What is just about squat.
It would be what the market value would be if the power line were properly located on the easement.
And this is all assuming that it is not properly on the easement.
If he built his house on the power company easement then his only recourse is if the easement isn't properly recorded and if it is properly recorded why the civil engineer that did the site plan didn't locate the house with the required set backs. In California anyway, only a certified engineer can do the site plan. There are many issues to consider. Drainage, set backs, easements, topology, fire truck access etc.