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

[TommyO]

You sure missed it alright. in the state where you live for one.

Well I can address CA quite well.
California requires the utilities to do net metering.
Battery systems are NOT an economically beneficial option here.

With net metering and time-of-use, many people in CA get credit from the utility of MORE per kwh for the power they produce vs. the power they buy the the POCO during off-peak. So their solar install may only produce 2/3 of the kwh that they use, but because of net metering and time-of-use, they get a $0 bill with their POCO.
If instead you did a battery system, you'd have to generate at least 20% more than you use to get a $0 bill.
So you'd have to probably have 2x the PV array AND add in cost for batteries.

But CA is a big state, and there are some places where it IS a long way to the POCO lines. I can imagine some areas north of Tahoe where getting a power line into a property would be $$$$. And in those cases it makes sense to do an off-grid type system. But where POCO already is to the property, a battery system is just a waste of money.

Even where people aren't doing time-of-use (TOU) plans, battery systems still don't make economic sense because of net metering. If I can get $.11/kwh credit for each kwh I put into the grid, then pull power back from the grid for $.11/kwh, why would I buy batteries and the related equipment.
(BTW - $.11/kwh is utility rate for my home - people a few miles away have a rate of ~$.35/kwh - but it'd still be the same $.35/kwh for both selling and buying)

 

[PVfarmer]

Well I can address CA quite well.

Battery systems are NOT an economically beneficial option here.
I can imagine some areas north of Tahoe where getting a power line into a property would be $$$$. And in those cases it makes sense to do an off-grid type system. But where POCO already is to the property, a battery system is just a waste of money.

Even where people aren't doing time-of-use (TOU) plans, battery systems still don't make economic sense because of net metering.

Remember when smartphones first came out and they were $600 or $800?
Then 6 months later it was $400, then 3 months later it was $200. Now you can get them for free!
Same thing, really. Technology = technology and people don't adopt it unless it works...
No offense, but it seems like you're slightly behind the "duck curve" here.

California takes charge
“Energy storage and solar power have a synergistic relationship that is just beginning to be fully realized,” said Rebecca Feuerlicht, a CSE project manager. “Recent state legislation setting specific goals for energy storage deployment and the extension of generous state rebates are giving a boost to the solar and energy storage industries.”
California is the first state to mandate energy storage as part of the major utilities’ energy portfolios. Legislation passed in 2014 directs the state’s investor-owned utilities to procure 1,325 megawatts (MW) of energy storage by 2020, largely to support utility-scale integration of additional solar and wind energy. However, residential and commercial consumers also benefit as 200 MW of the storage mandate is required to be installed “behind the meter” at customer sites.
https://energycenter.org/article/optimizing-use-solar-power-energy-storage


California has repeatedly demonstrated that early procurement of modest quantities of emerging technologies drives scale, bankability, and ultimately cost-effective, high-volume quantities of new technologies and resources. With the energy storage procurement cycle in progress, let’s open the long-duration energy storage market in 2015.
Long-duration energy storage offers both the benefits of grid flexibility, similar to flexible gas plants, and the reuse of zero-marginal-cost midday solar during the evening energy ramp. Long-duration energy storage’s unique functionality uncaps the limits to growth of solar in California -- and beyond.
Less than a week before the January 11 daily-duck-curve milestone, Governor Jerry Brown used his 2015 inauguration speech to call for a 50 percent renewable energy future in California. Beyond air quality and climate-change mitigation benefits, California’s abundant renewable energy resources provide energy with zero marginal cost and zero fuel price volatility to our citizens, limiting rate shocks into the future.
California’s energy agencies are already collaborating to accelerate penetration of energy storage.
http://www.greentechmedia.com/articles/read/california-is-already-hitting-its-2020-duck-curve

 

[winnie]

But I still think if LCOE + LCOS < POCO price, why wouldn't you (get the BESS).
Or (same thing) LCOE < POCO price - LCOS.

If LCOE + LCOS < POCO then you _should_ have some form of energy storage!

But repeating myself hoarse:
_IF_ you have net metering, then the POCO provides a free 'virtual battery', and the free 'energy storage' provided by the poco is cheaper than the purchased battery system.

With 'net metering' LCOS using the POCO is _0_, which is less than the LCOS using the battery.

LCOS being...($ for BESS *100 / lifetime kWh used from BESS) minus LCOE of PV.
If the LCOE of PV is 12 cents and ($ for BESS*100 / lifetime kWh) is 24 cents, the LCOS is 12 cents, as you've already done the LCOE for PV, so the input to the BESS isn't technically FREE, but more paid for previously.

You did tax accounting previously, because that is the only place where the above math makes sense. *grin*

The whole point of 'levelized cost' is to express your up-front capital costs in terms of the cost per kWh. With both solar and batteries, the 'incremental cost' of each kWh is virtually zero, 'free'. But you had to pay lots of money up front for the system. You need some basis of comparison so you can decided 'should I buy the solar power system in the first place, or should I just put the money in the bank and use that money to buy power from the POCO?'

But assuming a levelized cost to generate 1kWh of PV is $0.12, and to store 1kWh is $0.24, then the cost to deliver 1kWh from storage is $0.36.

As you have noted: energy storage makes good sense from a total grid perspective. This is why I believe that 'net metering' is a bad idea. Net metering creates a free virtual battery, and as such creates a dis-incentive to install energy storage that is a benefit to the entire system.

-Jon

 

[wwhitney]

But that 1kWh is used at night, instead of buying it from the POCO, so...it cost you 15 cents but saves you POCO cost minus 15 cents.

Right. So for example, if POCO charges 15 cents daytime and nighttime, it saves you nothing.

If POCO charges 20 cents, you saved 5.

Indeed.

But I still think if LCOE + LCOS < POCO price, why wouldn't you (get the BESS).

Why do you still think that? You've just agreed that if your daytime credit rate and your nighttime usage rate are the same, you save nothing. Your formula clearly doesn't work. The formula for when batteries are economical is:

POCO (sell) + LCOS < POCO (buy)

LCOE of PV doesn't enter into it.

LCOS being...($ for BESS *100 / lifetime kWh used from BESS) minus LCOE of PV.

No, LCOS is ($ for BESS / liftetime kWh cycled through BESS) period. (If you want cents instead of dollars, you can multiply by 100). PV has nothing to do with it. LCOS applies even if you don't have PV. For example, if you are on a TOU plan and pay less at night than during the day, you might consider installing a BESS to time shift your usage to the night.

The input to the BESS isn't technically FREE, but more paid for previously.

The input cost to the BESS is how much money you are paying or forgoing to charge up the batteries. So if you would instead sell that energy to the POCO, the input cost is (POCO sell). Nothing to do with the PV LCOE.

Yours,
Wayne

 

[PVfarmer]

in italics

If LCOE + LCOS < POCO then you _should_ have some form of energy storage!

Ok! We've nailed that one down!

But repeating myself hoarse:
_IF_ you have net metering, then the POCO provides a free 'virtual battery', and the free 'energy storage' provided by the poco is cheaper than the purchased battery system.
With 'net metering' LCOS using the POCO is _0_, which is less than the LCOS using the battery.

I'm still trying to figure out how that's the case if the LCOE of PV (going into the grid) is less than the POCO price.
You'd be giving them kWh that cost you 15 cents and buying it back for 20 for instance. If LCOE of PV is = to POCO price, other factors come into play (as far as should it be done), and if LCOE of PV is > POCO price...why get PV?

You did tax accounting previously, because that is the only place where the above math makes sense. *grin*

HA! That's hysterical. Um...no.
No I didn't and...no, it probably makes no sense to anyone but the person who wrote it (me). Just like accounting!
:happyyes:

The whole point of 'levelized cost' is to express your up-front capital costs in terms of the cost per kWh. With both solar and batteries, the 'incremental cost' of each kWh is virtually zero, 'free'. But you had to pay lots of money up front for the system. You need some basis of comparison so you can decided 'should I buy the solar power system in the first place, or should I just put the money in the bank and use that money to buy power from the POCO?

Right- the LCOE of PV has nothing to do with the POCO price. Yet it has to be lower for positive cash flow. It doesn't change, even after you've broken even and start to get ROI...
So over time, your "money out of pocket" starts as a negative, goes up incrementally, and becomes positive.
LCOE for PV (FOR is better than OF there) is a constant.
POCO price goes UP incrementally (standard for estimates = 3% a year. My personal POCO price just went up 20-something %!! If it went up 20-something every year, there would be riots!)

But assuming a levelized cost to generate 1kWh of PV is $0.12, and to store 1kWh is $0.24, then the cost to deliver 1kWh from storage is $0.36.

But you didn't pay the POCO for that kWh, so it has to be subtracted from the 36 cents.

As you have noted: energy storage makes good sense from a total grid perspective. This is why I believe that 'net metering' is a bad idea. Net metering creates a free virtual battery, and as such creates a dis-incentive to install energy storage that is a benefit to the entire system.

Yes! We've nailed that down too. (The "not so good" part, not so much the "free battery" part...)

To rephrase my OP again-
PV + storage is a viable option for millions of people, but ONLY when you've nailed the costs down to the PENNY.

Hmm, to do that you need to know usage, weather in the future, and the exact cycles amount for the batteries.
So..take three guesses and make a "real" number out of them.
What can you really do at that point- take your best guess and then over-engineer by 10%?
6%?
:huh:
My diligence exceeds my accuracy here! Does anyone have an Advil?

This is an excellent blog piece-
Conclusion

It seems that in each blog article we have to emphasise that, even though the marketing campaigns of various providers are claiming that they found the one and only right way to do residential storage, it is not a simple “black and white” issue that we are talking about.
From an academic level, lower battery voltages offer better battery costs at higher system integration costs, whereas higher voltages turn that comparison the other way round. In the end, only accurate and diligent system integration can cut costs. To close, allow us one final commonplace observation: the more battery prices decrease, the more system costs move into focus and correspondingly, more accuracy has to be invested in the system design.

http://storage.pv-tech.org/guest-bl...hats-the-right-solution-for-household-pv-plus

This is great too, except this house uses A LOT of kWh.
The only reason for that would be 4 people using an electric water heater.
"Oh, you want a BESS in your home? Do you have electric hot water?"
"Yes."
To self: "Ugh. That's really too bad..."

What It Takes To Create An Off-Grid Household In The Bay Area (California) Using Rooftop Solar & Battery Storage Only (Exclusive)

http://cleantechnica.com/2015/07/13...nia-using-rooftop-solar-battery-storage-only/

The biggest enemy of PV + batteries in homes is really electric water heaters. Really.
The Powerwall will run a water heater for a hour, if you have a high-efficiency one...except the PW doesn't put out enough at peak to run one! 3.3kW at 240 is only 13.75A...

 

[wwhitney]

P.S. Forget batteries for a moment. Suppose you have a PV system and are a net generator of electricity. Your POCO credits you $0.10/kWh for the generation, but your LCOE of PV is only $0.06/kWh, so you are making money on your PV system. (Time value of money issues aside).

Now you decide you want to install some electric heating in your house, so you are going to increase you usage. What is the cost per kWh you are paying for that new usage? The answer is $0.10/kWh. You are going to reduce your credit from the POCO by $0.10/kWh for your extra usage, your credit will go down. The fact that your PV system has an LCOE of $0.06/kWh doesn't enter into it. The profit on the PV system ($0.04/kWh) is something you are going to get regardless. You are still losing $0.10/kWh in money from the POCO for your extra usage.

The same thing applies to batteries, if you use energy during the daytime to charge up your batteries.

Cheers, Wayne

 

[PVfarmer]

LCOE of PV doesn't enter into it.

LCOS is ($ for BESS / liftetime kWh cycled through BESS) period. (If you want cents instead of dollars, you can multiply by 100). PV has nothing to do with it. LCOS applies even if you don't have PV. For example, if you are on a TOU plan and pay less at night than during the day, you might consider installing a BESS to time shift your usage to the night.

The input cost to the BESS is how much money you are paying or forgoing to charge up the batteries. So if you would instead sell that energy to the POCO, the input cost is (POCO sell). Nothing to do with the PV LCOE.

If you don't have PV, the LCOS for the BESS is = to (cost of BESS equipment / amount of kWH cycled through) + POCO price.
So doesn't it follow that with PV, the LCOS for BESS is = to (cost of BESS equip. / amount kWh cycled) + LCOE for PV?

So we're agreeing up until the sentence after this one. Sounds like progress!
The input cost to the BESS is how much money you are paying or forgoing to charge up the batteries.

 

[ggunn]

But repeating myself hoarse:
_IF_ you have net metering, then the POCO provides a free 'virtual battery', and the free 'energy storage' provided by the poco is cheaper than the purchased battery system.
With 'net metering' LCOS using the POCO is _0_, which is less than the LCOS using the battery.

I'm still trying to figure out how that's the case if the LCOE of PV (going into the grid) is less than the POCO price.

Those two rates being the same is what net metering means. Of course, Time Of Use can figure into it, but as others have said, if the daytime rate is higher than the nighttime rate, you can buy low and sell high with batteries without PV in the mix at all. Whether the differential is enough to pay off the battery system in a reasonable amount of time is another question, of course.

 

[PVfarmer]

P.S. Forget batteries for a moment.

Certainly! Any thoughts on this? Same storage-PV-tech link as a few comments back.
http://storage.pv-tech.org/guest-bl...hats-the-right-solution-for-household-pv-plus

The 4:1 ratio makes sense, but how come these transformers say 120/240V Pri - 12/24V Sec, but there are no numbers anywhere near 12 or 24 in the wiring chart?
http://www.temcoindustrialpower.com/products/Transformers_-_General/HT2944.html

That is strange- time to search buck boost in this forum...

Turning a blind eye to the battery technology, and anticipating a standard PV inverter with MPP-Trackers (maximum power point), a DC link and a semiconductor bridge on the grid side, the lowest system costs for battery integration will be achieved with the least sophisticated topology engineers can imagine. Asking experienced power electronics engineers, the results will most likely be that coupling a battery to the DC link of a standard PV inverter with a state-of-the-art buck-boost-converter looked most promising. With a minimum effort on windings and switches (only two are needed), this topology is unbeatable regarding costs.

To allow the utilisation of this technical approach, the voltage-level difference between the DC link and the battery should not exceed a ratio of 4:1 to allow acceptable efficiencies. As a practical example, a battery to be connected to a 400V DC link should not provide a minimum voltage below 100 V. Lower battery voltages would require galvanic separation, and this means a transformer and more switches, and thus higher costs. So in general, high voltage batteries allow for lower system costs – if the system integration is done properly and some mandatory degrees of freedom in the design are available.

 

[PVfarmer]

Those two rates being the same is what net metering means. Of course, Time Of Use can figure into it, but as others have said, if the daytime rate is higher than the nighttime rate, you can buy low and sell high with batteries without PV in the mix at all. Whether the differential is enough to pay off the battery system in a reasonable amount of time is another question, of course.

When the rate paid by POCO and the rate paid to POCO are the same, that's equal exchange of $.
But it leaves out the cost on one side- the to-POCO rate is always the POCO rate, but if you spend too much on PV it ruins your benefit on the from-POCO rate.

 

[winnie]

I'm still trying to figure out how that's the case if the LCOE of PV (going into the grid) is less than the POCO price.
You'd be giving them kWh that cost you 15 cents and buying it back for 20 for instance. If LCOE of PV is = to POCO price, other factors come into play (as far as should it be done), and if LCOE of PV is > POCO price...why get PV?

Because, _in the case of net metering_ you are _not_ giving the kWh to the POCO and then buying it back later. You are 'selling' them to the POCO for the same price that you are buying them back later. I put selling in quotes because what 'net' metering means is that you can bring your _net_ (or total over time) usage down to zero. For every kWh that you put into the grid, you get a credit (by means of your meter moving backward) that lets you take one back out for free.

It doesn't matter (to you) what the _normal_ POCO price is at night if you don't see the charge.

So over time, your "money out of pocket" starts as a negative, goes up incrementally, and becomes positive.
LCOE for PV (FOR is better than OF there) is a constant.
POCO price goes UP incrementally (standard for estimates = 3% a year. My personal POCO price just went up 20-something %!! If it went up 20-something every year, there would be riots!)

This sort of thinking is reasonable, and how one could justify an installation which in the near term is more expensive that POCO power. This sort of reasoning requires guessing which way POCO prices will move, and also requires trusting that the solar installation will have good reliability and longevity.

But assuming a levelized cost to generate 1kWh of PV is $0.12, and to store 1kWh is $0.24, then the cost to deliver 1kWh from storage is $0.36.

But you didn't pay the POCO for that kWh, so it has to be subtracted from the 36 cents.

It is part of the _total_ cost of getting that kWh. Either you buy it from the POCO, generate it with PV, or make it some other way; there are costs involved in getting it to put it into the battery.

The cost of energy coming out of the battery is the cost to generate it in the first place plus the cost to store it.

From an academic level, lower battery voltages offer better battery costs at higher system integration costs, whereas higher voltages turn that comparison the other way round.

I don't get this point. Different battery voltages mean different issues in terms of 'balance of system' (current handling capacity of wires, voltage limits of switches, etc. But in terms of the batteries themselves, the cost per kWh stored is the same no matter how the batteries are arranged.

-Jon

 

[ggunn]

When the rate paid by POCO and the rate paid to POCO are the same, that's equal exchange of $.
But it leaves out the cost on one side- the to-POCO rate is always the POCO rate, but if you spend too much on PV it ruins your benefit on the from-POCO rate.

I don't know what you are driving at. In net metering the to-POCO and from-POCO charges are the same. It's just net kWh they are measuring; kWh's go into your house, kWh's come out of your house, and the net kWh in is what you get charged for. It could be a negative number, i.e., a credit. There is indeed a disincentive in many locations for building a PV system which produces more in a year (or in a month - check your local regs) than your home uses because at the end of that period they zero out your bill and start over, and any credits you have accumulated are lost.

Make no mistake, POCO's are for the most part not at all interested in your setting yourself up to make money supplying electricity to the grid either with PV or some sort of shell game with batteries. Even if you come up with a scheme where you could theoretically turn a profit (and you haven't yet as far as I have seen), you still have to get the POCO's permission to interconnect your hardware with their system. If they won't do it you are SOL.

 

[PVfarmer]

Originally Posted by PVfarmer From an academic level, lower battery voltages offer better battery costs at higher system integration costs, whereas higher voltages turn that comparison the other way round.

I don't get this point. Different battery voltages mean different issues in terms of 'balance of system' (current handling capacity of wires, voltage limits of switches, etc. But in terms of the batteries themselves, the cost per kWh stored is the same no matter how the batteries are arranged.

I *think* it means:
From an academic level, lower battery voltages

She's talking about how lithiums are good for 48V *or* "higher voltage" (up tp 400+), while AGMs and such are only for 48V and below, so above 48 is "higher voltage".

48V-Modules are available and accepted as standard for the telecommunication market – the modules can be found from different manufacturers in different sizes, ranging from somewhere around 1kWh to 4kWh - if Li-Ion Batteries are used.
And the 48V are certainly more adequate if you want to use different battery technologies. (AGM, etc.)
With a parallelization either on cell or module level, <--that confuses the issue somewhat...

basically all required storage sizes can be covered (but this might be accompanied by higher costs). On the other hand, other technologies can cover a very broad range of storage sizes without any additional system costs. (Less BOS for lithium)
The flexibility of the high voltage system is more limited – the coverage for the smaller storage sizes (lithium covers less of the load...range?) will result in a very specific design and the voltage level will probably not be at 400V, but lower. High voltage in residential systems somehow seems to be a lithium ion-specific topic, and most other technologies will have difficulties in following that trend.

Not sure what's wrong with putting sixteen 6 volt batteries in series for 96V, however.

lower battery voltages offer better battery costs at higher system integration costs, whereas higher voltages turn that comparison the other way round.

Those are my thoughts in bold.

Lower V= less $$ for batteries, more for BOS.
Higher V= more $$ batteries, simpler/less BOS.

 

[jaggedben]

]Make no mistake, POCO's are for the most part not at all interested in your setting yourself up to make money supplying electricity to the grid either with PV or some sort of shell game with batteries. Even if you come up with a scheme where you could theoretically turn a profit (and you haven't yet as far as I have seen), you still have to get the POCO's permission to interconnect your hardware with their system. If they won't do it you are SOL.

And not only that, but in many places where it's legal to export to the utility from PV, it's still illegal to do so from batteries.

 

[ggunn]

Originally Posted by PVfarmer From an academic level, lower battery voltages offer better battery costs at higher system integration costs, whereas higher voltages turn that comparison the other way round.




I *think* it means:
From an academic level, lower battery voltages

She's talking about how lithiums are good for 48V *or* "higher voltage" (up tp 400+), while AGMs and such are only for 48V and below, so above 48 is "higher voltage".

IIRC, for batteries with voltage higher than 50V the rules in the NEC change.

 

[wwhitney]

If you don't have PV, the LCOS for the BESS is = to (cost of BESS equipment / amount of kWH cycled through) + POCO price.

No. I'm defining

LCOS = lifetime (cost of BESS equipment / amount of kWH cycled through)

It's just the cost of storage, it doesn't tell you where you got the KWh. So it follows that:

Cost of kWh out = LCOS + Cost of kWh in.

Now when you are exporting power during the day and the POCO is giving you a credit, and you decrease your exports to instead charge a battery, the cost of the kWh into the battery is the credit you give up. That is the cost you face, your bill is going to go up (or your refund go down). It doesn't matter where that kWh came from, or how much it originally cost you. You were going to sell it for some money, and you didn't. The money you gave up by not selling it is your cost to charge the battery.

Wayne

 

[TommyO]

Remember when smartphones first came out and they were $600 or $800?
Then 6 months later it was $400, then 3 months later it was $200. Now you can get them for free!
Same thing, really. Technology = technology and people don't adopt it unless it works...
No offense, but it seems like you're slightly behind the "duck curve" here.

And I'm attempting to explain to you that IT DOESN'T WORK
At least not for residential US consumers - definitely not for residential CA.
Perhaps that's not entirely accurate - it "works" - but it isn't economically viable.
And not economically viable means people won't adopt it.

I certainly couldn't recommend to any residential customer in CA that they should do it. At least not with a clear conscience.

California takes charge
“Energy storage and solar power have a synergistic relationship that is just beginning to be fully realized,” said Rebecca Feuerlicht, a CSE project manager. “Recent state legislation setting specific goals for energy storage deployment and the extension of generous state rebates are giving a boost to the solar and energy storage industries.”
California is the first state to mandate energy storage as part of the major utilities’ energy portfolios. Legislation passed in 2014 directs the state’s investor-owned utilities to procure 1,325 megawatts (MW) of energy storage by 2020, largely to support utility-scale integration of additional solar and wind energy. However, residential and commercial consumers also benefit as 200 MW of the storage mandate is required to be installed “behind the meter” at customer sites.
https://energycenter.org/article/optimizing-use-solar-power-energy-storage

Only way you'll really see it at residential customers is if the POCO pays the entire cost for the battery pack.
The residential customers aren't going to see any economic benefit.

Commercial might have some reason to pay a little for battery packs - since their rate structure is different and they might have some benefit.

But my bet is that you'll see some utility scale storage added but the '200 MW of the storage mandate is required to be installed “behind the meter” at customer sites.' will not happen. IMO the utilities will ask for (and get) a waiver on that - allowing them to delay when they have to meet that goal.

 

[TommyO]

Commercial might have some reason to pay a little for battery packs - since their rate structure is different and they might have some benefit.

Actually thinking about it - I do see one large customer that will probably go for behind-the-meter storage - Tesla in Fremont.
(More for the PR than anything. It'd be great PR)

 

[SolarPro]

To my knowledge, Hawaii is about the only place in the US where it is possible to build a business model around residential grid-connected energy storage right now. In the short-term, the most interesting grid-connected energy storage applications are in commercial and industrial applications. While these are relatively small markets right now, they are also growing rapidly. I suspect that 2015 is going to be a big year for energy storage. California is leading the way, but it's not alone.

If you are interested in these types of projects, you might check out these SolarPro articles (the first is from 2014, the others are hot off the presses):

Solar Energy Storage: Emerging Technologies, Markets and Applications

Distributed Energy Storage Systems

Deploying Solar-Plus-Storage Microgrids

 

[PVfarmer]

IIRC, for batteries with voltage higher than 50V the rules in the NEC change.

Yep, but there are a few interesting angles.
The bolded parts-
690.7? Weather correction factor? That would only apply DC to DC then? As in 690.72?

I hadn't heard of the "requiring steel cases" thing as of yet...isn't that more like "they require grounding", for some reason?

The most interesting is H- if the BESS is less than 5 feet away from what it's running, you're avoiding all that BOS after H...
And the buck boost thing- all it's saying is "use the right size wires for the amperage/voltage".
---
(B) Dwellings.
(1) Operating Voltage. Storage batteries for dwellings
shall have the cells connected so as to operate at a voltage
of 50 volts, nominal, or less.
Exception: Where live parts are not accessible during rou-
tine battery maintenance, a battery system voltage in ac-
cordance with 690.7 shall be permitted.


D) Battery Nonconductive Cases and Conductive Racks.

Flooded, vented, lead-acid batteries with more than twenty-
four 2-volt cells connected in series (48 volts, nominal)
shall not use conductive cases or shall not be installed in
conductive cases. Conductive racks used to support the
nonconductive cases shall be permitted where no rack ma-
terial is located within 150 mm (6 in.) of the tops of the
nonconductive cases.
This requirement shall not apply to any type of valve-
regulated lead-acid (VRLA) battery or any other types of
sealed batteries that may require steel cases for proper op-
eration.


(H) Disconnects and Overcurrent Protection. Where en-
ergy storage device input and output terminals are more
than 1.5 m (5 ft) from connected equipment, or where the
circuits from these terminals pass through a wall or parti-
tion, the installation shall comply With the following:
( I ) A disconnecting means and overcurrent protection shall
be provided at the energy storage device end of the
circuit. Fused disconnecting means or circuit breakers
shall be permitted to be used.

(2) Where fused disconnecting means are used, the line
terminals of the disconnecting means shall be con-
nected toward the energy storage device terminals.

(3) Overcurrent devices or disconnecting means shall not
be installed in energy storage device enclosures where
explosive atmospheres can exist.

(4) A second disconnecting means located at the connected
equipment shall be installed where the disconnecting
means required by 690.71 (H)(1) is not within sight of
the connected equipment.

(5) Where the energy storage device disconnecting means
is not within sight of the PV system ac and dc discon-
necting means, placards or directories shall be installed
at the locations of all disconnecting means indicating
the location of all disconnecting means.

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690.72 Charge Control.

(A) General. Equipment shall be provided to control the
charging process of the battery. Charge control shall not be
required where the design of the photovoltaic source circuit
is matched to the voltage rating and charge current require-
ments of the interconnected battery cells and the maximum
charging current multiplied by 1 hour is less than 3 percent
of the rated battery capacity expressed in ampere-hours or
as recommended by the battery manufacturer.

AH adjusting means for control of the charging process
shall be accessible only to qualified persons.

Informational Note: Certain battery types such as valve-
regulated lead acid or nickel cadmium can experience ther-
mal failure when overcharged.

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690.72(C) Buck/Boost Direct-Current Converters. When buck/
boost charge controllers and other dc power converters that
increase or decrease the output current or output voltage with
respect to the input current or input voltage are installed, the
requirements shall comply with 690.72(C)(1) and (C)(2).

(1) The ampacity of the conductors in output circuits shall
be based on the maximum rated continuous output cur-
rent of the charge controller or converter for the se-
lected output voltage range.

(2) The voltage rating of the output circuits shall be based
on the maximum voltage output of the charge control-
ler or converter for the selected output voltage range.