Technology inside Tesla Powerwall

Technology inside Tesla Powerwall
Posted by station240 on 11 Jan, 2016 01:23
I've been interested in what is actually inside the Tesla Powerwall, but we are yet to see anyone pull one down to look inside.
So I did a lot of poking around and found some information.

Firstly we have the install manual
https://www.teslamotors.com/sites/default/files/pdfs/powerwall/Powerwall%20Installation%20and%20User%27s%20Manual-online-B.pdf

It has a single DC input/output (bi-directional) .
capacity: 6.4kWh
power in/out: 3.3kW 350-450V 9.5A
cells: nickel-manganese-cobalt (5000 hours)
comms: CAN/modbus (hardware switchable)

The basic concept is to use a DC-DC converter to convert the voltage from the battery to ~400VDC which is fed directly into the inverter's main DC rail. Power can flow both ways, so during the day the batteries are charged from the same rail that feeds the H bridge in the inverter.

Now the DC-DC converter is a ?uk converter, Dr Slobodan ?uk works for Tesla, and they have access to his various patents. It's a simplified combined buck/boost converter easily converted to bi-directional operation.

I don't believe the CAN/modbus protocols are publicly available, which is a problem as they are needed to switch the Powerwall between charge and discharge mode,

According to this article http://www.catalyticengineering.com/top-ten-facts-about-teslas-350kwh-powerwall-battery/
the battery pack likely uses two modules the same design as the Model S. Each module has 6 groups, and 74 cells in parallel per group. This makes a total of almost 900 cells, with an operating voltage of about 48 VDC. I've not seen any confirmed information on the pack voltage.
The pack is packed in a coolant, as in the Model S, Tesla stated this somewhere.

Anyone else found useful information on the Powerwall ?
It's difficult to get beyond the news stories in the search results.

#1 Reply
Posted by miguelvp on 11 Jan, 2016 01:44
According to this case study:
http://www.nrel.gov/docs/fy16osti/64987.pdf

On page 10:
Code: [Select]
Table 3: Tesla Powerwall Specifications [13] Property Value Price $3000 Capacity 7 kWh Power 2.0 kW continuous, 3.3 kW peak Efficiency 92% Voltage 350 – 450 V Current 5.8 A nominal, 8.6 A peak Weight 100 kg Dimensions 1300 mm x 860 mm x 180 mm
It also states the following:
Quote
This analysis assumed that 7 kWh of energy can be cycled daily within the minimum and
maximum state of charge limits, which are assumed to be 30% and 100% respectively. This
implies a full capacity of 10 kWh which is assumed to cost $3000, implying a price of
$300/kWh. We assume this cost includes installation and permitting, but additional analysis
would be required to incorporate these costs at a specific site.
This analysis assumed that the battery begins with 7 kWh of daily cycle life and is replaced once
the maximum capacity has degraded to 70% of the original value. As detailed lifetime cycling
information is not readily available, we assumed that the batteries can be fully cycled daily for
five years beyond the stated 10-year warranty period before the battery capacity degrades to 70%
of the original installed capacity, at which point the battery bank must be replaced. This implies
about 365 cycles per year, for 15 years, or 5475 cycles.

#2 Reply
Posted by orion242 on 11 Jan, 2016 02:18
http://www.modbus.org/

Full spec is there.

#3 Reply
Posted by station240 on 11 Jan, 2016 03:18
Quote from: orion242 on 11 Jan, 2016 02:18
http://www.modbus.org/

Full spec is there.

Rubbish, look at it in detail, modbus is simply a way to set memory address X with value Y.
You still need documentation for each device to know what you are changing !
There is a SunSpec Alliance, which adds solar specific concepts, but is a work in progress and hasn't gotten to batteries yet.

#4 Reply
Posted by orion242 on 12 Jan, 2016 00:19
Didn't say it wasn't rubbish. Welcome to the wonderful world of modbus.

#5 Reply
Posted by reagle on 03 Feb, 2016 01:52
Hmm, how would one use it with a grid tied system using ACPV panels? Looks like I'd have to take its output, feed it into a dedicated inverter then somehow feed that into combiner box that connects to my array? Sounds like it'd break all kinds of anti-islanding rules

#6 Reply
Posted by station240 on 03 Feb, 2016 08:48
Quote from: reagle on 03 Feb, 2016 01:52
Hmm, how would one use it with a grid tied system using ACPV panels? Looks like I'd have to take its output, feed it into a dedicated inverter then somehow feed that into combiner box that connects to my array? Sounds like it'd break all kinds of anti-islanding rules

Ah we call those tiny inverters on the back of panel Micro Inverters, real problem for use with batteries.

Easy solution would be to connect a battery charger to the mains, set to only run when there is excess solar power. Then run another inverter off the battery to power the house. You can get all in one units with the charger and inverter in one box.

Aternative option is to replace the micro inverters with a set Solar Edge Power Optomizers, and their related big inverter.
http://www.solaredge.com/groups/powerbox-power-optimizer
I recall their system is one of the few that work with the Powerwall, not cheap however.

#7 Reply
Posted by AndyC_772 on 03 Feb, 2016 09:15
Modbus? Really? Out of choice, in a world where at least one protocol that's not Modbus exists?

(For those unfamiliar with it, Modbus is a multi-master serial interface, a bit like RS485. The end of a message is indicated by a time gap 3.5 characters long - no more, no less - and replies from slave devices contain no information about what they're actually replying to... just their own device ID, length, data and CRC).

#8 Reply
Posted by mtdoc on 03 Feb, 2016 09:29
Quote from: AndyC_772 on 03 Feb, 2016 09:15
Modbus? Really? Out of choice, in a world where at least one protocol that's not Modbus exists?

For better or worse, I believe it's the standard communications protocol used in the RE industry.

#9 Reply
Posted by mtdoc on 03 Feb, 2016 09:36
Quote from: station240 on 03 Feb, 2016 08:48
Quote from: reagle on 03 Feb, 2016 01:52
Hmm, how would one use it with a grid tied system using ACPV panels? Looks like I'd have to take its output, feed it into a dedicated inverter then somehow feed that into combiner box that connects to my array? Sounds like it'd break all kinds of anti-islanding rules

Ah we call those tiny inverters on the back of panel Micro Inverters, real problem for use with batteries.

Easy solution would be to connect a battery charger to the mains, set to only run when there is excess solar power. Then run another inverter off the battery to power the house. You can get all in one units with the charger and inverter in one box.

The common way to do it is to create what is called in the solar PV industry an AC coupled system.

The big obstacle for incorporating the Tesla Powerwall into a standard battery back up (or off grid) system is that the voltage is too high for the currently available battery based inverters.