A Guest Post by Islandboy


The EIA released the latest edition of their Electric Power Monthly on January 24th, with data for November 2017. The table above shows the percentage contribution of the main fuel sources to two decimal places for the last two months and the year 2017 to date.

Nuclear generated 623 Gwh (0.9%) more than it did in October but, the decrease in the total generation meant it’s percentage contribution increased by a little over 1% to 21.71% from 20.66% in October. With the winter solstice approaching the absolute contribution from Solar plunged by about 32% from 6810 to 4651 GWh, with the corresponding percentage contribution decreasing to 1.52% from 2.13% in October. The percentage contribution from solar has again gone below 2% as it was in January and February. With the year to date percentage contribution now being exactly 2% Solar should end the year with a contribution of slightly less than 2%. The gap between the contribution from All Renewables and Nuclear widened slightly as the 0.53% increased contribution from All Renewables was less than the 1.05% increase in the contribution from Nuclear. The amount of electricity generated by Wind decreased by about 6%, (1469 GWh) resulting in the percentage contribution decreasing very slightly by 0.16%. The contribution from Hydro increased 2633 Gwh (15%) in absolute terms with the decrease in total generation resulting in the percentage contribution increasing by 1.08%. The combined contribution from Wind and Solar decreased to 9.12% from 9.89% in October and the contribution from Non-Hydro Renewables also decreased to 10.76% from 11.3%. The contribution of zero emission and carbon neutral sources, that is, nuclear, hydro, wind, solar, geothermal, landfill gas and other biomass increased to 38.94% from 37.34% in October.

The graph below helps to illustrate how the changes in absolute production affect the percentage contribution from the various sources.


The graph below shows the total monthly generation at utility scale facilities by year versus the contribution from solar. The left hand scale is for the total generation, while the right hand scale is for solar output and has been deliberately set to exaggerate the solar output as a means of assessing it’s potential to make a meaningful contribution to the midsummer peak. In November 2017 the output from solar continued to decline heading into the winter solstice.


On January 16th an article was posted on the PV Magazine web site written by Christian Roselund that picks up on the point I have been trying to illustrate with the above graph, He wrote:

“July and August are the hottest months of the year, and as such electricity demand, driven by widespread use of air conditioning, peaks during these months. This means that the output of renewable energy in the United States is following a seasonal pattern that is mismatched with demand. Additionally summer peak demand, which could be served by solar, is in many regions largely being met with costly power from “peaker” gas plants and imports of electricity.”

In 2017 the peak monthly output for solar was estimated at 8796 Gwh in June with output for July and August closer to 8,000 Gwh. The difference in the total amount generated at utility scale facilities between the months of April and July was roughly 106,000 Gwh. If solar output were to double over the next couple of years the mid summer output would climb to somewhere in the region of 17,500 Gwh and a further doubling would take it roughly 35,000 Gwh. This would translate to solar output satisfying roughly 35% of the increase in demand over the summer months as opposed to roughly 7.5% for 2017. One more doubling would take the figure close to 70%. With the doubling time for solar currently standing at roughly two years, it is not hard to imagine solar shouldering most of the additional mid summer demand by 2025.

The graph below shows the monthly capacity additions for 2017 to date. In November only 4.7 percent of capacity additions were Natural Gas. Solar added 33.8 percent and and Wind contributed 61.3 percent of new capacity. Batteries had relatively minor capacity addition of 0.13 percent. In November the total capacity added was 1571.2 MW, marginally more than the amounts added in each of the first three months of 2017 but, less than the amounts added in April Jun and July.


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