Is our winter generation amount about right?

[MikeGrahamT21]

Hi

 

we have an east west split 50/50, 2kwp on each, and a sunnyboy string inverter with each side of the roof on a different circuit. Now our generation in December and January has never been great, usually around 50kwh each month, and I’ve never really thought there was anything wrong with that, however my suspicions were raised when speaking to a battery supplier the other day.

 

the west side is main concern, it faces slightly more north than south and roof pitch is around 35degrees, so less than ideal at this time of year id say. Yesterday afternoon we had full sun in the back, around 2pm, I was speaking to the battery person and he said you must be generating about 1.5kw (which I thought at the time was a bit optimistic), when in fact we were generating 220w. Does this sound about right. December and January we peak at around 1kw of power at best, generally in the morning.

 

if this doesn’t seem right I’m thinking of getting a local company out to inspect it all (our installers went bust and ‘forgot’ to register our insurance based warranty) and give them a clean at the same time (hardly much more money over inspection alone).

 

what do people think??

 

regards

mike

[ProDave]

A Sunny boy will report on it's display the string voltage and string current.  Next Sunny day you get, record those peak values that you see for each string.

[MikeGrahamT21]

It does indeed, I’ll get those figures off and post them. Shame I’m not in today as it’s a lovely day. Also worth noting there’s no trees or other high objects nearby to shade us at any point in the day.

[Ed Davies]

Using PVGIS and assuming azimuths of 100° (10° North of West) and -80° (10° S of E) gives 48.5 kWh and 59.9 kWh for December and January respectively so your 50 kWh/month looks pretty reasonable. That's for a point at the southern end of the main runway at Sutton Bank (Yorkshire Gliding Club) which will have a pretty clear horizon from east round through south to west.

 

It seems to me that 1.5 kW would be a bit optimistic with the low sun and the awkward angle on to the panels. Still, 200 W does sound a bit disappointing.

 

(Does the “T21” in your name have any gliding significance?)

[Jeremy Harris]

FWIW, we have a 6.25 kWp array, facing slightly west of south, inclined at 45 deg.  I can count the days on one hand where we've generated more than about 3 kWp at any time, and the total generation so far since the beginning of December is about 200 kWh, so around 4.2 kWh/day, although there have been lots of days when we've generated next to nothing, which is pretty normal for this time of the year.

[Ed Davies]

If @MikeGrahamT21's arrays were on the south-facing end (4 kWp, azimuth 10° W of S but still 35° elevation) then PVGIS says they'd produce 116 and 124 kWh in December and January, so just about double an east/west split. E/W split is good for self consumption in the summer but really hammers winter production. Cranking the south-facing ones up to 45° elevation would increase these to 131 and 137 kWh. Then moving them to the N end of the runway at Old Sarum would up them to 135 and 158 kWh. So 200 kWh for half as much again for a month and a half is cromulant though a little below the estimate.

 

By the way, for quite a while I collated and published people's reported monthly PV outputs and compared them with PVGIS estimates. Generally speaking, PVGIS at that time was very realistic but comfortingly pessimistic. About 3/4 of the time actual output was better, 25% worse. They've fiddled with the databases a bit since then but I'm moderately comfortable they're quite likely to be reasonable.

Edited January 17, 2019 by Ed Davies

[jack]

1 hour ago, MikeGrahamT21 said:

Yesterday afternoon we had full sun in the back, around 2pm, I was speaking to the battery person and he said you must be generating about 1.5kw (which I thought at the time was a bit optimistic), when in fact we were generating 220w. Does this sound about right. December and January we peak at around 1kw of power at best, generally in the morning.

 

Your battery guy's numbers sound optimistic to say the least.

 

I've got 8.5kW in a mixed system (some east-west, some just west of south, all with a relatively low pitch) and the highest hourly production I've had in January is 590Wh.

[ProDave]

Sounds like the salesmen that keep pestering me offering to sell a "gadget" that will increase my PV output by 20%

[Jeremy Harris]

24 minutes ago, Ed Davies said:

(Does the “T21” in your name have any gliding significance?)

 

Completely off topic:

 

My first ever flight in any aeroplane was a T21 Sedbergh, an air experience flight when I was in the ATC, at RAF Halton in 1965.

[jack]

The guy who installed our solar array (excellent company, based in Guildford, Surrey - let me know if anyone wants details) now also does Tesla Powerwalls. He dropped by the other day after surveying my neighbour's house for solar. After hearing about some of his clients' Powerwall systems, I pointed out that our annual electricity bill is only £900, and that's through a relatively expensive supplier (Good Energy) and without even the slightest attempt at optimising consumption. That was more or less the end of the conversation, as the payback time doesn't look so good when that's your entire energy consumption!

 

He also said that he doesn't expect the price of the Powerwall to fall much in the near future. Since Musk was kicked out, the management has adopted a more profit-focused view, compared to Musk's focus on gaining market share at any cost. This means prices have actually gone up, and aren't likely to come down in any particular hurry.

[billt]

I wouldn't expect much from WNW facing panels at this time of year; the sun isn't over the horizon from that direction and what sun there is will be at a very oblique angle.

 

I'd also point out that this winter has been pretty cloudy round here so the generation has been much lower than expected or that PVGIS (which is based on averages) would predict.

 

Although looking at Decembers figures, PVGIS classic prediction is 75kWh, PVGIS climate modelling prediction 106kWhr. Average actual production over 8 years 86kWhr, best month 123 kWh, last December 71kWh, worst December 57kWh. This is for a 3.8kW array facing SSW.

 

Winter production has much greater variability than summer production as daylight hours are very short and if you get thick cloud during those hours you'll get very little production. With the longer days of summer you're much less likely to get several days with total cloud cover during the generation period.

 

This month is looking pretty bad with generation so far of 29 kwh against a PVGIS classic prediction of 110kWh, but if we get 15 days of unbroken sunshine it might should get closer to the average!

[Jeremy Harris]

Right now our Sunamp was fully charged to its maximum capacity of ~9 kWH by about 11:00 this morning and we've been exporting well over 3 Kw for the last hour or so, so it looks as if today will be probably our best generation day since early December, probably be around 12 kWh, maybe more, which is well above average for this time of year. 

 

I've been sitting here watching the monitor, knowing that my car is now fully charged, the Sunamp is fully charged (after me having to do the usual daily reset to make the damned thing work) and we're still exporting at a fair old rate.  Definitely need some batteries to be able to better use all the energy we generate!

[le-cerveau]

So far today we have peaked at 3.78kW / 945Wh and already produced 13.5 kWh, however if I go back to Saturday it was peak 0.28kW / 71 Wh total for the day 0.94 kWh.  Not teh worsk 15 December 0.56kWh, compared to 22 June 18 70.2 kWh!!!  Over 100 fold variation.

 

My array is just under 10kW split SE/SW.

[Ed Davies]

1 hour ago, le-cerveau said:

peaked at 3.78kW / 945Wh

 

What does the “/ 945Wh” bit mean?

[Jeremy Harris]

4 hours ago, JSHarris said:

... it looks as if today will be probably our best generation day since early December, probably be around 12 kWh, maybe more, which is well above average for this time of year. 

 

 

Today's PV generation exceeding my best guess, at 18.3 kWh for the day. 

 

The downside of this was that despite the reflective film on the windows, the big shading overhangs (which do sod all at this time of the year), the relatively cool outside air temperature and the fact that our heating hasn't come on at all for the past two days, the house reached well over 24 deg C this afternoon and the cooling system came on (thankfully powered by the PV generation, so effectively free). 

 

The maximum outside air temperature I saw was 8 deg C, and it was down to 7 deg C when the cooling came on.  The house is still a bit warm now the cooling is off, at 22.9 deg C, so even though it's expected to be cold overnight I doubt that we'll need heating tomorrow as the fabric of the house will still be holding a lot of heat for the next day or so.

 

 

[Nickfromwales]

11 hours ago, ProDave said:

Sounds like the salesmen that keep pestering me offering to sell a "gadget" that will increase my PV output by 20%

Buy 5 and you'll be up 100% !!!

What are you waiting for? 

[NSS]

6 hours ago, JSHarris said:

 

Today's PV generation exceeding my best guess, at 18.3 kWh for the day. 

 

Blimey, we only managed 4.7 kWh today. Granted it wasn't sunny all day, and at this time of year we do get a bit of shading in the morning, but that still seems a lot to have generated at this time of year. The last time we generated 12 kWh (pro rata 2/3 of what you did today as we only have 4k on the roof) was 9th October.

Edited January 17, 2019 by NSS

[le-cerveau]

13 hours ago, Ed Davies said:

What does the “/ 945Wh” bit mean?

 The peak is the maximum at any given point in kW so max power at a given point the 945Wh is power generated over a 15 minute period.  It is the way enphase reports.

 

[billt]

9 hours ago, NSS said:

Blimey, we only managed 4.7 kWh today. Granted it wasn't sunny all day, and at this time of year we do get a bit of shading in the morning, but that still seems a lot to have generated at this time of year. The last time we generated 12 kWh (pro rata 2/3 of what you did today as we only have 4k on the roof) was 9th October.

 

The shading and cloud will account for the energy lost.

 

We had a good day yesterday with the 3.8kW system generating 8.7kWh and total generation of 42kWh.

 

Looking at the output graph shows shading of the 3.8kW system in the morning which probably lost 2kWh and cloud in the afternoon which lost another kWh. Without the shading and cloud the generation would be similar to that of JSHarris.

 

If you get clear sunshine in the winter the power is pretty much the same as in the summer, it just doesn't last long and is easily reduced by cloud.

 

[Jeremy Harris]

10 hours ago, NSS said:

Blimey, we only managed 4.7 kWh today. Granted it wasn't sunny all day, and at this time of year we do get a bit of shading in the morning, but that still seems a lot to have generated at this time of year. The last time we generated 12 kWh (pro rata 2/3 of what you did today as we only have 4k on the roof) was 9th October.

 

 

TBH, I was surprised when I looked at the daily total, as based on the generation until about lunchtime I was expecting we'd get around 12 kWh.

 

Today looks like it might be another good day.  Cold last night but bright this morning, with just a bit of light high cloud.  Nice to start generating again in earnest, as December was pretty dire.

[Gone West]

16 hours ago, JSHarris said:

the house reached well over 24 deg C this afternoon and the cooling system came on (thankfully powered by the PV generation, so effectively free). 
 

My life wouldn't be worth living if I cooled the house down when it reached 24C. The other day Wendy used the pyrolitic cleaning function in the oven and the kitchen temperature went up to 25C, Wendy was basking in there.

[jack]

16 hours ago, JSHarris said:

Today's PV generation exceeding my best guess, at 18.3 kWh for the day. 

 

Wowsers, we only managed 11.9kWh and we have 8.5kW!

 

 

Shows you what a difference angle and orientation makes on a sunny winter's day. We're stuck with a relatively flat array, much of which is east west.

I also need to get up on the roof and clean mine!

[MikeGrahamT21]

On 17/01/2019 at 09:50, Ed Davies said:

Using PVGIS and assuming azimuths of 100° (10° North of West) and -80° (10° S of E) gives 48.5 kWh and 59.9 kWh for December and January respectively so your 50 kWh/month looks pretty reasonable. That's for a point at the southern end of the main runway at Sutton Bank (Yorkshire Gliding Club) which will have a pretty clear horizon from east round through south to west.

 

It seems to me that 1.5 kW would be a bit optimistic with the low sun and the awkward angle on to the panels. Still, 200 W does sound a bit disappointing.

 

(Does the “T21” in your name have any gliding significance?)

Yeah, I thought 1.5KW sounded very optimistic too.

 

Annoyingly today the clouds are out in force, while i was out yesterday it was a perfect day, in which we generated 4.5kWh. I've got a firmware upgrade to do on the inverter today, no idea what it fixes as they haven't included release notes, after i've done that i'll see what data I can drag from Sunny Explorer.

 

T21 doesn't have any gliding significance, its just the first three letters from my car registration plate! Not very imaginative i know...

[MikeGrahamT21]

12 minutes ago, jack said:

 

Wowsers, we only managed 11.9kWh and we have 8.5kW!

 

 

Shows you what a difference angle and orientation makes on a sunny winter's day. We're stuck with a relatively flat array, much of which is east west.

I also need to get up on the roof and clean mine!

 

Thats another thing I want to ask about. There is a local solar company who I contacted as they were advertising extended warranty for the SMA inverters (though since found out I can do this myself on SMA's site, which i'll be doing), and they do a maintenance package as a one off full inspection and clean for £110+VAT. Since we are getting ever more concerned over the original installation (company went bust) and we have no insurance backed warranty, as they decided not to bother paying it and registering it before they went bust, it seems reasonable to get it checked over, and we have had a few niggles over the years such as a tripping consumer unit, in october and november (no idea why its only these two months). Is the cleaning worth it? Plenty of wood burners round here, and the velux windows are dirty, so i can't see the solar panels not being, without the cleaning inspection only is £60+VAT.

[jack]

7 minutes ago, MikeGrahamT21 said:

Is the cleaning worth it? 

 

An interesting thing about PV, especially if you're using a standard inverter rather than micro-inverters or similar, is that the worst-performing panel limits the power that can be generated by all the rest on the same string. That means that if even one panel is shaded or dirty, it drags down the amount the rest of the panels can generate, often by a surprising amount. Even shading a couple of cells on a panel can be enough to make a difference:

 

[Edited to add:] https://blog.aurorasolar.com/shading-losses-for-pv-systems-and-techniques-to-mitigate-them/.

 

Cleaning may therefore be worth it, especially if you have any panels that have algae or dust on them (even if only in a corner or along the bottom).