Low Solar readings

Martyn1981

Yoshii wrote: »

yes you are correct in that the other 10 panels face WNW.

inverter is SMA 4000TL and Generation Meter is the ElsterA100C

Thanks Yoshii. The reason I asked way back about being a split system was the kW figure you quoted 1-1.3kW max. That seemed too low, but is starting to make a lot more sense now.

So inverter is fine, really good model, and good shade management tech. Your June July figures seem to bear that out. But ...... if you don't generate more than 6kWh on any day in September, then I can only agree with others that the shading you are now getting is far worse than you think (assuming nothing has gone wrong with the kit and both strings E & W are both still working). If shading is that bad, and affects the WNW too, then you might want to consider micro-inverters or SolarEdge, but depends on whether your installer is open to this alteration, as it will cost, and involve scaffolding.

It's difficult to draw too may comparisons, but for early Sept, in the afternoon I'd have thought 2kW would have been easy, with 1.5 to 2kW from the WNW plus 200 to 400W from the ESE, so there must be a problem.

Also generation wise 4-6kWh is seriously low (not just low). Comparing my system for Sept, and allowing an extra 50% (for size and ESE preference (compared to your WNW preference)) I've looked for the number of days generation exceeded 6kWh to 9kWh, my results were:

More than 6kWh = all except for one day
More than 9kWh = all except for 3 days
More than 10kWh = all except for 5 days.

This proves little to nothing as location and weather would have differed, but the scale of the difference suggests a problem.

There is a bod who posts occasionally on the 'Talking bout our generation' thread on the Green and Ethical board who has a 2.5kWp ENE + 1.5kWp WSW system, so a mirror to yours. Unfortunately I can't remember his name, but you could introduce yourself on there and ask for comparative data.

Mart.

PS. Regarding an improvement now that the leaves have fallen ..... I wouldn't hold your breath. M.

tunnel

Just wondering if the installers got lazy, isn't the SMA 4000TL a 2 string inverter? Could it be possible that they've only used one for both sides of the roof?

I ask that because my WNW only does about 100Wh at 1pm around this time of year coupled with an ESE probably fading at just over 1000Wh, so not far off from the OP....just a thought

Martyn1981

Ok Yoshii, here we go, I think I have an answer for you. I like puzzles and this one got under my skin, as I simply couldn't understand the huge drop off, and couldn't understand how the shading (needed) could be so great, and un-noticed.

1. You said in the first post that generation for the last 2 months had just been generating 4 to 6kWh. I read that as an average of approx 5kWh per day, so Sept would have been 150kWh. But your figure for Sept is 220kWh, an average of 7.33kWh per day.

2. Looking at your gen(kWh):
Jun 420
Jul 490
Aug 370
Sep 220

I compared to PVGIS for Leeds. I wasn't sure what your roof pitch is, so chose 40d. [The steeper the roof the worse the figures for an off-south install. 50d pitch is approx 13% less than 30d pitch for WNW.]

PVGIS results (2.5kWp WNW (+110d) / 1.5kWp ESE (-70d)) :

Jun 404
Jul 402
Aug 326
Sep 235

There's a good chance I've mucked up somewhere, but initial thoughts are that your system (due to weather conditions) did very well in July and Aug, but was a bit behind in Sept. This makes it look like it suddenly went bad, but may not be unreasonable at all, you'll need to compare for a bit longer, ideally against an accurate PVGIS forecast.

3. I took a look at my system's performance for the last few months to compare drop off.

Total I got 738 for July, 545 for August (73.85% of July), and 428 for Sept (78.5% of Aug).

WNW I got 253 for July, 187 for August (73.9% of July), and 136 for Sept (72.7% of Aug).

You got 490 for July, 370 for August (75.5% of July), and 220 for Sept (59.5% of Aug).

I don't think those numbers reveal a drastic drop-off (when compared to each other) but as I said a few posts back, comparing different systems in different locations isn't ideal.

4. Conclusion. Don't panic, I think your numbers are reasonable/respectable. Having WNW panels will mean you see a faster drop at this time of year, but hopefully not a problem. But keep an eye on them, and see how you do over a year.

Hope this helps.

Mart.

PS Double check this long boring post, as I could easily have got sidetracked/confused as my brain was processing lots of different ideas. M.

Martyn1981

tunnel wrote: »

Just wondering if the installers got lazy, isn't the SMA 4000TL a 2 string inverter? Could it be possible that they've only used one for both sides of the roof?

I ask that because my WNW only does about 100Wh at 1pm around this time of year coupled with an ESE probably fading at just over 1000Wh, so not far off from the OP....just a thought

Hiya T. I was pondering that this morning. Trying to decide if the WNW should have 1 or 2 strings to help mitigate shading. But 5 panels (depending on panel type) might be close to the bottom range of the inverter, and possibly below the MPP point, so looked like 6 panels min on a string was better. [Edit: voltage limits.]

So I assume one ESE string of 6 panels into one MPPT and one WNW string of 10 panels into the other MPPT.

But I confess to guessing now. However previous performance looks good, so I suspect it's all been set up well (and proper).

Mart.

tunnel

Hi Yoshii,
Thought I'd give you a comparison for today,
My ESE made 3.2kWh(2kWp system)
WNW achieved 2.5kWh(2.05kWp)
Downsizing my ESE to match yours and I have a total today of 4.9kWh, I'm about 40 miles south as the crow flies so should be able to give you some sort of idea as to how your system is performing

agentk

4 or 5kwh a day this time of year for me see sig. waiting for spring . turbine weather today. Dont give me ideas.

Yoshii

Hi tunnel
On the 21st oct my system produced just over 4kwh. Thanks for your figures for a good comparison.

Yoshii

What are micro inverters

Cardew

Yoshii wrote: »

What are micro inverters

A micro inverter takes the output from each panel - so with 16 panels you have 16 micro invertors.


http://energyinformative.org/are-solar-micro-inverters-better-than-central-inverters/