Feedback very welcome, and please share with your EV-driving friends! 💚

The site can be added to the homescreen on your phone so it behaves like an app, which means it only takes a second to check just before you plug in.

We use carbon intensity forecasts from National Energy System Operator to tell you at a glance whether you should plug in your EV tonight, or if it’d be better to wait until the grid is greener. We think this approach could reduce the emissions from charging by up to 25%!

I don’t disagree. But unlike almost every other emitter of CO2 (transport, heating etc), at least this has a chance of resulting in net negative emissions. I think of it as an investment - the potential downside is *relatively* small but the upside would be hugely significant, if it pays off.

I think there’s a good chance of it happening. I think we’ll know more at the end of this year, once the next generation of LLMs appear.

Any usage of any battery will cause it to lose capacity. I have no idea whether 0.4kWh/year is a lot. ~3% per year doesn’t sound wildly out to me. It’s also unclear whether that will continue for the whole lifetime of the battery: my understanding is that a lot of degradation happens early on.

Also, hiding capacity is exactly what the Powerwall does: it’s advertised at 13.5kWh but from new it’s actually over 15kWh, so the first few years of degradation don’t impact the advertised capacity. I’m not sure if any other home batteries do this.

House batteries are all about getting maximum benefit, so fully charging and discharging is the best approach, even if it’s harder on the battery.

You’re right to say that DC fast charging can also be harmful to batteries, and that never happens to house batteries. It’s easier to be friendly to EV batteries because most people rarely do long journeys and can carefully control home charging.

Have you seen this monumental opus on the intersection of AI and energy by @mliebreich.bsky.social?

about.bnef.com/blog/liebrei...

Kinder in what way? My EV lives in the 20-80% range almost all the time. The Powerwall does zero to 100% and back every day (in winter anyway)

Fair, although I’d expect the two figures to line up once that number reaches 13.5kWh.

Trying to follow your approach: last Sunday, according to the Tesla app, my Powerwall discharged 12.9kWh (and charged 0% from solar). Backup reserve is 5% which suggests a capacity of 13.58kWh. Is that plausible?

521Wh lost in about 18 months. I expect it to start eating into the advertised capacity in another 2-3 years.

Tesla exposes nominal_full_pack_energy via the local API on the Powerwall. At the start of July 2023 (when my Powerwall was brand new and I started logging it daily) that value was 15,115Wh. Today, it’s 14594Wh.

Narrator: “but his maths was not right.”

The first bit is correct. But the second bit should be 28GWh, not MWh. So 83 minutes of UK very-windy-day wind output, not 5 seconds!

That’ll teach me to do maths in bed.

cc @simonwillison.net