Tesla Energy: Powerwall

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Mark

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Topic # 171807 1-May-2015 18:40

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Sounds quite interesting! You can't say Elon Musk has no dreams :-)

http://www.teslamotors.com/presskit/teslaenergy

Price seems to be quite good too, I hate to think how much the 10kW Lithium ion battery in my garage costs!

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Reply # 1295240 1-May-2015 18:59

I'd love to get one of those when they become available in this country. 7kWh would run all of our computers, fridge, freezer & lighting for up to a day during the frequent outages we have in the Far North. With some PV Panels on the roof, our power bills would be slashed as well. This is the missing piece of the jigsaw so far as I'm concerned. A big bank of Lead-Acid batteries doesn't appeal due to their cost and high maintenance. A Lithium-Ion battery requires no maintenance and if my quick calculation is right, it looks like it would be cheaper too.

MickeyD

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Reply # 1295242 1-May-2015 19:01

Yep looks like a game changer. When they become available here I'll sign up for solar for sure.

timmmay

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Reply # 1295264 1-May-2015 19:21

Like. Makes time shifted solar far more practical.

shk292

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Reply # 1295279 1-May-2015 19:34

$3500 for 10kWh in USA.

So probably $7999 is NZ. Plus GST

wellygary

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Reply # 1295280 1-May-2015 19:36

Can I ship it via youshop :) :)

shk292

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Reply # 1295284 1-May-2015 19:43

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wellygary: Can I ship it via youshop :) :)

No, the NZ retailer will have bought exclusive distribution rights so that would be a breach of copyright

tdgeek

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Reply # 1295304 1-May-2015 20:07

shk292: $3500 for 10kWh in USA.

So probably $7999 is NZ. Plus GST

Installer price, might be a small margin on that, plus inverter, plus installation.

Nice idea

xlinknz

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Reply # 1295312 1-May-2015 20:49

MickeyD: Yep looks like a game changer. When they become available here I'll sign up for solar for sure.

Time will tell whether it will be a game changer

I considered a grid tied 7kWh system but a 12 year+ payback didn't stack up, there is a reason solar PV hasn't taken off [yet]

change in the energy industry occurs at a glacial pace

MickeyD

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Reply # 1295324 1-May-2015 21:38

MickeyD: Yep looks like a game changer. When they become available here I'll sign up for solar for sure.

Time will tell whether it will be a game changer

I considered a grid tied 7kWh system but a 12 year+ payback didn't stack up, there is a reason solar PV hasn't taken off [yet]

change in the energy industry occurs at a glacial pace

Sure, if electricity prices stay the same over those 12 years then for purely economic reasons that may be true. However, the benefits of going green (even if only a feel-good factor) and redundancy in the event of a power cut (not uncommon where we're building) tip the balance.

xlinknz

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Reply # 1295659 2-May-2015 13:06

MickeyD:

MickeyD: Yep looks like a game changer. When they become available here I'll sign up for solar for sure.

Time will tell whether it will be a game changer

I considered a grid tied 7kWh system but a 12 year+ payback didn't stack up, there is a reason solar PV hasn't taken off [yet]

change in the energy industry occurs at a glacial pace

Sure, if electricity prices stay the same over those 12 years then for purely economic reasons that may be true. However, the benefits of going green (even if only a feel-good factor) and redundancy in the event of a power cut (not uncommon where we're building) tip the balance.

This article pretty well sums it up

Don't get me wrong I actually walk the talk and use biofuel at extra cost but I am not prepared to make 12-20 year commitments which is what Powerwall still is unless the benefits are real and achievable

Niel

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Reply # 1295732 2-May-2015 14:37

What makes lead acid worse is that the charging efficiency is only about 70% (chemically, excluding charging circuit) and they are not good for fast discharge.

What makes Li-Ion worse is the cycle life.

There is a good reason why network distribution is still so successful and efficient, economies of scale. A game changer would be if the power authority places energy absorbers/reservoirs in neighbourhoods to deal with power fluctuation, and system supplied to end users at trade price rather than RRP (like the home insulation subsidies of a few years ago which where you could get better deals yourself).

You can never have enough Volvos!

grant_k

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Reply # 1295869 2-May-2015 20:20

Niel: ...
What makes Li-Ion worse is the cycle life.
...

How many cycles do you think a Li-Ion battery bank like this would provide Niel?

I know several people who have lived Off-Grid for years, and with a lot of care and regular maintenance, it's possible to get 10 years + from the Exide Energy Store batteries which are designed for this sort of thing. They say that the key is not discharging the battery too deeply, or it shortens the life. One person I heard of got 12 years from his bank of batteries, but he was pretty anal about maintenance and monitoring the discharge level, so that is the exception rather than the rule. A bank of 24 x 2 Volt Exide 1085AHr batteries cost $15k last time I looked, but that was a while ago.

Do Lithium Ion batteries last longer if you don't deeply discharge them, or not?

timmmay

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Reply # 1295897 2-May-2015 20:59

Battery university knows the answer.

Niel

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Reply # 1296086 3-May-2015 13:05

timmmay: Battery university knows the answer.

Good one. we actually bought the book. That is where I've learned most of my battery knowledge, but also through many years of designing products using them.

You can never have enough Volvos!

Niel

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Reply # 1296089 3-May-2015 13:24

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grant_k:
Niel: ...
What makes Li-Ion worse is the cycle life.
...

How many cycles do you think a Li-Ion battery bank like this would provide Niel?
Do Lithium Ion batteries last longer if you don't deeply discharge them, or not?

The number of cycles is hard to answer, as it depends on what you consider how much capacity loss equals end of life. I've got lead acid batteries that were not that well maintained but still good after 10 years when you are supposed to replace them every 2 years.

It depends on the exact chemistry, but Li-Ion typically is charged above 4V per cell. Charging to 4.2V gives you higher capacity but less cycles than charging to 4.1V. Typical cycle life for consumer Li-Ion is around 300 cycles to 100% discharge, with a loss of 20% capacity. LiFePO4 has a lower terminal voltage but with 1000-2000 cycles for the same conditions. There are a few other "mixes", but nothing (publicly) known with more than a couple thousand cycles.

LiFePO4 (and one or two others) has a higher cycle life because the chemical structure in the charged and discharged state is very similar, where as Li-Ion (or I should rather say Li polymer) is very different between charged and discharged so it wears out faster (mechanically). Add to that, Lipo had a relatively high internal impedance which increases over time (unlike LiFePO4) adding to apparent capacity loss (can't get it out as fast as you used to) and increasing losses. Due to the mechanical wear, if you want high cycle count from Lipo then you need to do slow charge/discharge and no more than 80% discharge. With LiFePO4 you simply don't have these issues, they don't apply.

These are just a couple of differences affecting cycle life, about 5 years ago I've written a technical paper on it.

Safety of LiFePO4 comes from the terminal voltage (2.5V-3.6V) being lower than the ionic voltage for lithium metal plating to occur (around 3.8V), but this also means the Watt-hour of the same weight Lipo is higher (and more attractive for manufacturers/consumers). So in one you get higher safety, in the other you get higher energy.

I'd love to know what Li chemistry is in the Tesla pack, but so far could not find that info. I have however seen that they do only 80% discharge and it is liquid cooled, suggesting Lipo or Li Cobalt or one of the others I don;t want (in that size) in my home (or car). Fine when everything is good, but when it goes wrong...

You can never have enough Volvos!

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