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

[ButchDeal]

You have it backwards for the U.S.
The first powerall to ship is the 10kwh, and is for backup. Musk reiterated this at the Edison Institute last week.

That might be so BUT if you are planning to add a Powerwall to a SolarEdge inverter you don't have a backup solution without adding quite a bit of equipment. The SolarEdge system can easily be adapted to have time of use shifting with a software update and set of clamps to measure consumption. To get backup capability you will need a bit more equipment at minimum to disconnect from the grid and probably a sub panel for emergency loads... so a bit more money.

[Sunking]

I agree with you. The 10kWh unit was designed for backup but can only be cycled about once a week. Which is ok (but expensive) for an emergency power source unless you live in a area that gets lots of power outages.

More money that you know what to do with, or a green Kool-Aid drinker.

[SunEagle]

You have it backwards for the U.S.
The first powerall to ship is the 10kwh, and is for backup. Musk reiterated this at the Edison Institute last week.

I agree with you. The 10kWh unit was designed for backup but can only be cycled about once a week. Which is ok (but expensive) for an emergency power source unless you live in a area that gets lots of power outages.

[donald]

keep in mind that what they are initially doing does not have any backup capability, just load shifting to help with time of use. The inverter just has a set of clamps on the main lines to monitor consumption, and manages the inverter output to match consumption.
There is no way to disconnect from the grid and work independently. That would take more equipment and cost more.

You have it backwards for the U.S.
The first powerall to ship is the 10kwh, and is for backup. Musk reiterated this at the Edison Institute last week.

[ButchDeal]

Some cost guidance from Tesla's CTO last week puts the cost of lithium ion at "about $100/kwh by the end of the decade". I think the argument that most solar installs in a few years will include some storage is reasonable. Personally I wouldn't pay $3500 for 10kwh of battery backup. But I would probably pay $1500-$2000.

keep in mind that what they are initially doing does not have any backup capability, just load shifting to help with time of use. The inverter just has a set of clamps on the main lines to monitor consumption, and manages the inverter output to match consumption.
There is no way to disconnect from the grid and work independently. That would take more equipment and cost more.

[donald]

Some cost guidance from Tesla's CTO last week puts the cost of lithium ion at "about $100/kwh by the end of the decade". I think the argument that most solar installs in a few years will include some storage is reasonable. Personally I wouldn't pay $3500 for 10kwh of battery backup. But I would probably pay $1500-$2000.

[Sunking]

. There are many ways of organizing approx. 680 cells to generate 350v,

No Sir there is only one way. 85S8P is the only way it can work with 680 cells to get 350 volts. There is no other combination that could possible work.

[Cosmacelf]

Yes, yes, I know the relationship between series/parallel, voltage amperage, etc. I didn't put a lot of thought into the rumor, just relaying it. There are many ways of organizing approx. 680 cells to generate 350v, some ways will maximize maximum amperage draw better than others.

[Mike90250]

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. .....

Nope. If they rewire internally, then the voltage will go down. You can't magically move some wires, and then get more power. It had to be a software change, or printer error.

[Sunking]

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

That is impossible. A 1 gallon tank is a 1 gallon tank no matter what shape it is in.

A 7 Kwh battery can be

350 volts @ 20 AH
175 volts @ 40 AH
87 volts @ 80 AH
44 volts @ 160 AH

If you understand the physics, then you know wit is pure BS. If you do not know, you drank the Kool-Aide and will believe anything. When you keep changing the story and specs means you have vaporware.

[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.

[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]

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]

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.

[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.