Less carbon means more flexibility

Costs have been falling and, not coincidentally, capacity has been rising. Indeed, around the world, renewables accounted for almost half of additional generation in 2017. In the United States, renewables (including hydropower, which is a little less than half of the total, but not growing) accounted for about 17 percent of all electricity generation, and most new capacity; in the European Union, it is more than 30 percent of generation, two-thirds of it non-hydro; worldwide, it is 25 percent, a record high.

And given both economic and regulatory momentum, these figures are not likely to represent peaks.

For the utility industry, these trends are something short of a blessing. When wind and solar hit critical mass, problems can emerge for the grid.

The issues will vary from place to place, depending on what kind of renewables are being used, the availability of transmission and distribution (T&D) capacity, the fleet of nonrenewable generating stations, and the shape of electricity demand. In California, for example, renewables are regularly dispatched at zero or even negative variable cost, a phenomenon that can stress equipment—and that is surely not a sustainable business model.