Is it still worth exporting your home battery?

[T1 Terry]

I had my system setup nicely for exporting surplus energy during the evening all automatically done, no intervention required by me. Looking at the amount earned and the potential degredation of batteries, I switched the system off and no longer export during the evenings. I no longer participate with the saving sessions either for the same reasons, it's just not worth it.

Maybe Tesla will come up with something more attractive?

Do you know what chemistry the house batteries are? LFP don't degrade with cycling, in fact, they actually improve if the cycling is within sensible cell voltages.

T1 Terry

 

[Gomev]

We're interested in ASHP, but have doubts the old house would be efficient enough for it to be practical. Need to do some more research.

We have the opposite problem but same resulting dilemma. Newish build, 2018, so reasonably well insulated but designed for a gas combi boiler. Absolutely nowhere to put a hot water tank.

 

[Everest]

Do you know what chemistry the house batteries are?

LOL... I suspect @johnb80 knows His DIY system was built with 16 x 280 Ah EVE LiFePO₄ cells

DIY enclosure for home storage | EV + Charger + Solar + Battery + Tariff Advice

 

[T1 Terry]

LOL... I suspect @johnb80 knows His DIY system was built with 16 x 280 Ah EVE LifeP04 cells

Post in thread 'DIY enclosure for home storage'

Aug 28, 2024

Mine isnt such a posh housing as Gadget Geek's, it was a very tight space and this toolshed from Amazon worked well.

It is fastened back to the wall, two conduits, one on each side connect to the house. The one on the far side is the electricity supply, the one that can be seen here carries the data cables. The ventilation fan can be seen at the top.

In the lower half there are 16 x 280 Ah EVE LifeP04 cells, theyre stood on vivarium heater mats and their enclosure is insulated. The heater mats are used (rarely) in winter time to keep the temperature above 5 degC...

• johnb80

• 
• 

Ah, very nice system, no idea why he is concerned about "the potential degredation of batteries," as LFP cells don't suffer cycling degradation as long as the voltages remain withing the 3 V min and 3.6 V max.
Most of the degradation occurs when a cell gets low and a high current draw drags the voltage below the 3 V threshold .... it can go as low as 2.8 V short term, but generally, if the voltage dips to 2.8 V under load, all 100% of the capacity has been used and that 2.8 V rapidly becomes 2 V or less and damage starts ....

T1 Terry

 

[Everest]

no idea why he is concerned about "the potential degredation of batteries,"

agree - as I commented earlier in the thread, IMHO calendar ageing will be as big a factor in degradation as cyclic usage.

 

[mikgle]

Some time last October I saw, I think on Twitter, that Octopus was offering to fix the 7p rate for 12 months, for anyone who would agree to a small increase in the peak rate. It seemed like a no-brainer to me, as I don't use any peak-rate electricity worth mentioning, so I did it. I had an email conversation with someone who even wanted to know my car registration number, and it was done.

I think that's what's given me the 3.49p rate. The email I had last week said that when I fixed my rate they bought the electricity in advance to supply me, and because of that I was getting the 3.5p reduction from the 7p rate. Turned out rather better than I had envisaged.

Just had my email ref OIG.. cheap rate dropped from 7p/kWh to 5.2p, standard rate dropped from 29.5p to 27.7p but standing charge increased by 2.63p. I'm in Devon.
Let's see what July brings but I won't be using any day rate from April on until October.

 

[T1 Terry]

agree - as I commented earlier in the thread, IMHO calendar ageing will be as big a factor in degradation as cyclic usage.

LFP cells don't calendar age either, that was nonsense put out by the fossil fuel people.
I had 12 yr old LFP cells that I finally charged and used rather than them remaining as a show and tell item when I needed a battery for my Mazda motorhome and the next shipment was delayed .... They still work fine now, they keep our second fridge running 24/7 and charged by the solar panels still on the roof. They would have to be 17 yrs old at least now from date of manufacture .....

T1 Terry

 

[Everest]

Just had my email ref OIG.. cheap rate dropped from 7p to 5.2p, standard rate dropped from 29.5p to 27.7p but standing charge increased by 2.63p. Im in Devon

Were/are you on the flexible rate, or fixed for 12months

 

[mikgle]

Were/are you on the flexible rate, or fixed for 12months

Variable. They give an option to fix but its 8.2p cheap rate so im sticking..

 

[Everest]

LFP don't degrade with cycling, in fact, they actually improve if the cycling is within sensible cell voltages.

LFP cells don't calendar age either

Hmm... so, you are saying that LiFePO4 cells don't have calendar ageing and improve with cycling within correct voltage range. That means they will last forever and get better as they mature - TBH I find that hard to believe

 

[mikgle]

agree - as I commented earlier in the thread, IMHO calendar ageing will be as big a factor in degradation as cyclic usage.

I think you'll find all batteries suffer by varying degrees of cycling degradation. But its true, keeping it above 10% does help . I've put a threshold of 8% minimum on mine.

 

[Rolfe]

I was letting mine drop to 4%, which is the default, but after hearing similar advice I put a 10% limit on.

 

[T1 Terry]

Hmm... so, you are saying that LiFePO4 cells don't have calendar ageing and improve with cycling within correct voltage range. That means they will last forever and get better as they mature - TBH I find that hard to believe

Everything has an end of life, even amazing units like me :lol: but the calendar life thing doesn't really occur the way it does for lead acid. Sit a lead acid battery on the shelf after the acid has been added and no matter if you have it connected to a maintenance charger for the 10 year period, at that point, it has very little remaining capacity.
An LFP cell will sit on a shelf at 3.2 V for 10yrs, charge it up and start to cycle it twice a day if you want, it will still have good useable capacity after another 10 yrs or more

T1 Terry

 

[Everest]

I think you'll find all batteries suffer by varying degrees of cycling degradation.

I hope I made that clear too

 

[T1 Terry]

I hope I made that clear too

We still have regular customers who get their batteries serviced ever 3 to 4 yrs, they cycle every day and during ever day, 365 days a yr and now over 12 yrs old, and they still deliver the manufacturers advertised capacity at the 2C load the manufacturer used to rate the battery capacity, still holding better than 3 V under load and over 12 yrs old now.
One of the systems is the camp kitchen for a contract harvesting mob, mum and dad roll up with the caravan in the stinking hot paddocks at Christmas harvest time (Dec through to Jan) run the air con and air fryer and multicooker, all off the batteries and solar, it still powers the freezer and fridge and Waeco compressor esky for the cold tinnies, the generator cycles on if the solar can't keep up, but often it stays off all day if there are no clouds .....
Quality LFP cells like to work, keep them within the upper and lower voltage ranges and they will happily cycle away .....

T1 Terry

 

[johnb80]

Ah, very nice system, no idea why he is concerned about "the potential degredation of batteries," as LFP cells don't suffer cycling degradation as long as the voltages remain withing the 3 V min and 3.6 V max.
Most of the degradation occurs when a cell gets low and a high current draw drags the voltage below the 3 V threshold .... it can go as low as 2.8 V short term, but generally, if the voltage dips to 2.8 V under load, all 100% of the capacity has been used and that 2.8 V rapidly becomes 2 V or less and damage starts ....

T1 Terry

Youre probably right, it's just a gut feeling, all of this tech, looking after itself with Home Assistant getting the weather forecast, watching the outdoor temperatures and even the average daily consumption map 7 days per week and then deciding how much to dump into the grid and at what rate.
Seplos active balancer keeping a tight hold on battery voltages max and min at cell level and overall pack level should keep my EVE cells happy.
BUT, the derisory sum you can earn from this setup isn't worth it in my mind. If they offered a higher export rate to cover periods of maximum demand I would probably consider that changing the Home Assistant setup accordingly.

 

[Rolfe]

Yes. If they offered a higher export tariff around 6-8 or whenever I'd export then. I'm sure it would be worth their while.

 

[johnb80]

Ah, very nice system, no idea why he is concerned about "the potential degredation of batteries," as LFP cells don't suffer cycling degradation as long as the voltages remain withing the 3 V min and 3.6 V max.
Most of the degradation occurs when a cell gets low and a high current draw drags the voltage below the 3 V threshold .... it can go as low as 2.8 V short term, but generally, if the voltage dips to 2.8 V under load, all 100% of the capacity has been used and that 2.8 V rapidly becomes 2 V or less and damage starts ....

T1 Terry

I used the figures that EVE supplied and keyed them straight into my active balancer. The active balancer shows SOH 100% and this is it's 5th year of operation.

 

[johnb80]

Yes. If they offered a higher export tariff around 6-8 or whenever I'd export then. I'm sure it would be worth their while.

It would make more sense to me, theyre charging more for electricity at those times therefore they can afford to pay more.

 

[Rolfe]

That's what I thought. If they gave me a better export price at these times I'd just set the battery to routinely discharge then, and it would be easier for me too.