---- INIT ----
script.on_init(function()
	storage.power_entities = {}
end)

---- ON EVENT ----
script.on_event({defines.events.on_robot_built_entity, defines.events.on_built_entity}, function(event)
	if event.entity.type == "artillery-shell" or event.entity.type == "flamethrower-turret" then
		event.entity.disabled_by_script = true
		storage.power_entities[event.entity] = event.entity.surface.create_entity{
			name = event.entity.name.."-power",
			position = event.entity.position,
			force = event.entity.force,
			direction = event.entity.direction,
			destructible = false
		}
	end
end)

script.on_event({defines.events.on_entity_died, defines.events.on_robot_pre_mined, defines.events.on_pre_player_mined_item}, function(event)
    if storage.power_entities[event.entity] then
		storage.power_entities[event.entity].destroy()
		storage.power_entities[event.entity] = nil
    end
end)

local refresh_rate = 20 -- how often to check whether an out-of-power turret should be re-enabled
local energy_per_shot = util.parse_energy("8kJ") -- set to whatever you want

script.on_event(defines.events.on_script_trigger_effect, function (event)
	if event.effect_id ~= "turret-consume-energy" then return end
	local turret = event.cause_entity -- or should it be event.source_entity?
	local interface= storage.power_entities[turret] 
	if interface.energy >= energy_per_shot then
		interface.energy = interface.energy - energy_per_shot
	else
		turret.disabled_by_script = true 
	end 
end)
script.on_nth_tick(refresh_rate, function(event)
    for turret, interface in pairs(storage.power_entities) do
        if turret.disabled_by_script and interface.energy >= energy_per_shot then
			interface.energy = interface.energy - energy_per_shot 
			turret.disabled_by_script = false 
		end 
	end 
end)