Full disclosure: I built the thing I'm about to describe, and I want honest technical feedback before opening it up wider. I'm not selling anything — there's an always-free tier and that's what I want people on.
Why post here? Because this is where I started. I'm a California solar + EV owner, and I got tired of the backwards pattern: my roof makes power all afternoon, I export the surplus to SCE/PG&E for a few cents, then my car charges overnight from the grid at 5–10x that rate (NEM 3.0 made this worse for a lot of us).
The DIY fix — which this group was hugely helpful for — was Home Assistant + TeslaMate + scripts. It worked, but it took real tinkering and ongoing babysitting (ramp oscillation when the Powerwall discharged, spurious sensor triggers, charge-command sequencing). Tesla's Charge on Solar is good but needs a Powerwall and a 2021+ Model X — I just missed the cutoff. The other apps I tried polled too aggressively and kept the car awake.
So I rebuilt my automation as a hosted service: Sundial EV. It connects over the manufacturer cloud APIs (Tesla Fleet, SolarEdge, Enphase — no hardware, no electrician), watches real-time surplus, and only charges when the sun's covering it, with a floor so you're never caught under-charged. The whole config is two sliders: 'always charge to X%' and 'use excess solar up to Y%.' Savings show live on the dashboard.
The honest tradeoff vs. a local HA setup: this is cloud-based, not a replacement if you love your local control. On credentials: it's all OAuth, don't story anything or require access to anything sensitive (location).
Requirements today: Tesla + SolarEdge or Enphase. Happy to share a link if that's allowed here — mods, let me know, otherwise I'll drop it in whatever the right thread is.
