Solar options for home in 2022.

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2052 posts

Uber Geek

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#3258621 12-Jul-2024 10:01

I feel like you've got some units confused in that somewhere.

A 5kW unit is not going to be able to make 9kW, and 4.8kW mid winter sounds pretty good - you also haven't mentioned the weather conditions.

Dilbonius

16 posts

Geek

#3258623 12-Jul-2024 10:04

Yesterday it was sunny. I'll just post the screenshot and let others interpret it. The output seems too high for a 7.1kw system in winter by my maths. Would love to see someone elses chart too.

Ge0rge

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#3258627 12-Jul-2024 10:11

You've said you have a 5kW inverter. You can't make any more than 5kW at any one instant, because that's it's rated output.

You made 17.59kWh for the day, which seems pretty reasonable in the middle of winter.

LightbulbNeil

57 posts

Master Geek

#3258631 12-Jul-2024 10:16

Being winter that would seem about right to me. Today if it's fine will be a better indicator for you.
There is a bit more each day nowas we are 3weeks past the solstice.
Rule of thumb, winter can be as low as 5% of the generation of peak summer.
Just need to be patient and see what is happening.
One thing that can happen when thd export is limited to 5kva 4.66 kw, if you are not using any power it will be throttled back. If you are using enough to keep the export below 4kw rate you will see the daily production being higher on those days.
Neil

Dilbonius

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#3258633 12-Jul-2024 10:17

"You've said you have a 5kW inverter."

Yeah that's my point. If the Fronius numbers are right then the inverter is too small. But it doesn't make any sense to me how 7.1kW of panels would make 4.8kW in winter when the optimal roof angle is 65 degrees. I need to see some data from other systems.

Ge0rge

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#3258634 12-Jul-2024 10:20

Panels are generally oversized for the inverter, so that you can get better production in winter. If you only have 5kW of panels, your winter output would be significantly lower.

You inverter will clip at 5kW in summer, but that's the price you pay to have higher generation in winter.

traderstu

332 posts

Ultimate Geek

#3258643 12-Jul-2024 10:32

OK, we're in the Waikato but the comparison is still interesting. Our setup is 12.45kW of panels, 30deg roof pitch, 2 phases. The roof design is fairly complicated with a few panel facing northish, with the rest either NW or NE. Our peak output yesterday was 8917W. I looked back at a few random days in Jan and got peaks of 13912W, 13405W peak

So, to do the maths. Yesterday you were 4800/7100=0.676. We were 8917/12450=0.716, so not miles apart. I had a quick look back at January and we got peaks up around 13405kW. So, 13450/12450=1.07. All things equal, you might expect 7100x1.07=7597 (If you could squeeze it through your inverter)

I asked my installer, how come we get more than the rated output? He said probably due to hole in the ozone, high UV. Spose he's right.

EgorNZ

50 posts

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#3258716 12-Jul-2024 11:22

You might expect total output (kWh) over a month in winter to be half the total output over a month in summer. But that doesn't mean you can't achieve high peak production (kW) numbers at moments on a fine day in winter. Most of the difference between seasons is due to the shorter days and poorer weather conditions rather than a significant reduction in light intensity in winter.

So it's no surprise you can hit your inverter's 5kW limit with those panels on a clear day at this time of year. The reason for over-speccing the panels relative to the inverter is to increase performance in cloudy or shaded conditions (vs. cost of an over-specced inverter).

I'm not sure how you have calculated an optimal roof angle of 65 degrees. The general rule of thumb is that panel tilt should correspond to your latitude, which in Canterbury is about 43 degrees.

I asked my installer, how come we get more than the rated output? He said probably due to hole in the ozone, high UV. Spose he's right.

Ultraviolet light isn't really used by PVs, so I doubt that theory.

Panel output ratings are based on standard test conditions (STC): a temperature of 25C and light intensity of 1000 Wm2. If you have more favourable conditions, the rating can be exceeded. On a fine winter morning if you're lucky you could have low air temperatures and high light intensity leading to better than rated performance.

Dilbonius

16 posts

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#3258720 12-Jul-2024 11:30

That's really interesting that the panels can make more power than the nominal power rating. I would have thought the nominal output of the panels is in ideal conditions in a very hot climate at the perfect angle etc. Is there some industry standard W/m2 the panel manufacturers are using?

So it would seem like my inverter will be shedding a lot in peak summer. It may have given a higher ROI to go with fewer panels or a larger inverter but Harrisons didn't really convey this in their proposal charts or comms with the sales person.

I find the lack of net metering in NZ a huge pain in the ass as well since you hit this awkward cliff where you'd need to jump up heaps in cost to export more than a single phase. If we had net metering it would be a no-brainer to go with a cheaper 3-phase balanced inverter.

eonsim

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#3258721 12-Jul-2024 11:31

5kW of panels in the Waikato facing ~30 degrees off north, array is split in two strings one 1.8kWp string at 45 degrees, and a 3.3kWp at 10 degrees.

The 45 degrees string peaked at 72% efficiency
The 10 degree string peaked at 48% efficiency

We get some shade just before the sun reaches it's peak so the 10 degree string is under performing during winter.

Also have access to a large 220kWp system on a commercial site, mainly north facing panels at low angles (10-20 degrees) that system peaked at 56% yesterday.

Dilbonius

16 posts

Geek

#3258722 12-Jul-2024 11:34

"I'm not sure how you have calculated an optimal roof angle of 65 degrees" - this is the optimal angle at July at noon. I used this sun path chart and took the perpendicular angle. https://www.wgtn.ac.nz/architecture/centres/cbpr/resources/pdfs/chc_sunpath.pdf

eonsim

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#3258726 12-Jul-2024 11:39

There is a pretty massive reduction in light intensity (for a flat surface) between winter and summer.

In the Waikato December/Jan get up to ~1,300W/m2 in June/July ~400W/m2.

eonsim

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#3258732 12-Jul-2024 11:47

traderstu:

I asked my installer, how come we get more than the rated output? He said probably due to hole in the ozone, high UV. Spose he's right.

Panels are typically graded so the performance sold is the minimum expected, with a 0-5W or 0-10W bin. So new 400W panels in perfect conditions could deliver between 400 and 405 (or 410 for some models), combine that with better temperatures and more intense light than standard test conditions and your system could out preform it's rated spec. If your panels are cooler than 25C they will start to out perform there rating (often ~1% per 3-4 degrees below 25C), likewise if the light intensity is >1000W/m2.

EgorNZ

50 posts

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#3258780 12-Jul-2024 11:54

eonsim:

There is a pretty massive reduction in light intensity (for a flat surface) between winter and summer.

In the Waikato December/Jan get up to ~1,300W/m2 in June/July ~400W/m2.

According to NIWA Solarview, for a north-facing install at 45deg tilt in Hamilton, you can expect peak light intensity up to 1014Wm2 in January, falling to 892Wm2 in June with cloudless conditions at midday. That's not a massive range of variation (in terms of peak potential).

HarmLessSolutions

969 posts

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#3258785 12-Jul-2024 12:06

Dilbonius:

That's really interesting that the panels can make more power than the nominal power rating. I would have thought the nominal output of the panels is in ideal conditions in a very hot climate at the perfect angle etc. Is there some industry standard W/m2 the panel manufacturers are using?

So it would seem like my inverter will be shedding a lot in peak summer. It may have given a higher ROI to go with fewer panels or a larger inverter but Harrisons didn't really convey this in their proposal charts or comms with the sales person.

I find the lack of net metering in NZ a huge pain in the ass as well since you hit this awkward cliff where you'd need to jump up heaps in cost to export more than a single phase. If we had net metering it would be a no-brainer to go with a cheaper 3-phase balanced inverter.

Worth noting that high temperatures can negatively effect output as PV uses light but not heat to generate and heat can cause resistance in the electrical components.

Our system is ~9.5kW of panels through an 8.2kW Fronius single phase inverter. Half of our panels are bifacials so actual maximum output can exceed 9.5kW.

Our production over the past two days (in Taranaki) are as below. Worth noting that the 32kWh 0n 10th which had a near perfect bell curve is near half of the 63kWh we did on January 7th.

https://www.harmlesssolutions.co.nz/

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