It's not "changeable", it's "variable". Also, more weather rpediction options.

First off: keep it up! The game is really fun to explore despite its lack of contentm i haven't gotten bored yet (50 hours on record so far). The description of the windmill says that its power output is "changeable" which makes it sounds as if it can be changed, but in fact, it can change due to the speed of the wind. The better word for this would be "variable" which makes it very clear that the power output can vary depending on circumstance.
And since we already have a weather forecast meter, can you maybe include the strength of the wind in that forecast? I can imagine that a weather station would allow for such a forecast while also producing a small amount of science.
I think you can do great things with the weather system and I am excited to see what other kind of weather conditions and catastrophes we may see in the future.