Hey,
Love the game so far. One thing I feel is missing though is a bit more information on the wind/solar graphs to allow me to better plan ahead. There's no scale on the graphs and no indication of what each solar panel will power. While you can work it out yourself I think it'd be a good idea to at least put 'capacity' figures to plants. Not sure how in depth you'd want to go but at least a number to each plant, or a numbered scale on the graphs. Perhaps the forecast of wind and solar could be something else you could upgrade, e.g. start with the next few hours of forecast but pay to get longer forecasts or more accurate forecasts (eg have graph that estimates a range of values for the next day). Having MWh values on the batteries and hydro storage would also help planning and show the difference between energy and power for those unfamiliar with the difference between a MW and a MWh in energy storage. (I love that you have choices to add more MW capacity to the batteries separate from upgrading how long they last already!)
Other ideas.... demand side response - option to pay an industrial user to turn down their output. Levels in different climates where the sun is less reliable / shorter days. Nuclear plants where the upfront cost is huge but provides stable power.
Thanks for your work and looking forward to seeing it develop!