bladerunnervf avatar image
bladerunnervf asked

Do ordinary smart solar MPPT work with shading / shadow like the Multi RS series now do?

Hi folks,

I've been reading this thread, and its earlier ones, with interest,

It seems that the Smartsolar MPPT RS series can deal with shading and shadow much better now than before.

Q1) Do/will the smaller victron Smartsolar MPPTs, e.g. 150/45, have the same new shade tolerance capability as the larger RS?

Q2) Does the improvement to Smartsolar MPPT RS mean that solaredge optimisers would no longer be needed?

I had thought from reading around the web that harsh shading on one (or more) panels in a string (e.g. chimney) would drop the overall voltage of the string, potentially preventing any power from being generated if it goes too low.

One common workaround seems to be to use TIGO(s) on the affected panel(s) and hope that the remaining string voltage would remain sufficient after by-passing the affected panel(s). I gather from this series of threads that TIGO are a no-no if used with Victron MPPTs.

I had been thinking that I would need to use solaredge for my potential system to cope with hard shading (from own roofline) onto 1 panel of 4/5 and to cope with shadow from neighbours roofs up to about 10am and moving shadow from trees morning and evening.

I did a search but didn't find an obvious thread with an answer

MPPT ControllersMPPT SmartSolarmppt rssolaredge
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1 Answer
furyjk98 avatar image
furyjk98 answered ·

I own two half-cut panels, of 42V and 13A maximum Power points, connected to 100/50 MPPT in series connection. In the morning, I get a shade on one of the strings of a panel. The MPPT adjusts its MPP to 70V and I get the max power. However, if it starts tracking at 84V, I get half the amps that I was getting at 70V.

The beta update could have a new update to detect shading with some new algorithms when there is a sudden amp drop or a comparative tracking based on previous data based on time.

However, what mine does is, it tracks the MPP by sweeping through VBatt to VOC and finding the maximum amps at the voltage it has tracked. Which will take around 5 - 10 seconds to complete, and at 10-minute intervals in Bulk Charging mode.

In Float mode, it manages its MPP based on the Load applied. If there is more load and voltage is dropping for 10 minutes or more, it does the MPP sweep again to find the MPP of the panel and continues the above behavior.

If you are comparing the String Optimizers to MPPTs, it's two different concepts. String optimizers work on a module level, sending maximum power out in a string wire.

To put it in an example. If you have 5 Half-Cut modules in a series with 42V MPP and 10 Imp, and each of them is divided into 3 strings internally using 3 bypass diodes.

Now, you have got shading on one of the panels, blocking two of the strings in the panel. The Half-Cut panels will have two MPPs.
14V x 10Amp or 42V x 5Amp. The MPP is the one is 42v x 5A = 210 Watts.

In a Solar Optimizer, this MPP is tracked and power is optimized in the string, and passed onto the inverter.

In an MPPT, you cannot lower the Amps of the entire string at a higher voltage. The MPPT will bypass those two strings by tracking 14Vx10Amp in that panel. So your overall Production will be higher, instead of getting locked into the lower MPP.

So with 5 Panels in Series, your MPP Voltage is 210V, since there is a shading on two strings in a panel, the MPPT tracking will get lowered to 182V and will track maximum Amps. Instead of getting stuck at 210V, and tracking half the amps.

So if you compare a string inverter to MPPT, your power loss with MPPT is 70 Watts.
Optimizer: 42Vx10Ax4 Panels + 42Vx5Ax1 Panel = 1890Watts.
MPPT: (42V x 5 Panels) - 28V x 10A = 1820Watts.

This is just for a comparison, there will be more complications based on Bypass Diode Voltage, Length of the Cable, the Temperature of the Solar Cells, Hotspots, etc.

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