Low Efficiency from Panels - What Numbers Should I be Seeing?

Bianchiintenso

just by way of comparison my 8kw SSW - E-W system produced a peak of 2295w at 12:40 in North Yorkshire

ABrass

JKenH said:

ABrass said:

My 4kW WNW string was producing a peak of 600W today in the afternoon. Your numbers seem about right. 

That’s still around twice the “efficiency” the OP was reporting around lunchtime. 

Edit: what was your SSE array producing - just curious?

A very similar peak of 600ish W, I think a different time of day but the graphs are a bit naff. Earlier in the day it was producing 500W to the WNW's 300W.

A total system peak of just over 1kW btw.

With a clean E/W split then the two strings should be working almost entirely separately at this time of year with only a little overlap around midday, so it should be fairly comparable in the afternoon.

chris_n

Nsar1 said:

chris_n said:

With panels facing East - West at this time of year the sun is never anywhere near 90 degrees to them, it is also very low in the sky. If you want better generation in winter you need to fit some panels on your South facing wall. Even then light levels are much lower even on a clear day as the sun's radiation has to pass through more of the atmosphere.
I am guessing you are new to solar, this is normal for December. 

New to solar panels, not to the points of the compass or indeed that winter days are shorter. But thank you for your comment.

Putting your panels into PVGIS  gives a December output for the whole month of 49.82 kWh per panel set so round about 3.2 kWh per day average for the whole system. Looking at the figures you quote you would have been well above this. The sun is only 14 degrees above the horizon in your location and at best at close to 45 degrees away from perpendicular to them in the East - West plane. It can often give better results when the sky is slightly overcast when you are that far away from facing the sun. If just one set of your panels was facing due south at the same inclination you would be making 114 kWh.

Waywardmike

Sorry, I misread your OP.  the ridge line runs S/N so the panels are facing east west?

If so, then yes, what you're seeing is probably around normal.  Wait till spring/summer and you'll be laughing all the way to the bank.

Petriix

It's very hard to know from the information given, but the sun is very low at this time of year. Without optimisers or micro-inverters a small amount of shading could have a significant effect. E/W arrays will always generate less in winter than South facing panels. I suspect there's no issues with the installation, just suboptimal orientation for winter generation. 

k_man

Isn't it also the case with E/W, that even in the height of summer you will rarely/never get even 50% efficiency of peak (as half the panels are far from direct facing, when the other half are), but the benefit is a more even output during more of the day.

And if you have N/S ridge, you don't have much choice.

Nsar1

Update....my badgering of the installer got them to send someone out yesterday and Sunsynk (who have been very unhelpful throughout) updated the firmware this morning and at 11.33 (another cloudless morning) I was seeing 1550W off the roof, which is showing as 17.2% efficiency. At 12.25 it was 2196W (24.4% efficiency)

At 09.25 when the sun would have been better angled for the East panels I was getting 1261W (14%).

So it feels that having East and West facing panels flattens out the curve that people with pure South facing panels get.

I will continue to monitor but feel like I'm in the right ballpark now.

Thanks for replies 

Bianchiintenso

when we've had cloudless sky in last week,  best I've managed is 11% efficiancy showing on the Sunsynk app, so looks like you've got it sorted!

JKenH

k_man said:

Isn't it also the case with E/W, that even in the height of summer you will rarely/never get even 50% efficiency of peak (as half the panels are far from direct facing, when the other half are), but the benefit is a more even output during more of the day.

And if you have N/S ridge, you don't have much choice.

It’s nowhere near as bad as 50% in summer. On a very good day with our 4.2kWp WSW roof we have seen clipping with our 3.6kw inverter and in excess of 5kWh/kWp. In fact on odd occasions in 2020 we saw in excess of 6kWh/kWp compared with around 7.5 kWh/kWp max from a south facing system. Our ENE roof will rarely get above 4kWh/kWp. Once you go past due East or due West it really does fall off. 

In the depths of winter my  E/W roofs only generate about 50% what a south facing roof might- less relatively on sunny days bu5 when it is overcast the differential is nowhere near as bad.

norsefox

This has been really useful, particularly the earlier link to the JRC website.  

Our roof is very shallow, perhaps 15 degrees or so, and almost E/W.  Living in Scotland further dampens the potential output.

That website has been quite reassuring - suggesting no more than 29kWh in December (from a 4.9kW system).  That seems pretty close to what I've seen on average for the week it has been installed.  For context, it projects 530/450kWh in the summer months.

For all the research I did into this decision, no matter how much you plan, it's only now that I appreciate just how absurdly low in the sky the sun is at this time of year, and how some shadows are being created from objects nowhere near the property...