On-grid domestic battery storage

mickyduck55

Newly installed batteries... So close to filling them up today This is end of day from 10% charge at 6 am , looks .like 8-10 month of the year I will be doing OK,

mickyduck55

mickyduck55 said:

I am trying to enable backup power "on my lux inverter, when ever I click enable I get the error below anyone shed any light on this and the solution?

Sorted.. Inverter has to be in standby to enable the EPS function

EVandPV

Best day with the batteries so far and still at 100% so should get us through till the pv kicks in again tomorrow.
Hoping for our first nil import day tomorrow.

chamelion

Folks, would this be a 'fair' calculation to use to work out the per kwh unit cost of battery storage over it's lifetime? This completely ignores the cost of electricity and 'savings' in this regard (which would just add to the below cost, not subtract from it).
Price per kwh = install price / (Usable capacity * lifetime (days) * cycles / day) 

So, if I'm installing a 7.2kwh £3500 system that lasts 10 years where I cycle the battery once a day, my per unit price could be:
price per kwh = £3500/(6.48kwh * 3650 * 1) = 14.8p/kwh. 

This effectively tells me that each kwh of energy I'm storing and using from my battery costs me 14.8p based on the install price?
So, for battery storage to be effective, the price above needs to be BELOW the unit price you currently pay for electricity - unless you think you can stretch out the lifetime to >10 years or do multiple cycles per day? (although even then, there's a lifetime number of cycles - so 6000 would mean 16 years with one cycle a day, or 8 years with 2 - presumably with some degredation). 

Solarchaser

I think its a fair calculation.
However it ignores a couple of things.
Namely the round trip efficiency, usually around 90% iirc, so you dont get a kwh of storage for every kwh applied, only 0.9kwh which makes your figures worse.

However if you are using solar, which i am(and you are), there are quite a few ocassions where the battery saves more than its capacity in a day due to it filling in when the clouds come over and doing micro cycles.
Also there are some days where you may not fill it completely, nor drain it completely.

My batteries have been filled to 100% the last couple of days, but not drained down to 15% , so not a full cycle.

Ive been using 7.2kwh (6kwh) for around 16 months, yet they have done only 200 cycles.

Exiled_Tyke

chamelion said:

Folks, would this be a 'fair' calculation to use to work out the per kwh unit cost of battery storage over it's lifetime? This completely ignores the cost of electricity and 'savings' in this regard (which would just add to the below cost, not subtract from it).
Price per kwh = install price / (Usable capacity * lifetime (days) * cycles / day) 

So, if I'm installing a 7.2kwh £3500 system that lasts 10 years where I cycle the battery once a day, my per unit price could be:
price per kwh = £3500/(6.48kwh * 3650 * 1) = 14.8p/kwh. 

This effectively tells me that each kwh of energy I'm storing and using from my battery costs me 14.8p based on the install price?
So, for battery storage to be effective, the price above needs to be BELOW the unit price you currently pay for electricity - unless you think you can stretch out the lifetime to >10 years or do multiple cycles per day? (although even then, there's a lifetime number of cycles - so 6000 would mean 16 years with one cycle a day, or 8 years with 2 - presumably with some degredation). 

I prefer the calculation performed against the number of cycles rather than number of days. Hopefully this is more reliable and realistic?  It also brings the per unit cost down although some of the return is so far into the future it may not mean too much in reality. 

chamelion

Exiled_Tyke said:

chamelion said:

Folks, would this be a 'fair' calculation to use to work out the per kwh unit cost of battery storage over it's lifetime? This completely ignores the cost of electricity and 'savings' in this regard (which would just add to the below cost, not subtract from it).
Price per kwh = install price / (Usable capacity * lifetime (days) * cycles / day) 

So, if I'm installing a 7.2kwh £3500 system that lasts 10 years where I cycle the battery once a day, my per unit price could be:
price per kwh = £3500/(6.48kwh * 3650 * 1) = 14.8p/kwh. 

This effectively tells me that each kwh of energy I'm storing and using from my battery costs me 14.8p based on the install price?
So, for battery storage to be effective, the price above needs to be BELOW the unit price you currently pay for electricity - unless you think you can stretch out the lifetime to >10 years or do multiple cycles per day? (although even then, there's a lifetime number of cycles - so 6000 would mean 16 years with one cycle a day, or 8 years with 2 - presumably with some degredation). 

I prefer the calculation performed against the number of cycles rather than number of days. Hopefully this is more reliable and realistic?  It also brings the per unit cost down although some of the return is so far into the future it may not mean too much in reality. 

I guess there are a million different ways to do the math - and none give me pretty figures where I'm thinking "ah f* it i'll just get it given i've been looking at this for years!"

With cycles:
Price per kwh = install price / (Usable capacity * cycles)
= £3500 / (6000 * 6.48) = 9p?

That's better I guess. Basically saying for the lifetime of the system, however many years that'll be, if your electricity is more expensive than 9p then you'll have a reachable ROI. 

Personally I need the time window to work out my ROI. Using SolarChaser's input that he's done 200 cycles in 16 months, that's 200 cycles in 487 days. So 6000 cycles would take 40 years. That tells me more over the 9p calculation...

Solarchaser

I keep saying ill do a write up with some figures for mine, but havent got round to it.
Not sure if its worth its own thread, or just to post it here.

But i will put it up tonight, i just need to gather some figures

Thrugelmir

Apologies if this has been asked before. Do your costings take into account the replacement cost of the battery pack itself? 

Solarchaser

Generally not i would say.
The batteries are expected to survive 6000 cycles, so 20 years anyway