Hydropower Calculation

I have assigned the elevation and the volume flow to each point at a river (with v.to.db and v.what.rast). Now I want to calculate the Elevation difference between each pair of points and then calculate the Hydropower between them by using P=density * Q * delta_h * g. Here you can see an example of my Attribut Table (I know the differences are too small but it is only an example):

I dont know how to do this. Is there a way in GRASS or how can I realize that? Thanks in advance.