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Generator or Giant Battery Bank?
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Generator or Giant Battery Bank?

randvegetarandvegeta Member, Host Rep

Every few years or so, our building's power gets shut down for routine maintenance. We have a Diesel generator in place to handle such outages. Power in HK is incredibly stable and reliable, and other than the odd brown out during severe weather conditions, there hasn't been a single un-planned outage in over 6 years.

As such we don't use it much and it kind of gets a bit neglected. As long as it's working, it will likley stay in place, but I'm wondering weather or not generators still make sense in the future (of course some places will have more justification than others).

Wondering if large battery banks are starting to make sense. Batteries are getting denser and cheaper. Flow batteries also look very promising as they apparently do not degrade (ever) and have extremely deep cycles (can fully charge and discharge without any adverse effects).

Anyone using very large battery banks over generators? What's your capacity at full load (in hours)?

Would end users have any less confidence in a host that primarily relied on large battery banks rather than a traditional generator?

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Comments

  • lurchlurch Member

    The old DC's I used to work at had ups's with rows of batteries when power failed batteries took over and then the generator locked it keep them topped up while the ups smoothed the power delivery. There was also a backup generator around 2000kva. Not sure how long you would get just on modern batteries you would need to do some calculations.

  • raindog308raindog308 Administrator, Veteran

    randvegeta said: Would end users have any less confidence in a host that primarily relied on large battery banks rather than a traditional generator?

    I have zero confidence with a host that cannot tell me what class their DC is.

    If you know what class your DC is or what class you want it to be, your questions are already answered.

    Thanked by 2Aidan doughmanes
  • Lets assume a 44U rack with 100w per 2u unit, with some spare room for switches etc, at 2KW per rack. Lets say you want to get the thing to run overnight (12h), that'd mean 24KWh. Lead acid batteries do about 100Wh per liter, so you'd need about 250L worth of space for batteries (per rack). A rack is about a meter in depth (give or take), and half a meter wide. This would mean you'd need about half a meter high worth of rack space to store enough batteries for a single rack. (around 12U lost, or a fifth of your total space is eaten by batteries).

    Same calulation for mass: lead-acid do about 40Wh/kg, so you'd need around 600kg worth of batteries. Do you really want to be lugging 600kg worth of batteries per rack every 5-10 year?

    And then for price: wikipedia lists them as "7-18 Wh/usd", so lets call that around 12 Wh/usd, or around 2000 usd "per rack you want to get power to"

    This ofcourse scales with battery density and "how long you want to be able to run it". Lead-acid are probably your best bet for cost-effectiveness (battery-wise) though.

    Ebay lists 20KW generators (enough for 10 racks) for anywhere between 500 usd (https://i.ebayimg.com/images/g/iT0AAOSw5ipaoGQs/s-l500.jpg , probably not the type you want), with "normal" pricing being beteen 5 and 10k, meaning the initial investment in a generator will be about a quarter to half of your initial investment in batteries, with the possibility to extend power delivery to your servers almost indefinitely (granted that you get someone to refuel the things)

    I'd say a generator is a pretty good thing to have for any outage that lasts for over 3 hours.

  • randvegetarandvegeta Member, Host Rep

    teamacc said: I'd say a generator is a pretty good thing to have for any outage that lasts for over 3 hours.

    Well we have the generator in HK as it is so for as long as the generator continues to work, we will likely not need to replace it.

    I'm thinking about new installations.

    But if we used my HK example, our generator can easily do 100KW. Using your estimated figures of 2KW per rack, that's 50 racks worth. Realistically though I'd say 25 racks to account for cooling, which in HK, you cannot shut off for any extended period of time.

    But let's say you have a 100KW load, and you want enough battery capacity for 12 hours. That would be 1,200KWH of batteries. No doubt that would be costly, you can pick up used EV batteries for less than $100 / KWH (usable). Probably doable for around $100k USD. And EV batteries are Li-Ion, so they are far denser, smaller and lighter than Lead Acid. I estimate it would take roughly the same amount of space as our generator (think 12x Tesla Battery Packs) currently uses. 1,200KWH worth of diesel translates to around 400 litres. That's obviously much less space/volume than 1,200kwh worth of batteries, but it's not nothing.

    Assuming you are comparing full load for 12 hours, and everything works, then the generator makes the most sense economically, by a wide margin, but it's not a particularly fair comparison.

    Batteries are more dynamic, and you can quite easily increase capacity as needed (space and budget permitting). Also, it is rare to need the full rated capacity of your generator, and it may be extremely rare in some places for power to be out for such extended periods of time that actually require such large capacity.

    Assuming you can source Li-Ion batteries at $100 /kwh, and each rack uses 2kw, and you need a 24kwh bank per rack, that would cost about $2,400. Which in my mind doesn't sound half bad. It would only use about 60L worth of space and weigh 160KG. Far less than Lead Acid.

    The Li-Ion batteries could last decades too, if maintained properly.

    I don't think $2,400 per rack is THAT much. The equipment that goes into a rack is considerably more. The ACTUAL size of the battery and inverter might be a bit of an issue, but I think the real question is whether or not a 12 hour at max load is a sufficient safety net for most customers? For context, in HK, I've never seen an unplanned outage EVER. And planned outages have rarely exceeded 2-3 hours.

    What do DC's do when their generators run out of Diesel? :D

    raindog308 said: I have zero confidence with a host that cannot tell me what class their DC is.

    If you know what class your DC is or what class you want it to be, your questions are already answered.

    Do you mean tier?

    I'm not sure why a battery bank could not replace a generator and still satisfy tier requirements.

  • randvegetarandvegeta Member, Host Rep

    Regarding my question about what happens when you run out of diesel, I do realize that some large DCs have contracts with providers that guarantee delivery of fuel in a crisis. And for very very large data centers using megawatts of power, that's very understandable since they essentially run a sizable power station. But for a small DC operation, if you can get a contract for a supplier to bring in diesel when needed, then it would also seem likely you can rent a generator in the event you may need more than 12 hours of power.

    The 12 hours of battery would then be sufficient to hold you over till the rented diesel generator arrives.

    In other parts of the world, the battery may be topped up by wind or solar :-).

  • Ifi read it correctly from your first answer you have done your calculation, if you think battery will suficient just do it, end user just care as long as their server worked

    Thanked by 1doghouch
  • FHRFHR Member, Host Rep

    randvegeta said: The Li-Ion batteries could last decades too, if maintained properly.

    Li-Ion batteries will not last decades if kept in fully charged state - which is exactly the state you want your batteries to be in for an always online backup power source.

    randvegeta said: you can pick up used EV batteries for less than $100 / KWH (usable)

    Tinkering with this in your home is fine, but I'm not sure I would want a DIY solution in a DC.

    Unlike Lead Acid batteries which will survive almost anything (and if they don't, no major event happens either way), Li-Ions require VERY careful monitoring and management.

    Each cell has to be monitored independently, as temperature and voltage are extremely critical. Balancing is also equally important (ensuring each cell is charged to the precisely same voltage as other cells).

    +100mV on a cell and you've got a miniature sun in your DC.

    Sure, these technical complications can be solved (look at Tesla Powerwall), but don't expect it to be as cheap as you envisioned.

    Thanked by 1Aidan
  • omelasomelas Member
    edited March 2018

    I wouldn't care about battery backup, but if it's used EV batteries hacked together....

  • Regarding generators, note that there are different choices of fuel. Propane may be a choice, but natural gas might be available in the building and could thus provide continuous running without refueling. Also note that generators are normally inspected and tested by running for 30 minutes once a month which could be a consideration when deciding on what to use.

  • randvegetarandvegeta Member, Host Rep

    FHR said: Li-Ion batteries will not last decades if kept in fully charged state

    At 100%, true. At 80 - 90%, it should be fine. 50% would apparently be optimal for long term storage, but even at 90%, the life span (at least for Tesla batteries) seems to be pretty good.

    FHR said: Each cell has to be monitored independently, as temperature and voltage are extremely critical. Balancing is also equally important (ensuring each cell is charged to the precisely same voltage as other cells).

    Are you sure about this? This doesn't sound right. As far as I am aware, even Tesla's battery packs do not have individually monitored cells. Rather they are modularized.

    I may be wrong of course. I'm no expert. Where did you read this?

    FHR said: Sure, these technical complications can be solved (look at Tesla Powerwall), but don't expect it to be as cheap as you envisioned.

    Using new batteries will definitely be more costly, but battery prices are trending down any way, so it may not be too long before new batteries are $100 / kwh. Probably will reach this price point within the next 3 years or so.

    omelas said: but if it's used EV batteries hacked together.

    This is what the old EV batteries are destined to be. Battery packs may be retired from EVs as a result of degradation, but they may still retain 70-80% of their original capacity. They retire them from EVs because the reduced capacity reduced the vehicle's range, but for static storage, it really doesn't matter all that much. So life as static storage may exceed the time being an EV battery.

    As for being 'hacked' together, I don't see it as being any different to stringing together new batteries. It's not like I'm suggesting hacking together the UPS / Inverter side of things. Just talking about batteries here.

  • JSCLJSCL Member, Host Rep

    Generators are not cheap to run for long periods... battery backup would be better and any DC should really have both in place for UPS.

    I know that a DC here on the IOM is to be installing a bunch of Tesla Powerwalls to backup their new GPU environment... apparently that's quite a cost effective thing to do.

  • randvegeta said: This is what the old EV batteries are destined to be. Battery packs may be retired from EVs as a result of degradation, but they may still retain 70-80% of their original capacity. They retire them from EVs because the reduced capacity reduced the vehicle's range, but for static storage, it really doesn't matter all that much. So life as static storage may exceed the time being an EV battery.

    Can you get the appropriate electronics for those? I believe they're like 300 volts. Not 12, 24, or 48 volts. So are not going to work with standard converters.

  • randvegetarandvegeta Member, Host Rep

    Ole_Juul said: Can you get the appropriate electronics for those? I believe they're like 300 volts. Not 12, 24, or 48 volts. So are not going to work with standard converters.

    It's not that hard. There are a number of V2G systems already available. They tend to be limited to 6KW of output, so that may make a difference with regards to installation. I'm not sure how big these things are or if it is more cost effective to have many smaller systems or 1 large centralized system. But I don't think it make sense to think about things in terms of 12, 24 or 48 volts when dealing with Li-Ion. Most UPS sysems are designed to work with Lead Acid, and so the voltages and currents are all a bit off.

    JSCL said: Generators are not cheap to run for long periods

    Well fuel is expensive for sure but the up front capital is considerably less. Would need to consider the total cost of ownership over a given time-frame.

    As mentioned above, we have had to use our diesel generator only a couple of times, and each time, only for a few hours. We have tanks full of diesel that's just been sitting for over 5 years, un-used. Even if diesel was 10x the price, it would not be of any concern to us.

    I'm more concerned about ongoing maintenance and servicing, and the general life span of the generator, and when it comes to replacing it, which will make more sense.

    Ole_Juul said: Propane may be a choice, but natural gas might be available in the building and could thus provide continuous running without refueling.

    It's hard enough using Diesel, but gas/propane is not all that common in HK, so that I think would only add to the difficulties.

    From what I gather, no one is really using a pure battery back up solution.

    JSCL said: battery backup would be better and any DC should really have both in place for UPS.

    In our case we have multiple banks that can supply all equipment with enough power for upto 1 hour at full load (assuming the battery is in decent condition). The batteries get replaced every 5 years or so. After 5 years, those batteries would probably only last 15-20 minutes. Generator needs a couple of minutes to kick in if the power goes out. As the batteries age, they are really only good for handling brownouts, and super quick power maintenance work.

  • ClouviderClouvider Member, Patron Provider
    edited March 2018

    So you want to replace your generator with battery installation. What if your battery capacity is 4 hours and outage happens to last unusually long, say 3 days? You'll lose the load?

    Properly maintained generators (plural!) running in at least N+1 resilience, coupled with a decent fuel supply contract and plenty of capacity in the UPS system to keep the load while the generators are starting up is the insurance policy against the unusual problems.

    Thanked by 3J1021 MCHPhil lazyt
  • randvegetarandvegeta Member, Host Rep
    edited March 2018

    Clouvider said: So you want to replace your generator with battery installation. What if your battery capacity is 4 hours and outage happens to last unusually long, say 3 days? You'll lose the load?

    As long as our generator works, there is no plan to replace. I'm thinking about the future, for future build outs or in the even the generator goes tits up.

    Where did you get 4 hours from? I've been talking about 12 hours at max load.

    As for an outage lasting 3 days, that's unheard of in HK. I reckon if such an outage ever occurred, there would be far greater problems than the downtime of a data center. But yes, downtime would be inevitable.

    Clouvider said: Properly maintained generators (plural!) running in at least N+1 resilience

    Yeah that's not really an option. Space is a bit of a premium in HK. Power + UPS + Generator is as good as it gets for a small Data Center over here. I'm quite certain most small DC's here don't even have the generator. The only alternative I can think of would be to rent an additional generator if and when needed. One that would fit on the back of a truck or in a trailer.

    I have some other ideas about doing things in Lithuania. A very large battery bank, supplemented with dual power feeds to the grid with solar and wind. But that's quite a bit more expensive.

  • J1021J1021 Member

    Have to echo what @Clouvider says. Regardless of the size of your battery install, it is a finite supply. When those batteries go flat, there is no 'battery supply' contract to call upon.

    With a diesel generator when your fuel supplies start to look low, you call your fuel supply contract and top it up. Run time is infinite.

    Thanked by 2Clouvider MCHPhil
  • J1021J1021 Member

    randvegeta said: Yeah that's not really an option. Space is a bit of a premium in HK

    If space is a premium and you really must squeeze on it - go for DRUPS.

    It's crazy to think that any data centre operator would ever consider moving from a power generating model to a power storage model as a mains failure contingency.

    It sounds like you've discovered some cow boys. Looking over the facility specifications for Equinix and Telehouse facilities in HK, they all have standby diesel generators.. just as you'd expect.

    Thanked by 1Clouvider
  • randvegetarandvegeta Member, Host Rep

    kcaj said: It's crazy to think that any data centre operator would ever consider moving from a power generating model to a power storage model as a mains failure contingency.

    You must have missed the part where I mentioned you could simply rent a generator on the same basis that you can get a contract for a supply of fuel for a generator.

    Storage of energy is storage of energy. How much Diesel can be stored on site is also finite. Relying on a 3rd party to supply diesel, is not much different, in my mind, to having a contract from a supplier who also provides a suitably sized generator.

    Am I missing something here?

    kcaj said: It sounds like you've discovered some cow boys.

    There are quite a lot of small providers, but I don't think it would be fair to refer to them as 'cowboys'. Not every company has US$100M to spend on building a DC.

  • FHRFHR Member, Host Rep

    randvegeta said: FHR said: Each cell has to be monitored independently, as temperature and voltage are extremely critical. Balancing is also equally important (ensuring each cell is charged to the precisely same voltage as other cells).

    Are you sure about this? This doesn't sound right. As far as I am aware, even Tesla's battery packs do not have individually monitored cells. Rather they are modularized.

    I may be wrong of course. I'm no expert. Where did you read this?

    Yes, I'm sure.

    Regarding temperature control, Tesla's battery packs are water-cooled, so they don't have to monitor the temperature of each cell but just the coolant.

    Regarding voltage monitoring and balancing, you don't have to monitor each cell, but rather an each group of cells.

    Tesla 85kWh battery pack is composed of 7104 cells in 16 modules. Each module contains 6 groups of batteries in series and each group is composed of 74 cells in parallel.
    In technical notation, the battery pack designation is "96S74P" - 96 groups in Series with each group having 74 Parallel cells.

    Each of these 96 groups is individually monitored and controlled by a BMS - battery management system.

    There's a one BMS per module, each servicing 6 groups (you can see the "CELL 0 - 6" connector on the right side of the board). So 16 BMS modules per the whole battery pack.

    This BMS ensures that each group of cells is charged to the precisely same voltage - and if it isn't, it will try to balance them by discharging the overcharged ones.

    Source - teardown pictures: https://teslamotorsclub.com/tmc/threads/pics-info-inside-the-battery-pack.34934/

    It works exactly like a laptop battery (which are usually in 3S1P or 3S2P configuration - and yes, you will find a BMS in each laptop), just on a much larger scale.

  • randvegetarandvegeta Member, Host Rep

    FHR said: Yes, I'm sure.

    Regarding temperature control, Tesla's battery packs are water-cooled, so they don't have to monitor the temperature of each cell but just the coolant.

    Ahh fair enough. Well I was thinking about using old Tesla batteries any way. If we could obtain the whole pack, then perhaps we could use the same BMS and cooling systems. Though that may be more difficult than it sounds.

  • AidanAidan Member

    Insurance can get a bit dicey if you're stacking that many batteries, lead-acid will require proper ventilation & any type of lithium will require a proper fire-control system.

    Batteries are meant to keep you up long enough to switch to a generator/2nd power line.

    Thanked by 1Clouvider
  • randvegetarandvegeta Member, Host Rep

    Aidan said: Insurance can get a bit dicey if you're stacking that many batteries, lead-acid will require proper ventilation & any type of lithium will require a proper fire-control system.

    Good point about insurance.

  • raindog308raindog308 Administrator, Veteran

    randvegeta said: Do you mean tier?

    I'm not sure why a battery bank could not replace a generator and still satisfy tier requirements.

    Yes: tier, class - different terms for same thing.

    I was under the impression that the different levels mandated specifics in terms of power (i.e., generator/battery mix), but perhaps they only mandate experience. I'm not a DC guy, but I interact with them and all the pros I've dealt can rattle off their datacenter certifications and ratings. If you're working on a serious DC, I'd try to align with industry standards.

  • @randvegeta said:

    kcaj said: It's crazy to think that any data centre operator would ever consider moving from a power generating model to a power storage model as a mains failure contingency.

    You must have missed the part where I mentioned you could simply rent a generator on the same basis that you can get a contract for a supply of fuel for a generator.

    When would you start calling a generator company for that though? Immediately at the outage? When your batteries are halfway through? (6h seems like quite short-notice) When your batteries are 2h away from dying?

  • raindog308raindog308 Administrator, Veteran

    randvegeta said: Storage of energy is storage of energy. How much Diesel can be stored on site is also finite. Relying on a 3rd party to supply diesel, is not much different, in my mind, to having a contract from a supplier who also provides a suitably sized generator.

    I was curious...

    https://en.wikipedia.org/wiki/Energy_density

    You can store a lot more energy in Diesel than you can in Lithium Ion in the same size of space. Even with the generator to convert it to usable electricity, I suspect that diesel will win any energy density comparison.

    Of course, for maximum efficiency you should use deuterium, which is five orders of magnitude more energy dense than diesel. Then if your mains fail, you just need to touch off a fission bomb to kick start it.

  • ClouviderClouvider Member, Patron Provider
    edited March 2018

    Who would deliver generators up to specs and guarantee it, and install it in time when half of the town has no power ?

    Where would you put it and the tanks if you have no space ?

    This is fantasy world.

    Thanked by 1J1021
  • doghouchdoghouch Member
    edited March 2018

    @raindog308 said:

    randvegeta said: Storage of energy is storage of energy. How much Diesel can be stored on site is also finite. Relying on a 3rd party to supply diesel, is not much different, in my mind, to having a contract from a supplier who also provides a suitably sized generator.

    I was curious...

    https://en.wikipedia.org/wiki/Energy_density

    You can store a lot more energy in Diesel than you can in Lithium Ion in the same size of space. Even with the generator to convert it to usable electricity, I suspect that diesel will win any energy density comparison.

    Of course, for maximum efficiency you should use deuterium, which is five orders of magnitude more energy dense than diesel. Then if your mains fail, you just need to touch off a fission bomb to kick start it.

    Why not buy a CANDU reactor? I mean, it’ll only set you back a few...errr...hundred million, but you’ll have power to weather through any outage.

    Edit: an added bonus is the radioactive waste it generates :]

    Thanked by 1raindog308
  • raindog308raindog308 Administrator, Veteran
    edited March 2018

    doghouch said: Why not buy a CANDU reactor? I mean, it’ll only set you back a few...errr...hundred million, but you’ll have power to weather through any outage.

    I read a little further down in that Wikipedia article and would like to present an improved proposal.

    Antimatter. 100% energy efficiency. No fission bomb needed, and no radioactive waste.

    True, a gram is estimated to cost $62.5 trillion to produce, which is nearly the entire annual global GDP. But with a few black friday promos...

    Thanked by 3MCHPhil FHR doghouch
  • randvegetarandvegeta Member, Host Rep

    Clouvider said: Who would deliver generators up to specs and guarantee it, and install it in time when half of the town has no power ?

    Where would you put it and the tanks if you have no space ?

    This is fantasy world.

    LOL. You're unbelievable selective in what you think contractors can and cannot fulfil.

    So on the one hand you think that a contract for fuel supply is perfectly doable, but not a portable generator? Now obviously I'm not talking about a multi-megawatt generator used by behemoth data centers, which obviously cannot be easily transported. But a 100KW generator, which is more than ample for most small DCs, which is what I'm talking about here, can quite easily fit in a trailer. Cabling for 100KW is also not so difficult.

    If expecting a company to supply a generator is living in a fantasy land, then so too is it a fantasy that a company can deliver ample supply of fuel.

    There are plenty of companies that lease out generators. And there would be no reason why they would not be able to deliver the generator on demand in the same way fuel is delivered. Should there be a road block or anything like that then delivery of fuel is also affected.

    I don't think you can have it both ways.

    teamacc said: When would you start calling a generator company for that though? Immediately at the outage?

    Do most contracts for fuel supply not include some guaranteed delivery time? It's very much the same question as for diesel. When do you call for a refill?

    If the SLA for fuel delivery is say... 4 hours, I'd say you should probably call when you have around 6-8 hours remaining. Or indeed just have it on stand-by for scheduled maintenance work that may exceed the capacity of your energy storage.

    raindog308 said: You can store a lot more energy in Diesel than you can in Lithium Ion in the same size of space. Even with the generator to convert it to usable electricity, I suspect that diesel will win any energy density comparison.

    Yes the energy density of Diesel is far far greater than any battery storage. It does not diesel can pretty much last forever too (doesn't degrade over time or go bad), and is not flammable, so storage wise is safer. But generators do take up quite a lot of space, and the maintenance and servicing also need to be factored in.

    Again, this is just an alternative to having on site generators. Traditionally, battery storage has been very expensive, but the cost is falling dramatically, and the typical outage in the developed world tends to be incredibly short. Of course having a large battery bank that can last a DC for 12 hours would be much more costly than having a generator with fuel that can last 120 hours, but you need to over provision power with a generator, whereas you can expand your battery capacity over time, so I think there may be some cost benefits.

    I think with new high capacity battery banks, it opens up new possibilities for how data centers can handle redundancy, and at scale. For example, you could start with a smallish 6KW UPS with 72KWH battery, which would not cost that much (less than $10K), and possibly have a contract for a fuel and generator supply for that level of load. As your load increases, your contract will grow too, so you need not necessarily worry about the infrastructure.

    This is all just hypothetical of course, since batteries are still kind of expensive, and the prices I am mentioned are for 2nd hand, and certainly the availability of second hand batteries could could not satisfy the demand of data centers. But battery production is ramping up at an incredible rate, and prices are falling just as fast. Is such a scenario truly just a fantasy?

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