solar excess.js

function calculateDivert ({
  now,                // current Date
  cycle_surplus_Wh,   // accumulated surplus (feed in - consumption) in this cycle
  cycle_feed_in_Wh,   // accumulated feed-in in this cycle
  cycle_minutes,      // minutes in a cycle
  load_kW,            // load consumption
  load_status,        // load on/off status
  max_demand_kW,      // max provisioned demand in kW
  grid_consumption_kW // current consumption from grid
}) {
  const cycle_seconds = cycle_minutes * 60
  const remaining_seconds = cycle_seconds - (now.getMinutes() * 60 + now.getSeconds()) % cycle_seconds
  const surplus_kWh = cycle_surplus_Wh / 1000
  const feed_in_kWh = cycle_feed_in_Wh / 1000

  const load_per_second_kWh = load_kW / 60 / 60
  const elapsed_seconds = cycle_seconds - remaining_seconds
  const feed_in_per_second_kWh = feed_in_kWh / elapsed_seconds

  return {
    debug: {
      now,
      cycle_surplus_Wh,
      cycle_feed_in_Wh,
      cycle_minutes,
      load_kW,
      heater_status: load_status,
      grid_consumption_kW,
      cycle_seconds,
      remaining_seconds,
      surplus_kWh,
      feed_in_kWh,
      load_per_second_kWh,
      elapsed_seconds,
      feed_in_per_second_kWh,
    },
    enabled: (() => {
      if (load_status === 'on') {
        // keep on until feed-in has been drained
        // @todo predict if surplus would go negative before end of cycle
        return grid_consumption_kW < max_demand_kW && cycle_surplus_Wh > 0
      } else if (remaining_seconds < 30) {
        // don't bother cycling the relay
        return false
      } else {
        // turn on as late as possible within a cycle
        return (grid_consumption_kW + load_kW) < max_demand_kW &&
          surplus_kWh >= remaining_seconds * (load_per_second_kWh - feed_in_per_second_kWh)
      }
    })()
  }
}