[bboygravity]

Tesla power wall?

No batteries I know of will make economical sense though. Batteries are expensive, wear down and/or require maintenance. After x years / cycles your batteries will be dead and will need to be replaced.

Storing your "free" energy in a battery will end up costing more than just buying the energy when you need it.

Expensive energy storage is a big part of the reason why "green" energy countries like Germany have some of the highest energy prices in the world. And also some of the highest CO2 emissions per kWh in the EU (they need coal and gas powered plants as backups for when there's no wind and solar, because batteries don't make economical sense).

[ziga]

I agree about home batteries being too expensive, hopefully prices will come down with scale.

But the part about battery degradation is not true. Tesla Powerwall has a 10 year warranty[1] with 70% capacity retention. This means that Tesla has data showing that the battery will have higher capacity than 70% after those years. That's a lot of cycles and a lot of renewable energy that the battery will provide in its lifetime.

[1] https://energylibrary.tesla.com/docs/Public/EnergyStorage/Po...

[bboygravity]

There's a reason why Tesla picks 10 years (8 years for car batteries) as a warranty period. Ask yourself: why 8 years and not 10 for cars? Why 10 years and not 15 or 20 years for home batteries? It's not arbitrary.

Battery degradation is not linear. It's not like: 10 years = 70%, 20 years = 40%. It's probably closer to 20 years = 20 % capacity left. The decay becomes exponential-like after a relatively linear period of roughly 10 years.

If you want to get an idea, this is what the decay of battery capacity roughly looks like: https://www.researchgate.net/profile/Simon-Montoya-Bedoya-2/...

The Tesla warranty will fall under "first life" in the image in the link above.

So batteries (even Tesla Powerwalls) do degrade and do degrade to the point where you need to replace them a bunch of times during lifetime of a house.

[LUmBULtERA]

Tesla and other car makers set their warranties at the mandatory minimums. Why would they offer more when they don't have to and consumers find them long enough and/or other car makers aren't competing on warranty length? That doesn't tell you anything about battery longevity.

Edit: Does my MacBook Pro die after 1 year when it's applecare warranty is over?

[bboygravity]

The mandatory minimums? Got a source of the mandatory minimum for cars (US and/or EU) as well as power walls?

The fact that other car makers aren't competing on warranty length seems to me to prove my point, but you seem to think it doesn't? What I mean is: if battery degradation for cars isn't that bad after 8 years, then why are other brands not offering significantly longer warranties to compete with the Tesla one? Not sure about the competition argument anyway, since Tesla didn't have any competition initially and arguably still doesn't have real competition (depending on what features of the car you value most).

Edit: Does my MacBook Pro die after 1 year when it's applecare warranty is over? --> Pretty close yes IMO. My personal experience is that my laptop and phone battery capacities degrade very fast after 1 year and need to be replace after about 2 years, 3 years if you really really push it and are OK with constantly charging.

[LUmBULtERA]

Interesting, it seems to be a statement that's spread around, but the sources do seem to be lacking, e.g., https://www.reddit.com/r/electricvehicles/comments/vp2e7p/us...

RE: MacBook Pro dying close to a year right after it's warranty it over --> well now you're just trolling. My iPhone 15 pro battery still maintains 100% battery health a year after its manufacturing date. It obviously won't need replacing in 1-2 more years even if I "really really push it and are OK with constantly charging". I used an iPhone XS until last year after it was about 5 years old, 5x longer than your supposed device-dead date. I don't think this is unusual.

[guerby]

LFP cells prices for direct sale to consumer are about 70 EUR/kWh right now. With 5000 cycles that's 1.4 EUR cent per kWh cycled out of the battery, so it fully makes economical sense in all electricity markets.

Fully integrated consumer battery prices haven't (yet) followed the decline in cell price, probably because there's lot of demand for this kind of product.

[bboygravity]

Yes, that's correct and confirms what I just wrote.

Dutch example: 0,12 EUR / kWh assuming 5000 cycles with 0 degradation. Example source: https://www.otovo.nl/blog/kennisbank/lfp-batterijen/

The real number is likely still significantly higher than 0,12 EUR / kWh due to battery capacity (and charge discharge efficiency) going down due to wear over time.

It does look like when the price of integrated storage products goes down more, it could become interesting for countries who have had very expensive energy policies (Denmark, Germany, Netherlands etc).

[guerby]

Your computation is off: it's 0.014 EUR/kWh, ten time less and far below kWh market prices about everyhere in the world.

As for cycling the industry standard is give the number of cycles to 80% capacity remaining so the battery is far from dead at 5000 cycles. The simple division I used is conservative.

[bboygravity]

No, it's not. From the link I posted (in Dutch unfortunately, I'll translate the relevant bit):

Small integrated battery:

    3.5 kWh
    Starting at about € 2.100,-

You yourself indicated in your post that integrated batteries (as in: the ones with battery management, that you can actually use to store energy in as opposed to a bunch of lose cells) are more expensive. They are more expensive indeed. I did the calculation. They boil down to 0,12 EUR / kWh in the example above.

The price of cells is not directly relevant, since you can't actually buy cells and just throw them at your house to magically start charging/discharging when you desire.

[guerby]

Well I bought cells a few years ago and use them with the necessary components, and those don't multiply the system price by ten.

BTW because I'm lazy to expand my system I just ordered 14 kWh of fully packaged LFP battery (box, BMS, cells, breaker) for $1800, $130/kWh, $0.026/kWh cycled.

[geysersam]

> "green" energy countries like Germany

Not sure why you consider them to be "green" given the facts you brought up. Germany has never been particularly green energy wise. It's a big population and lots of heavy industry with relatively little energy resources like hydro.

The are building solar and wind quickly now. Maybe that's why you got the impression that they are "green".

[pjc50]

Germany is still very much captured by its coal lobby. The extent to which they are green is that they have a fairly vocal green party .. with 14% of the vote. https://en.wikipedia.org/wiki/Alliance_90/The_Greens

(This is incomprehensible to Anglosphere FPTP two-party systems)

[bboygravity]

The reason I wrote "green" is because, Germany actively hypes itself up as being very green and many people believe them because they have such a vast amount of solar and wind installed.

[baq]

Germany's energy policy is one huge cognitive dissonance at best, gross mismanagement in the base case and a three-decade-long foreign intelligence job at worst.

[bboygravity]

I completely agree. Keyword: Gerard Schroder for those who are curious about "three-decade-long foreign intelligence job".

[Symbiote]

For all the criticism Germany's energy policies get on HN, they're still approximately as "green" as Texas, and better than several other US states.

Set https://app.electricitymaps.com/ to the yearly view and see the CO₂ figures.