Lava Power Controller (1.16.5)

threshold = 0.8
notifThreshold = 0.25
mon = peripheral.find("monitor")
modem = peripheral.find("modem")
notifSentFlag = false

cells = table.pack(peripheral.find("thermal:energy_cell"))

function notifSend (text)
  modem.transmit(1337,1,text)
end

function writeMonStatus (state,pct)
  mon.clear()
  if mon.setTextScale ~= nil then
    mon.setTextScale(1)
    local width, height = mon.getSize()
    if width < 15 or height < 5 then -- Small monitor - scale down
      mon.setTextScale(0.5)
    else -- Large monitor - scale up
      local scale = math.min(width / 14, height / 2, 5)
      scale = math.floor(scale * 2) / 2 -- multiple of 0.5
      mon.setTextScale(scale)
    end
  end
  mon.setCursorPos(1,1)
  mon.write("State: " .. (state and "On" or "Off"))
  mon.setCursorPos(1,2)
  mon.write("Energy: " .. pct .. "%")
end

function main ()
  local energyCur = 0
  local energyMax = 0

  for _,cell in ipairs(cells) do -- ipairs avoids returning count (key "n")
    energyCur = energyCur + cell.getEnergy()
    energyMax = energyMax + cell.getEnergyCapacity()
  end

  local energyFraction = energyCur/energyMax
  print(energyFraction)
  local energyPercent = string.format("%.2f",
    math.floor(energyFraction*10000)/100)

  if energyFraction < notifThreshold then
    if not notifSentFlag then
      notifSentFlag = true
      notifSend("Warning: Base power capacity at "
      ..energyPercent.."%")
    end
  else
    notifSentFlag = false
  end

  local state = energyFraction < threshold
  redstone.setOutput("top",state)
  writeMonStatus(state,energyPercent)
end

while true do
  status,err = pcall(main)
  if not status then print(err) end
  sleep(5)
end