A self-learning production forecast that runs entirely on your own Home Assistant. It starts from the physics, then corrects itself with what your panels really do, and feeds the official Energy dashboard, the Helios card, and a clean, well-organized set of sensors.
A cloud service predicts a generic panel at your coordinates. Helios starts there too, then corrects it with what your home actually recorded. Flip the toggle: the gap is everything a cloud model can't see.
With no API key, Open-Meteo provides the hourly weather at your location: global, direct and diffuse irradiance, the plane-of-array irradiance for each of your orientations, plus cloud cover, temperature, wind and snow. The very data the Helios card reads, and your location is only ever an approximate point.
From that weather, Helios computes the sun's position (checked to about 0.3 degrees against the NOAA reference), transposes the irradiance onto each tilted array, applies a cell-temperature derate, a snow-cover factor, and clips at your inverter limit. A multi-orientation install is summed by each array's share of the kWp.
This is where a cloud service can't follow. Helios keeps a rolling 60-day history of what your panels actually produced. For the hour being forecast, it finds past hours where the sun position, cloud cover and temperature were similar, and reads the spread of what you truly made then. The median becomes a forecast calibrated to your site; the 10th and 90th percentiles become a free uncertainty band.
A reliability score blends how mature the learning is, the gap between recent forecasts and reality, and how predictable today's sky is, then decays across the 7-day horizon the way weather-model accuracy really does. A trend value shows whether today now looks better or worse than it did at 06:00.
All of it runs on your own Home Assistant. Nothing about your production leaves your instance; the only thing that goes out is an approximate location, to fetch the weather from Open-Meteo.
39 entities per panel line, useful on their own in automations and history graphs, with or without the card. The values match the example install charted above, around noon on a mostly clear day.
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Power now | 4 820 | W | Instant predicted AC output right now. |
| Power now (low) | 4 210 | W | P10 floor of the analog uncertainty band. |
| Power now (high) | 5 260 | W | P90 ceiling of that band. |
| Power next hour | 5 090 | W | Predicted average power for the hour ahead. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Energy this hour | 4.70 | kWh | Predicted production this hour. |
| Energy next hour | 5.02 | kWh | Predicted production next hour. |
| Energy today remaining | 18.34 | kWh | Still expected between now and midnight. |
| Energy | Peak power | Peak time | |
|---|---|---|---|
| Today | 34.2 kWh | 5 480 W | 12:40 |
| Day 2 | 31.8 kWh | 5 310 W | 12:10 |
| Day 3 | 12.4 kWh | 2 240 W | 13:20 |
| Day 4 | 28.9 kWh | 5 020 W | 12:35 |
| Day 5 | 33.1 kWh | 5 460 W | 12:45 |
| Day 6 | 30.5 kWh | 5 180 W | 12:20 |
| Day 7 | 9.7 kWh | 1 890 W | 13:05 |
Three sensors, Energy day 1…7, Peak power day 1…7 and Peak time day 1…7, across the seven-day horizon: 21 entities.
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Cloud cover | 12 | % | Archived Open-Meteo cloud cover. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Global irradiance | 720 | W/m² | Shortwave radiation on the horizontal. |
| Direct irradiance | 560 | W/m² | The beam component. |
| Diffuse irradiance | 160 | W/m² | The scattered, sky component. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Temperature | 26.4 | °C | Outdoor air, drives the cell-temperature derate. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Wind speed | 11.2 | km/h | Wind at 10 m. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Snow depth | 0.00 | m | Feeds the snow-cover factor. |
Fetched from the remote Open-Meteo API, the only exchange that leaves your instance, and only as an approximate location: your exact coordinates never go out.
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Forecast reliability | 84 | % | Confidence: maturity, recent skill, sky predictability. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Today forecast trend | +1.6 | kWh | Change in today's total since 06:00. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Predicted power | 4 820 | W | Archive: powers the card's past predicted curve. |
| Entity | Value | Unit | What it is |
|---|---|---|---|
| Predicted energy | 4.70 | kWh | Archive: predicted production, hour by hour. |
There is no Helios server and no account. The physics comes from keyless Open-Meteo, the learning happens entirely inside your recorder history, and the result plugs straight into the official Energy dashboard as a native forecast provider. Add it once per panel line, and each roof orientation gets its own forecast, device and entities; two strings that report only one combined sensor fit in a single entry and are summed by kWp share.
I'm Jérôme, 44, the developer behind Helios. After years spent across the whole stack, backend, frontend, 3D, games, embedded, I wanted to build something that truly matters to me.
A card won't save the planet, I know. But guilt and numbers nobody reads change no one: we change when we can finally see what's happening in our own home. That's the whole point of Helios: make energy visible, tangible, even beautiful, so that acting stops being a chore and becomes the obvious thing to do.
Helios is free and open source, built by a single person, in full transparency.
Helios is an independent community project. It is not created or endorsed by, nor affiliated with, the Open Home Foundation or Home Assistant. Home Assistant and the Home Assistant logo are trademarks of the Open Home Foundation.
ReikanYsora - Jérôme CREMOUX - 2026
