Tesla Powerwall, The Specs, Numbers, and Implementation Absolutely Brilliant

[Cosmacelf]

Yeah, 5kW continuous, 7 kW peak. He also said something else interesting at the Tesla shareholder's meeting. Normally with a backup generator, it only powers a critical load panel. Musk indicated that with one or more of these Powerwalls, you could flip this around and power the whole house, minus the high energy, non-critical loads like air conditioners in a backup scenario.

[Sunking]

Yeah, 5kW continuous, 7 kW peak. .

So now he changes his story line. You know what that means right?

[SunEagle]

Yeah, 5kW continuous, 7 kW peak. He also said something else interesting at the Tesla shareholder's meeting. Normally with a backup generator, it only powers a critical load panel. Musk indicated that with one or more of these Powerwalls, you could flip this around and power the whole house, minus the high energy, non-critical loads like air conditioners in a backup scenario.

First off which system (7kw or 10kw) are you referring to?

Second, did Tesla change the software or hardware to increase the 2kw to 5kw output with a 7kw peak output?

Seems like the first version is so unusable for most people that they needed to make changes very quickly. I wonder how much Beta testing went into the new version.

[donald]

First off which system (7kw or 10kw) are you referring to?

Second, did Tesla change the software or hardware to increase the 2kw to 5kw output with a 7kw peak output?

Seems like the first version is so unusable for most people that they needed to make changes very quickly. I wonder how much Beta testing went into the new version.

I assume the inverter controls the discharge rate. So they have probably only changed the spec. the inverter software programmer can use.

[SunEagle]

I assume the inverter controls the discharge rate. So they have probably only changed the spec. the inverter software programmer can use.

Maybe. By going with a higher discharge rate (from 2kw to 5kw) those batteries must be able to handle a fasted C/x rate then before. That could be just a program change that allows a faster discharge rate or maybe the battery chemistry has been tweaked.

[Cosmacelf]

The rumor I heard is that they changed the internal series/parallel cell wiring to allow for higher discharge rates at the battery level. They realized that it would be more useful to have more power for a shorter period of time than to string out the power for longer. Presumably this changes other spec items as well. Since the batteries have yet to ship, and are still 3 months away from shipping, at best case, they could make this change without too much trouble. They made the change in response to partner criticism about the initial specs.

The 5kw/7kw power output changes are supposed to be for both the 7kwh daily cycler battery and the 10 kWh backup battery. They also said the 7kwh battery has a lifetime 5,000 cycles, whereas the 10kwh battery can do 1,200 cycles. They didn't specify what degradation percentage you are left with at the end of these cycles.

[donald]

I think Tesla initially picked a low C rate because they had not decided on the final spec. They then created some buzz by improving the spec. Plus it leaves all the company's that announced home battery products in their wake somewhat wrong footed.

[donald]

The rumor I heard is that they changed the internal series/parallel cell wiring to allow for higher discharge rates at the battery level.

I doubt it. The cell count, cell voltage, and pack voltage is a constant in the powerwall.

If you look at how the individuals cells are wired in the car battery there is nothing to change to improve the C rate. Choosing the C rate is about battery longevity, not wiring.

[donald]

Seems like the first version is so unusable for most people that they needed to make changes very quickly. I wonder how much Beta testing went into the new version.

Tesla uses half the worlds lithium battery production. Tesla cars have driven a billion miles. Tesla has half the market cap. of Ford, and 11,000 employees.
Yeah, they are just throwing product out into the market without much thought.

[Cosmacelf]

I know there is a lot of skepticism here about Tesla and their, currently, specware battery. But I think it is misplaced. Tesla is truly the world leader in making high performance, low cost, low degradation large lithium ion batteries. Just as the other car manufactures haven't been able to match Tesla's battery cost, I suspect Tesla will also be a leader in home storage batteries too. While there will be some cost advantage for FLA, I think it'll be offset by the ease of install, compact footprint, and lack of maintenace for the lithium ion batteries. The only warranted skepticism is when will it ship since Tesla isn't known for keeping to promised schedules.

[SunEagle]

Tesla uses half the worlds lithium battery production. Tesla cars have driven a billion miles. Tesla has half the market cap. of Ford, and 11,000 employees.
Yeah, they are just throwing product out into the market without much thought.

I understand they have had a lot of experience concerning batteries for EV's. But a home battery system will be used differently and have much different results in real trials then driving EV's.

I am not trying to knock Tesla, but I think they have jumped into the "home energy storage" market before they understood some of the dynamics. Otherwise why did they start with only 2kw and now have 5kw.

Most homes have at least a 5kw emergency gen set available. A 2kw is almost useless to provide power for appliances except for small ones or while camping. That is something they should have "KNOWN" up front before the made their press release. Making the change now IMO shows me they do not understand what the market wants and are scrambling to get it right. Which is why I say they have a good start but it is not yet a practical or economical home energy storage system. Hopefully in a year they will have what we need.

[SunEagle]

I know there is a lot of skepticism here about Tesla and their, currently, specware battery. But I think it is misplaced. Tesla is truly the world leader in making high performance, low cost, low degradation large lithium ion batteries. Just as the other car manufactures haven't been able to match Tesla's battery cost, I suspect Tesla will also be a leader in home storage batteries too. While there will be some cost advantage for FLA, I think it'll be offset by the ease of install, compact footprint, and lack of maintenace for the lithium ion batteries. The only warranted skepticism is when will it ship since Tesla isn't known for keeping to promised schedules.

You forgot to mention that Tesla doesn't currently manufacture their batteries but gets them from Panasonic. So until the mega factor in NV is finished and producing all of their batteries (EV & Home) come from overseas.

IMO that can add to delivery schedules.

[Cosmacelf]

You forgot to mention that Tesla doesn't currently manufacture their batteries but gets them from Panasonic. So until the mega factor in NV is finished and producing all of their batteries (EV & Home) come from overseas.

IMO that can add to delivery schedules.

To be precise, Tesla DOES indeed manufacture batteries, they just don't manufacture cells, yet (until Gigafactory, mid next year). But by now, they have figured out logistics for their cell supply since they use so many for the cars. People tend to downplay the battery and focus on the cells, but the battery itself has a LOT of complexity in it (BMS, cooling, etc.) that isn't easy to replicate. Li-ion cells are no where as easy to use as FLA cells, meaning that the battery itself has a lot of technology in it.

[SunEagle]

To be precise, Tesla DOES indeed manufacture batteries, they just don't manufacture cells, yet (until Gigafactory, mid next year). But by now, they have figured out logistics for their cell supply since they use so many for the cars. People tend to downplay the battery and focus on the cells, but the battery itself has a LOT of complexity in it (BMS, cooling, etc.) that isn't easy to replicate. Li-ion cells are no where as easy to use as FLA cells, meaning that the battery itself has a lot of technology in it.

I agree there is a lot of technology going into those systems. That is what worries me a little.

Knowing the "cooling system" has to work properly (or can result in a fire) will there be enough diagnostics and warnings to alert a home owner should a system start to fail?

I beleive there are monitoring and warning devices on the EV but I didn't see anything mentioned in the home energy system. You can get out of a car and run away but it is not so easy to evacuate a home at night.

[Cosmacelf]

Well, the Tesla car battery has sensors up the wazoo to ensure that it shuts down in the event of a problem, so I can't image they would have any less sensors in the home battery. Sensors are relatively cheap and they already have a BMS, so there is no extra cost to include such technology.

The fire risk is way overrated. The main reason Tesla uses liquid cooling is to prolong the life of the battery. But regardless, the battery will have sensors and cutoffs for abnormal situations. Do note that there hasn't been a single Tesla car battery fire that wasn't started because of an accident. Absent a puncture, not a single one has caught fire.