Solar panels and battery - any real world reccomendations?

[Ron-ski]

Showing 55v or so from the batteries currently

55v is very close to full battery voltage, 58.4v would be 100% full/charged, but no one normally charges to that, as that would be 3.65v per cell.

For nerds in the room, here's the technical explanation:
https://givenergy.co.uk/pdfs/messages/GivEnergy SOC Statement.pdf

I'm gobsmacked that Givenery are using the voltage to show how much battery is remaining, but I guess they do it that way so as the cells age its still somewhat accurate.

The problem with LifePo4 is this, the cells have an absolute minimum of 2.5v per cell, 16 cells equals 40v, and a maximum of 3.65v, 16 x 3.65v = 58.4v. But the drop off between from 3v down to 2.5v is very quick, and like wise at the other end 55v to 58.4 is very quick. The section in between is very flat, and therefore trying to use that to calculate how much battery is remaining is not very accurate.

Chart from https://www.powerstream.com/LLLF.htm

The way that Victron does it, is it measures how much power flows in and out of the battery using a shunt, you tell it the capacity of the batteries, and it works out the rest, it is very accurate, but I can see in many years perhaps when there is less capacity it would be less accurate unless you lowered the capacity, but I think it recalibrates itself. I think you tell it the lowest voltage, and the highest voltage, and then that range is 100%.

 

[SoliD]

So could potentially my batteries have been sat there over the last few weeks showing 4% and not draining even though they actually had charge? Be very very annoyed if so.

 

[94JDH]

Oh flat roof is totally different then, and you'll need a more discrete mount method to stay within planning laws. By plugin inverter, you mean a direct to 3-pin device? If so then I don't rate them for larger arrays, you'll be limited to 13A realistically, and that isn't something I'd trust over a very long sunny day.

Most likely get 4 East & 4 West on that size in landscape configuration @10 degrees using something like the Van Der Valk L10 E/W system (2 East/2 West/ 2 East/ 2 West)

 

[Ron-ski]

So could potentially my batteries have been sat there over the last few weeks showing 4% and not draining even though they actually had charge? Be very very annoyed if so.

Potentially, the document Katie linked to states a cell voltage if roughly 2.75v for 4%, which is a battery voltage of 44v, so if your voltage was higher then state of charge is higher. Bear in mind that charging voltage is always higher than battery at rest voltage.

 

[Tavis75]

I had a significant jump on my GivEnergy battery in the last few days as well from 56% to 100%, which was the highest I'd seen, came after several days of really bad charging days with the battery barely creeping above 5%, so wonder if that had some impact. Also had two days of significant internet outage, so that hasn't helped my readings!

Carried on with my little programming attempt at charging based on solar forecasts, got it grabbing 2 week's worth of usage data to calculate average usage for each half hour period of each different day and also pulling in the solcast forecast. Then using those to calculate the amount of power needed to make it to the next cheap rate period, and also the amount of power required to get to the point of the day that there is enough power available to avoid grid draw. Seems to be spitting out some sensible numbers i.e. Saturday forecast suggested a small charge to 7% to cover the start of the day, then it was a good solar day so full charge achieved from solar after that, which covered the rest of the day. I have also got a function that will charge the battery to a given percentage at a given time (checking and adjusting the charge rate every half hour), so just now a case of tying that all together and getting it to run on an overnight schedule (when my Economy 7 tariff goes live).

Obviously, I am reliant on the solar forecast being somewhat accurate so will be interesting to see how it goes, suspect I'll need to factor in a bit of wiggle room to account for days when the forecast is off, but hopefully will at least get it roughly working on predicting good and bad days and charging appropriately, even if it isn't 100% spot on.

 

[SoliD]

Potentially, the document Katie linked to states a cell voltage if roughly 2.75v for 4%, which is a battery voltage of 44v, so if your voltage was higher then state of charge is higher. Bear in mind that charging voltage is always higher than battery at rest voltage.

So gone back and checked a few dates randomly and can't see battery dropping below 52v whatsoever and generally around 56V max.

 

[Ron-ski]

Seems Givenergy have a major problem, hope they sort it quickly, at least they are on it already.

 

[Axeboy]

Think this is an amazing quote for the times we find ourselves in, same guy as before but a bit of back and forth…




He’s also mentioned he managed to get some reservations in on Q.Cells new home core kit here https://www.q-cells.eu/products/energy-storage/qhome-core.html if I’m interested. Will find out a price next week when I catch up with him - looks like a pretty neat bit of kit to me.

Seems a wild price for the batteries. Worth getting that checked as the £5200 would be about right for a single 10kw. Maybe its 2 x 5kw making 10. I doubt its £5200 for 20kw

 

[Mercenary Keyboard Warrior]

Seems a wild price for the batteries. Worth getting that checked as the £5200 would be about right for a single 10kw. Maybe its 2 x 5kw making 10. I doubt its £5200 for 20kw

Thats what i took it as 2x 5 as it would match the (xxx) from the panels. Ie its a total of qty x "power"

 

[kvo]

Think this is an amazing quote for the times we find ourselves in, same guy as before but a bit of back and forth…




He’s also mentioned he managed to get some reservations in on Q.Cells new home core kit here https://www.q-cells.eu/products/energy-storage/qhome-core.html if I’m interested. Will find out a price next week when I catch up with him - looks like a pretty neat bit of kit to me.

Do you mind sharing the company that provided the quote? I'm looking for a pretty identical quote, except, I can get around ~5.5kWp on my roof.
It looks pretty competitive, if it's a 20kWh system!

 

[BUDFORCE]

Foggy all day today, generated a whopping 0.4khw

 

[Zeeflyboy]

Seems a wild price for the batteries. Worth getting that checked as the £5200 would be about right for a single 10kw. Maybe its 2 x 5kw making 10. I doubt its £5200 for 20kw

Thats what i took it as 2x 5 as it would match the (xxx) from the panels. Ie its a total of qty x "power"

Do you mind sharing the company that provided the quote? I'm looking for a pretty identical quote, except, I can get around ~5.5kWp on my roof.
It looks pretty competitive, if it's a 20kWh system!

It’s 2x 5kw Purestorage II for a total of 10kwh, I can see how it’s slightly ambiguous on the invoice but it’s definitely just two 5kwh (they only make 5kwh modules for the purestorage hybrid packs).

I’m not sure I need more as I’ll have an electric car plugged in fairly often (when it finally arrives next year!), so can hopefully shove a decent amount of excess in there.

Kvo - won’t be much use for you I think, you are weeeeeeell outside their coverage area up there! Obviously I can’t rate them yet either, but I made the first invoice payment for the G99 application today so the adventure has begun… he’s a very switched on sounding guy and I get a good impression from him so fingers crossed. Didn’t really want to publicly post them yet until I can say how they’ve been for me, but can private message you if you still want to know with the caveat that they are as yet untested!

 

[Freefaller]

It's a lot of money but also a lot of kit for the money.

Its good value for the kit for the prices at the moment. "a lot of money" is relative to your circumstances and why you're getting solar.

 

[redfist]

Just checking my Eleccy statement and just realised that my batteries have been charging from 12 each night since the beginning of the month when the system was upgraded. I now have 16kWh at 38p.

 

[SoliD]

First daylight hours I'm seeing 0 generation. It really is horrible out there!

 

[Journey]

First daylight hours I'm seeing 0 generation. It really is horrible out there!

It's dire, just started to see lighter grey skies, and a few Wh starting to be pushed in.

 

[HungryHippos]

Generated today 0 kwh

 

[Mercenary Keyboard Warrior]

Was supposed to be my install date today
End of next week though so I can wait it out if generation is that poor, only real loss is pulling cheap units into batteries!

I wonder if I am going to see any real notable generation until we get to March time in reality

 

[HungryHippos]

Rained off?

 

[Siliconslave]

Just checking my Eleccy statement and just realised that my batteries have been charging from 12 each night since the beginning of the month when the system was upgraded. I now have 16kWh at 38p.

no off peak rate?

Had a few teething problems with the battery and inverter software, but now seems to be all up and running:





Just waiting for SolarEdge to setup our account, which apparently takes a week or so, and our Export MPAN (not that theres any rush, on a good rate till may so will wait to change.)

Don't seem to be generating today, but charged the batterys on the cheap last night so drawing from there