First shot for power=generator (cf #109)
Add extent_from_subquery=true (cf #48)
extent on Datasource (cf #48)
Remove ST_PointOnSurface for now, it fails on world db

NOTICE:  TopologyException: found non-noded intersection between LINESTRING (4.34315e+06 6.74297e+06, 4.34316e+06 6.74298e+06) and LINESTRING (4.34315e+06 6.74298e+06, 4.34318e+06 6.74297e+06) at 4343157.4826180348 6742974.5944957305
ERROR:  GEOS pointonsurface() threw an error!

One option is to replace with ST_Centroid, but I prefer understand why I need it before
Less shadow on hillshade