Connecting mini-grids in an optimal way

[pz-max]

A single isolated bus can be easily connected with a https://docs.scipy.org/doc/scipy/reference/generated/scipy.spatial.KDTree.html to the main network. However, what if multiple isolated points exist that could be connected?

Connecting grids in a simple way minimum spanning tree:
https://en.wikipedia.org/wiki/Minimum_spanning_tree

If some (optional) buses can be created to shorten the overall grid length
then the Steiner tree problem is suitable:
https://en.wikipedia.org/wiki/Steiner_tree_problem

A nice paper on optimal Steiner tree problem vs heuristics (optimal = shortest distance)
https://www.sciencedirect.com/science/article/abs/pii/S0360544218313240?via%3Dihub

Note: while all methods only consider minimal distances as optimal, it can be the case that a grid connection that is not minimal in terms of distance can lead to lower total system cost. I.e. the shortest distance connection might be further away from generation (sometimes more expensive).

Co-contributed: Daniel Rehfeldt