Quickstart

from datetime import date, datetime, timedelta
from zoneinfo import ZoneInfo
import json

BERLIN = ZoneInfo("Europe/Berlin")

def interval_count(day: date) -> int:
    """96 normally, 92 on spring-forward, 100 on fall-back."""
    start = datetime(day.year, day.month, day.day, tzinfo=BERLIN)
    end = start + timedelta(days=1)
    return int((end.astimezone(ZoneInfo("UTC"))
                - start.astimezone(ZoneInfo("UTC"))).total_seconds() // 900)

day = date(2026, 9, 1)
n = interval_count(day)

payload = {
    "delivery_day": day.isoformat(),
    "unit": "MW",   # average power per quarter-hour
    "series": [
        {"kind": "production",  "control_area": "TenneT",
         "values": [round(1.2 + i * 0.001, 3) for i in range(n)]},
        {"kind": "consumption", "control_area": "TenneT",
         "values": [round(2.0, 3)] * n},
    ],
}
print(json.dumps(payload))

const BERLIN = "Europe/Berlin";

/** 96 normally, 92 on spring-forward, 100 on fall-back. */
function intervalCount(day: string): number {
  const startUtc = zonedMidnightUtc(day);
  const next = new Date(startUtc.getTime());
  const [y, m, d] = day.split("-").map(Number);
  const endUtc = zonedMidnightUtc(nextDayIso(y, m, d));
  return Math.round((endUtc.getTime() - startUtc.getTime()) / 900_000);
}
function zonedMidnightUtc(day: string): Date {
  // Midnight local time expressed in UTC, DST-correct.
  const probe = new Date(`${day}T00:00:00Z`);
  const offsetMin =
    (Date.parse(probe.toLocaleString("en-US", { timeZone: BERLIN })) -
      Date.parse(probe.toLocaleString("en-US", { timeZone: "UTC" }))) / 60_000;
  return new Date(probe.getTime() - offsetMin * 60_000);
}
function nextDayIso(y: number, m: number, d: number): string {
  const next = new Date(Date.UTC(y, m - 1, d + 1));
  return next.toISOString().slice(0, 10);
}

const day = "2026-09-01";
const n = intervalCount(day);
const payload = {
  delivery_day: day,
  unit: "MW",
  series: [
    { kind: "production",  control_area: "TenneT",
      values: Array.from({ length: n }, (_, i) => +(1.2 + i * 0.001).toFixed(3)) },
    { kind: "consumption", control_area: "TenneT",
      values: Array.from({ length: n }, () => 2.0) },
  ],
};
console.log(JSON.stringify(payload));

# jq builds the 96-value arrays; fine for a smoke test, use a real
# timezone library for production DST days.
jq -n '{
  delivery_day: "2026-09-01",
  unit: "MW",
  series: [
    {kind: "production",  control_area: "TenneT", values: [range(96)] | map(1.2)},
    {kind: "consumption", control_area: "TenneT", values: [range(96)] | map(2.0)}
  ]
}' > forecast.json