startup.lua

threshold = 0.6
mon = peripheral.wrap("monitor_1")

cells = {
    peripheral.wrap("thermal:energy_cell_1"),
    peripheral.wrap("thermal:energy_cell_2"),
    peripheral.wrap("thermal:energy_cell_3"),
    peripheral.wrap("thermal:energy_cell_4")
}

function writeMonStatus (state,fraction)
  local pct = math.floor(fraction*10000)/100
  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

while true do
  local energyCur = 0
  local energyMax = 0

  for _,cell in pairs(cells) do
    energyCur = energyCur + cell.getEnergy()
    energyMax = energyMax + cell.getEnergyCapacity()
  end

  local energyFraction = energyCur/energyMax
  print(energyFraction)

  local state = energyFraction < threshold
  redstone.setOutput("left",state)
  writeMonStatus(state,energyFraction)

  sleep(10)
end