Battery banks et al.

[David HK]

Hello,

How nice to see a few old names that still use this web site.

I need a bit of advice.

Between 15 and 20 years ago somebody posted on this web site an article about renewable energy battery storage banks. The detail was interesting and devoted to size, type, and capacity of the banks either as one big bank, or multiple banks set up in series and /or parallel,

The writer went on to state that he was providing a gratis introductory discussion to his local Fire Service or Fire Department. The theme was what fire fighters could expect in the way of battery bank sizes, how dangerous they were if fire flames were close by, the hazard to fire-fighters themselves, the location of master isolation switches and how to identify them, and many more details that people using this site will be aware of, or, not aware of.

I am now in a similar situation where residents in my housing estate are installing some large scale roof top solar voltaic panels to create energy some of which is sold back to the utility company.

I would therefore like to create an information paper for the Management of my estate, and also write to the head of the Fire Services to enquire what training is being given to fire fighters who may come across renewable energy battery banks with, or without, warning.

Any contributions readers can post in response to this article will be much appreciated.

In passing has anybody yet dabbled with the use of hybrid car batteries for storing renewable energy generated electricity?


Thank you.

David in HK

[JW]

I think flooded lead acid battery's are okay safety used.

When you get NIMH and Lithium batt banks I think there is a danger.  These systems use higher voltage than flooded lead acid battery banks. 

[Scruff]

Voltage is discretionary. Nothing's stopping me from making a 1kV Lead battery that'd vapourise a crowbar.

Short Circuit Current is the one to watch. Most Li-Ion self-combust with a sustained short circuit..although they often melt the conductor first. Watch them more.

My advice would be not helpful I expect...don't grid tie batteries; waste of time, money and invested energy.
As regards safety mechanisms...welcome to the Wild West. I see state rubber-stamped widow maker installs more than not in fact it's standard for Irish. The most prevalent of which is using knife switches as battery disconnects and A-type RCDs where B-type are required.

If it's an onboard BMS made of semi-conductors instead of contactors often a short circuit will destroy the Control FETs. Fortunately they're not failsafe so they'll often still work afterwards in a failed closed state bypassing the electronic disconnect safeties.

[clockmanFRA]

Hi David,

Yes, I am happy with lead acid management.

But the new tech stuff is just that, it seems every type and every manufacturer do there own thing.

LIFEPO4 seem to better understood.

I did a paper of recent tech batteries, it runs to about 5 pages of A4. I am constantly asked so it works as a hand out.

Heres a bit below........... 

NEW BATTERY TECHNOLGIES FOR OFF GRID, 2021.

This is the present situation from Off Grid folk and installers from around the World.  The 2 responses are from folk that actually have working systems of many years duration.

QUESTION asked ……

Hi all,
I am trying to get a better understanding of energy storage system design with lithium ion batteries. I work in developing countries where lithium ion batteries are still very uncommon outside of plug-and-play PV systems, but are likely to become more prevalent in the coming years. I only have experience with BMZ and Sonnen from years ago in the states. A few questions that I hope might lead to an interesting discussion:

1. It seems like LiFePo is the preferred chemistry for off-grid applications. It seems like Discover and SimpliPhi are popular and produce a good product. Are there other recommended brands? Any thoughts for what would be the most appropriate for smaller, very remote installations in the developing world?

2. Is anyone using NMC batteries here? If so, what brand?

3. Are there any other lithium-based chemistries that are currently commonly used for off-grid applications or will be in the future? Any that might be particularly interesting for developing country applications?

4. Is it possible to develop design general guidelines for energy storage system sizing with lithium ion batteries like has been done with lead acid batteries? Lead acid batteries definitely vary in their parameters by manufacturer, but there are some guidelines (DoD/cycles and charging/discharging current) that seem to hold reasonably consistent for AGM/Gel/FLA that can be used for design purposes.

Could this be done with the major lithium chemistries or do you see them as varying too much between manufacturer? For example:
LiFePo:

•   SimpliPhi recommends a maximum C/2 charge and discharge rate. Claims a useable DoD of 100%. Recommend an 80% DoD for best cycle life. Claims around 98% roundtrip efficiency.
•   Discover recommends a maximum C/1 charge and discharge rate. Claims a useable DoD of 90%. Claims around 98% roundtrip efficiency.
•   Blue Planet Energy recommends a maximum C/2 discharge rate. Claims a useable DoD of 100%. Claims around 98% roundtrip efficiency.
Would it work to use general sizing parameters for LiFePo like:
•   Maximum charge/discharge of C/2. (Is this reasonably consistent?)
•   Recommended DoD 80% (Would provide a storage buffer. Does this tend to provide best LCOE?)
•   Roundtrip efficiency 98% (Should this be more conservative?)
•   Minimum charging temperature 0C.
Any/all thoughts welcome!

RESPONSE  No1,,,,,,,,,

1) Lead acid batteries are forgiving, and generally "die" gracefully

2) Li batteries are unforgiving.   1 overcharge or 1 deep discharge, and they are toast.   Might get a few more cycles out of them before they die, but either condition damages the battery.

3) LFP / LiFePo / LP4 (all the same battery, just different abbreviations) are the "safer" batteries that tend to just fail, or swell up and stink.   Any of the other Li chemistry mixes, involve failure with fire or going bang.   
Comment from Jim, “Swell up and fail is a 'true' statement. Most LiFePO4s are made in China. They do not advertise that the battery needs to be caged and compressed. But, when push come to shove, they will admit this. All of their test data on prismatic cells are in a test cage with 12 psi applied the sides of the cell. Without a cage and compression, the cell will swell. The swelling causes internal cell damage and drastically shortens cell life. The cage and compression is a 'pain in the neck'. Once you assemble a bank, you don't move them easily”.

4) Some Mfg's include the top and bottom 10% safety margins internal their BMS systems.
 Some don't and you have to program that into your loads and chargers.  Your Mileage May Vary. Some rate the full capacity, but only deliver 70% of capacity.
 Lead acid batteries like 50% -100%, so same protocols will NOT work for each.
Comments from Jim,   “Some Mfg's include the top and bottom 10% safety margins internal their BMS systems.
 Some don't and you have to program that into your loads and chargers.  Your Mileage May Vary. Some rate the full capacity, but only deliver 70% of capacity.
 Lead acid batteries like 50% -100%, so same protocols will NOT work for each.

LiFePO4 batteries operate from 2.5 volts to 3.65 volts. Lead acid battery protocols will not work for LIFePO4 batteries. Totally different chemistry. Totally different characteristics. These cells have proven to deliver 100%+ of their rated capacity between these two voltages. My research and experience shows that they have a very flat charge/discharge curve at 3.2 volts over most of there capacity. When you approach the end of discharge, the voltage drops off quickly from 3.2 volts to 2.5 volts. The same on the charge side. The voltage slowly rises from 3.2 volts to 3.4 volts. Then the last 5% of the charge cycle, the voltage rapidly rises to 3.65 volts. If you limit the operating voltage zone of the battery from 3.0 volts to 3.4 volts, you will get 90% of the rated capacity every cycle AND you will avoid the over charging and over discharging associated with early cell death. These are programmed into the LiFePO4 chargers and BMS. The BMS is the safety device to protect the battery and ensure long life. I also program these charge parameters into my solar charger and inverter.
I am still fairly new to LiFePO4 batteries (24 months). So far they are performing well.
I will keep you posted as time goes by. I am not afraid to admit I was wrong, if and when they fail. Keeping my fingers crossed.
Hopes this helps to understand the LiFePO4 prismatic batteries better. Just a note. The cage and compression does not apply to the round cylinder cells. Only the rectangular prismatic cells.”

4) Some Mfg's include the top and bottom 10% safety margins internal their BMS systems.
 Some don't and you have to program that into your loads and chargers.  Your Mileage May Vary. Some rate the full capacity, but only deliver 70% of capacity.
 Lead acid batteries like 50% -100%, so same protocols will NOT work for each.

RESPONSE No 2………….
Each lithium type has its advantages and disadvantages, mostly related to energy density, specific power, life expectancy, performance, cost and safety. LiFePo4 is more of a compromise, it isn't the lightest nor can it deliver the current some others can however they are one of the safest, which is why they are a popular choice. The pre-assembled batteries or battery systems are roughly double the price of building a bank using prysmatic cells, some system can be integrated with other equipment, inverters etcetera, able to communicate information from the BMS regarding state of charge.

2. There are some I believe who are using NMC in the form of Nissan leaf batteries. Note, A forum member in Norway re-repairs and re-uses Nissan Leaf battery packs very successful, its sort of unofficial but he still gets them from Nissan Norway and re-cycles the packs.

3. Generally, a battery is chosen for a specific application, LIPO for example is extremely light with high performance capabilities, which is why they are the choice for drones, they are however dangerous. , Since weight is not as important but safety is makes LiFePo4 an ideal choice for off grid. There are variations even within that LFP made to enhance certain aspects of performance, according to some articles I've read. Not sure there is anything specifically available for developing countries but one thing is known, lithium batteries do not perform in temperatures below 0°C.

4. There are some manufacturers of drop in replacement type LFP who advertise that their battery can be discharged to 100% of the listed capacity, but in fact the actual capacity is greater, the BMS cuts the load when ~20% to protect against damage. Simpliphi has different warranty periods for differing charge /discharge levels, it is good practice when building a DIY bank to keep within certain parameters, commonly 90% and 20% of capacity. This extends the cycle count expectancy, programmable BMS's are available which can be set to whatever value is desired, but manufacturers will be cautious to preserve their reputation, one would hope.
 
My Thanks to the FORUM, ‘Northern Arizona Wind & Sun’, especially to the Moderator ‘Bill’…….  Thanks also to Jim from the ‘Fieldlines’ Forum Online Community for Discussing Solar Power, Wind Power, And Other Forms Of Renewable And Alternative Energy.   

From the Fieldlines forum
JimOK
Re: battery information
« Reply #17 on: May 21, 2021, 06:10:00 PM »
1)   Lead acid batteries are forgiving, and generally "die" gracefully.

Unless you accidentally run them dead one time, then they lose capacity and start dying pretty quick.

2) Li batteries are unforgiving.   1 overcharge or 1 deep discharge, and they are toast.   Might get a few more cycles out of them before they die, but either condition damages the battery.

Same as lead acid. Many expensive L16s have been run dead by accident. Their 15 year expectancy dropped to 1 or 2 years. That's why I stuck with the 6 volt golf cart batteries. Just in case I screwed up. Been known to happen. 

3) LFP / LiFePo / LP4  are the "safer" batteries that tend to just fail, or swell up and stink.

Swell up and fail is a 'true' statement. Most LiFePO4s are made in China. They do not advertise that the battery needs to be caged and compressed. But, when push come to shove, they will admit this. All of their test data on prismatic cells are in a test cage with 12 psi applied the sides of the cell. Without a cage and compression, the cell will swell. The swelling causes internal cell damage and drastically shortens cell life. The cage and compression is a 'pain in the neck'. Once you assemble a bank, you don't move them easily.

 4) Some Mfg's include the top and bottom 10% safety margins internal their BMS systems.
 Some don't and you have to program that into your loads and chargers.  Your Mileage May Vary. Some rate the full capacity, but only deliver 70% of capacity.
 Lead acid batteries like 50% -100%, so same protocols will NOT work for each.

LiFePO4 batteries operate from 2.5 volts to 3.65 volts. Lead acid battery protocols will not work for LIFePO4 batteries. Totally different chemistry. Totally different characteristics. These cells have proven to deliver 100%+ of their rated capacity between these two voltages. My research and experience shows that they have a very flat charge/discharge curve at 3.2 volts over most of there capacity. When you approach the end of discharge, the voltage drops off quickly from 3.2 volts to 2.5 volts. The same on the charge side. The voltage slowly rises from 3.2 volts to 3.4 volts. Then the last 5% of the charge cycle, the voltage rapidly rises to 3.65 volts. If you limit the operating voltage zone of the battery from 3.0 volts to 3.4 volts, you will get 90% of the rated capacity every cycle AND you will avoid the over charging and over discharging associated with early cell death. These are programmed into the LiFePO4 chargers and BMS. The BMS is the safety device to protect the battery and ensure long life. I also program these charge parameters into my solar charger and inverter.

I am still fairly new to LiFePO4 batteries (15 months). I have done a lot of research. So far they are performing well.
I will keep you posted as time goes by. I am not afraid to admit I was wrong, if and when they fail. Keeping my fingers crossed.

Hopes this helps to understand the LiFePO4 prismatic batteries better. Just a note. The cage and compression does not apply to the round cylinder cells. Only the rectangular prismatic cells.
 

[Scruff]

but one thing is known, lithium batteries do not perform in temperatures below 0°C.

Even that is an untruth CM. They derate below 15°C and above 45°C...remember; that's cell temperature not atmospheric.





Most manufacturers only protect against 100% duty charging at the O°C threshold if they even bother.

Because these batteries are small and expensive C-Rates are high usually.


Another thing to be aware of is most grid tied li-ion have zero to negligble back-up/off-grid capability and are often anti-islanding meaning they not only stop working in a power outage but also take the solar with it.

If you want backup power this has infinite scalability.



Have you found the memory effect of LFP yet CM...it's a b@st*d if you had plans on not recharging to 100% SOC...diminishing returns in chemistry. Very hard to measure but it's definitely a thing. They confuse the charger into returning 2% less every cycle until you fully recharge them which isn't recommended because it makes their lives shorter.

Here's another thing, most of the people successfully integrating Li-Ion are electrical engineers.
I built two they're my least useful. In fact they are off 5 months a year because they can't power the quiescent nor thermal management system.   

If you store lithium it likes to be cold and empty. So Don't charge it and store it for backup..you're damaging it.

[clockmanFRA]

Thanks Scruff, i do like your empirical evidence.

To be honest Scruff I am not an Electrical Engineer, i am just a boring, terminology from my family, mechanical engineer who specialises in small stuff, but i did spend some time when young working in real engineering works with huge Cincinnati machines and the like, but mostly doing my own projects, SSSSHHH dont tell anyone. 

I think the new tech stuff batteries are a nightmare to fully understand for normal folk, and sadly the marketing boys and sales reps in most of the shady/dodgy companies around the world, spin lots of untruths about their batteries abilities.  So hence me directing people towards good Lead Acid.

Recently i had argument with a French seller Rep about new tech stuff, so gave him a French translation of my above put together document.  Never seen him again, but a friend who knows him said, "since he read your document, he has got out of the new tech battery market and gone back to selling Renault cars". ....... 

Scruff with your permission, may i put your above comments into my document,? as i say i do love actual empirical evidence.

 

[Scruff]

Thanks Scruff, i do like your empirical evidence.

I made a workaround here and here

Look at it this way I installed my 7kVA 20kWh lead acid backup in 3 days, I spent 2 years making a 4kVA 2.5kWh LFP work (while having to custom build a BMS that's appropriate). It's comfort operating temperature zone hobbles it's practical applications.
LFP is a huge liability. Very easy to break.

I'm about €3k into the useful backup and ~€10k into the LFP assuming I ballpark paid myself for the time it took.
 

To be honest Scruff I am not an Electrical Engineer

I disagree. You have an engineering (critical) mind and you work with electrical. In my book that counts more than letters after your name and having spent half a decade being indoctrinated.

I think the new tech stuff batteries are a nightmare to fully understand for normal folk, and sadly the marketing boys and sales reps in most of the shady/dodgy companies around the world, spin lots of untruths about their batteries abilities.  So hence me directing people towards good Lead Acid.

True that. Then there's the untruths about lead acid. Nothing wrong with the battery every issue I've ever found has been charger/installation or user regime related.

Recently i had argument with a French seller Rep about new tech stuff, so gave him a French translation of my above put together document.  Never seen him again, but a friend who knows him said, "since he read your document, he has got out of the new tech battery market and gone back to selling Renault cars". ....... 

That's hilarious CM. You know Renault are the most polluting diesels in production? IIRC 9 times above EU Nox emission standards SINCE dieselgate?

Scruff with your permission, may i put your above comments into my document,? as i say i do love actual empirical evidence.

Granted.

What annoys me the most is a lottov people believe the BS. Hence are reiterating it as a truth due to their own ignorance on the matter..if I tell a lie to an honest man they'll repeat it as their truth. They defend them with religious fervour but in all my days no one telling me black was white, singing the praises of LFP ever had any application data to support their beliefs and assumptions. I have lots of data that contradict the popular belief.
What I like about science is it's very easy to measure a fact. Just try before opening your mouth* _{*saying it to nobody in particular}
I've a big problem with installers/manufacturers who don't use their own hardware.

The upshot is people and resources are getting exploited for a Nil Sum Gain and those people are the ones actually trying to do some good.

The biggest problem Lead Acid has is profit margins and weight.
Manufacturers don't want to pay for shipping and installers don't like lifting 'em. Same reason GTIs are all HF these days.

[Mary B]

An interesting battery tech that is under development, Aluminum graphene batteries https://graphenemg.com/energy-storage-solutions/aluminum-ion-battery/ few years off yet... will be interesting to see if they can bring it to actual production.

[David HK]

It seems that I have bitten off more than I can chew.

A visited to Wikipedia has produced a list of battery types which are numerous enough to warrant an Excel file.

Trying to sort out which is which and what would best suit a renewable energy system at this moment in time would take years, and by that time some types will have disappeared and new ones would have arrived.

Suffice to say that the well known and much tried lead acid battery may well be an adequate technology for the time being.

Nobody seems to have picked up on the subject of how to isolate large battery banks in a dire emergency such as fire or flooding or some other catastrophe that I cannot immediately think of.

And secondly, how to warn anyone associated with the emergency services that your home (or other place)  has a large electrical battery storage system in operation.

The other bits and pieces posted by corespondents is quite interesting except that some people write in abbreviations which means difficult reading, so I simply ignore them.

Scruff's schematic is a pleasure to peruse, and if that is a replica of something in a home then I wish I had it in mine. Drawings like that take a lot of time and patience to produce even with the right software. Well done.

Thank you to those that have posted so far.

Out of curiosity can anyone suggest what would happen if I had 200 large-ish lead acid batteries set up into four separate banks, all stored in the same room if:-

a)  I lived in a delightful old wooden house built in 1766 and the battery room was part of the house when it was being consumed by fire?

b) The batteries were suddenly immersed by sea water flooding?

c)  Pyroclastic lava started to flood the battery room?

David
 

[Scruff]

Thanks David,

Yurp those drawings take a lottov time alright and my dodgey Russian software license expired. Faster build the thing, except that costs money. Hence it's old and I don't update them. Presentations like that invite tyre kicking on a quote.

I'd recommend a Class T fuse these days instead of ANL. Also a separate DC disconnect for the inverter DC input and you can make 24v PC fans if you use 2 x 12v in series so KISS and lose the buck regulator on the fridge condenser coolers.

For a battery disconnect my preferred choice are Albright magnetic latching contactors...but any Ignition protected Switch-Disconnect with a DC rating for appropriate voltage and current is fine.

If it's genuine it'll carry this hallmark.



I know plentya boats sank with lead onboard. Some owners told me they worked better after. 

Out of curiosity can anyone suggest what would happen if I had 200 large-ish lead acid batteries set up into four separate banks, all stored in the same room if:-

a)  I lived in a delightful old wooden house built in 1766 and the battery room was part of the house when it was being consumed by fire?

Probably melt the cases and add acid to the party. If cable retention was ok then might not be an electrical problem until an inverter melts a board...fuse would protect against that.

b) The batteries were suddenly immersed by sea water flooding?

They'd power the water until they can't, then drown in it.

c)  Pyroclastic lava started to flood the battery room?

Least of yer problems. Case damage pool of molten goo. A certain amount of extra sparks smoke and H₂

[mab]

Scruff beat me to it but here's my 2p worth

I Don't suppose I can tell you much about how to isolate big batteries; most properly installed systems would have an isolator on the battery itself I should think, but rely on the primary fuse/breaker to isolate automatically if a fire or flood causes a short.

In the UK there's still the requirement for a fireman's switch on the outside of a shop in some circumstances,  but I think it's a carry over from the days of high voltage neon signs. I suspect it'll take a few 'incidents' with house batteries before legislation is put in place for something similar for batteries - but even then, an isolator won't help the situation when the fire/flood reaches the battery itself.

To answer the end questions:-

A. Having a big lead battery in the old wooden house during a fire - well apart from the plastic casing I doubt a lead acid battery would burn very well. A bigger issue is ventilation ( or lack thereof) during equalisation charging.

B. Chlorine gas - bad - was an issue on submarines.

C. Err... I don't know; hope I'd  be a safe distance from the house by then anyway. If pyroclastic lave is flooding your house I'm not sure a lead battery will make the situation any worse.

[Scruff]

PS. there's an Albright ED-252 (Emergency Disconnect 250A - 2Pole) indicated straight off the battery after the Master Fuse on that drawing. ^

[Scruff]

Recombinant gas caps are supposed to recirculate the gassed electrolyte after cooling and depressurising...there's a few makers, Bater, Hoppeke, US battery maybe....
Closed system.

Supposedly they turn a flooded battery into better than an AGM without the drawbacks. I'm trialing them on a friend's system I'll let you know in a coupla years if we have to add water.

[mab]

Recombinant gas caps are supposed to recirculate the gassed electrolyte after cooling and depressurising...there's a few makers, Bater, Hoppeke, US battery maybe....
Closed system.

Supposedly they turn a flooded battery into better than an AGM without the drawbacks. I'm trialing them on a friend's system I'll let you know in a coupla years if we have to add water.

I've heard that the caps only last a year or two then have to be replaced - and are quite expensive.  I'll probably have forgotten this conversation in 2 years but I would be interested in you findings.

[David HK]

Hello 'mab'.

Your paragraph 3 echoes the direction of my thoughts that as renewable energy progresses there will come a time when Governments pass control legislation.

Hence my questions in this thread.

The other curiosity which (again) no one has picked up on, concerns hybrid car batteries and how many people have tinkered with the idea of looking at these from a renewable energy storage point of view. I have seen some of the hybrid car battery packs stacked up warehouse style in a local car service centre and they are very large indeed. I believe the battery bolts to the underside of the car frame.

I have no idea what voltage they are, nor do I know what is inside them.

I have no idea what would happen in a traffic accident if a car flew through the air and landed on something that punctured the battery pack.

The same puncture type damage could happen to a conventional renewable energy battery in one way or another.

Again, this arouses my curiosity to ascertain what fire service personnel are being told - and trained - about large battery packs, and how they should deal with them.

In a similar vein, insurance companies do provide insurance protection for battery powered and hybrid vehicles, but I have never heard of the disclaimers, or whatever, for secondary damage by ruptured vehicle batteries.

In tandem with this, how many people inform an insurance comopany that they have a renewable energy system in operation.

And how many insurance companies "twig" to ask a lot of searching questions if fairly large storage banks are involved.

I am British (Anglo Saxon I believe) and remain living in Hong Kong, and in my estate there are quite a lot of households with roof mounted photo-voltaic panels which provide some home voltage supply and feed any excess back into the grid system. I know for certain that the China Light & Power Company requires the owners to take out substantial insurance as a condition of connection.

Scruff, indeed I did spot a fuse near the batteries in your drawing - this was my first point of interest.

My line of questions is a divergence from the norm and I therefore hope readers find the scope interesting.

David





 

[mab]

As for electric cars in accidents - I'm not sure a battery is necessarily any worse than driving around with a can/tub full of highly volatile distilled petroleum spirit - but after a century of trial & error we've gotten quite good at building cars to minimise the risks of fuel fires; we may have to do the same with new batteries.

Don't know about house insurance in the UK:- my lead battery & inverter are in an outbuilding. I guess as long as the installed kit has he appropriate approvals,  CE UL, etc, it's assumed safe for in house installation until proved otherwise. I'm sure the insurance companies will move very quickly to ask the questions and put up premiums if it proves otherwise.

[Scruff]

I've heard that the caps only last a year or two then have to be replaced - and are quite expensive.  I'll probably have forgotten this conversation in 2 years but I would be interested in you findings.

Water misers melt alright Mab. They're basically a stop valve. I'm talking about these things. I'll let you know my verdict in 3 - 4 years, I won't forget.

[Rob Beckers]

I've heard that the caps only last a year or two then have to be replaced - and are quite expensive.  I'll probably have forgotten this conversation in 2 years but I would be interested in you findings.

Water misers melt alright Mab. They're basically a stop valve. I'm talking about these things. I'll let you know my verdict in 3 - 4 years, I won't forget.

Actually I've had very good result from Water Miser caps for the modest investment they represent. I'm using them on my forklift battery, and instead of watering the batteries every 6 - 8 weeks it's now a twice-yearly event. Quite remarkable the difference it makes.

Water Miser caps do not recombine hydrogen & oxygen, they don't have a catalyst to do that (and caps that do are far more expensive), they simply trap the mist of fine water vapour coming off a bubbling battery by forcing it through a layer of small plastic beads and 'condense' it so it drips back into the battery cell. Given the difference I see that seems to account for the bulk of the water loss in batteries. I leave them on (and closed) during regular charging and equalizing, so far without any issue. And no, I've never seen any melt. They have been on there about 4 years now.

From my perspective they do the job very well!

-RoB-

[Mary B]

As far as fire the local fire chief knows where the disconnect from the solar panels is on the back of the house, and where the the one is at the solar panels in case they can't get close to the one on the house, 90 volts DC at 15 amps is not something I want to grab by accident! he also knows I have a battery bank and where it is located, and that it is fused right at the battery terminals(positive AND negative) so he could safely cut thru the DC wiring and it will just trip the fuse. Same for the garage roof mounted bank of solar. 2 disconnects, one next to the other on the back of the house, one on the side of the garage.

[Mary B]

It seems that I have bitten off more than I can chew.

A visited to Wikipedia has produced a list of battery types which are numerous enough to warrant an Excel file.

Trying to sort out which is which and what would best suit a renewable energy system at this moment in time would take years, and by that time some types will have disappeared and new ones would have arrived.

Suffice to say that the well known and much tried lead acid battery may well be an adequate technology for the time being.

Nobody seems to have picked up on the subject of how to isolate large battery banks in a dire emergency such as fire or flooding or some other catastrophe that I cannot immediately think of.

And secondly, how to warn anyone associated with the emergency services that your home (or other place)  has a large electrical battery storage system in operation.

The other bits and pieces posted by corespondents is quite interesting except that some people write in abbreviations which means difficult reading, so I simply ignore them.

Scruff's schematic is a pleasure to peruse, and if that is a replica of something in a home then I wish I had it in mine. Drawings like that take a lot of time and patience to produce even with the right software. Well done.

Thank you to those that have posted so far.

Out of curiosity can anyone suggest what would happen if I had 200 large-ish lead acid batteries set up into four separate banks, all stored in the same room if:-

a)  I lived in a delightful old wooden house built in 1766 and the battery room was part of the house when it was being consumed by fire?

b) The batteries were suddenly immersed by sea water flooding?

c)  Pyroclastic lava started to flood the battery room?

David

after the 200 largish lead acid batteries go thru the floor of your old house you will no longer have the issues! That would take one stout floor and foundation!

[SparWeb]

Hello David
Firstly, what a delight to see you return to FL! 

Also, I think I remember the discussion to which you are referring.  Here is an article from SolarPro magazine that I kept after learning about the potential for electrical fires that can start in the wiring of rooftop solar installations.

PDF:  PV_roof_fire_Brooks.pdf (567.43 kB - downloaded 252 times.)

[SparWeb]

Of course, the "complete" answer is the electrical code.  From this side of the world, obviously I look at a different code and many thing will be quite different in HK that I won't appreciate from this distance. 

Some key elements to a safe system:
1) grounding paths that do not have loops
2) Insulation with a safety margin and suited to the environment
3) Operating voltage well within specification of all items of equipment
4) Conductors sized for operating current with a safety margin
5) Overcurrent protection sized to disconnect before conductor limits are reached
6) Obvious and effective disconnecting means that can be used by emergency personnel

Just off the top of my head.
Every item is a design exercise in itself, and playing them all together means you cannot solve one without affecting the other considerations.

But frankly you don't have to solve everything yourself.  There are professionals who can help you develop the specification and the system design to meet the spec that you and your neighbours want to have.  A detailed specification is also your best protection against overrunning costs and shortfalls in the performance after it is installed.