Used to specify priority of energy usage in the Electric network.
"primary-input" and "primary-output" (previously just "primary")
As input used for the most important machines, currently used for laser turrets. As output used by solar panels.
"secondary-input" and "secondary-output" (previously just "secondary")
As input used for all other machines. As output used in steam generators.
As input/output used for accumulators, to collect the overproduction or provide energy when neither primary/secondary output can't.
Default value, used in input/output doesn't allow the machine to have input/output flow of energy from the network.
usage_priority = "primary-input" (older versions) input_priority = "primary" (older versions) input_priority = "primary"