The difference between an APU and a GPU in aviation: what is better?
First it is important to define what both an APU and a GPU is. The former stands for ‘auxiliary power unit’ and is installed in the aircraft and provides power to the electrical system as a supplement to or in place of engine-driven generator power. The latter stands for ‘ground power unit’ and is usually designed to be moveable around the ramp, from one parking place to another. It functions in a similar way as an APU, providing power in place of engine-driven generator power.
The differences between the two
From the definitions alone you can see they both provide the same functionality – however there are a few differences. The main difference is the mobility – an APU is installed in an aircraft while a GPU is mobile can be used on different aircrafts. Another notable difference is they are only used to energize depending on the aircraft design – i.e. GPUs aren’t used for all aircrafts, likewise APUs aren’t either. Despite that, there are certain aircrafts that are powered by both.
Which is better?
This is very situational and difficult to answer. If we have a choice regarding which one should be used, i.e. providing the aircraft functions correctly from both power sources, GPU wins hands down. It wins because it more efficient, it runs on diesel fuel and therefore is cheaper to operate during long periods of ground operation, likewise it can be used on multiple aircrafts. Moreover and extending on the previous point – the GPU is independent of the aircrafts fuel, which can really complicated operations if an APU is used for a long period of time.
In short though, they are both good and effective if used correctly i.e. GPU should be used as an engine heater and starter power source, whereas an APU should be used for powering the air con system and auxiliary power for the systems in general.