Bills can be less than zero, giving you money instead

[bugpacks]

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 1.66
What expansions, game packs, and stuff packs do you have installed? all
Steps: How can we find the bug ourselves? 1. Build very eco friendly house. 2. Wait until bills arrive.
What happens when the bug occurs? You'll get some money!
What do you expect to see? Make the bills expensive like the good old days.
Have you installed any customization with the game, e.g. Custom Content or Mods? Not now. I've removed them.
Did this issue appear after a specific patch or change you made to your system? Neutral/Not Sure 

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[Thats_Me_Madz]

Are you generating power and water (through solar, dew collectors, wind turbines etc)? These can reduce your bills.

Additionally, any excess power/water you generate can be sold and you'll get the money in exchange.

[meubanks68]

This is a feature, not a bug. If you are generating more power than you use. the excess gets sold for money. Easily avoidable. Just don't put power generating objects and eco friendly items on the lot. 

[meeshmeesh3]

@bugpacks Eco friendly -> Saves energy, water, etc. -> Don't pay for these things.

I am not so sure about *getting* money, and why that would occur (unless you are selling excess water or something).