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

[ggunn]

I'm not sure what point you are trying to make, but if you think you would save enough money by storing energy in batteries (instead of on the grid) to pay for the batteries, the battery inverters, and all the BOS gear that goes with it, you are mistaken. You can't just go out and buy some batteries and stick them onto a grid tied PV system.

 

[jaggedben]

So how would you define "cost to charge"? The point in "paying" to store energy is that, when it is cheaper than what you pay the POCO, you are saving money.

NO, that is NOT enough. It also has to be the case that you aren't losing all the money you would make by selling it to the POCO.

Think about it harder.

The cost to charge, btw, is whatever the cost is to receive or generate the energy that charges the batteries. Presumably that's PV and the levelized cost is cheaper than the utility rate.

 

[PVfarmer]

I'm not sure what point you are trying to make, but if you think you would save enough money by storing energy in batteries (instead of on the grid) to pay for the batteries, the battery inverters, and all the BOS gear that goes with it, you are mistaken. You can't just go out and buy some batteries and stick them onto a grid tied PV system.

The point is that batteries are an option for some people now, not in 10-15 years, and that the "cost" is usually way over-estimated, because it's calculated in a strange way.
Storing and using energy is the only way to pay for the battery system, there's no upside if they are only used a few days a year.
If the cost of doing that is less than what you pay for power, it's worth it.
It doesn't make any sense to me to put a bunch of kWh into the grid during the day (with an oversized PV system), and then use up some other power at night, just to get to zero.

If you already had a grid tied system, you would need equipment other than batteries, yes.
Like this inverter for instance- you can buy batteries and this. Plus a battery enclosure ($750 or so) and wiring.

If you are starting from scratch, you can get 10 less panels for your system because you have batteries- 10 less panels pays for this inverter...
http://invertersupply.com/index.php...&cPath=0_241&gclid=CILOuebO2cYCFUNhfgodx4gP1w

The new report, on the other hand, speculates about the potential economic impact of customers with smaller and less costly solar panel/storage battery systems that decrease but don’t eliminate dependence on the grid. The report’s authors projected that the number of customers who would opt to disconnect from the grid entirely was small and that a much larger number of customers would choose to be connected to the grid with solar-plus-battery systems.

“Since such systems would benefit from grid resources, they could be more optimally sized, thus making them smaller, less expensive, economic for more customers sooner and adopted faster,” the report said. The report focuses on how such a configuration could evolve over time, and how many customers, how much power and how much revenue that could amount to.

It asked, “What are the potential implications for utilities, third-party solar and battery providers, financiers/investors, customers and other electricity system stakeholders? And what opportunities might be found in grid-connected solar-plus-battery systems?”
Projecting through 2050, the report looked at the economics of three configurations in five cities—Los Angeles, Honolulu, San Antonio, Louisville, KY and Westchester, NY. And it saw plenty of good news. It found that the most economical system for the customer evolves over time from grid-only, to grid-plus-solar, to grid-plus-solar-plus-battery. In three of the five cities, the grid/solar systems were economically beneficial to consumers today and they would be so in all five cities within a decade. The report also found that systems that included battery storage would be economical in three of the cities within 10-15 years.
http://ecowatch.com/2015/04/07/solar-energy-grid-battery-storage/

 

[jaggedben]

You lost me there.
"Doesn't offer bi-directional metering"....that means....you're off grid?

He's talking about states where the utility is not required to allow you to feed any power onto their grid, and thus the amount you would receive for any energy that you exported would be zero.

It doesn't make any sense to me to put a bunch of kWh into the grid during the day (with an oversized PV system), and then use up some other power at night, just to get to zero.

What if I paid you a million dollars for a kWh that you exported into the grid during the day, and charged you a penny for a kWh you imported at night? Would you still want to store that kWh and use it at night? Does that get it across to you that it depends on rates and policy?

Read this sentence from my first post again, and think about it hard.
"If the price of grid electricity is higher than the cost of PV generation, which in turn is higher than what you get paid for exporting energy to the grid, then batteries are worth it if their price per kWh of energy stored and used is less than the grid-price minus the PV price."

The only other situation where batteries make monetary sense is a location that is not connected to the grid, and the levelized cost of getting a connection installed is more than the levelized cost of PV+batteries.

 

[TommyO]

The point is that batteries are an option for some people now, not in 10-15 years, and that the "cost" is usually way over-estimated, because it's calculated in a strange way.

Actually you are the one calculating it in a very strange way.
The simplest way to calculate it is to just look at how much you spend in each scenario over 10 years.
And the scenarios you suggested result in you spending >$4k MORE if you have batteries.

The bottom line is that almost anywhere in the US where you have grid available, you're NOT better off financially with using batteries.

It is true that batteries are a reasonable option for some people now - but the reason that they're reasonable for those people is because it's the ONLY option for them.
If/when batteries and the related equpment come down in price AND the POCOs are paying way less for feed-in compared to what they charge for consumption, THEN it will potentially make economic sense for batteries.
But we're not there yet. (10-15 years, maybe, but IMO probably not)

It doesn't make any sense to me to put a bunch of kWh into the grid during the day (with an oversized PV system), and then use up some other power at night, just to get to zero.

A system where you're consuming as many kwh (throughout the year) as you produce is NOT oversized.
That sizing is perfect for most net metering situations, which I believe is most of the US.
I look at it as "what gets the bill to 0? And is that a good return-on-investment for the investment in the equipment needed?"
Putting kwh into the grid and getting them back out at the same price makes solar a much more attractive investment - no reason to pay for batteries then because you get ALL the fuctionality of a battery FOR FREE

If you are starting from scratch, you can get 10 less panels for your system because you have batteries- 10 less panels pays for this inverter...

That makes no sense to me.
If you put in 10 less panels you have even less power generated, and therefore fewer kwh, so you're just going to wind up purchasing more from the POCO - and probably have nothing available to put in the batteries, so they become completely useless.

 

[K8MHZ]

You lost me there.
"Doesn't offer bi-directional metering"....that means....you're off grid? Or you have two PV systems, one for output and one for backup?
I still don't get "grid storage" at all. They charge you for "buying it back". So when the price is the same in/out, you have a zero bill, but you spent more than you should have on solar panels.

Bi-directional metering is where your alternative energy source periodically exceeds your use and the excess feeds back into the grid and the meter actually tallies backwards. Not all meters can do this, and not all POCOs will allow it. In fact, most POCOs that do allow it are forced to do it by state law, and some some are allowed to have a cut off point.

Our POCO can make electricity for about 6 cents. With all the fees, we the customers pay them about 13 cents. So when the meter spins backwards, the POCOs are 'paying' 13 cents for what they can make for half that. POCOs don't like that.

If you don't understand grid storage and directional metering, you really are missing a big point of alternative energy. I spent a few hundred bucks a couple years ago and took a credited course at our local college on solar energy that was taught by an electrical engineer that actually installed solar systems. It was money well spent. Please, take no offense, but I think you should look into doing the same as I did. I also found the class to be extremely informative and enjoyable.

 

[PVfarmer]

He's talking about states where the utility is not required to allow you to feed any power onto their grid, and thus the amount you would receive for any energy that you exported would be zero.

What if I paid you a million dollars for a kWh that you exported into the grid during the day, and charged you a penny for a kWh you imported at night? Would you still want to store that kWh and use it at night? Does that get it across to you that it depends on rates and policy?

Read this sentence from my first post again, and think about it hard.
"If the price of grid electricity is higher than the cost of PV generation, which in turn is higher than what you get paid for exporting energy to the grid, then batteries are worth it if their price per kWh of energy stored and used is less than the grid-price minus the PV price."

The only other situation where batteries make monetary sense is a location that is not connected to the grid, and the levelized cost of getting a connection installed is more than the levelized cost of PV+batteries.

Well, hence my confusion, because you can export (in some places) without a bi-directional meter.

That sounds like a terrible deal!
So I'll rephrase - batteries aren't a good thing in all 50 states...BUT, they are in the Northeast, if you do them right.
When PV system last 20+ years and batteries 10+ years, and batteries will be possibly be a good idea in 5 years almost everywhere...
Going by this:
http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a

"If the price of grid electricity is higher than the cost of PV generation, which in turn is higher than what you get paid for exporting energy to the grid, then batteries are worth it if their price per kWh of energy stored and used is less than the grid-price minus the PV price."

The storage costs and "usage" costs should be calculated separately.
What does it cost to take power from the batteries? That depends on whether you're adding an extra battery inverter, or if you set it up in the first place with a hybrid- if you're using one hybrid inverter, that's really part of the PV cost, not the batteries.

Here's the equation:
price in dollars * 100 / (kWh * cycles * %DOD * %efficiency) = cents per kWh.
The DOD is the "wiggly" number there, if that makes any sense.

So, in the case of the Powerwall, 7 kWh means that the battery can hold up to 7 kWh of electricity at one time, similar to how a 5-gallon jug of water can hold up to 5 gallons of water. You have to multiply that capacity rating by # of cycles (# of times the battery will be filled up and then emptied), depth of discharge (whether the battery can be fully emptied during each cycle or needs to be only 80% emptied, 70% emptied, etc), and efficiency (how much electricity is actually transmitted, not lost, in each cycle), and then divide by price to determine a per-kWh price for all of the kilowatt-hours your system is expected to produce… before degrading to 80% of its rated capacity, that is (at which point it’s actually still useful, but that’s apparently the global standard for “end of product life”).
As you can see, there are a number of assumptions you have to make to perform these calculations, and even if all of your assumptions are correct, it’s not like the products are completely dead at the end of the studied time period. This also leaves out operational costs (which we’ll assume to be $0 in the calculations below).
http://cleantechnica.com/2015/05/09/tesla-powerwall-powerblocks-per-kwh-lifetime-prices-vs-aquion-energy-eos-energy-imergy/

1. Actually you are the one calculating it in a very strange way.
And the scenarios you suggested result in you spending >$4k MORE if you have batteries.

2. The bottom line is that almost anywhere in the US where you have grid available, you're NOT better off financially with using batteries.

3. It is true that batteries are a reasonable option for some people now - but the reason that they're reasonable for those people is because it's the ONLY option for them.
If/when batteries and the related equpment come down in price AND the POCOs are paying way less for feed-in compared to what they charge for consumption, THEN it will potentially make economic sense for batteries.
But we're not there yet. (10-15 years, maybe, but IMO probably not)

me-
If you are starting from scratch, you can get 10 less panels for your system because you have batteries- 10 less panels pays for this inverter...

4.That makes no sense to me.
If you put in 10 less panels you have even less power generated, and therefore fewer kwh, so you're just going to wind up purchasing more from the POCO - and probably have nothing available to put in the batteries, so they become completely useless.

1. No, they don't, you aren't just spending more. That's the whole point. The economic advantage of batteries is underestimated.

2. Or un-estimated...not sure how you're reaching that conclusion.

3. So...describe someone for whom it's the only option- I'm still confused.

4. If you use more power at night then during the day, a smaller amount of panels is needed to fill your batteries, instead of over sizing the system and putting in a bunch that you are just going to take back at night to meet the load.
But it still works out even if day/night are equal, or if day use is MORE than night, depending on where you are again.

Bi-directional metering is where your alternative energy source periodically exceeds your use and the excess feeds back into the grid and the meter actually tallies backwards. Not all meters can do this, and not all POCOs will allow it. In fact, most POCOs that do allow it are forced to do it by state law, and some some are allowed to have a cut off point.

Our POCO can make electricity for about 6 cents. With all the fees, we the customers pay them about 13 cents. So when the meter spins backwards, the POCOs are 'paying' 13 cents for what they can make for half that. POCOs don't like that.

If you don't understand grid storage and directional metering, you really are missing a big point of alternative energy. I spent a few hundred bucks a couple years ago and took a credited course at our local college on solar energy that was taught by an electrical engineer that actually installed solar systems. It was money well spent. Please, take no offense, but I think you should look into doing the same as I did. I also found the class to be extremely informative and enjoyable.

I'm gonna look that up- any states that don't allow you to feed in are...wrong!
I have a lot of things to look up- the details of all 50 states policies is kind of on the back burner.
So- if you can't feed in, why not have batteries, so you don't have to buy at night?
You're avoiding paying 13 cents during the day by using PV, but then paying 13 at night. Why not just pay the POCO zero, by taking no power?
Which is why "if the LCOE of batteries is < what you're paying the POCO" applies to the USA as well as Germany!

 

[winnie]

One of the points of confusion here is that in many places the use of the grid for energy is subsidized by mandate. The utility company is _required_ to 'let the meter run backwards', turning the grid itself into a _free_ battery. Since most residential customers are charged a single price per kWh, day or night, when the meter runs backwards the utility effectively pay the retail rate per kWh.

When you have a free battery, one that _economically_ is 100% efficient (because the meter is just counting kWh, not actually storing them) it becomes hard to justify an expensive battery.

If your math works out that an expensive battery is cheaper than a free battery, then you'd better double check your math!

IMHO in a 'fair' system, when you export energy to the utility they will pay you what they are currently paying for generation, and when you buy energy from the utility you will pay them the current retail rate. In this sort of situation, batteries can make lots of sense...and in some cases they can be economically viable without the PV system.

-Jon

 

[TommyO]

"If the price of grid electricity is higher than the cost of PV generation, which in turn is higher than what you get paid for exporting energy to the grid, then batteries are worth it if their price per kWh of energy stored and used is less than the grid-price minus the PV price."

1. No, they don't, you aren't just spending more. That's the whole point. The economic advantage of batteries is underestimated.

You ARE spending more.
Notice the quote you have above that you put in bold.
If the price of grid is higher than cost of PV genration - Yes
Which in turn is higher than what you get paid for exporting - NO
if batteries price per kwh of energy stored is less than grid price minus PV price - NO.
So 2 of the 3 requirements are NOT met for batteries to be worth it.

"The bottom line is that almost anywhere in the US where you have grid available, you're NOT better off financially with using batteries."
2. Or un-estimated...not sure how you're reaching that conclusion.

Almost everywhere in the US grid power is $.05/kwh to $.35/kwh
Battery systems are >$.25/kwh (realistically I believe them to be in the $.50/kwh to $1/kwh range)
In areas where it's $.25 to $.35 per kwh, there are net metering options (ex. California)

3. So...describe someone for whom it's the only option- I'm still confused.

Houses where nearest POCO lines are miles away and would cost them many many thousands of dollars to bring in a power line.

4. If you use more power at night then during the day, a smaller amount of panels is needed to fill your batteries, instead of over sizing the system and putting in a bunch that you are just going to take back at night to meet the load.
But it still works out even if day/night are equal, or if day use is MORE than night, depending on where you are again.

I'm not understanding you.
Let's use concrete numbers. Lets say you use 50kwh in 24 hours, and you generate 50kwh from solar. 30kwh is used directly, 20 goes to the grid and comes back hours later.
Now if you use batteries instead of the grid, why are you able to use a smaller amount of panels?
The way I see it is if I cut my panels by 10%, I now have 45kwh from solar, 30 gets used, 15 goes to the batteries and comes out, and now I also need to buy 5kwh from the POCO.

"So- if you can't feed in, why not have batteries, so you don't have to buy at night?"
Because cost for extra panels to charge the batteries PLUS cost of the batteries & equipment is > cost_to_buy_from_POCO

I have a cousin in TX - he pays around $.10/kwh for POCO power. He has solar, and the rule with his POCO is the first ~500kwh per month that he feeds in he gets 1:1 credit for. >500kwh he gets paid $.04/kwh or something and if needed he buys it back at $.10/kwh later on. So unless/until batteries get down to about $.06/kwh, he's better off buying from the POCO, rather than buying batteries.

Where I live in CA, my POCO is completely 1:1 credit - no cap, so I get all the benefits of an infinite sized battery bank *for free*
1 mile away with a different POCO, it's a $ for $ cap - and most people generate fewer kwh during the day than they use, but the price differential between day and night makes that still be a $0 bill for them. (was talking with one who showed me his bill of $20 for the year.)

 

[ggunn]

If you don't understand grid storage and directional metering, you really are missing a big point of alternative energy. I spent a few hundred bucks a couple years ago and took a credited course at our local college on solar energy that was taught by an electrical engineer that actually installed solar systems. It was money well spent. Please, take no offense, but I think you should look into doing the same as I did. I also found the class to be extremely informative and enjoyable.

Agreed. Someone with limited understanding of the fundamentals of a situation doesn't always come in with unrealistic expectations and come to faulty conclusions. Not always, but nearly so.

Failing a technology breakthrough that makes energy storage much cheaper and much more efficient, a PV system with batteries is never going to be more economically viable than a simple grid tied PV system in an area with economical and dependable grid power. Not even close.

 

[jaggedben]

Failing a technology breakthrough that makes energy storage much cheaper and much more efficient, a PV system with batteries is never going to be more economically viable than a simple grid tied PV system in an area with economical and dependable grid power. Not even close.

You really need to consider that this is a policy issue, not a technology issue. If winnie's suggestion to pay wholesale rates for grid exports were widely adopted in areas of high electricity rates (California, Hawaii), then all of us solar industry people would have to quickly learn to install batteries and/or partner with people who do that. Given the utility pushback against net-metering that is being seen in some places, I don't think this is at all far-fetched over the next decade or two. How it will go is anyone's guess, but it's not far-fetched. Be ready.

 

[jaggedben]

I have a cousin in TX - he pays around $.10/kwh for POCO power. He has solar, and the rule with his POCO is the first ~500kwh per month that he feeds in he gets 1:1 credit for. >500kwh he gets paid $.04/kwh or something and if needed he buys it back at $.10/kwh later on. So unless/until batteries get down to about $.06/kwh, he's better off buying from the POCO, rather than buying batteries.

Or unless the utility raises its rates. If the real cost of batteries is $.10/kwh (optimistic, but possible soon?) then if the TX utility raises it's rates to $0.14/kwh you're getting to where batteries might make sense. Note that $0.14/kwh is about the minimum people pay in most of California.

But yes, good example.

 

[PVfarmer]

One of the points of confusion here is that in many places the use of the grid for energy is subsidized by mandate. The utility company is _required_ to 'let the meter run backwards', turning the grid itself into a _free_ battery. Since most residential customers are charged a single price per kWh, day or night, when the meter runs backwards the utility effectively pay the retail rate per kWh.
When you have a free battery, one that _economically_ is 100% efficient (because the meter is just counting kWh, not actually storing them) it becomes hard to justify an expensive battery.

If your math works out that an expensive battery is cheaper than a free battery, then you'd better double check your math!

IMHO in a 'fair' system, when you export energy to the utility they will pay you what they are currently paying for generation, and when you buy energy from the utility you will pay them the current retail rate. In this sort of situation, batteries can make lots of sense...and in some cases they can be economically viable without the PV system.

Ok- after the PV system has paid for itself, is the grid still a "free battery"? No, because the sun is free, and you're then paying XX cents for free power.
Either over time, or right away because of rates and/or many other things, the amount you pay the POCO is going to be more than the power is costing you from the PV.
There's your LCOE, then the amount the POCO pays you, and then the amount you pay them. They are interrelated but not just equal.

I don't get the fair system thing- the POCO paying a residential customer the same as their power station/wholesale price?
That doesn't seem fair, unless they charged you the same.

1. You ARE spending more.

2. Almost everywhere in the US grid power is $.05/kwh to $.35/kwh
Battery systems are >$.25/kwh (realistically I believe them to be in the $.50/kwh to $1/kwh range)
In areas where it's $.25 to $.35 per kwh, there are net metering options (ex. California)

3. Houses where nearest POCO lines are miles away and would cost them many many thousands of dollars to bring in a power line.

4. I'm not understanding you.
Let's use concrete numbers. Lets say you use 50kwh in 24 hours, and you generate 50kwh from solar. 30kwh is used directly, 20 goes to the grid and comes back hours later.
Now if you use batteries instead of the grid, why are you able to use a smaller amount of panels?
The way I see it is if I cut my panels by 10%, I now have 45kwh from solar, 30 gets used, 15 goes to the batteries and comes out, and now I also need to buy 5kwh from the POCO.

5. "So- if you can't feed in, why not have batteries, so you don't have to buy at night?"
Because cost for extra panels to charge the batteries PLUS cost of the batteries & equipment is > cost_to_buy_from_POCO

6.I have a cousin in TX - he pays around $.10/kwh for POCO power. He has solar, and the rule with his POCO is the first ~500kwh per month that he feeds in he gets 1:1 credit for. >500kwh he gets paid $.04/kwh or something and if needed he buys it back at $.10/kwh later on. So unless/until batteries get down to about $.06/kwh, he's better off buying from the POCO, rather than buying batteries.
Where I live in CA, my POCO is completely 1:1 credit - no cap, so I get all the benefits of an infinite sized battery bank *for free*
1 mile away with a different POCO, it's a $ for $ cap - and most people generate fewer kwh during the day than they use, but the price differential between day and night makes that still be a $0 bill for them. (was talking with one who showed me his bill of $20 for the year.)

1. It seems like YOU would be spending more, maybe. But it really isn't that simple. You aren't from the northeast- see #6.

2. You have to subtract the POCO price for power from the battery cost. Once you've done the cost of the batteries, the power is free. So if batteries=.25 and cost is .35, you're making a dime there.
Not sure where it's 5 cents.
http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a

3. That is for sure not the only people who want or have batteries (see #6)

4. The PV system only ouputs for say 6 hours a day- your "low use" hours are higher, say 12. Then at night you use the most. You can cram the power into the batteries because of "low usage" with less amount of panels in that 6 hours. The panels are covering the usage and charging the batteries, instead of covering usage for the entire 24 hours in 6.
You wouldn't need the amount of panels = to the amount you used in the 6 daytime/no PV hours.
If you need 36 panels to cover your bill with no batterries, you could probably get by with 30 panels+batteries, there's $1200 not spent on panels to spend on batterries.|

5. You don't need extra panels to charge batteries!

6.10 MW in Cali?
http://www.greentechmedia.com/artic...ies-Connect-Battery-Solar-Systems-to-the-Grid

Agreed. Someone with limited understanding of the fundamentals of a situation doesn't always come in with unrealistic expectations and come to faulty conclusions. Not always, but nearly so.

Failing a technology breakthrough that makes energy storage much cheaper and much more efficient, a PV system with batteries is never going to be more economically viable than a simple grid tied PV system in an area with economical and dependable grid power. Not even close.

10 MW in Cali. Pardon me, but you are missing something in your calculations.
A billion is a lot.

The idea of combining solar photovoltaics with energy storage for retail electricity customers in the U.S. has received tremendous attention in recent months in anticipation of the first wave of growth in markets such as California and Hawaii, matched by a flurry of announcements. Annual market value in dollars is expected to grow from $42 million in 2014 to more than $1 billion by 2018.
http://www.greentechmedia.com/research/report/us-solar-plus-storage

 

[GoldDigger]

Once and for all (maybe):

If you pay X/kWh for power and get X+N for what you sell, where N is greater than or equal to 0, you have no reason at all (other than grid failure backup) to put any of your power into batteries just so you can take it back out again.

The LCOE for power sent to the grid is just the amortized cost of the panels and the inverters (still not FREE).
If you put the same amount of power into a battery and take it out again the LCOE only of the power taken from the batteries is the amortized cost of the whole system including batteries.

There is no way in the world (other than grid outage or SHTF) that a 100% free virtual battery can cost you more or deliver less functionality than an amortized real battery. That is the bottom line and no amount of circular reasoning and comparing kilo-apples to kilo-oranges can change that.

Peak shaving and time shifting for the customer who has extortionate tier and /orTOU rates without any PV component is a totally separate calculation, but with current rate structures over most of the country PV with GTI is still more effective for that user than battery-storage time shifting without PV.

I rest my case (or rest on my keister).

 

[PVfarmer]

Once and for all (maybe):


There is no way in the world (other than grid outage or SHTF) that a 100% free virtual battery can cost you more or deliver less functionality than an amortized real battery.

Not yet!

The only way the grid is a free battery is if your LCOE for the PV system (no batteries) is = to your price you pay the POCO.
If the LCOE is lower, the grid is a more expensive battery. If the LCOE is higher the grid is cheaper.
Ideally, you'd want the LCOE of PV < POCO price *and* LCOE of batteries to be < the cost of power that you're replacing with them that you would have bought from the POCO.
There is possibly one number you could go with- if you are paying more than XX to the POCO, get batteries. I'll say 15 cents for a wild guess.

 

[GoldDigger]

Not yet!

The only way the grid is a free battery is if your LCOE for the PV system (no batteries) is = to your price you pay the POCO.
If the LCOE is lower, the grid is a more expensive battery. If the LCOE is higher the grid is cheaper.
Ideally, you'd want the LCOE of PV < POCO price *and* LCOE of batteries to be < the cost of power that you're replacing with them that you would have bought from the POCO.
There is possibly one number you could go with- if you are paying more than XX to the POCO, get batteries. I'll say 15 cents for a wild guess.

NO! NO! A thousand times NO.

If you get back from the grid exactly what you put into it, with no additional cost, then the LCOE for power from that "battery" is just the LCOE of producing it in the first place and putting it into the grid. Same as the cost of power that goes directly into the local loads without hitting the grid.
If the LCOE of PV without storage is greater than the POCO cost, then neither GTI or PV will do you any good at all.
If the LCOE of PV without storage is less than the POCO cost, then you benefit by using the POCO battery instead of your own!

If, on the other hand, you produce power and put at least some of it into batteries, the overall LCOE is increased by the amortized cost of the batteries.
I will leave out for now the difference in cost between standalone or hybrid inverters (not counting battery cost) and GTIs, but that should eventually be factored in too.

 

[winnie]

Imagine, for a moment, that you have a PV system which has 'paid for itself'. All power that comes off the unit is free, and you have no maintenance costs.

This system generates more power than you consume during the day, so you have extra kWh and you need to do something with them.

At night, the system does not supply any power, but you still have consumption, so you need to get the kWh from somewhere.

Your options are:
1) Use a battery.
2) Find ways to shift your power consumption to the day (eg. making ice for air conditioning at night)
3) Sell the power to the utility.

The economics of 1) depend on the cost of the battery, its life, the number of charge/discharge cycles, etc. The cost is always greater than or equal to zero. The cost of using a battery cannot be less than zero, and is likely much more.

I won't go into 2) because it depends on what your needs actually are.

For 3 the economics depends totally and completely on POCO policy, utility regulations, and the metering technology used.

A purchased battery can _never_ be cheaper to the PV customer/producer than the mandated 'free' POCO battery.

If the total costs of power production and distribution are considered, then the battery may be cheaper 'to society' (lots of handwaving there!) but on the basis of the existing incentive programs/mandates/subsidies, batteries do not make economic sense in many areas.

Going back to your (PVfarmers) first posts in this thread.

Assume that your PV production is 'free' (you've already amortized your investment, but the panels are still working, ignoring maintenance costs...) You have a few extra kWh production during the day, and you want to use a few kWh at night. Your POCO charges $0.20 per kWh, has 'net metering' and the 'LCOE' for the battery is $0.195.

Okay, just before dawn, your electric meter reads 7kWh (they put in a new meter the day before). During the day you have PV production, and the meter runs backwards. As the sun goes down, the meter reads 0kWh (because you generated an excess of 7kWh). In the morning your meter reads 6kWh; by sundown it reads 3kWh (cloudy day). This keeps going. At the end of 1 month you've 'banked and retrieved' 200kWh of electricity, roughly 7kWh each evening, and the meter reads 0kWh. The utility charges you nothing for the electricity, but presumably does charge some sort of monthly fee.

Now consider the same situation, but instead of 'selling' power to the POCO, you put it into the battery. Each kWh of 'free' electricity that you pull out of the battery costs $0.195, until the battery has been 'paid off'. So in the same month you will have $39 in battery costs. And that is _assuming_ the battery lives up to its claimed lifetime and you are actually using all of the battery capacity. Batteries age, so if you are only using 2kWh per night they will cost more (on the other side, the battery could outlast expectations and be cheaper).

The cost of the battery doesn't change even if your electricity is 'free'. (Well, it does get slightly cheaper because you don't pay dollars for battery inefficiency...)

But the point is that the _purchased_ battery will be more expensive that the 'legally created' free virtual battery provided by the POCO.

As others have said, once you start considering the different possible POCO charging schemes, batteries can make sense.

-Jon

 

[PVfarmer]

NO! NO! A thousand times NO.

If you get back from the grid exactly what you put into it, with no additional cost, then the LCOE for power from that "battery" is just the LCOE of producing it in the first place and putting it into the grid.

A purchased battery can _never_ be cheaper to the PV customer/producer than the mandated 'free' POCO battery.

But the point is that the _purchased_ battery will be more expensive that the 'legally created' free virtual battery provided by the POCO.

As others have said, once you start considering the different possible POCO charging schemes, batteries can make sense.

Say there's a house that uses 400kWh a month,2/3 of it at night.
They pay 15 cents to the POCO.
They get a new PV system with a hybrid inverter.
Strangely enough, the LCOE for that is also 15 cents.

They use (at 120V) 111 amps/24 hrs, so 73.3A a night.
73.3A at 120 is 183.15A at 48V.
They want half of that from batteries, so 91.6A of 48V.
That 91.6A also= 4.4 kW.
That's 30% of a 300A 48V bank, or 22% of a 400A bank.
Go with 400A, that gives you 2600 cycles (to 80% original cap.)
$450 each- 8 *450 = 3600.

So the LCOE for the batteries is:
360,000 cents / (4.4 * 2600 * .9) minus the 15 cents (not paid to POCO) = 20 cents.

Or-
Eight 6V 300A batteries at $350 = $2800
Also =48V in series.
300A @ 48V is 120A at 120V.
22% of 120A is 26.4A.
That's 26.4A = 3.17kW
280,000 cents / (3.17 * 2600 *.9)= minus the .15 = 22 cents/kWh

But if you get 3000 cycles instead of 2600 (not unrealistic) that comes out to:
15 cents/kWh for the 400A and 17 cents for the 300A.

So the house paying 15 cents to POCO wouldn't want the 300A version, but...with the 15 cent system, they'd have back up too.
A house paying 25 cents would want either!
Because that would be 5 or 7 cents, when you subtract .25 instead of .15.

Of course too MANY batteries can be a problem. That 22% discharge might be some kind of sweet spot as far as cycles/cost.

 

[TommyO]

Strangely enough, the LCOE for that is also 15 cents.

by "that", do you mean everything except the batteries, or entire system including batteries?

If you mean "with batteries", then it's cheaper without, so they're better off without.
If you mean "without batteries", then adding batteries is extra cost, so they're better off without.
(assuming net metering)

They use (at 120V) 111 amps/24 hrs, so 73.3A a night.
73.3A at 120 is 183.15A at 48V.
They want half of that from batteries, so 91.6A of 48V.
That 91.6A also= 4.4 kW.
That's 30% of a 300A 48V bank, or 22% of a 400A bank.

I think you're misusing units.
Do you mean a 400Ah 48V bank?
And it's simpler/more understandable if you are just using kwh and not talking about how many amps (or amp-hours) it is for 120V/240V.

 

[PVfarmer]

by "that", do you mean everything except the batteries, or entire system including batteries?

If you mean "with batteries", then it's cheaper without, so they're better off without.
If you mean "without batteries", then adding batteries is extra cost, so they're better off without.
(assuming net metering)


I think you're misusing units.
Do you mean a 400Ah 48V bank?
And it's simpler/more understandable if you are just using kwh and not talking about how many amps (or amp-hours) it is for 120V/240V.

"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.
How does net metering affecting either of the LCOEs?

Yep, 400 amp hours at 48V.

Same house.
Uses 400kWh a month.
30.42 days in a month- 400 / 30.42 = 13.15 kWh a day/night (24 hours).
13,150 / 120 (volts) = 109.6 amp hours at 120V.

They use (at 120V) 110 amps/24 hrs, 2/3 (66%) of that at night, so 72.6A a night.
72.6Ah at 120V is 181.5Ah at 48V. (120 /48 =2.5 ---- 72.6 * 2.5 = 181.5)

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...