What statistical method to use to analyse decrease in energy usage if production is always increasing?

Production at a factory is always increasing (tonelage), and energy (MWh) consumption is directly proportional, which would be a positive correlation. In parallel, there is investment and effort for increasing energy efficiency and decrease its usage:

How can I study how much actual energy is being saved from those efforts alone, if the energy increase because of production will always be more than what can actually be saved?

If production was stable, I could just see an overall decrease trend in energy and correlate that to the energy saving methods, but production is forecasted to keep increasing, and machinery and equipment still hasn´t reached its full capacity, so no way to know a baseline of energy consumption behaviour.

Is there a statistical method which would allow me to know an approximate of a certain decrease in consumption correlated to a specific efficiency improvement vs the normal increase trend of energy and Production?

Also, what would be the correct description of this phenomenon or situation?

Update:

• I don't understand. What is wrong with energy costs divided by turnover? Commented Apr 7, 2022 at 15:40
• In the end I´m trying to measure how much energy (as little as it may be) I´m saving. My energy performance is measured MWh/Ton of product produced. I´m not looking into finantial costs. For example, lets say a certain month my MWH/Ton = 1.0, the next month production was up and thus the efficiency increased so now MWh/Ton = 0.8; I produced a bit more and my energy consumption also increased but only a bit, but also I replaced a certain equipment to a more energy efficient one, but I´m not sure how much the influnce of changing that equipment actually was...
– Roy
Commented Apr 7, 2022 at 16:49
• Would you have expected the energy performance to stay constant without the replacement of equipment? Commented Apr 7, 2022 at 16:55
• No, it would still be getting more efficient, but because of the increase of production itself, not because of the small influnce of changing the equipment. Does the image I just added help?
– Roy
Commented Apr 7, 2022 at 17:42