How is LuaEntity::energy calculated? Compared to energy_usage and max_energy_usage

[Natha]

What is the difference between

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LuaEntityPrototype::max_energy_usage

and

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LuaEntityPrototype::energy_usage

for "normal" consumer entities? They return the same value, which is the maximum power consumption (in W) - drain and divided by 60 (result is Joules per tick).

When calling

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LuaEntity::energy

on a fully powered entity, the value * 60 is higher than the maximum power consumption. How is this calculated?
When not fully powered, the value matches the consumption in the power statistics GUI.

My goal is to retrieve a percentage of available power to that entity.