Don't let module energy usage effects influence pollution

[tiriscef]

TL;DR

Remove the influence of power usage effects on a machines pollution.

What?

This is kind of a follow-up of this bug report that turned out to be a (imho obscure) feature.

At the moment the pollution a machine produces is calculated like this:
pollution = base value * (1 + sum(pollution effects)) * (1 + sum(power usage effects))

Instead I would suggest to drop the power usage influence and calculate it as follows:
pollution = base value * (1 + sum(pollution effects))

Additionally the vanilla modules should/could be adjusted as to not change the existing balance.
For example the speed module has the following effects now:
+20% speed, +50% power usage (hidden: +50% pollution)
And could be adjusted to also grant +50% pollution.

Why?

1. because it is an oscure feature and nothing in the game that I know of indicates this behaviour. I managed to maintain a mod about modules and amass a 4-figure playtime without noticing it. The only place I found where this behaviour is mentioned are two sites in the factorio wiki.
I believe that it is a relict of the way the game calculated pollution before it got revisited in 0.17, as the EnergySource prototype used to have a 'emissions_per_second_per_watt' key.

2. because the entity tooltip doesn't even show it. In the example in the mentioned bug report the displayed pollution of the mining drill jumps from "10/min" without modules to "11.25/min (-25%)" with the modules. That is... confusing.

3. because this behaviour, together with the maximum of -80% pollution, limits the way mods can design modules to work.
For example: Currently it's not possible to have a module that decreases the pollution by -80% at the cost of +200% power usage. The 'hidden' pollution influence will render the actual effects as +120% pollution and +200% power usage - even if you adjust the pollution effect to -280% to cancel out the power usages influence.

[Koub]

I agree. I think pollution from industrial processes should be carried by the entity (assembling machine, chem plant, pumpjack, mining drill, ...) , but pollution from power usage should be caused by power production. Clean power sources would produce less pollution to produce power, thus overall pollution would be inferior.
The balance could be preserved by changing some values especially on modules.

I know this could be modded, but I think vanilla would benefit from this, because it would make the game more ... readable ? Logical ? I never really understood why there was a double penalty on pollution produced, once with augmented power usage, and once again with additional pollution due to the module, especially when the power-depandant additional pollution is already emitted because one needs more power to run the factory.

Let the power source pollute for the power usage, and the industrial facility pollute for the industrial process.

[NotRexButCaesar]

+1 I didn’t even know that was how pollution worked.

[Squelch]

Indeed it is an obscure metric, and seeing as pollution is one of the major influences for biter attacks, this either needs to be clearly exposed to the player, or as already suggested, dispense with the energy based pollution output per machine altogether. I'd even favour a slight increase in pollution for energy production if it is a matter of balance. At least it would become more transparent.