On-grid domestic battery storage

Thrugelmir

Solarchaser said:

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

I didn't realise that they would last that long. Presumably at some point the capacity of the battery to store starts to degenerate though. 

Martyn1981

chamelion said:

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...

You could also add in an average battery capacity based on the warranty. So, say the 6,000 cycles warranty promises an 80% capacity at the end, then it might be £3,500 / (6,000 * (6.48 * 90%)) = 10p.

But, whenever I did these calcs going back, I stressed over and over that I was calculating the cost based entirely on the warranty, which is unfair, but I was really scared that I might mislead anyone if I used a 'better' number of cycles. However I suspect(?) that most folk expect to get more than the warranted number of cycles, much more?

Another point I realised and made was that the economics improve significantly (with this method) if the warranted cycles are increased. So all factors remaining the same, if the manufacturer doubles the cycle warranty, which might happen over time if batts perform well, then the cost of using the batts halves.

I also (going back to the start) kinda assumed that batts would halve in price over 5yrs, which doesn't seem to be happening, perhaps due to the massive demand from the expanding automotive side. Damn!

Zarch

Here's a graph from my first week of using the 4.8kWh of batteries alongside my Solar.

Through targeted cheap-slot overnight imports on the Agile tariff alongside filling via springtime PV I've managed to keep the average import price per unit down to 5.3p

I think i'd need at least a third battery to get me to being closer to self sufficient.

What is satisfying though, is that i've shifted my usage % of generation waaaay the other way.  So rather than 70% of going back to the grid, i'm storing and later using most of what I currently generate.  This will obviously dip in % terms as more sun comes into play as we head into summer.

chamelion

Zarch said:

Here's a graph from my first week of using the 4.8kWh of batteries alongside my Solar.

Through targeted cheap-slot overnight imports on the Agile tariff alongside filling via springtime PV I've managed to keep the average import price per unit down to 5.3p

I think i'd need at least a third battery to get me to being closer to self sufficient.

What is satisfying though, is that i've shifted my usage % of generation waaaay the other way.  So rather than 70% of going back to the grid, i'm storing and later using most of what I currently generate.  This will obviously dip in % terms as more sun comes into play as we head into summer.

You've seen a lot of my posts in this thread where i'm trying to justify the expense to myself and it always works out against me. But just to see graphs like your above, even if not financially the right choice for me, makes me want to just drop the 3 grand today and pick up a battery system

Solarchaser

Thrugelmir said:

Solarchaser said:

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

I didn't realise that they would last that long. Presumably at some point the capacity of the battery to store starts to degenerate though. 

Yeah id imagine at that point they would have a bit less capacity, but would still retain say 70-80% of capacity and would still be useable.
However id assume that in 20 years time the price will have come waaaaaay down due to economies of scale, and finding cheaper materials to make them and so the replacement cost would be much less than it is today

chamelion

Martyn1981 said:

chamelion said:

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...

You could also add in an average battery capacity based on the warranty. So, say the 6,000 cycles warranty promises an 80% capacity at the end, then it might be £3,500 / (6,000 * (6.48 * 90%)) = 10p.

But, whenever I did these calcs going back, I stressed over and over that I was calculating the cost based entirely on the warranty, which is unfair, but I was really scared that I might mislead anyone if I used a 'better' number of cycles. However I suspect(?) that most folk expect to get more than the warranted number of cycles, much more?

Another point I realised and made was that the economics improve significantly (with this method) if the warranted cycles are increased. So all factors remaining the same, if the manufacturer doubles the cycle warranty, which might happen over time if batts perform well, then the cost of using the batts halves.

I also (going back to the start) kinda assumed that batts would halve in price over 5yrs, which doesn't seem to be happening, perhaps due to the massive demand from the expanding automotive side. Damn!

Lol we can make this formula as complicated as need be
Do the LUX systems themselves need replacement? I know solar PV ones they expect you need to replace your inverter after 10 years - is that the case with the battery systems too? I'm sure batteries last longer than the hardware managing them?

Solarchaser

Most inverters have a 2-5 year warranty.
The interesting thing about lux is they come with a 10 year warranty

mickyduck55

A little premature but at the moment my batteries stop supplying my home when they reach 10% remaining charge.  Will there be any benefit to the longevity of the battery condition to change this say 20 % in the summer when I will almost certainly NOT need the 9kW available at full charge overnight?

Zarch

chamelion said:

Zarch said:

Here's a graph from my first week of using the 4.8kWh of batteries alongside my Solar.

Through targeted cheap-slot overnight imports on the Agile tariff alongside filling via springtime PV I've managed to keep the average import price per unit down to 5.3p

I think i'd need at least a third battery to get me to being closer to self sufficient.

What is satisfying though, is that i've shifted my usage % of generation waaaay the other way.  So rather than 70% of going back to the grid, i'm storing and later using most of what I currently generate.  This will obviously dip in % terms as more sun comes into play as we head into summer.

You've seen a lot of my posts in this thread where i'm trying to justify the expense to myself and it always works out against me. But just to see graphs like your above, even if not financially the right choice for me, makes me want to just drop the 3 grand today and pick up a battery system

PMSL......... More graphs, more data, more geekery and to hell with the finances!! 

mickyduck55

Zarch said:

chamelion said:

Zarch said:

Here's a graph from my first week of using the 4.8kWh of batteries alongside my Solar.

Through targeted cheap-slot overnight imports on the Agile tariff alongside filling via springtime PV I've managed to keep the average import price per unit down to 5.3p

I think i'd need at least a third battery to get me to being closer to self sufficient.

What is satisfying though, is that i've shifted my usage % of generation waaaay the other way.  So rather than 70% of going back to the grid, i'm storing and later using most of what I currently generate.  This will obviously dip in % terms as more sun comes into play as we head into summer.

You've seen a lot of my posts in this thread where i'm trying to justify the expense to myself and it always works out against me. But just to see graphs like your above, even if not financially the right choice for me, makes me want to just drop the 3 grand today and pick up a battery system

PMSL......... More graphs, more data, more geekery and to hell with the finances!! 

Good morning Zarch... how do you collect the data?