All the best

Humberto

I apologize for the delayed response. I am unsure what you mean by positive and negative taxes. Are you entering carbon prices in the "Externality Cost" variable under the Effects branch found below Key Assumptions?

As for your results, the Capacity Credit affects the amount of capacity that is added. More capacity is added for technologies with a lower capacity credit. Renewable plants tend to have a lower capacity credit as they are considered to be less "reliable". If you have specified the capacity credit for renewable technologies to be lower than fossil fuel plants, this is likely why you are seeing more capacity being added in the carbon tax scenario.

The higher capacity is likely why you are seeing higher investment costs in the carbon tax scenario. The investment costs may also be higher if the capital and O&M costs specified for renewable technologies are higher than fossil fuel technologies.

Note that while the investment costs might higher, you should find that the overall social costs will be lower in the carbon tax scenario.

Hope this helps,

Emily