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Analysis of Powerwall Battery Retention

netzero.energy
2 points·by ziga·w zeszłym roku·0 comments

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ziga
·3 miesiące temu·discuss
Unless you add battery storage, which is increasingly the case:

https://pv-magazine-usa.com/2026/02/25/solar-and-storage-to-...
ziga
·10 miesięcy temu·discuss
> Oh, and also batteries such as the tesla power wall can only be charged and discharged about 1000 times before they have lost a lot of capacity.

Powerwall's cycle life is much better than 1000. The Powerwall warranty guarantees 70% capacity after 10 years of daily cycles (i.e. 3650 cycles). This means they expect the capacity to be substantially above 70%.

We posted an analysis of Powerwall capacity retention: https://www.netzero.energy/content/2025-02/powerwall-analysi...
ziga
·12 miesięcy temu·discuss
Ah, those are wholesale prices. And the form factor will increasingly be prismatic LFP packs, not cylindrical cells.

For buying LFP cells, I would start here: https://diysolarforum.com/
ziga
·12 miesięcy temu·discuss
Grid-scale storage (and increasingly EVs) use lithium-iron-phosphate battery cells, which don't require cobalt/nickel/manganese.
ziga
·12 miesięcy temu·discuss
https://about.bnef.com/insights/commodities/lithium-ion-batt...
ziga
·12 miesięcy temu·discuss
I think 12 years is an underestimate. Lithium-ion batteries will degrade, but they still have usable capacity. There are Tesla Roadsters still going strong, 15 years in. And the battery cell chemistry has since shifted to LFP, which has longer cycle life.
ziga
·w zeszłym roku·discuss
You can't really generalize cycles based on chemistry alone. Battery management and usage matters. But two examples with NCA/NMC chemistry:

- The Tesla Powerwall 2 battery warranty[1] is for effectively 3650 cycles (daily cycle for 10 years).

- Many cases of Tesla cars at 200k mileage (~1000 cycles, depends on battery size) with less than 15% capacity loss[2].

And these batteries didn't die after reaching the high number of cycles, they just retained less capacity.

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

[2] https://insideevs.com/news/723734/tesla-model-3y-battery-cap...
ziga
·2 lata temu·discuss
> It accounts for 20% of California’s renewable energy.

That doesn't sound right. It seems to come from Wikipedia with a 2019 date, but even then:

The Geysers produced 5,543 GWh in 2022 [1].

California generation from renewables:

2019: 64,336 GWh [2]

2023: 76,153 GWh [3]

[1] https://geysers.com/The-Geysers/Geysers-By-The-Numbers

[2] https://www.energy.ca.gov/data-reports/energy-almanac/califo...

[3] https://www.energy.ca.gov/data-reports/energy-almanac/califo...
ziga
·2 lata temu·discuss
We need all the renewables we can get, and I think you can have both -- utility-scale and rooftop. Rooftop solar (and battery storage) just needs to be cost efficient to offset the rising cost of electricity and make it a good return on investment.

The "attacks on net metering" are merely acknowledging that the proportion of renewables on the grid is high enough that balancing grid supply and demand is becoming an issue. I'm a big proponent of rooftop solar, but the reality is that 1:1 net metering just doesn't make sense once there's a critical mass of solar installed (the duck curve problem). This is not a problem unique to California or the US. If you look at other places with high solar adoption (Australia, EU), you'll find even stricter policies like negative feed-in tariffs: the utility will charge you for exporting solar to the grid.

Battery storage is a solution to that problem, but that's where prices are still too high. I'm actually surprised that battery storage is not mentioned in the article, because that's a critical component of allowing solar/wind to grow further.
ziga
·2 lata temu·discuss
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...
ziga
·2 lata temu·discuss
Dynamic tariffs (aka real-time or wholesale plans) are becoming more common in the UK an EU. These are usually priced by 30-min periods and announced 24h in advance. More modern utilities will offer apps that control when your car is charged (in exchange for cheaper rates). But I agree, optimizing this is fun too. I'm building support for configuring Tesla Powerwall systems based on dynamic tariffs.

If you have the option, the best time to charge your car would be during the day when there is abundant solar.