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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 13.5kW

by 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
      I'm pretty skeptical "energy through the night" is financially viable for anyone. Whenever I've looked into it, the cost-per-kwh on a battery blows away any savings over the cost of just paying for off-peak electricity. Which makes sense of course: if it didn't, then it would be more cost-effective for larger players to simply build grid batteries and arbitrage the power cost down to parity. The only real value I've seen is when your selling your own battery capacity under grid-stabilization programs (where some other power company is managing virtual power plants). And I'm still fairly skeptical if that's even a sensible business model (i.e. how much real estate cost can you be saving versus the costs of installing distributed batteries as opposed to centralizing them?)
Flopoto 3y ago
If you would buy a Tesla power wall you actually have a system which would keep running if you have a power outage. There are plenty of areas which would not mind paying a little bit more for this feature. If it doesn't make sense for you, all good. The batteries will get even cheaper I'm pretty sure. And the big batteries make their money through grid stabilisation. But there are a few companies which can leverage your battery at home and act as a big battery
ben_w 3y ago
If I'm reading the website right, UK prices for Tesla Powerwall units are now: "1 Powerwall £6,000, 1 Gateway £900": https://www.tesla.com/en_gb/powerwall/get https://www.tesla.com/en_gb/powerwall/get I think you may be pessimistic about it dying immediately after 80% capacity given most homes won't discharge a thing that size most days, and 10 years is 3652 days which seems like a reasonable number of cycles to 80% for a variety of specific batteries (some do more, some do less, but not only do I not know the cheapest nor do I know what Tesla uses, I wouldn't understand the answer if they gave it to me). Also, for grid users, it probably matters how many cycles[0] rather than how many years, and how much they cycle them depends on the entire rest of the grid. Also, as space isn't the limiting factor[1], any unit can probably be kept in the system down to 5% of initial capacity. [0] even that's a simplification, if you can store more joules in total over the lifetime by never charging to a full cycle [1] look how space inefficient hydro dams are, and yet we still use them; battery tendency towards spicy pillows, however, is always a concern.
thebruce87m 3y ago
£50 isn’t that hard to save. The octopus off-peak rate is 7p vs the normal 30p/kWh. If your bill is £70/month for electricity it suddenly becomes £20, so there is your £50 immediately. My bill is £140 so I would save £100.

by gwd 3y ago

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
    I'm pretty skeptical "energy through the night" is financially viable for anyone. Whenever I've looked into it, the cost-per-kwh on a battery blows away any savings over the cost of just paying for off-peak electricity. Which makes sense of course: if it didn't, then it would be more cost-effective for larger players to simply build grid batteries and arbitrage the power cost down to parity. The only real value I've seen is when your selling your own battery capacity under grid-stabilization programs (where some other power company is managing virtual power plants). And I'm still fairly skeptical if that's even a sensible business model (i.e. how much real estate cost can you be saving versus the costs of installing distributed batteries as opposed to centralizing them?)

Flopoto 3y ago

If you would buy a Tesla power wall you actually have a system which would keep running if you have a power outage. There are plenty of areas which would not mind paying a little bit more for this feature. If it doesn't make sense for you, all good. The batteries will get even cheaper I'm pretty sure. And the big batteries make their money through grid stabilisation. But there are a few companies which can leverage your battery at home and act as a big battery

ben_w 3y ago

If I'm reading the website right, UK prices for Tesla Powerwall units are now: "1 Powerwall £6,000, 1 Gateway £900": https://www.tesla.com/en_gb/powerwall/get https://www.tesla.com/en_gb/powerwall/get I think you may be pessimistic about it dying immediately after 80% capacity given most homes won't discharge a thing that size most days, and 10 years is 3652 days which seems like a reasonable number of cycles to 80% for a variety of specific batteries (some do more, some do less, but not only do I not know the cheapest nor do I know what Tesla uses, I wouldn't understand the answer if they gave it to me). Also, for grid users, it probably matters how many cycles[0] rather than how many years, and how much they cycle them depends on the entire rest of the grid. Also, as space isn't the limiting factor[1], any unit can probably be kept in the system down to 5% of initial capacity. [0] even that's a simplification, if you can store more joules in total over the lifetime by never charging to a full cycle [1] look how space inefficient hydro dams are, and yet we still use them; battery tendency towards spicy pillows, however, is always a concern.

thebruce87m 3y ago

£50 isn’t that hard to save. The octopus off-peak rate is 7p vs the normal 30p/kWh. If your bill is £70/month for electricity it suddenly becomes £20, so there is your £50 immediately. My bill is £140 so I would save £100.