Module level Optimisers

Inverters
1

Greetings and welcome to my promised post about Module Level Optimisers

I noted in another post that I am going this route and herewith the results of this experiment.

Problem Statement:

  • Various Roof directions (I have modules facing north, east and west)
  • Severe Afternoon shading on the West panels
  • Morning (early) and afternoon shading on the 4x North String

This necessitated me to look at alternatives and what can be done. There is still the option to negotiate with my neighbour to cut down the palm tree, but then I have to talk to my neighbour! (Me being an introvert and all).

I opted to canvas the market for module level DC/DC optimisers that can work with my current MPPT. I found them in the Tigo brand and got myself 8 at R200 per optimiser (Okay, the seller quoted them as SMA, but it is just Tigo… SMA 475W Optimizer (SOL-P-O-475))

And yes, you read correctly there… I am a bit worried that this is a non-reputable place and might have sent me know-offs as the normal price (various sources) is around R800 per optimiser. Hell the things got here and looked legit, so it went on.

My set up:

  • 2x 5.5kW Ohm branded Deye inverters, master/slave configuration
  • 4x Strings, Master PV 1 = 4x395W on the East Side, Master PV 2 = 6x405W on the North face, Slave PV 1 = 4x395W on the West and Slave PV 2 = 4x395W on the North Part (I will perhaps, maby, if I feel like it add the actual photos later)
  • Battery back-up that never reaches full capacity (I blame the tumble dryer, it just can’t be my water purification plant. I refuse to believe it (yes it is the purification pumps, but no!))
  • No grid feedback

The reason in pictures to why Optimisers were needed, note this was a clear sky day!

image
image911Ă—280 47.1 KB

As you can note, the morning one module is shaded (roof shading) then the palm tree strikes in the afternoon. The east side looks worse!

The process of data analysis (is this worth it):
To compare if the devices is worth it I took the Master North string as a reference and using clear sky day before and after the install to “calibrate” for differing irradiance (turns out the 11th had 1.034x the irradiance than the test day 15th).

The Results (in picture) of the North Face optimiser installation:

image
image931Ă—284 26.8 KB

One can immediately see the difference in the morning. I still did not win the palm tree…

When comparing this in terms of data the following picture comes out:

image
image2094Ă—812 56.6 KB

I did not win on the West optimisation at all, or rather minimally. The North optimisation wins by a lot. The sharp decline on the west side at that time has a few reasons, not just the palm tree… The only win here is that it smooths the dips and swells. So less strain on the MPPT?

Shortcomings of the analysis:

  • Limited period of comparison (2x similar winter days)
  • I have not compares string level energy generation against previous days (only inverter level)
  • Not sure how the wind blew on each day (palm tree moves quite a bit in wind…)

Overall results on energy at the inverter:

  • Not optimised: 9.8kWh
  • After Optimisation and including correction factor: 10.42kWh

This is around 6% overall increase in winter energy.
If we assume that this is so for entire year then the “increase” in energy would equate to around R1.86 per day.

Given the overall costs (8xR200 + installation) I will be getting a return of around 4years and 5 months…

In my opinion the benefits of using optimisers:

  1. Panel level MPPT allows for better overall performance
  2. Shading of a single panel no longer affects the other
  3. In the case of these optimisers additional quick shut down in case of fault
  4. You can get maximum out of 2 strings facing different directions without opting for another MPPT
  5. You can add different panels to the same string and get panel maximum performance.
  6. You can optimise 1 panel as opposed to the entire string (note performance here is a guess from my side, plonkster might argue differently here!)

Overall drawbacks:

  1. Additional component that can fail.
  2. More connections on the roof that can fail.
  3. Additional efficiency losses in the system (minor but can have an effect…)
  4. Wife noted that we have more energy now so she can run the tumble dryer more…
5 Likes
2

If they also include a high voltage clamp of sorts (eg some Trina “smart” modules), then it would make additional sense to have them. It allows for a slightly longer string without fear that you will exceed the MPPTs input voltage rating.

The reason why optimisers sometimes don’t work with MPPTs is because the MPPT rely on certain characteristics in the I/V behaviour. The optimiser messes with that and confuses the MPPT.

As an example, if you put a Fronius on a constant DC voltage, you confuse the daylights out of it. Present it with the correct I/V curve and it tracks the MPP very very fast because of that. And yes, I’ve actually done this. If I feed the Fronius on the test bench with a flat DC voltage, it has trouble latching on. Then I discovered the power supply I have in the bench is programmable and you can program it to simulate that curve… and voila, now it latches on properly.

3

Depending on how tall that palm tree has grown by then ?

4

You are right! If the tree grows the leaves will no longer be blocking my panels and thus the need for optimisers would be minimised!

Still winning on the northern panels morning shading thought!

I think I need to start negotiating with the neighbour.

1 Like
5

Hi @Rautenk

I’ve been thinking of doing something similar with some of my panels and came across the Tigo brand which works with any inverter and you don’t need it on all panels.

My problem is also some shading on 2 out of 8 panels in the morning because of a neighbor’s palm tree and some afternoon shade on another 2 panels due to the next neighbors trees.

I’ve got 2 Sunsynk’s so good to know that it works on the ohm.

Do you mind sharing info on where you purchased from.

6

So I am researching what to do about my shading problem. I found this video to be very interesting

You find a lot of infomation, but rarely actual testing. I think that modern solar panel designs have come a long way to address the problems of partial shading.

I am not an expert: but I notice you have 4 panels in most strings effectively giving you 180-190V ± … once one panel is shaded too much the bypass diode will effectively bypass the panel and you will lose the voltage of that panel (or section of the panel/s) which might put you below the min startup voltage of the MPPT (150V). Imho you would be better off adding at least 1 panel to the string of 4 especially if you want them produce power when partially shaded.

1 Like
7

Hi Vassen, for some reason my notifications were not coming through!

Have you found a place? The place I recently bought from is called Solarsupply.co.za and I was searching everywhere. These guys had enough stock and helped quickly. I did an upgrade and had to order more.
The shading ones still work a dream, but the two different orientations is giving me a bit of a headache. Not working as expected, but Tigo is assisting.

Cheers,

8

Hi Rautenk

I did get 2 optimizers, but I haven’t gotten around to installing them as yet. Too busy with other projects around the house.

I Wasn’t able to find them at your listed prices though. Will take a look at solar supply.

9

I’m considering these too to alleviate some chimney shading issues. You still happy with yours?

10

From 2, I decided to to get more. I now have the 8 panels in my north string all on optimizers and they work great. I don’t have the mo ironing device as they are crazily priced. Different panels get shade at different times of the day and the string doesn’t really get affected except for the panel that’s shaded.

The only non-shady looking (parking lot address) place I could find it at was re-volt automation in centurion. Was pretty impressed with their service.

1 Like