Tesla Powerwall

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Post by T1 Terry » Fri, 08 May 2015, 15:36

Another alternative is cooling the liquid cooler further.... although this may not be the temp sensitive part, it may be the DC to DC converter, then a cooling system to the air intake could be in order.
I wonder if anyone will put out a cell only offer at an affordable price, the EV West offer of US$990 for 3kW@50v would only give 10.6kW @ 57v for the same US$3,500 so another alternative is needed.

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Post by offgridQLD » Fri, 08 May 2015, 16:08

What are people expecting free batterys.

I think a lot of people complain to much about the price of batterys.

The trouble is they are trying to compare it to alternatives that are not really viable alternatives. Non renewable Grid electricity and liquid fossil fuels.

Battery's are not to expensive....electricity and liquid fossil fuels are just to inexpensive. Most people wast energy and have lost respect for it's true value to there lives.

People are happy to spend $2000 on a tv . Or $1000 on a smart phone. $3000 on 20" wheels for there car. All kinds of crap that when you boil it down has very little value to your basic needs.

Most of the crap people own is useless if you don't have power to run it or drive itImage



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Post by jonescg » Fri, 08 May 2015, 16:12

Amen brother!
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Post by Richo » Fri, 08 May 2015, 21:18

offgridQLD wrote:Throwing them in a small insulated room with a Air conditioner is the likely plan.
I have now refrigerated my power room with a small spit system. Never gets over 24C.
T1 Terry wrote: Another alternative is cooling the liquid cooler further.... although this may not be the temp sensitive part, it may be the DC to DC converter, then a cooling system to the air intake could be in order.
To me it just sounds like compromises for a sub standard system.
Even chundersky's at rated for 85DegC
Outside my house got to just over 46DegC in summer.
So no air-con and no insulation for batteries would be required.
It's more likely Musk's worry of thermal runaway on lipo's burning someone's house down.

Which Inverter for PV has liquid cooling?
Why would a powerwall that is only rated for 3kW suddenly need liquid cooling?

By the time a powerwall is shipped in, added installers margins and installation fee I doubt it would be cheaper then local stuff.

The way I see it the only reason to get a powerwall is to go "baa". Image
So the short answer is NO but the long answer is YES.
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offgridQLD
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Post by offgridQLD » Fri, 08 May 2015, 22:42

I'm not voting for any Tesla products. I try to just look at each product for what it is regardless of brand.

"To me it just sounds like compromises for a sub standard system.
Even chundersky's at rated for 85DegC
Outside my house got to just over 46DegC in summer.
So no air-con and no insulation for batteries would be required."

All my gear and many other examples that are refrigerated don't (require) refrigeration but it's just common practice with power electronics & batterys. More so in commercial installation's to make things happier and last a lot longer.

See how long your thundersky cells last for at 85C in fact see how long they last for at even 50C.

Why are life expectancy numbers of electronic components given at different temperatures because it makes a difference.

Server rooms, telcom buildings. show me a remote atcobuilding or similar containing commercial stationary power electronics that doesn't have at least a window rattler hanging out of it or multiple spit systems.

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Last edited by offgridQLD on Fri, 08 May 2015, 12:43, edited 1 time in total.

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Post by T1 Terry » Sat, 09 May 2015, 17:51

Victron inverters are seriously derated at 40*C, many other brands are the same, electronics simply don't enjoy getting overheated and we al know that. With inverter air conditioning being so cheap and energy efficient these days it makes sense to have the battery and electronics room temperature controlled rather than environment thermal control. If the Powerwall was to be inside the house wall mounted the power requirement for air conditioning to limit the room temperature to between 40*C and what ever the min operating temperature was should also be factored in, it would make living inside a tad more comfortable as well :lol:

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Post by Richo » Mon, 11 May 2015, 21:14

offgridQLD wrote: All my gear and many other examples that are refrigerated don't (require) refrigeration but it's just common practice with power electronics & batteries. More so in commercial installation's to make things happier and last a lot longer.


True but commercial installations usually someone else is paying the power bill.
Foe the average consumer would be the point of getting 10kWh of batteries that need 4kWh per day of cooling?
offgridQLD wrote: See how long your thundersky cells last for at 85C

I suspect they would last longer than me Image
offgridQLD wrote: Why are life expectancy numbers of electronic components given at different temperatures because it makes a difference.

Electrolytics and LED's being the obvious example.
So a cap rated at 5000hrs at 105DegC.
10khrs@95Deg - 1 year
20khrs@85deg - 2 years
40khrs@75Deg - 4.5 years
80khrs@65Deg - 9 years
160khrs@55Deg (18 years)

Yep so the power electronics in a power wall @ 55 Degrees should last longer than the batteries claim.
That is unless they put in crap caps or death valley sets a new world temp record.
offgridQLD wrote: Server rooms, telcom buildings. show me a remote atcobuilding or similar containing commercial stationary power electronics that doesn't have at least a window rattler hanging out of it or multiple spit systems.


Most of your examples are sealed rooms with large amounts of power and inefficient heat generation.
It's not the battery pack requiring the cooling.
A Server room is different - they have PC's in them.
This is different to life expectancy but stability over temp and usually of the smaller RF devices.

Nothing that should affect a 10kWh pack with sub 1C output.
So the short answer is NO but the long answer is YES.
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Post by weber » Mon, 11 May 2015, 21:45

Kurt is right. All other things being equal, batteries of any chemistry age twice as fast (useful life is halved) for every 10 degrees Celsius rise in temperature. It's the single most important factor in the aging of Lithium ion cells, once you have a BMS preventing extreme voltages, currents or states of charge.

This is a basic rule of thumb for any chemical reaction. It's based on Arrhenius' equation.
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Post by offgridQLD » Mon, 11 May 2015, 23:14

"True but commercial installations usually someone else is paying the power bill.
Foe the average consumer would be the point of getting 10kWh of batteries that need 4kWh per day of cooling?"

That's a valid point. Particularly if it required refrigeration every day or most of the year. Middle of the desert up north.

The reality is even if it had a hard cutoff at 43C (It would need to be confirmed if that's operating temp or ambient temp)If its ambient temp. Then it would only reach this on extreme days. In a small room (few square meters) You might run the air conditioner for a few hrs on extreem days. Perhaps a month or two over summer in some areas during the day. My small split system uses about 200w due to the small room so 5hrs during the peek of the day is only 1kwh.

Though my initial response to suggest using refrigeration was in response to the comment that (commercial installations would benefit but 43C was a issue)

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Post by Richo » Tue, 12 May 2015, 20:37

weber wrote: All other things being equal, batteries of any chemistry age twice as fast (useful life is halved) for every 10 degrees Celsius rise in temperature.

So opposite to the Cap example I gave for the power electronics.

So is 43 Degrees a continuous maximum rating to achieve the 10 years an a powerwall?
The 47 Degrees it was outside in summer around my house was the peak for a few hours on 1 out of 365 days.
And over 24 hours and 365 days a year on average well less than the 43 degree rating.

Still doesn't justify cooling a battery pack or the power electronics.
Based on the half the capacity for twice as long theory. Image

The 43 Degree limit is just to cover his ass for popping and not achieving the claimed 10 years I suspect.
So the short answer is NO but the long answer is YES.
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Post by weber » Wed, 13 May 2015, 02:05

Richo wrote:So opposite to the Cap example I gave for the power electronics.
No. Exactly the same as the cap example. The caps halve their life for every 10 degree rise too.
So is 43 Degrees a continuous maximum rating to achieve the 10 years an a powerwall?
I doubt it. More likely a short term peak rating. But who can tell anything about a powerwall?
The 47 Degrees it was outside in summer around my house was the peak for a few hours on 1 out of 365 days.
And over 24 hours and 365 days a year on average well less than the 43 degree rating.
What matters is the log-mean-exponential temperature (analogous to root-mean-squared but far more biased towards the peaks).

We had to leave 10 cells out of the MX-5, compared to what we had before we weighed the corners. So we took out the 10 cells that had the highest internal resistance (greatest sag under load) and put them on a shelf in the workshop (no aircon, but out of the sun). A year or two later, the cells that poke through what was the parcel shelf in the back window of the MX-5 now all have higher internal resistance than those 10 that were on the shelf, even though I used a reflective thingy in the back window when ever I left it out in the sun. The cells that are immediately above the motor and immediately behind the chargers are noticeably higher R than the others too. All the others are fine, despite me pulling 5C current peaks all the time and leaving them at 100% charge for days on end, and running them completely flat (2.5 volts) 3 times.

With lithiums, temperature is (almost) everything.
Still doesn't justify cooling a battery pack or the power electronics.
Maybe not. One can do the maths of the economic analysis. But if you're installing an aircon partly for human comfort, then it makes sense to use it to shave the temperature peaks for the batteries and electronics, even if there are no humans around.
Based on the half the capacity for twice as long theory. Image
I don't know what theory you mean by that.
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Post by PlanB » Wed, 13 May 2015, 15:27

Given that cell resistance & batt life both go down with increasing temperature, if you were going to air condition a solar house pack what is the sweet spot temperature? Around 20 Celsius?
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Post by offgridQLD » Wed, 13 May 2015, 15:47

Looking at that linked study in the PIP4048 thread. Relevant part(Page 8)

http://www.cse.anl.gov/us-china-worksho ... %20BMS.pdf


You don't start seeing any real drop off In performance Until around 15C. You still have 98% of the capacity at 15C then you do at 25C. Though I think A more practical temp is around 25C. Particularly if your cooling the entire room.

Most of the year in QLD that can be achieved through insulation and good ventilation.

I'm still working on a automated way to switch my power room from ventilated to sealed up(refrigerated) . For now it's a manual change over from winter - summer. Though I would like Automation even in summer for Day/night.

As you can see by my bank temps at the moment 10AM today. Ventilated.

Temperature:
FET: 26.0°C     PCB: 35.2°C
BAT: 20.3°

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Post by Rusdy » Wed, 13 May 2015, 17:00

Anyone know why Tesla powerwall claims better lifecycle with NMC? Click here

I thought NCA is always better regardless (Click Here):
Image

Oh, it's interesting to see LFP performs better in hot temperature (with shallower DoD) from the experiment above

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Post by TooQik » Wed, 13 May 2015, 17:18

Some relevant news for Powerwall in Australia...

http://www.energymatters.com.au/renewab ... =EM150513C

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Post by offgridQLD » Wed, 13 May 2015, 17:27

Tesla Q1 , questions and answers conference call. In there somewhere is Questions regarding communication issues around the power wall specs.

Relevant discussion to power wall starts at 9:20 seconds.clarification around the DC/DC inverter is at 25:00. At the 26:00 they talk about the operating temp spec and say it's a error in the spec listing (it's capable of operating at a much higher range)
              
http://edge.media-server.com/m/p/hdd83nv6

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Post by TooQik » Wed, 13 May 2015, 17:43

Rusdy wrote:Anyone know why Tesla powerwall claims better lifecycle with NMC?
I'd hazard a guess that it's because NMC lifecycle is impacted less by temperature change and the cooling capacity of the Powerwall is limited.

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Post by weber » Wed, 13 May 2015, 18:27

Thanks Kurt. Your link is broken. I think you just needed the http:// on the front.
http://edge.media-server.com/m/p/hdd83nv6
From 24:40 to 26:30 is the part where Elon Musk complains that "people who think they are experts" got it all wrong about needing an inverter, and admits only that Tesla could have communicated better about the "DC to DC inverter"[sic] (should have said "DC-DC converter") which means that if you already have a PV system with an inverter you don't need an "incremental" inverter (i.e. another inverter).

Sounds like weasel words to me. And it still doesn't explain how anyone could go off-grid without another inverter (i.e. an inverter other than the grid-feed kind since they shut down when there's no grid) as he clearly implied in the announcement.
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Post by offgridQLD » Wed, 13 May 2015, 18:33

Yes just to clarify I call it a DC/DC converter though I was quoting musk and his experts calling it a DC DC inverter Image

Is it just me thinking Elon musk sounds like a nervous wreck when he is public speaking.

60 - 70 cycles pr year from the 7kwh pack isn't impressive.

Though I do like how they mention they get a lot of false promises in new battery tech that doesn't eventuate. I think this is a common view from a lot of people thinking something ground breaking is just around the corner. Taking news story's about breakthrough super battery tech to seriously. For the most part it's just been slow and steady incremental steps.

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Post by weber » Wed, 13 May 2015, 19:10

Rusdy,

Thanks for the link to that paper. Anyone who saw that table you posted without its caption, might assume these were cycle life and calendar life figures for the different chemistries. They are not!

That paper was merely an interim report on the experiment, and these numbers are merely the numbers of cycles and months that each chemistry had so far been subjected to, at the time the paper was written (April 2013). The only reason the LFP have lower numbers in that table is that they started testing them 6.5 months after they started testing the others.

It seems they never published their final results! See
http://www.helios-eu.org/?cat=12
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Post by Rusdy » Wed, 13 May 2015, 23:43

weber wrote:
Anyone who saw that table you posted without its caption, might assume these were cycle life and calendar life figures for the different chemistries. They are not!


Thanks, I missed that. Although the next figure kinda consistent with the numbers (with LFP the lowest)

Image

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Post by 4Springs » Thu, 14 May 2015, 02:49

offgridQLD wrote: 60 - 70 cycles pr year from the 7kwh pack isn't impressive.

That was for the 10kWh pack, designed as occasional failover power backup. The 7kWh is the daily cycle one - 365 cycles per year, they said they expect it to last about 15 years at that rate.
That is why the similar pricing for the two packs - they are for different applications.

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Post by offgridQLD » Thu, 14 May 2015, 03:11

Ok 10kwh pack then.

I just don't get it wasn't the price differences between the 7kwh and 10kwh was less than $1000 wasn't it?

the 7kwh is expected to last 15 years with 60 cycles a year and the other is expected to last 10 years with 365 cycles a year....?

So the 10 kwh pack you get say (using 80% DOD) 8kwh pr day x 60 days x 15 years 7200kwh lifetime output.

The 7kwh unit you get (using 80% DOD) 5.6KWh x 365 days x 15 years . 30,660kwh

Why on earth would you purchase the 10kwh unit?

30,000kwh vs 7000kwh

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Post by 4Springs » Thu, 14 May 2015, 03:39

offgridQLD wrote: I just don't get it wasn't the price differences between the 7kwh and 10kwh was less than $1000 wasn't it?

the 7kwh is expected to last 15 years with 60 cycles a year and the other is expected to last 10 years with 365 cycles a year....?

So the 10 kwh pack you get say (using 80% DOD) 8kwh pr day x 60 days x 15 years 7200kwh lifetime output.

The 7kwh unit you get (using 80% DOD) 5.6KWh x 365 days x 15 years . 30,660kwh

Why on earth would you purchase the 10kwh unit?

Yes, 7kWh is $500 cheaper.

7kWh = 365 cycles per year.
10kWh = 60 cycles per year.
(I think you realised this, just a slight typo Image )
They "expect" that they will last for 15 years but the warranty is less than that.

My impression is that the 10kWh spec means 10kWh available - not 80%. This is not just a battery, it is an appliance. The 7kWh unit therefore gives you 7kWh every day for 15 odd years - but is guaranteed for some shorter length of time (the 10 years you mentioned perhaps).

So if I had a solar system and wanted to shift my power usage into the evening then I'd get (say) 3 x 7kWh units. If my inverter was smart enough then that is all I would have to purchase (ok, excluding wiring and installation).

If I lived in an area where power failures were common and I wanted a whole-house UPS then I'd purchase a single 10kWh unit. The capacity is enough that I could run a couple of appliances for a few hours when everyone else in the street is in blackout. I could get a 7kWh unit, but that is more $ per kWh and won't last me quite as long. For this installation I'd also need to get more hardware - an inverter and a battery charger.

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Post by offgridQLD » Thu, 14 May 2015, 04:03

7kwh - 10 kwh whatever .

Occasional use Whats the point in that. It's a battery I want to use it when I want how I want they don't last for ever...(use it or loose it)...shelf life.

60 cycles pr year what a joke! ...900 cycles life expectancy over 15 years. Why bother. It sounds useless.

Kurt


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