Winter stats and the real savings made

EcoScruples

Calling all long term solar users, I'm sure lots of new people are wondering like me what the real savings are over a winter period, Nov to Jan especially.
How much of the solar you generate do you use?
Do you have a battery and if so how does that effect your winter usage? Do you find that you use 99% of what you generate?

Also what's the long term average of what you generate to what you export?

Stats, graphs and data would be very welcome.

QrizB

My experience has been that December and January are pretty terrible for solar.

• December 2021 was particularly poor; I generated 15 O's all month.
• January is almost always better than December and January 2022 followed the trend; 31 O's generated.

Over those two months I generated 125kWh and exported 24kWh. At the time I only had a tiny 1kWh battery; if I'd had even 2kWh I'd have exported much less, maybe 5kWh total.

With 101kWh of self-consumption, savings at the then-SVT of 21p/kWh would have been about £21. In practice I was on Go and so my savings were more like £16.

I suppose the point I'm trying to make is - the savings from solar are made in the two summer quarters, not the two winter ones.

EcoScruples

That's useful info thank you, I'm curious how my battery will do in winter, I know it will remain empty for ling periods but I'm assuming that means anything I generate will be used by me or my battery.
I can't imagine there will be many days I'll get the 10kw I need.

QrizB

EcoScruples said:

That's useful info thank you, I'm curious how my battery will do in winter, I know it will remain empty for ling periods but I'm assuming that means anything I generate will be used by me or my battery.
I can't imagine there will be many days I'll get the 10kw I need.

Here's a site near me with a similar array to mine and with 10 years of data on PVGIS:

https://pvoutput.org/aggregate.jsp?id=5900&sid=4709&v=3&t=m

(If you look you might be able to find a site near you with a 4kWp array, that you can compare yours with.)

October to February they're producing, on average, less than 2O's a day - the "efficiency" column (there's the occasional exception). Since you need 2.5 O's to fill your 10kWh battery from your 4kWp array, plus you have daytime loads to service, you can expect your battery to be very rarely full (and quite often empty) for those five months.

If you have a multi-rate tariff, those are the months to consider charging your battery during the cheap-rate period.

1961Nick

I'm still on Octopus Go @ 5p/kWh

The average cost of import (inc vat) over the past 8 months has been quite consistent:

Nov: 6.01
Dec: 6.28
Jan: 5.55
Feb: 5.62
Mar: 5.71
Apr: 5.58
May: 5.88
Jun: 5.67

Total export this year is 58kWh verses generation of 2511kWh - 98% utilisation.

Solarchaser

From March to end of October you should do pretty well.
November to Feb will be poor, you should expect to consume everything pretty much in those months.
This is a 4kw array pointing sse in central Scotland  last year.
Ignore the first couple of months export, inverter was set wrong.


Battery usage is from charging using octopus go faster and then running the house in that charge

EcoScruples

My target monthly average will be around 350kw.
I'd written off Dec/Jan/Feb and also part of Oct/Nov so I guess 7 months good production might smooth out those other 5.

Interesting to see what people make in those dark months, what are people's longest non generation periods? Days? Weeks?

QrizB

EcoScruples said:

Interesting to see what people make in those dark months, what are people's longest non generation periods? Days? Weeks?

Not my graph - this is @Patrol 's 5.44kWp system last December (from here). Mine was a similar shape but roughly half the value.

Less than an O each day from the 6th to the 14th (and I'm not sure about the 5th!), and for the whole second half of the month from the 17th to the 31st.

Or, put another way, more than an O on 5 days max all month.

michaels

I think we average about 120kwh in Nov, 70 in Dec and 100 in Jan on a 4kw system that does about 3.6Mwh per year total - over 7 years.  However it is W facing, according to pvgis, a S facing system shouldn't suffer quite so badly in winter.

EcoScruples

Thanks guys, really appreciate all the feedback info.
Although mine is south facing I think it will suffer a bit more in the winter due to its shallow angle but we'll see.

Martyn1981

Hiya, if you use the PVGIS tool, it will give a monthly breakdown of the annual guesstimate in a graph.

For a south facing 35d pitch roof, you'll probably see a best to worth month ratio of about 4:1, maybe 3.5:1 if steep pitched (50d), and 4.5:1 if shallower. But, as they say 'results may vary', and shading can be more severe in the winter when the sun is lower.

I have an E/W install, so my difference is about 7:1.  


PS - Just to rub it in for us Brits, if you pop the PVGIS pin in southern Spain, then 1kWp of PV at a steep 50d pitch will vary from about 115kWh worst months to about 150kWh best months ...... I'm very jealous.