let's talk about battery banks- I reckon the "they aren't worth it" thing is wrong

[jaggedben]

I don't know how many ways we can all say it ...:roll:

The cost to store a kWh in a battery is on top of whatever it cost to generate that kWh. So storing in a battery that you paid for is always an additional cost. It doesn't matter how well or badly you've calculated that cost, it's still an additional cost, and not the whole cost of the energy.

The only way it makes sense is if:
a) the price you'd be paid for selling your daytime excess is less than it cost you to generate that excess, so that you don't lose money on generation
AND
b) the price you'd pay for someone other generation at night (e.g. utility) is greater than your own generation plus storage costs, so that you're not paying more than you have to for energy.

Without addressing these questions, you're just spinning yourself (and us) in circles, or engaging in charity.

 

[winnie]

How does net metering affecting either of the LCOEs?

This time, an 800Ah battery bank- $7200 worth of 16 @ $450 ea-400Ah 6V AGM batteries.
Holds 800Ah at 48V- two groups of 8 in series, groups in parallel.
Which is also 320 amp hours of 120V.
Using 22% of that 320Ah, you're using 70.4Ah.
Batteries will then last..who knows. Say 2800 cycles.
The 70.2Ah at 120V is also = 8448w or 8.45kW.
So- 720,000 cents / (8.45 * 2800 * .9) =33.8 cents.
Then you subtract the price you pay the POCO from that.

If they last 3000 cycles, that's 31.5 cents- which is too much if you're paying POCO 15 cents, but a great deal if you're paying 25 cents.
Notice the 70.2Ah taken from batteries *almost* matches the 72.6Ah the example house uses a night...

Okay, so you now have a simplistic estimate of the cost of _storing_ energy in a particular battery pack. It doesn't assume anything about the _cost_ of money (interest rates) or the cost of the inverter. But lets run with this number.

If you have _free_ electricity going in, then the cost per kWh is 31.5 cents.

1) I don't see how electricity at 31.5 cents per kWh is a better deal than power from the POCO at 25 cents per kWh.

2) If you are in a place with 'net metering', then when you send power to the POCO the meter 'runs backwards'. If you send 1 kWh to the POCO, and then take 1 kWh from the POCO, the net result is that your meter totalizes _0_ kWh. The POCO price is irrelevant in this case; the cost to 'store' 1kWh is _zero_. If you have free electricity going in, then the cost per kWh at night is _0_ cents.

-Jon

 

[PVfarmer]

The only way it makes sense is if:
a) the price you'd be paid for selling your daytime excess is less than it cost you to generate that excess, so that you don't lose money on generation
AND
b) the price you'd pay for someone other generation at night (e.g. utility) is greater than your own generation plus storage costs, so that you're not paying more than you have to for energy.

Okay, so you now have a simplistic estimate of the cost of _storing_ energy in a particular battery pack. It doesn't assume anything about the _cost_ of money (interest rates) or the cost of the inverter. But lets run with this number.

If you have _free_ electricity going in, then the cost per kWh is 31.5 cents.

1) I don't see how electricity at 31.5 cents per kWh is a better deal than power from the POCO at 25 cents per kWh.

2) If you are in a place with 'net metering', then when you send power to the POCO the meter 'runs backwards'. If you send 1 kWh to the POCO, and then take 1 kWh from the POCO, the net result is that your meter totalizes _0_ kWh. The POCO price is irrelevant in this case; the cost to 'store' 1kWh is _zero_. If you have free electricity going in, then the cost per kWh at night is _0_ cents.

a) You aren't just losing on generation- you're also offsetting usage. You don't have to generate as much if you aren't using as much at night.
b) The LCOE of the PV is based on its output- that happens during the day. The LCOE of the battery bank is based on its output, which is at night. That's why you subtract the price you would have paid at night from the battery LCOE- the storage cost is already factored into that LCOE, so power from batteries at night is free for use.

---
Interest rates are also an assumption- people pay cash. And how would you factor the inverter in if it is both putting out to the grid and to the batteries? How much of what cost goes where?
1. 31.5 is a better deal because it's paid for- you then subtract 25 cents, and your power at night costs 6.5 cents.
2. The POCO may be irrelevant, but the LCOE vs. the price you pay the POCO matters. The cost to store isn't zero if your LCOE is lower than the price you pay.

 

[TommyO]

"That" means the panels, PV inverter, and BOS for the generating side- if you get a hybrid inverter, it is part of the PV cost- it generates the power- there's a different (but related) LCOE for the batteries/storage side.

OK - so $.15/kwh for the power generated from PV
And $.15/kwh for the power from POCO.
(Seems a bit un-economical to do that - but for the sake of this discussion we can assume the person installing it is OK with just break-even)

How does net metering affecting either of the LCOEs?

Well, net-metering means that for each kwh you "store" into the grid you get a kwh back out.
AND YOU GET THAT FOR FREE!

So your scenario was 13.1kwh/day; 8.6kwh used at night.
Here's now that works out:

no batteries: you put the 8.6kwh into the grid during the day, and at night you pull that 8.6kwh right back out - and the $1.30 credit from your generation is equal to the $1.30 charge when you pull the power back out.

With batteries:
you put the 8.6kwh into the batteries during the day, and at night you pull that 8.6kwh right back out.
The cost of the batteries is $4000 (low but let's say it's right.)
So you've spent $4k you didn't spend without batteries.
What benefit has that extra $4k in spending gotten you?
Well - I suppose you could argue that you now have ability to be grid-free. So I suppose you save the ~$10/month charge for POCO's "meter fee" or "connection fee" or whatever. But that is a poor return on $4000 - much less the cost which is likely much much higher.

Even if you say those batteries will last you for 10 years (~$.13/kwh). You're STILL spending an extra $4k that isn't giving you any additional benefit.

 

[jaggedben]

a) You aren't just losing on generation- you're also offsetting usage. You don't have to generate as much if you aren't using as much at night.

Total nonsense.

In order to reduce what you consume from the utility at night, you have to generate that same amount during the day and then some, because of round-trip inefficiency.

Batteries result in more overall consumption of energy, at least on your side of the meter.

 

[PVfarmer]

(Seems a bit un-economical to do that - but for the sake of this discussion we can assume the person installing it is OK with just break-even)

Well, net-metering means that for each kwh you "store" into the grid you get a kwh back out.
AND YOU GET THAT FOR FREE!

So your scenario was 13.1kwh/day; 8.6kwh used at night.
Here's now that works out:
no batteries: you put the 8.6kwh into the grid during the day, and at night you pull that 8.6kwh right back out - and the $1.30 credit from your generation is equal to the $1.30 charge when you pull the power back out.

The cost of the batteries is $4000 (low but let's say it's right.)
So you've spent $4k you didn't spend without batteries.
What benefit has that extra $4k in spending gotten you?
Even if you say those batteries will last you for 10 years (~$.13/kwh). You're STILL spending an extra $4k that isn't giving you any additional benefit.

Yes, but what about the other person who is paying 25 cents instead of 15, so the power is only costing 10 cents?

No it is not free- in some cases it may be. The equip. that costs money put it there- so the LCOE vs. price really does matter.

Not sure where you got $1.30?

The benefit of spending 4k is that you don't spend however much to use the power that the 4k produces- without it, you are paying the POCO. With it, you are getting power that you paid for already, which can be cheaper than the POCO price, as we have figured, in some cases. Like the entire northeast for instance!

 

[jaggedben]

b) The LCOE of the PV is based on its output- that happens during the day. The LCOE of the battery bank is based on its output, which is at night. That's why you subtract the price you would have paid at night from the battery LCOE- the storage cost is already factored into that LCOE, so power from batteries at night is free for use.

More total nonsense.

The LCOE of the batteries bank is as follows:

LCOE = (cost per kWh cycled in and out of the battery) + (cost of the kWh that charges the battery/efficiency) - (price you would pay for the kWh if you didn't have batteries)

Net positive LCOE for the battery is a bad thing. Net negative cost (i.e saving money!) is a good thing.

Remember: THE BATTERY IS NOT A SOURCE OF ENERGY.
This is my last try. :slaphead::slaphead::slaphead:

 

[wwhitney]

LCOE = Total Life Cycle Cost / Total Lifetime Energy Production

If the battery system costs $3000, and you are using it to replace 7kWh every night...a little under 58A at 120V, or 145A at 48V(batteries/bank=400A total, 145A=27% average drain).

7kWh * 365 =2555kWh a year.
If the batteries only last 6 years that's 15330kWh over the lifetime.
That's a LCOE of 19.5 cents - less than 20 cents!

Nope, that doesn't include the cost of the electricity you put into the batteries. That is your basic accounting error.

The example calculation above shows that the cost of storing the electricity in the batteries is 19.5 cents/kWh plus whatever else the electricity cost you.

If you use your excess solar generation to charge batteries instead of selling it to the grid, the cost of that electricity is whatever payment from the grid you are forgoing. So in your example, the batteries are only a good deal when your usage costs is at least 19.5 cents/kWh higher than the rate at which you get reimbursed for surplus generation.

Cheers, Wayne

 

[PVfarmer]

Total nonsense.

In order to reduce what you consume from the utility at night, you have to generate that same amount during the day and then some, because of round-trip inefficiency.

Batteries result in more overall consumption of energy, at least on your side of the meter.

The round trip efficiency is not as big a factor as battery price and # of cycles.
When you've already factored the round trip into the LCOE...you don't count it twice.
Usage is how much the house uses- consumption is the amount of that the house gets from the grid, so the only way batteries= more consumption is if you charge them and don't use them!
Batteries result in less efficient or less total output to the grid, but they also cause less usage from grid or consumption, hence the offsetting.
When you're self-consuming, you're paying the grid less.

 

[PVfarmer]

LCOE = (cost per kWh cycled in and out of the battery) + (cost of the kWh that charges the battery/efficiency) - (price you would pay for the kWh if you didn't have batteries)

Remember: THE BATTERY IS NOT A SOURCE OF ENERGY.
This is my last try. :slaphead::slaphead::slaphead:

LCOE = .15 + .15 - .15 : you have a $3000 backup system.
But if the price you pay per kWh goes up to .20, both of the .15s will go down.
Even if they go down .01, .28 - .20 is .8.
8 cents is pretty cheap, and a lot less than .20.

The battery is a source at night when there is no PV.

You sure about that? :bye:

 

[wwhitney]

When you've already factored the round trip into the LCOE...you don't count it twice.

But you haven't done that. Your calculation in the first post ignores the cost of the electricity to charge the batteries, so your LCOE for energy taken from the batteries is wrong.

If you say "but the sun is free, the marginal cost to generate that electricity is zero", you are ignoring the opportunity cost. Instead of charging the batteries, you could have sold that electricity back to the grid. So your cost for electricity to charge the batteries is the money you are foregoing by not selling the electricity back to the grid.

Cheers, Wayne

 

[PVfarmer]

The example calculation above shows that the cost of storing the electricity in the batteries is 19.5 cents/kWh plus whatever else the electricity cost you.

The calculation shows how much you are paying for the energy stored and then used.
If you add in what it cost you to put there, you also minus what you would have paid the POCO for it- can't leave that minus out.

 

[TommyO]

1. 31.5 is a better deal because it's paid for- you then subtract 25 cents, and your power at night costs 6.5 cents.

No - it's still $.315/kwh
And $.315/kwh is more than $.25/kwh
6.5 cents more.
If you are using batteries which come out to $.315/kwh over their lifetime you're paying 6.5 cents more per kwh for that power at night to come from batteries than you would for it to come from the POCO. (And really it's even MORE than that, because you need to add the power needed to charge those batteries )

 

[wwhitney]

The LCOE of the batteries bank is as follows:

LCOE = (cost per kWh cycled in and out of the battery) + (cost of the kWh that charges the battery/efficiency) - (price you would pay for the kWh if you didn't have batteries)

Actually, that's the net profit/cost per kWh for adding batteries. The LCOE for energy cycled through the battery is just

LCOE = (cost per kWh cycled in and out of the battery) + (cost of the kWh that charges the battery/efficiency)

So as you conclude it is only when that number is less than (price you would pay for the kWh if you didn't have batteries) that batteries are economically favorable.

Cheers, Wayne

 

[wwhitney]

The calculation shows how much you are paying for the energy stored and then used.

No, it is just what you are paying for the storage. You still have to pay for the electricity.

If you add in what it cost you to put there, you also minus what you would have paid the POCO for it- can't leave that minus out.

If you want LCOE, you just add what it cost you to put it in there. Then you can compare that LCOE to what the POCO charges to see which is cheaper.

By subtracting what you would have paid the POCO, you are calculating how much extra it is costing you to use batteries. If that's a positive number, the batteries are costing more than just using the grid; if that's a negative number, the batteries would save you money.

Cheers, Wayne

 

[winnie]

The calculation shows how much you are paying for the energy stored and then used.
If you add in what it cost you to put there, you also minus what you would have paid the POCO for it- can't leave that minus out.

Still sticking with the assumption that you have free energy from a PV array.

If you use that energy during the day, then it is 0 cents per kWh.

If you use a battery to store that energy and then use it at night, then you pay the _battery_ LCOE per kWh (plus the 'zero' cost for the 'paid off' PV array.)

If you buy energy from the power company, it costs you X cents per kWh.

The cost for using energy from the battery might be more or less than the cost for using energy from the POCO, but there is _no reason_ to subtract the POCO cost from the battery cost if your goal is to figure out how much that particular kWh costs.

 

[ggunn]

Pass the popcorn...

 

[PVfarmer]

Pass the popcorn...

Yep, you got me- I really own a popcorn company- trying to bump up my profits here... SOLAR popcorn, as a matter of fact! No electricity needed! :happyyes:

Originally Posted by jaggedben
The LCOE of the batteries bank is as follows:

LCOE = (cost per kWh cycled in and out of the battery) + (cost of the kWh that charges the battery/efficiency) - (price you would pay for the kWh if you didn't have batteries)

Originally Posted by wwhitney The example calculation above shows that the cost of storing the electricity in the batteries is 19.5 cents/kWh plus whatever else the electricity cost you.

me-

The calculation shows how much you are paying for the energy stored and then used.
If you add in what it cost you to put there, you also minus what you would have paid the POCO for it- can't leave that minus out.


So! It seems like me and ben are...trying to agree with each other here?

ww- When you've done the cost of generation and storage, you have to do something with the POCO price/cost to you- what else can you do but subtract?

 

[wwhitney]

OK, let me try this:

You have some solar panels generating electricity, you generate more than your demand during the day. Let's ignore what that system cost, maybe you inherited it.

A company offers to lease you some batteries to store your surplus daytime generation for use at night and charges you per kWh stored, say $0.20/kWh. This is your battery "LCOE" calculation in the first post.

Let's say your electricity rates are high: $0.30/kWh at all times of day, with net metering.

Now you have two choices of what to do with your excess daytime generation:

A) You sell it to the grid at $0.30/kWh. That goes towards the cost of your nighttime usage, so you save $0.30/kWh of surplus daytime generation.

B) You store it in your batteries at a cost of $0.20/kWh. But you use the electricity in the batteries to displace some of your nighttime usage, at a savings of $0.30/kWh on that. Your net savings is $0.10/kWh of surplus daytime generation.

Which is a better deal? Option A obviously.

Cheers,
Wayne

 

[wwhitney]

ww- When you've done the cost of generation and storage, you have to do something with the POCO price/cost to you- what else can you do but subtract?

OK, you can subtract the POCO price, but that gives you a number that is the differential cost of using batteries versus the grid. I.e. if the result is positive it costs you extra to use batteries, if the result is negative, you save money.

Put another way, if you subtract the POCO price, you don't then compare the final result to the POCO price--that would be using the POCO price twice.

Cheers, Wayne