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Author Topic: My PowerVault - small milestone  (Read 10404 times)
dan_b
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« Reply #15 on: September 19, 2017, 05:10:52 PM »

They're physically bigger and heavier than the batteries that were removed - the engineer said they weighed about 3kg more each than the others. 
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3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery
RIT
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« Reply #16 on: September 19, 2017, 05:49:13 PM »

They're physically bigger and heavier than the batteries that were removed - the engineer said they weighed about 3kg more each than the others. 

Which should indicate that the plates (well tubes) are thicker than those used in the old batteries - always a good sign.

Were the old batteries branded? Or were they some no-name product that PowerVault may now be regretting trying.
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2.4kW PV system, output can be seen at  - https://pvoutput.org/list.jsp?userid=49083

Why bother? - well, there is no planet B
TheFairway
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« Reply #17 on: September 19, 2017, 06:02:50 PM »

Is your 4kWh (your sig says 4kW) taking into account (say) 70% DOD or you you really only have usable 1.2kWh before you reach the 70% DOD mentioned earlier where capacity is severely limited.

Or does some other process prevent loss of capacity after a relative short period of time?

Or am I confusing 70% DOD as 70% capacity remaining ie 30% usable, instead of 30% remaining, 70% used.

Even if latter, 2.8kWh capacity would still only be a small percentage of daily usage. But theni guess, from DNO perspective, its not about powering for long periods, its about smoothing demand.
« Last Edit: September 19, 2017, 06:19:07 PM by TheFairway » Logged
dan_b
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« Reply #18 on: September 19, 2017, 07:03:50 PM »

The original spec of the LA AGM battery i got supplied with was an 8.8kWh battery pack, with a warrantied usable capacity of 4kWh down to 50% DoD for 800 cycles.
It looks like these are Tubular Gel batteries? According to PowerVault that should be a 5.kWh pack with a usable capacity of 4kWh down to 70% DoD for 1800 cycles.
Do we think that's reasonable?  With 6 of these in there, is that the right maths?

I didn't manage to snap any pictures of the old batteries, so don't know what make they were.
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3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery
RIT
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« Reply #19 on: September 19, 2017, 08:32:43 PM »

The original spec of the LA AGM battery i got supplied with was an 8.8kWh battery pack, with a warrantied usable capacity of 4kWh down to 50% DoD for 800 cycles.
It looks like these are Tubular Gel batteries? According to PowerVault that should be a 5.kWh pack with a usable capacity of 4kWh down to 70% DoD for 1800 cycles.
Do we think that's reasonable?  With 6 of these in there, is that the right maths?

I didn't manage to snap any pictures of the old batteries, so don't know what make they were.


With 6 of those, I think you have a very good long-term deal. It also seems that PowerVault is leaves a lot of slack in its specs as those batteries provide 5.8kWh with a C5 rating and 6.5kWh with a C10 rating, which seems to be the operational rating they use in their specs (6 x 90Ah)
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2.4kW PV system, output can be seen at  - https://pvoutput.org/list.jsp?userid=49083

Why bother? - well, there is no planet B
dan_b
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« Reply #20 on: September 20, 2017, 10:16:40 AM »

Managed to discharge 4.75kWh from the new batteries last night which is interesting considering they were only commissioned at 2pm yesterday afternoon.  I assume they must have been fully charged when delivered?

It's all a learning experience...
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3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery
TheFairway
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« Reply #21 on: September 21, 2017, 06:13:06 PM »

Out of curiosity, did you need to get G83(?) permission. If so how long did that take?

I was speaking to Tesla today and was surprised that it needed G83 or higher permission depending on what level the Powerwall output is capped - 3.6kWh or 5.xkWh - and that took some time to arrange. Apparently batteries are a bit of an education topic for the DNOs.

Also, the function to time shift charging is a UK only option, and will be available via software update later this year. But the battery backup functionality will not be available in UK until later 2018 - iirc its available in Aus now as it was primarily developed for that market. But that adds more boxes and cost to the install - advised it probably would not be worth it in UK as grid stability for most is good - still like idea of having lights on during a power cut to impress the neighbours - how vain!
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dan_b
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« Reply #22 on: September 21, 2017, 07:11:06 PM »

No grid permission was required or even mentioned.  Maybe the very high output power of the Telsa PowerWall (which can hit 7kWp with 5kW sustained) has something to do with that?  My PowerVault only outputs at up to 1100W, so nowhere near the 4kW solarPV connection restriction.

Funnily enough my PowerVault was installed as part of a trial being run by my DNO specifically to look at the impact of domestic-size batteries on the local network.  The UKPN Trial includes battery systems from PowerVault, Sonenbatterie and a couple of Tesla PowerWalls, so they are looking at it.

PowerVault has an option to re-charge overnight on low-tariff electricity.  In fact they're running a trial with one of the utility firms (Tonik I think) to see what a good time-of-use tariff looks like for domestic battery owners, and whether they can actually offer it as a package deal.

The recent video about the PowerWall on FullyCharged talked about Tesla developing a module that would allow you to use the battery as a house back-up in the event of a powercut - it's certainly not availble in the UK at the moment.  The PowerVault actually has 1x 13A socket on the front panel to which you can connect a device and it will power that in the event of a powercut - maybe a fridge or something...
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3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery
RIT
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« Reply #23 on: September 21, 2017, 07:11:40 PM »

But the battery backup functionality will not be available in UK until later 2018 - iirc its available in Aus now as it was primarily developed for that market. But that adds more boxes and cost to the install - advised it probably would not be worth it in UK as grid stability for most is good - still like idea of having lights on during a power cut to impress the neighbours - how vain!

Well if all the doom and gloom merchants are right I can see another use for battery backup/home isolation. Their claim is that with all the PV being installed local areas will see their voltage rise so much that the PV inverters will start to back off and so cause stability problems as they keep switching on and then off. I get the feeling that the real chance of this is sod all, but if you have a nice isolated house you can just disconnect and get on with life.
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2.4kW PV system, output can be seen at  - https://pvoutput.org/list.jsp?userid=49083

Why bother? - well, there is no planet B
M
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« Reply #24 on: September 21, 2017, 07:40:32 PM »

The DNO 'stuff' threw me a while back, till I realised it was the control of excessive export issue again. I wonder if the Powerwall 3.68kW takes the PV system into account, or if under some very odd circumstances they could both be exporting? Though of course, why empty your batt to the grid, but what if we're being paid for it, but then why would the grid be desperate for battery discharge if PV gen is high ...... head hurting!

I've got a 5.9kW export limit, so I wonder how that applies to the batt, if at all.

Fun times ahead, again.
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Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
Tiff
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« Reply #25 on: September 21, 2017, 09:25:14 PM »


A power wall/vault system is an embedded generator and in theory treated the same as a PV system of the same TIC with regard to DNO and G83/G59.

Dan - I'm really not surprised those lead batteries failed, I don't think they are suitable for a powerwall type system, lithium batteries are vastly better for a powerwall application. It would have been interesting to monitor the SG of the lead batteries over that time rather than voltage.

Sounds like they have used better batteries as a replacement so maybe you will get 12 months out of this set. Rinse and repeat the warranty replacements until the end of warranty and then get some nice LiFePO4.
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dan_b
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« Reply #26 on: September 22, 2017, 08:35:40 AM »

Tiff, what does SG mean?
They have replaced them with a different type of LA battery it would seem yes, so we'll see. As you say though, if I end up burning through another set within the warranty period and they replace them again I'll be doing ok - just not particularly green is it!

In the 3 days since the new batteries have gone in, the daily diversion is at least 1kWh/day higher than before.
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3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery
Tiff
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« Reply #27 on: September 22, 2017, 09:05:17 AM »

SG - specific gravity. The most reliable way to tell the state of charge. The problem with lead acid in this type of use, especially if deep discharges are a regular thing is that the batteries may not be getting a full recharge often enough. That last 5-10% of charge on lead can take some time and is also very inefficient, a lot of the input energy is just used to make bubbles. Once the lead is fully charged, if you still have surplus PV output then you can't store it.

That's where lithium has a major advantage, no need to worry about getting full or equalisation charges. The lithium will even last longer if never fully charged.

Battery banks in this setup is a very different use case to off grid. Off grid focuses on lifespan and keeping em fully charged. Powerwalls its all about cost per kWh stored, so it may make more sense to work the batteries hard. For many lead batts you get the same lifetime kWh regardless of 10% DOD or 90% DOD.

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sam_cat
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« Reply #28 on: September 22, 2017, 09:06:02 AM »

Tiff, what does SG mean?

Specific Gravity

https://www.freeasestudyguides.com/battery-specific-gravity-test.html

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brackwell
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« Reply #29 on: September 22, 2017, 09:10:35 AM »

I am having issues with domestic batts and i have come to the conclusion that they can only work if we have time of use tariffs otherwise,

Once one has used the self generated leccy then it cannot be used twice obviously.  So when the load is greater than supply then batts have no function. This naturally occurs in winter but can occur at other times if you increase the loads.
So if all one is doing is charging a batt instead of supplying one of these loads then nothing is achieved in fact worse with the batt losses.

So if we have enough load there is nothing for batts to do and so we need to use the loads sequentially and have enough of them.

The cost of the batts installed and replaced every x yrs make it very questionable.

The losses of the batts 20% ?  means that one is no worse off energy wise than if they had not bothered to capture that 20%  

Due to charge and discharge rates of the batts means that significant amounts of leccy must get exported to the grid and high demand loads cannot be supplied without the grid.

This is like off grid living whilst connected to the grid and that does not work either in my opinion.

I just dont get it.

Ken
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