Energize Weekly, October 17, 2018
Wind and solar electric generation make up an average of only 8 percent of U.S. power supplies, but in 10 states these renewable resources provided 20 percent or more of the electricity supply in 2017, according to Federal Energy Information Administration (EIA) data.
This group is led by Iowa and Kansas where wind generation respectively made up 37 percent and 36 percent of electricity supplies. Iowa also had a small solar component. In March 2017, renewable generation accounted for 52 percent of the electricity in Iowa.
In some months, solar made up 20 percent of the electricity supply in California. For the year, solar averaged 15.6 percent. Overall California got 22 percent of its electricity from wind and solar. In May 2017, California’s wind and solar share reached 28 percent of in-state electricity generation.
The top five states were all in the Midwest or Central Plains and were served by wind generation. The state with the sixth highest renewable energy output, Vermont, was almost evenly split between wind and solar generation. California, Nevada, Massachusetts and Arizona had higher solar generation than wind.
The states with 20 percent renewable electricity supplies in 2017 were:
- Iowa—37 percent
- Kansas—36 percent
- Oklahoma—32 percent
- South Dakota—30 percent
- North Dakota—27 percent
- Vermont—24 percent
- California—22 percent
- Maine—20 percent
- Colorado—20 percent
- Minnesota—20 percent
Increasing levels of renewable generation come with operating challenges because of the variability of the generating output, the EIA noted.
“Wind and solar resources are unique among sources of electricity,” the EIA said. “Unlike most other generating technologies, grid operators generally do not dispatch wind and solar generation because these generators produce electricity only when the associated resources are available. Even so, some wind and solar plants may allow for limited dispatcher control on a minute-to-minute basis.”
Grid operators are managing to more effectively use variable renewable energy generation by setting operating levels lower than achievable levels, leaving them the option of increasing output, the EIA said.
For example, by setting operating levels to slightly lower than achievable levels for current conditions, operators have some flexibility to increase or decrease output in response to market signals.
While natural gas-fired generation is flexible and dispatchable, other conventional sources, such as nuclear, have limited flexibility and cannot adjust quickly.
“Conventional hydroelectric generation can be either dispatchable or non-dispatchable,” the EIA said. “Hydroelectric facilities with reservoirs have some control over the dispatch of their electricity, and run of the river generation is non-dispatchable because it generates electricity as water passes through it. Hydro facilities can also have seasonal limits on dispatch based on available water resources.”
