Gen3 5KW inverter
1x 9.5kWh battery
Hi all,
Been looking at my data/use and coupled with the tariff i am on - Cosy. I am not using the last 25-30% of my battery.
Would i see any benefit of limiting the charge on my battery to 85% so that it when charges overnight on the cheap, starts to be used, solar kicks in and charges back to 85% then starts exporting the surplus?
or is there a better approach?
Couple of things here:
Its good practice to regularly exercise the full range of your battery, allow it to empty, rest empty for a little while, and be filled up completely. Doing this ensures that the battery management system can best keep track of what the battery level is. There is a youtube video from givenergy on this, but basically once a week or so would be good. If you keep your video full-ish all the time then the battery can loose track of its state of charge and then suddenly correct itself when it realises its figures are wrong.
If you have an export tariff then financially you need to look at the cost of filling your battery from grid vs solar. Cosy for me used to be 13.2p overnight import and 15p export, so on paper 1.8p cheaper to fill overnight than fill on solar. However this misses out the conversion losses of AC to DC and in and out of the battery which typically total around 10-20% for the round trip. So in reality it was only about 1/2p better to charge from grid.
Since the Cosy rates increased yesterday its now more expensive to charge overnight.
Of course this assumes you have enough solar generation to fill your battery from solar, and in particular to avoid peak rate import. If you don’t then its still worth importing to avoid that extra cost.
Its not simple!
Its worth looking at you gen to use ratio’s, and consider the tariffs.
I’ve just jumped from COSY and Export to IOF.
Last week for me (6kWp on roof, 5kW gen3 and 9.5 battery)
Thanks for taking the time to reply in detail. the reasoning behind my query was not necessarily one for battery life/longevity, that doesn’t really concern me.
After having 12 months on Agile and religiously checking the dashboard every day and inputting manually the cheap slots i wanted to charge up from, to then the last few months using Octopus R&D and setting thresholds to auto charge on the cheap ones, to finally having enough of the stupid rates and moving to Cosy and seeing how simple/painless it is getting 3x fixed cheap slots a day on the cheap and not having to do the work daily/weekly to ensure i was getting optimum rates to charge from.
it was what i always wanted - autonomy!
my thoughts then went, "i don’t use the whole capacity of the battery every day, so why not limit the charge to 90% via grid on the 4am - 7am slot, PV then takes over powering/charging and throughout the day, the battery rides at 90% whilst excess is exported. i finish charging off the grid earlier using less [10%] and i export more sooner [10%] as i do not need it to hit 100%. which means it costs me less/earns me more. when autumn returns, i remove the limit and return to 100% grid charging over night and battery use during the day.
but you say don’t do that.
so i’ve knocked the 10pm to midnight charge on its head and just use battery power overnight, the battery then does a 30% to 95% re-charge on the 4am slot instead.
arguably, i cannot see how i am not using the same amount of energy. surely its the same whether i charge from a lower percentage to full or a higher percentage to full - but over 2 slots.
typical day and sunny [had a few recently] charging on the 4am to 7am and 10pm to midnight slots
yesterday just the 4am grid charge and the rest PV and battery over night.
to this morning/today… a longer charge
@jammyb there’s no right or wrong answer to what to do, I can just share my experience and thoughts.
You’re right, it makes no difference to the amount of energy you use if you charge the battery in one, two or three Cosy charging slots. But some thoughts for you:
My current strategy on Cosy is not charge from the grid at all. Overnight I do a force discharge from 6am to empty the batteries before the sun comes up. I then don’t let any battery charging start until 9am when I let the battery charge up at 1.4kW from solar. This trickle charge during the day ensures I minimise clipping and convert the most solar I can.
I then let the batteries run the house through the evening and overnight, then repeat the discharge of any remaining charge the next morning.
I too was on Agile up to about the end of January when I got fed up with the continual high rates and moved to Cosy. I may go back to Agile if the overnight rates make it worthwhile, or I’ll stick on Cosy and just not charge from grid unless the next day’s solar forecast means the batteries wouldn’t fill up on solar.
Time to change tariffs.
I’ve just set the battery to charge on GO tariff from tonight and I will accept the OE GO terms tomorrow so the tariff change migrates over tomorrow too.
It can then do one charge over night on 8p and charge/export the rest of the time.
Makes sense. A lot of people are on EV tariffs for the summer for just that reason.
Well, after the firmware update and it didn’t charge from programmed Cosy slot 3 I then could see that it could last most of the night before a charge.
May as well enjoy 8p for a bit.
After you do a firmware upgrade you have to reprogram all the charge and discharge slot settings. The inverter deletes them as part of the upgrade but the portal doesn’t realise this, so you just have to set them up again
Well it remembered slot 1 and 2. Just not slot 3.
All wiped and programmed to GO for 1 charge now. 
