A surge of interest in residential solar arrays threatens traditional utilities’ outdated business model of selling more and more electricity, prompting them to adopt a controversial fee that hurts efficiency and diminishes long-range cost savings -- even for themselves.

Mandatory fixed fees on utility bills force consumers to pay up no matter how much, or how little, electricity they use. Utilities are increasingly pushing higher fees, skewing rate plans to erode benefits for customers with rooftop solar that offsets power demand and eases strain on the grid.

Solar and conservation advocates call it a knee-jerk response from utilities facing upheaval in a fast-evolving marketplace. As rooftop arrays become more accessible, traditional power providers have showcased a toolbox filled with tactics for curbing the viability of solar -- including by piling on costs.