As you can see on the bill it is rate of change and it is listed as being per day so if two days had the exact same power production it should say 0 but I think you need to wait a long time for that to happen.
@Psychotps All of the modifiers you mention are what I would expect to see in the game so I am glad you have verified those. Solar panels function better on sunny days and wind turbines better on windy days. I'd be more disappointed if all of these things acted otherwise. Even the Green Eco footprint bonus makes sense to me as a reward for players who invest resources and effort in green upgrades-- just as people can see an energy bill reduction for doing these things in real life.
The 490% power drain has not yet popped up during regular game-play in my several weeks of testing so whatever it is it must be rare and perhaps intentionally catastrophic. I think it would be cool to see what could actually do this (I like a little random destruction in my game-- there's not enough of that in Sims 4). The wind turbines have an upgrade option to act as a lightning rod while the solar panels do not so that is why I brought up lightning in my previous post. The coding might even be an artifact from the pack development for testing something that never made it into the game. Maybe just lazy programming? I mean kudos to you for testing it but I'm not sure it's something regular Sims players should be overly concerned with.
@jpkarlsen Thanks for that explanation on the Rate of Change. That makes a lot of sense! In my testing I see a slightly positive change during daylight hours and slightly negative change at night (from the solar panels) but the actual energy bill stays right around zero (which is where I want it for my testing). In my other Brindleton Bay test house I've added more wind turbines, solar panels, and dew collectors (without going too crazy) just to see how much power and water my Sim can generate with a modest increase in renewable resources. It typically looks like this:
I've never seen a large enough rebate to make all of this worthwhile from a strictly financial point of view. I think it's more about a way of life for some Sims who want to improve the environment in their area-- which is exactly what happened in my game when my neighborhood Eco footprint improved to Green. There are many in-game benefits to a Green Eco footprint beyond earning a few Simoleons.
