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Tesla Megapacks come with a 15-year "no defect" and "energy retention" warranty. A 10 or 20 year "performance guarantee" is available for an additional cost. (a

Tesla Megapacks come with a 15-year "no defect" and "energy retention" warranty. A 10 or 20 year "performance guarantee" is available for an additional cost. (an example of Li-Ion based storage, I assume it won't differ wildly with other producers) I think they can in principle last longer if used well. You can control the temperature, you can use weather forecast (as part of some network-wide forecast of future required capacity) to decide how much you should charge the batteries. You'd use the "unhealthy" charging/discharging only in extreme situations, while in the day-to-day cycles you'd keep the batteries within the healthy voltage range.

adrianN 3y ago
We will probably also switch to different chemistries for grid batteries. Sodium batteries for example are cheaper. Iron oxide is also interesting.
gwd 3y ago
Two years ago when I was considering installing a battery along with my solar panels, here was the estimations I did: 1. Additional cost of installing a 13.5kWh Tesla Powerwall was quoted as being around £12,000 2. Warranty was 80% capacity after 10 years Now, my experience with batteries in general is that once they start to go, they deteriorate pretty rapidly; so 80% after 10 years to me basically account 10 years as the lifetime of the battery. £12k for 10 years is £1.2k per year, or £100 per month: that is, the battery would have to allow me to save £100/month in electricity just to break even -- and that's before factoring in the cost of capital (i.e., if I take that £12k and invested it somewhere else, I'd have a lot more than £12k after 10 years). Even if the batteries managed to eke out a reasonable capacity for 20 years -- which seems pretty unlikely to me -- I'd still have to somehow save £50/month to break even. All in all the battery just didn't make financial sense for me as an individual. One expects that the companies doing this on an industrial scale have done the math and managed to find some economies of scale that make it profitable; but it's not out of the realm of possibility that due to a combination of optimism, overselling on the part of battery companies, and FOMO, that they've drastically overestimated the performance of their batteries, and are going to find 15 years down the road that they're beginning to fail without having paid back the capital investment used to buy them.
- pbmonster 3y ago
  Is there a reason you did the math with a 13.5kWh battery? Do you heat a large house electrically? Do you need to charge an EV at night off that battery? Most people can get away with a significantly smaller battery - if your goal is to just get a normal house through a single night. That goal can be achieved pretty economically, especially if you're willing to use grid electricity on mornings with little sun on your panels or nights with unusually high demand.
  - gwd 3y ago
    Basically the quote we got from the local company gave us the option of a 10kWh non-Tesla battery for about £10k and a 13.5kWh Tesla battery for £12k. The math doesn't change that much between the two. I had also looked into battery sizing previously based on our annual usage; but that was over 3 years ago so I don't remember what I came up with.
  - XorNot 3y ago
    What is the point of a grid battery if you don't heat your house electrically, particularly from the point of view of climate change which is meant to be the real reason we're doing this.
    - pbmonster 3y ago
      The difference is mostly financial. Lots of people around me install/upgrade their rooftop PV system right now, and most of them get a small battery to make it through the night. Both a new PV system and a battery is subsidized, and the money is easy to get. Heatpump upgrades to existing houses are much more expensive, and for some reason the subsidies are incredibly complicated to get, and there's no guarantees for exactly how much you'll get approved. Baby steps, I guess. Financial incentives (and the extreme price drop in batteries and PV modules) mean we're starting with switching normal household electricity consumption to renewables. We'll do household heating... some other time.
      - XorNot 3y ago
wolverine876 3y ago
Warranty or not, I don't think I'm relying on Tesla's performance claims as data. I know, it's warrantied - 'but wasn't it your fault? What humidity level did you store it in? The moisture sensor says ...'

adrianN 3y ago

We will probably also switch to different chemistries for grid batteries. Sodium batteries for example are cheaper. Iron oxide is also interesting.

gwd 3y ago

Two years ago when I was considering installing a battery along with my solar panels, here was the estimations I did: 1. Additional cost of installing a 13.5kWh Tesla Powerwall was quoted as being around £12,000 2. Warranty was 80% capacity after 10 years Now, my experience with batteries in general is that once they start to go, they deteriorate pretty rapidly; so 80% after 10 years to me basically account 10 years as the lifetime of the battery. £12k for 10 years is £1.2k per year, or £100 per month: that is, the battery would have to allow me to save £100/month in electricity just to break even -- and that's before factoring in the cost of capital (i.e., if I take that £12k and invested it somewhere else, I'd have a lot more than £12k after 10 years). Even if the batteries managed to eke out a reasonable capacity for 20 years -- which seems pretty unlikely to me -- I'd still have to somehow save £50/month to break even. All in all the battery just didn't make financial sense for me as an individual. One expects that the companies doing this on an industrial scale have done the math and managed to find some economies of scale that make it profitable; but it's not out of the realm of possibility that due to a combination of optimism, overselling on the part of battery companies, and FOMO, that they've drastically overestimated the performance of their batteries, and are going to find 15 years down the road that they're beginning to fail without having paid back the capital investment used to buy them.

pbmonster 3y ago
Is there a reason you did the math with a 13.5kWh battery? Do you heat a large house electrically? Do you need to charge an EV at night off that battery? Most people can get away with a significantly smaller battery - if your goal is to just get a normal house through a single night. That goal can be achieved pretty economically, especially if you're willing to use grid electricity on mornings with little sun on your panels or nights with unusually high demand.
- gwd 3y ago
  Basically the quote we got from the local company gave us the option of a 10kWh non-Tesla battery for about £10k and a 13.5kWh Tesla battery for £12k. The math doesn't change that much between the two. I had also looked into battery sizing previously based on our annual usage; but that was over 3 years ago so I don't remember what I came up with.
- XorNot 3y ago
  What is the point of a grid battery if you don't heat your house electrically, particularly from the point of view of climate change which is meant to be the real reason we're doing this.
  - pbmonster 3y ago
    The difference is mostly financial. Lots of people around me install/upgrade their rooftop PV system right now, and most of them get a small battery to make it through the night. Both a new PV system and a battery is subsidized, and the money is easy to get. Heatpump upgrades to existing houses are much more expensive, and for some reason the subsidies are incredibly complicated to get, and there's no guarantees for exactly how much you'll get approved. Baby steps, I guess. Financial incentives (and the extreme price drop in batteries and PV modules) mean we're starting with switching normal household electricity consumption to renewables. We'll do household heating... some other time.
    - XorNot 3y ago

wolverine876 3y ago

Warranty or not, I don't think I'm relying on Tesla's performance claims as data. I know, it's warrantied - 'but wasn't it your fault? What humidity level did you store it in? The moisture sensor says ...'