Sarah Kurtz

Professor, UC Merced School of Engineering

How can renewable electricity be a negligible contributor of electricity, but, at the same time, have grown so big, it’s difficult for further growth?

Generation of renewable electricity is relatively expanding rapidly but is still small as shown by the logarithmic graph.

Plot of world electric generation by year

The deployment of capacity to generate electricity is similarly represented below.

Plot of world electric generation capacity by year

While renewable electricity is still a small fraction of electricity generation, it is now more than half of the net expansions in electricity generating capacity each year as shown by this animation.

We have entered a new era in which the growth of renewables must either slow or we must increase electrification to replace use of fossil fuels for transportation and industrial uses and create demand for installation of more renewable electricity generation. The graph below shows simplistically how extrapolation of recent trends results in solar growing to equal the total capacity in just a few years.

Plot demonstrating that the world's solar capacity will intersect the world's total electricity capacity by the mid 2020's if both maintain their current growth rate

In September 2018, California set targets for 50%-60% renewable electricity in 2026 and 2030, respectively as shown schematically here:

Plot showing California electricity generation with targets from 2010 to 2030

California also set a 100% zero-carbon electricity target for 2045 as shown schematically here:

Plot showing California zero carbon electricity targets

Some plants generate electricity most of the time. Other plants are only turned on when the demand becomes very high. The capacity factor is defined as the fraction of electricity generated relative to what would have been generated if the plant runs at rated power 100% of the time. The trends for the capacity factor for different technologies is shown in the next graph.

Plot showing capacity factor for various generation technologies since 1980.  Capacity factor for most technologies is relatively stable over time, with fossil fuels, hydro, biomass and the overall total being 40-60%.  Nuclear and geothermal have higher capacity factors, while wind, solar, and tidal have lower capacity factors.