What your home's standby power costs, reported every morning

1// Standby power report: finds the lowest power your home draws overnight and tells2// your phone through ntfy what that always-on load costs a year. Needs a Shelly energy meter.3 4let CONFIG = {5  fromTime: "01:00",6  toTime: "05:00",7  pricePerKwh: 0.30,8  ntfyTopic: "",9  meterId: 0,10};11 12// One reading a minute, averaged over ten, so a fridge switching off for a13// moment doesn't count as the house's lowest load.14let SAMPLE_SEC = 60;15let AVG_SAMPLES = 10;16// Hours in a year, to turn watts into kilowatt-hours a year.17let HOURS_A_YEAR = 8760;18 19let recent = [];20let nightLow = null;21 22function nowTime() {23  let s = Shelly.getComponentStatus("sys");24  return s === null ? null : s.time;25}26 27function inWindow(t) {28  if (CONFIG.fromTime < CONFIG.toTime) return t >= CONFIG.fromTime && t < CONFIG.toTime;29  return t >= CONFIG.fromTime || t < CONFIG.toTime;30}31 32function readPower() {33  let m = Shelly.getComponentStatus("em1", CONFIG.meterId);34  if (m === null || typeof m.act_power !== "number") return null;35  return m.act_power;36}37 38function onSent(res, err) {39  if (err !== 0 || res.code !== 200) print("Couldn't send the report to ntfy.");40}41 42function send(msg) {43  print(msg);44  if (CONFIG.ntfyTopic === "") return;45  Shelly.call("HTTP.Request", {46    method: "POST",47    url: "https://ntfy.sh/" + CONFIG.ntfyTopic,48    body: msg,49    headers: { "Content-Type": "text/plain" },50    timeout: 15,51  }, onSent);52}53 54function report() {55  let w = Math.round(nightLow);56  let kwh = Math.round(w * HOURS_A_YEAR / 1000);57  let cost = Math.round(kwh * CONFIG.pricePerKwh);58  send("Overnight, the lowest your home drew was " + w + " W. Left on all year, that's " +59    kwh + " kWh, about $" + cost + " at " + Math.round(CONFIG.pricePerKwh * 100) + "c a kWh.");60}61 62function sample() {63  let t = nowTime();64  // Without the clock it can't tell when night is, so it does nothing.65  if (t === null) return;66  if (!inWindow(t)) {67    if (nightLow !== null) report();68    else if (recent.length > 0) print("Too few readings overnight for a report.");69    recent = [];70    nightLow = null;71    return;72  }73  let p = readPower();74  if (p === null) return;75  recent.push(p);76  if (recent.length > AVG_SAMPLES) recent.splice(0, 1);77  if (recent.length < AVG_SAMPLES) return;78  let sum = 0;79  for (let i = 0; i < recent.length; i++) sum += recent[i];80  let avg = sum / recent.length;81  if (nightLow === null || avg < nightLow) nightLow = avg;82}83 84Timer.set(SAMPLE_SEC * 1000, true, sample);85print("Standby power report started. Watching from " + CONFIG.fromTime + " to " +86  CONFIG.toTime + " each night.");