whole day, instead of peaking at 11am and then tapering off to not much by mid-arvo.
Hope that makes sense.
I thought that extremely poorly done video proved that blocking diodes are bullshit. Yet, people were left with the idea that they were needed. I have 1500W of panels facing every which way going into a 500W charge controller. Panels even with minimal ambient light still produce the same open circuit voltage.
Every combination of coupling - whether series, parallel with diodes, orientation etc will LOSE efficiency. The amount depends on the mismatch and can be quite high !
The ONLY interconnection method is with a micro-inverter on EVERY panel or panel segment. That is because the relationship between the "power generator" and the "storage system" (or inverter) is tightly matched to create an MPPT profile. Micro-inverters then handle the "differences" by synchronous adjustment (via direct data link to each other) and achieve MAX I/O transfer. You'll find ALL newer "competent" installers now use micro-inverters. We have been doing that on our solar cars for 30+ yrs, for that very reason. It's taken a while for home installs to catch up - but then, there's a lot of bad practices in that area (which is another long story :-) )
I thought that extremely poorly done video proved that blocking diodes are bullshit. Yet, people were left with the idea that they were needed. I have 1500W of panels facing every which way going into a 500W charge controller. Panels even with minimal ambient light still produce the same open circuit voltage.
Common misconception? What does the forward voltage (drop, I assume you mean...) of the cells have to do with blocking diodes???
That diode starts conducting at around 0.5V (it's kind of squishy), and this is what establishes the cell open-circuit voltage. If you put a voltage on the panel that exceeds the sum of the cell diode drops then reverse current will flow. The series blocking diode prevents this reverse current.
Note that we have been discussing blocking diodes, not shunt diodes.
If I were making my own, I would use 2 diodes rated at least 40A, 1000V, in series with a high-energy 10A 600V minimum fuse between them and robust 600V MOVs across each one.
I thought that extremely poorly done video proved that blocking diodes are bullshit. Yet, people were left with the idea that they were needed. I have 1500W of panels facing every which way going into a 500W charge controller. Panels even with minimal ambient light still produce the same open circuit voltage.
.... Panels even with minimal ambient light still produce the same open circuit voltage.