Pulling Solcast data from Home Assistant (how-to)

[tfnico]

I suspect we are quite a few who combine EVCC, Home Assistant (HA) and forecast data from Solcast.

We occasionally run into the dreaded 429 status code, a.k.a. rate limit of only being allowed 10 calls a day to Solcast.

One could probably divvy it up so that HA and EVCC get 5 calls each daily, or one could even register a duplicate account at Solcast to bypass the limitation (probably in violation of their terms).

I figured it'd be more elegant to have one service gather the data, and then expose it to the other.

The https://github.com/BJReplay/ha-solcast-solar integration in HA offers a lot of features, so I figured this would be the best "master" of data.

There are some existing discussions on doing this with MQTT, but I wanted to do it with polling/http, and now that I got it working, I'd like to share the recipe here.

The goal format: EVCC expects forecast data in a certain form:

[
...
  {
    "start": "2026-06-07T19:00:00+02:00",
    "end": "2026-06-07T19:30:00+02:00",
    "value": 3736.0
  },
  {
    "start": "2026-06-07T19:30:00+02:00",
    "end": "2026-06-07T20:00:00+02:00",
    "value": 2720.6
  },
  {
    "start": "2026-06-07T20:00:00+02:00",
    "end": "2026-06-07T20:30:00+02:00",
    "value": 1536.0
  }
...
]

The data can stretch around 5 days or more into the future.

The Solcast integration offers no single sensor that exposes all that data.

So I (with some help from Gemini/Claude) wrote a python script that will gather the data from the relevant Solcast integration forecast sensors and keep them together in one:

# python_scripts/generate_evcc_forecast.py

from datetime import datetime, timedelta, timezone

HALF_HOUR = timedelta(minutes=30)

DAYS = [
    'sensor.solcast_pv_forecast_forecast_today',
    'sensor.solcast_pv_forecast_forecast_tomorrow',
    'sensor.solcast_pv_forecast_forecast_day_3',
    'sensor.solcast_pv_forecast_forecast_day_4',
    'sensor.solcast_pv_forecast_forecast_day_5',
    'sensor.solcast_pv_forecast_forecast_day_6',
    'sensor.solcast_pv_forecast_forecast_day_7',
]

def to_datetime(value):
    """Coerce a period_start value (datetime or ISO string) to an aware datetime."""
    if isinstance(value, datetime):
        return value
    # Strip trailing 'Z' and treat as UTC; handles "+HH:MM" offsets via fromisoformat
    return datetime.fromisoformat(value.replace('Z', '+00:00'))

raw_slots = []

for day_entity in DAYS:
    state = hass.states.get(day_entity)
    if not (state and 'detailedForecast' in state.attributes):
        continue
    for slot in (state.attributes['detailedForecast'] or []):
        period_start = slot.get('period_start')
        if period_start is None:
            continue
        raw_slots.append({
            "start": to_datetime(period_start),
            "value": round(float(slot.get('pv_estimate', 0)) * 1000, 1),
        })

raw_slots.sort(key=lambda s: s["start"])

forecast = [
    {
        "start": s["start"].isoformat(),
        "end":   (s["start"] + HALF_HOUR).isoformat(),
        "value": s["value"],
    }
    for s in raw_slots
]

hass.states.set(
    'sensor.evcc_solcast_live_cache',
    'active',
    {'forecast_json': forecast},
)

Note that python scripts need to be enabled in HA configuration.yml for this to work (probably requires a HA restart as well):

# Enable python scripts:
python_script:

After placing the script, execute it manually using HA Dev Tools:

Later on, it can be automatically updated using an automation:

- id: refresh_evcc_solcast_cache
  alias: "Refresh EVCC Solcast Cache"
  trigger:
    - platform: time_pattern
      minutes: "/30"
    - platform: homeassistant
      event: start
  action:
    - service: python_script.generate_evcc_forecast

In order to access the sensor via http, you'll need to generate a Long-lived access token for EVCC (HA menu -> Profile -> Security).

Time to test (using httpie) and jq to pick out the relevant parts of the JSON:

http -A bearer --auth ${TOKEN} get http://${HA_HOST}:8123/api/states/sensor.evcc_solcast_live_cache|jq .attributes.forecast_json

Replace TOKEN with the long lived HA token value, and HA_HOST with the hostname or ip address of your instance.

Expected response:

[
  {
    "start": "2026-06-07T00:00:00+02:00",
    "end": "2026-06-07T00:30:00+02:00",
    "value": 0.0
  },
  {
    "start": "2026-06-07T00:30:00+02:00",
    "end": "2026-06-07T01:00:00+02:00",
    "value": 0.0
  },
...

Now we tell EVCC where to get the data:

Configuration -> Tariffs & Forecasts -> Add forecast

• Add Solar Forecast
• Title: Solcast via HA
• Provider: User defined forecast

And enter the equivalent to what we ran above:

tariff: solar
forecast:
  source: http
  uri: http://<HA host here>:8123/api/states/sensor.evcc_solcast_live_cache
  method: GET
  headers:
    - content-type: application/json
  auth:
    type: bearer
    token: <paste token here>
  jq: .attributes.forecast_json | tostring

And voila:

I hope this helps someone who comes along the same path as I did. Have fun!

PS: It would be cool if EVCC could integrate with the HA Solcast sensors directly, i.e. use the HA integration for auth and pull data from the relevant sensors. Just an idea.

[cschlipf]

Meine Empfehlung: Steige auf OpenMeteo um. Hier gibt es keine Limits und es erlaubt die Vorhersage noch viel mehr feinzutunen zum Beispiel für Schattensituationen morgens oder abends. Zudem kein Rate Limit.

Ich war zuvor auch bei SolCast und hatte zwei Accounts: Einen für EVCC und einen für HA. Mit OpenMeteo kann ich eine Konfiguration und mehr als nur 2 Arrays in beiden Systemen direkt konfigurieren.

Deutlich einfacher als der Aufwand, den Du hier getrieben hast. Will jetzt nicht Deine Arbeit schlecht machen. Es ist toll, dass Du das geteilt hast. Aber ich denke es gibt für die meisten eine einfachere Alternative.

[tfnico]

I think I skipped evaluating Open-Meteo further as I saw there were no options to configure multiple arrays/roofs in EVCC, and I've got an east/west roof. Can you just add each roof as a separate forecast configuration?

[cschlipf]

That is wrong... You can add as many arrays/roofs as you want, while Solcast has a limit to 2 per account in the free version.

These are two arrays configured via Open Meteo and I could add arbitrary more.

[tfnico]

Gotcha. I wasn't aware that EVCC can combine several forecasts like this, but that makes sense.

[saschde]

Man, exactly what I was going to look for right now! Great! TY!

[saschde]

Got it, but something seems to be wrong. When I test the script I get "Error executing script (ImportError): Not allowed to import datetime" and cannot find the reason at the moment.

[tfnico]

Strange.. are you on a recent HA version? Did you restart after enabling Python scripts?

[saschde]

Yes, I did. Maybe I misunderstand that "config folder" topic? It is the folder where the configuration.yaml is, right? Exactly there I create the python_scripts folder and place the file there, right? And in the configuration.yaml I just place that single line, not the path that I created, right?

[tfnico]

I don't have access to my instance at the moment, but will compare the file later. Meanwhile, might find some tips in https://www.home-assistant.io/docs/configuration/ and the trouble shooting page linked there..

[tfnico]

So, here's mine:

# Enable python scripts:
python_script:

# Loads default set of integrations. Do not remove.
default_config:

# Load frontend themes from the themes folder
frontend:
  themes: !include_dir_merge_named themes

automation: !include automations.yaml
script: !include scripts.yaml
scene: !include scenes.yaml
template: !include templates.yaml
sensor: !include sensors.yaml

Not sure what the relevant diff is. Maybe having python_script: at the top? Maybe your includes/packages on top are shadowing something? I'm afraid I don't know HA enough to say.

I'm running Home Assistant OS 17.3 in a VM, for what it's worth, HA version 2026.6.1.

[saschde]

Same version information here, running in Proxmox VM. Strange because it must be some access rights topic but still I cannot find the root cause.

Neverteheless, I got it solved: there is no need for that "import" line in the script. So I just deleted it and put "datetime." in front of every usage, so it looks like this now:

And the sensor data looks somehow exactly the same as the original Solcast sensor, so it seems to be fine.

Great! TY!

[tfnico]

Odd about those imports 🤷

Glad you got it working!

[saschde]

Hi,

After 2 days now it really seems quite good.
Well done and thanks again for sharing!