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My 2.5kW array is only putting out 1kWh in an entire day

 
Solar Photovoltaic (PV)
Last Post by David999 1 year ago
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 David999
(@david999)
Reputable Member Member
Joined: 2 years ago
Posts: 324
Topic starter 04/02/2025 4:10 pm   [#2076]

My 2.5kwp array is only putting out on a decent day about 1kwp in an entire day.  Seems the sun is just too poor right now.  I was contemplating doubling that this year but it seems pointless unless I want to balance my costs during the summer months on feed in tariff which is only 15p kWh.  I charge my batteries at 7p kWh.

Would I be better off installing another battery than more panels do you think. I then get a little longer when it’s 22p kWh.  

not sure where the break even is here,  better on panels or another battery.

 

anyone give some pointers please. 



   
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 Old_Scientist
(@old_scientist)
Honorable Member Member
Joined: 2 years ago
Posts: 405
04/02/2025 6:01 pm  

I generated 6.4kWh on Saturday 2.8kWh on Sunday and 7.4kWh yesterday from my south facing 3.65kWp array - Saturday and yesterday were very good days with lots of sunshine.

I've just been considering a similar dilemma - do we add more solar (I could add another south facing 3.4kWp giving ~7kWp total) or do we add a 5kW battery.

We are on the Agile Cosy Tariff, so cheap slots for me are 12.86p and day rate is 26.22p. My average import rate is currently ~20p per kWh, so I figure shifting more usage from the 26.22p day rate to the 12.86p cheap rate may save me around 7p per kWh in winter and maybe less in summer. Very rough back of an envelope calculations tell me I may be able to save £400-500 per year for a 5kW battery system that is likely to cost me £4-5K to install, so likely to pay for itself over it's 10 year lifespan. I don't really see the investment case whilst SEG rates are 15p for exported solar and the difference between cheap rates and my import rate are only 7p per kWh.

Given current pricing, I'd be inclined to add more solar and just export as much excess as possible in the summer at 15p - view this as your annual 'battery' - using this to offset your costs later in the year.

Your economics are different as you already have a battery, and your margin (7p vs 22p) is wider giving you twice the leverage I have as 22p - 7p = 15p per kWh, so more battery storage may be better for you. Even in summer you can leverage the system by charging at 7p and using that during the day whilst exporting solar at 15p.

The main issue I see is that so much can change in the current pricing regimes over the lifetime of these products. The current 15p SEG rates could disappear or massively reduce swinging things towards battery storage to make the most of the excess solar you generate, which makes it really hard to price these long term investments.


Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.


   
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 David999
(@david999)
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Joined: 2 years ago
Posts: 324
Topic starter 04/02/2025 10:55 pm  

@old_scientist no easy solution for this I think, with these battery banks being built to store wind energy I’m thinking as yourself that the FIT might go leaving me with loads of free solar for the grid.



   
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