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True i did forget to take in account that heat pumps move significantly more heat than they consume. But still a block of ice remains very cheep because its just water, all the cost is in the container around it and this is easily expandable. It's not uncommon to have water heaters that hold more than 100kg of water, so the size of such ice storage would not get unpracticaly large just to store one day worth of air conditioning cold.
As for storing heat energy for half a year to cover the summer and winter difference is not easy. This does reach unpracticaly large sizes to store enough of it. Since latent heat can't be used for this, it makes it even worse (Tho molten wax can store heat pretty efficently). If you really wanted to have an advantage in terms of heating/cooling the best solution is to have an underground house. The ground temperature only varies by a few degrees trough the year. Tho in most climates the average ground temperature is too low to be comfortable, but some insulation and the waste heat from all the electrical appliances could bring that up closer to comfortable. But building such a house is expensive and you end up living in a windowless basement so it's not that great of an idea.
Geothermal is also in most cases too cold to be directly useful, but even the cold groundwater in winter is still a much better source for feeding a heatpump rather than the freezing air outside, can work for air conditioning tho. Unless you end up on top of a hot geothermal spring, those are very useful for heating, but are rather rare.
If you're still curious, the back-of-the-envelope is around 40 tonnes H2O.
That's assuming 1MWh for the season (guessing that's an overestimate for most houses? Didn't look it up), no heat loss to environment and no heat pump dissipation, and a temp swing of 20K in the reservoir.
The heat pump I don't think changes anything, as it's always dissipating its heat somewhere, and the house and tank tend to dissipate that heat to the environment in turn. The tank will end up biased on average, some degrees above/below average outdoor temperature, depending on which need is greater overall (cooling/heating). Interesting is the bias is nonlinear, because of course the heat pump is less efficient for greater differences.
Or maybe it doesn't matter because you'd need a thermal time constant over a year to have this make any sense, and that's actually hard to do (not sure). And if a random tank in the yard or ground has a shorter time constant, then that means you have more heat flux available through ambient dissipation, and the reservoir is simply irrelevant -- the solution reduces to a normal in-ground system.
Certainly, it seems it's at least good enough to do it that way, and you'd only stand to gain a few percentage points by, essentially, putting a bypass capacitor on one side of the heat pump. That is, the ground-to-buried-line impedance acts like ESR, and a capacitor can average it out over some cycles (say, a time constant of one or a few days) -- which could be provided by a more economically sized reservoir. Maybe doing double duty as, say, the water in a water softener brine tank or something, Idunno. Or if you have well water, an oversized surge tank could do, heh.
Tim -
This is pretty much the idea behind the ground based heatpumps. The soil has a large amount of heat capacity just because there is so much of it, while also not being all that good of a heat conductor so it insulates itself from the varying air temperature above. So its just using a big mound of material that is already in your yard as a heat capacitor.
The groundwater approach is the same except with water. So it doesn't really make all that much sense to bury a giant water tank in the yard for the purpose of heat storage.
However brick is also good at storing heat. We have a brick house and use it to scrape by without air conditioning by opening windows during the night and closing them during the day. When a heatwave hits it actually takes a few days for all the brick to actually warm up and the temperature inside to get uncomfortably hot. Unfortunately it also holds that heat so it also takes a few cold nights to cool it back down after a heat wave. There is one drywall addition to the house that is not brick and that thing has basically no thermal inertia, it quickly gets hot in the day and cold in the night despite having more insulation. -
Using the ground as thermal storage is not without side effects though. While you store heat during the summer you dry out the soil and in spring it will stay frozen for longer. This has an impact on what you are able to do with the land. I recently talked to a guy who is using this approach for heating his home during winter, it seems planting something on this patch of land is not a good idea any more.
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Using the ground as thermal storage is not without side effects though. While you store heat during the summer you dry out the soil and in spring it will stay frozen for longer. This has an impact on what you are able to do with the land. I recently talked to a guy who is using this approach for heating his home during winter, it seems planting something on this patch of land is not a good idea any more.
This needs to be dimensioned right so that it's not only "using" charge from the "capacitor", but also letting it charge via natural conduction (both geothermal from inside the planet, and from above, basically by solar energy). Make it large enough, and temperature differences will be small. But yeah, ground source heat pumping is an expensive investment so it's appealing to try with a minimized collector area to reduce that cost. Here such installations are fairly common for household heating and the differences between installations (freezing wells vs. those that Just Work) are huge. Those who ask for a few quotes then pick the one who suggested the largest one and asks for +20-30% extra dimensioning will be satisfied.
But everyone doing this in densely populated areas will have consequences. Here it works best in the northern parts of country where air-source heat pumping is out of question and population density is near zero as well. -
Update on the investigation in to the commissioning event.
https://mobile.abc.net.au/news/2021-09-28/fire-at-tesla-giant-battery-project-near-geelong-investigation/100496688
Commissioning has its risks! Perhaps exacerbated by contractual pressure to get through written test procedures on individual blocks without having someone on site with an intimate awareness of underlying risks when all the safeguards are not in place (due to the act of commissioning). -
Update on the investigation in to the commissioning event.
https://mobile.abc.net.au/news/2021-09-28/fire-at-tesla-giant-battery-project-near-geelong-investigation/100496688QuoteFire at Tesla giant battery project near Geelong was likely caused by coolant leak, investigation finds
[...]
An investigation conducted by Energy Safe Victoria found the "most likely" cause of the fire to be a coolant leak in the Megapack cooling system, which caused a short circuit that led to a fire in an electronic component.
[...]
ESV said several changes had since been made to prevent any future fires, including each Megapack cooling system being inspected for leaks before on-site testing, and the introduction of a new "battery module isolation loss" alarm to firmware.As for what happened here, the Tesla battery pack designs are liquid cooled which should make them incredible tolerant to fire, as long as coolant is present (not even pumped, just sitting in and filling the coolant lines). Given this occurred during construction, my guess is that during commissioning there was some fault with coolant not being in the system whether that be insufficient or not at all filling the coolant or a coolant leak then during a commissioning load testing the pack with faulty coolant fill could have overheated and caught fire. The propagation testing only guard against limited individual cell failure, not a whole pack overheating.
Vindication! Although they attribute the coolant failure more to causing the catastrophic failure via short circuit rather than allowing failure propagation.
Regardless, something went very wrong with the system/installation process. -
I wouldn't SHOUT about your assumed vindication as your proposed fault path was not correct. We only see a sanitized snippet of what happened and why. It seems to me that far more than one 'fault' led to this event, given they only owned up to about 3-4 cascading faults.
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I wouldn't SHOUT about your assumed vindication as your proposed fault path was not correct. We only see a sanitized snippet of what happened and why. It seems to me that far more than one 'fault' led to this event, given they only owned up to about 3-4 cascading faults.
My proposal is that a coolant system failure was the "primary" cause of failure. This would have lead to the currently suspected short circuits (though I think this may change) as well as cascading faults of thermal failure propagation. For the coolant system failure to be allowed to propagate, there must have also been a failure (or lack of) coolant system monitors. -
https://esv.vic.gov.au/wp-content/uploads/2021/09/VBB_StatementOfFindings_FINAL_28Sep2021.pdf
"The affected Megapacks failed safely despite total loss"
I'm not sure I see how they "failed safely" when one of them caught on fire due a coolant fault?
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Source:
Those reports look pretty final.
https://esv.vic.gov.au/news/cooling-system-leak-led-to-victorian-big-battery-fire/
and
https://esv.vic.gov.au/wp-content/uploads/2021/09/VBB_StatementOfFindings_FINAL_28Sep2021.pdfQuoteRoot cause
The most likely root cause of the incident was a leak within the Megapack cooling system that caused a short circuit that led to a fire in an electronic component. This resulted in heating that led to a thermal runaway and fire in an adjacent battery compartment within one Megapack, which spread to an adjacent second Megapack.QuoteThe Megapack that caught fire had been in service for 13 hours before being switched into an off-line mode when it was no longer required as part of the commissioning process. This prevented the receipt of alarms at the control facility.
• A key lock was operated correctly to switch the Megapack to off-line service mode (which was no longer required for ongoing commissioning) but this caused:
o telemetry systems for monitoring the condition of the (now out of service) Megapack to shut down and so remove visibility of the developing event
o the battery cooling system to shut down
o the battery protection system to shut down, including the high voltage controller (HVC) that could have operated a pyrotechnic fuse to disconnect the faulty battery unit.QuoteConclusion
The incident was most likely initiated by a Megapack coolant leak. The absence of a number of monitoring and protection systems that would have been available had the initial Megapack not been subsequently switched to off-line service mode allowed the initial fault to go undetected and resulted in the total loss of two Megapacks.
The affected Megapacks failed safely despite total lossQuoteESV requires Tesla to provide the final results of its investigation (when available) into why the fire resulted
in the loss of a second Megapack and what it is to do to prevent that circumstance arising again."The affected Megapacks failed safely despite total loss"
I think they mean no one (public, workers or emergency services) was hurt or exposed to unmanaged hazard as a result.
I'm not sure I see how they "failed safely" when one of them caught on fire due a coolant fault? -
The murky and unclear statement imho is "The most likely root cause of the incident was a leak within the Megapack cooling system that caused a short circuit that led to a fire in an electronic component". Given that the megapack was being tested for 13 hours prior, and apparently passed what was likely some cycling at high rates, that could mean a few suspects for where the short circuit occurred. It would seem that the short circuit caused the battery to feed the fault, and likely at such a rate that battery cooling was required to cope with the fault current (that in itself is suspect as the fault current level may well have been beyond the capability of the cooling system).
If the megapack was off-line at the time the short-circuit occurred then that may exclude power conversion to the line (unless there was latent heat in power conversion parts that were just surviving from say fan cooling, or from just enough coolant still being available at the end of testing). Another possibility could be an accessory process such as balancing was automatically kicking in and it assumed cooling was available.
The description of the other subsequent fault items is fairly clear, although I'd have to say that doing commissioning of a megapack with the Scada still having safety related punchlist items open sounds like bordering on negligence. -
https://esv.vic.gov.au/wp-content/uploads/2021/09/VBB_StatementOfFindings_FINAL_28Sep2021.pdf
"The affected Megapacks failed safely despite total loss"
I'm not sure I see how they "failed safely" when one of them caught on fire due a coolant fault?
Perhaps they mean that it only caught fire and didn't blow someone's head off. Dunno. Failed safely from what? It's no doubt worded so the lawyers and insurance ghouls don't go bonkers. -
What a bunch of bullshit.
"The supervisory control and data acquisition (SCADA) system for a Megapack took 24 hours to ‘map’ to the control system and provide full data functionality and oversight to operators. The Megapack that caught fire had been in service for 13 hours before being switched into an off-line mode when it was no longer required as part of the commissioning process. This prevented the receipt of alarms at the control facility."
You simply poll the status registers all the time, MODBUS works well. You never have datapoints taking 24 hours of magic, what is this fake excuse they had no visibility of the packs?
When I'm doing site commissioning, it's the whole system and alarms that are mapped, never partials.
P.S. Did we ever find out if this is older Lithium or newer Lithium iron phosphate Megapacks? -
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Perhaps they mean that it only caught fire and didn't blow someone's head off. Dunno. Failed safely from what? It's no doubt worded so the lawyers and insurance ghouls don't go bonkers.
That's the only conclusion I can gather as well. -
The big thing for me is given that this overheat occured AFTER the charging stopped, AND the pack was taken offline, what caused the heating that the cooling system had to cool down and couldn't because it was leaky? If no power incoming or outgoing, and the pack is "offline", nothing should be getting hot, surely?
And why isn't the monitoring and safety control done inside the megapack regardless of the remote connection? -
The big thing for me is given that this overheat occured AFTER the charging stopped, AND the pack was taken offline, what caused the heating that the cooling system had to cool down and couldn't because it was leaky? If no power incoming or outgoing, and the pack is "offline", nothing should be getting hot, surely?
https://esv.vic.gov.au/wp-content/uploads/2021/09/VBB_StatementOfFindings_FINAL_28Sep2021.pdf
And why isn't the monitoring and safety control done inside the megapack regardless of the remote connection?QuoteThe most likely root cause of the incident was a leak within the Megapack cooling system that caused a
short circuit that led to a fire in an electronic component.
Not lack of cooling - coolant leaking and shorting something -
What a bunch of bullshit.
"The supervisory control and data acquisition (SCADA) system for a Megapack took 24 hours to ‘map’ to the control system and provide full data functionality and oversight to operators. The Megapack that caught fire had been in service for 13 hours before being switched into an off-line mode when it was no longer required as part of the commissioning process. This prevented the receipt of alarms at the control facility."
You simply poll the status registers all the time, MODBUS works well. You never have datapoints taking 24 hours of magic, what is this fake excuse they had no visibility of the packs?
When I'm doing site commissioning, it's the whole system and alarms that are mapped, never partials.
Modbus is rarely used in the electrical generation\distribution world as with polling it's all too easy to miss transient events, unless there is the MacGyver Modbus "solution" of mapping log files into the 16 bit registers. Generally IEEE 1815 (DNP3), IEC 60870 or IEC 61850 is used in these environments with event reporting. -
I think that was a pretty well done video summary of the reports.
As for why the safety/monitoring systems got inactivated, I would presume there is some sort of deactivation or "off" state used for shipping so that the monitoring and safety systems don't deplete the batteries below 0% SoC and cause damage (or danger) during transport and storage. Perhaps this state was improperly reactivated or they don't have a proper "in-commission but inactive" mode?
I have no idea about the SCADA stuff. I've no experience with these larger scale industrial plant systems. -
Maybe very dumb solution to neighbouring racks catching fire:
Would some emergency spring loaded ejection system work? When overheating/fire is detecting, shove the module(s) outside of the rack? Possibly into some kind of concrete ditch in front of the system filled with sand/gravel? -
As for the inactive cooling system leak allowing fire, it makes sense that an external (to the batteries and coolant system) short circuit and heat generation event could cause sufficient heat input to overcome passive safety design for thermal failure propagation. I would have thought they would design any potential system which could be exposed to a coolant leak to not cascade into this sort of runaway thermal failure. Perhaps there are such systems in place but they were improperly deactivated? It seems they are changing it so these safety systems which could have prevented catastrophic failure can't be inadvertently deactivated.Quote
The following actions have been put in place to prevent a recurrence of this incident.
[...]
*The high voltage controller (HVC) that operates the pyrotechnic fuse remains in service when the key lock is isolated. -
The big thing for me is given that this overheat occured AFTER the charging stopped, AND the pack was taken offline, what caused the heating that the cooling system had to cool down and couldn't because it was leaky? If no power incoming or outgoing, and the pack is "offline", nothing should be getting hot, surely?
https://esv.vic.gov.au/wp-content/uploads/2021/09/VBB_StatementOfFindings_FINAL_28Sep2021.pdf
And why isn't the monitoring and safety control done inside the megapack regardless of the remote connection?QuoteThe most likely root cause of the incident was a leak within the Megapack cooling system that caused a
short circuit that led to a fire in an electronic component.
Not lack of cooling - coolant leaking and shorting something
Yep. Read that wrong.
The power to sustain it must have come from the battery, so it would be interesting to know if they safety systems that disabled when it went offline could have prevented that.
They didn't say that, but it's a "contributing factor".
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As for why the safety/monitoring systems got inactivated, I would presume there is some sort of deactivation or "off" state used for shipping so that the monitoring and safety systems don't deplete the batteries below 0% SoC and cause damage (or danger) during transport and storage. Perhaps this state was improperly reactivated or they don't have a proper "in-commission but inactive" mode?
They would likely have something for transport, but I'd imagine that would be a big physical interlock or something? Once on site plug in the big red jumper link. -
I am at a loss to appreciate how leaking coolant could lead to a (I assume) prolonged and effectively bolted short circuit. I can envisage that circa 1kVdc could lead to a leakage current (due to coolant acting as creepage pollution) that then progresses in to an arc, and perhaps that arc is across a metallic surface that then sustains the arc (or a charred insulation surface), but it beggars the question as to how a coolant system could be designed that a leak could allow such an outcome.
There is also the concern that the DC path did not include passive fusing or CB, as only the use of a pyro fuse was identified. Perhaps the short circuit was not bolted per se, but if it wasn't a substantial over current then why did the battery need cooling - maybe there was a current range in the middle.