Yes, the electric industry is excited about the solar eclipse as well!

One might assume that electric industry would be concerned about the effect of solar eclipse on the electric grid, after all, if the sunlight is blocked for a period of time, then the solar PV systems would not be able to generate any electricity, and thus adversely impact our grid. The logic is correct; however, consider a question- the sun does not shine at night, and the electric grid seems to be doing fine every night!

Balancing supply and demand

The fundamental principle underlying today’s electricity system is that the electricity that is consumed must be matched with the electricity that is generated at that very instant. When a lamp switch is turned on, the power station in that grid must generate the exact amount of energy required to power the lamp, and decrease generation by the same amount when the light is turned off. Essentially, at current economics, there is very minimum storage of electricity to draw from. All electricity demand must be met by generating electricity at that very instant. The electric utilities, balancing authorities, and system operator performs this job of balancing the demand and supply of electricity. The balance of the system measured in the frequency of the power supply is monitored very closely with a high degree of precision and accuracy.

Although the act of balancing each unit of energy consumed with each unit of energy supplied seems like an impossible challenge, grid operators are proficient at doing so. While energy from the solar output is will drastically decrease during the eclipse, the grid operators have a number of tools in both supply and demand side to help them prepare for the event. 

Managing supply side

Certainty: Unlike traditional power plants whose output can be precisely controlled by the grid operators, renewable energy sources like solar and wind are intermittent and the power output is dependent on the availability of resources. Most grid operators use sophisticated grid models to forecast what the renewable energy looks like which helps grid operations to plan ahead. In this case of an eclipse, the grid operators know with a high degree of certainty at what time and how much of the output will be disrupted due to the eclipse. Because of this high degree of certainty, the grid operators can plan well ahead in time to make sure that other power plants are turned on to meet the demand while the power from the solar systems are curtailed.

Redundancy: Electric power systems are designed with adequate redundancy so if any critical component fails, there is a backup available immediately. In terms of power capacity, the power plants are built and available to generate 10%-20% more than the peak demand of the system. Even if the power from the solar PV is reduced, there are power plants that can turn on and deliver the required power. Electric power markets have defined market rules to price and deliver energy and capacity during normal and critical moments.

Negligible portion: Our electricity comes from diverse sources. In 2016 electricity from the solar PV constituted less than 1% of the total electricity consumed in the U.S. The energy mix varies by utility, state, and balancing authority, but even in North Carolina- ranked second among states with the total solar PV capacity installed- solar PV accounts for about 1% of the total electricity delivered. Since solar PV total only contributes such a minimal amount of the energy delivered into the system, any impact due to eclipse is not going to have a tremendous impact on the grid.

Demand management: In addition to managing the supply of electricity during the eclipse, the grid operators also have the option to control the electric demand during the period of the eclipse, which should help with balancing. Commercial and industrial sector uses the bulk of the electricity generated at any given moment. Unlike the residential sector where the electricity rate is static, the electric rates for large industrial and commercial customers are more dynamic and most are enrolled in demand response programs that provides financial incentives to curtail energy use during periods of stress in the electric grid. The grid operators can call upon the large industrial and commercial users to reduce their load during the period of eclipse to help balance the energy shortfall from solar PV.

Figure 1: Solar PV array output the eclipse. Green shade provides the total energy generated by the solar array. The blue line provides the sun's irradiance, and yellow line follows the ambient temperature. Image courtesy FREEDM Center at NC State University. 

Still a not a easy task: Back to the earlier question- although the electric grid does run smoothly run at night when there is no sun, the eclipse does pose certain challenges. The grid operators may not have idea when a particular individual is going to turn on their light, but they have a really good sense of habits and seasonality of electric demand on aggregate. The grid operators are fairly adept at managing the predictable load profile. The solar eclipse will provide different circumstance when all of the solar PV output from the system will turn off in a short period during the eclipse, and all of them will come back up on after the eclipse. This sharp changes are challenging to balance. The grid operators will have to ramp up their generators during the eclipse, and rapidly ramp down after the eclipses. With certain exceptions, most electric power generators, usually not designed to ramp up and down at such short intervals.

The balancing of the grid during the eclipse will depend on how the grid operators are able to use their supply and demand tools to hand the sharp drop in solar PV production during eclipse, and rapidly increased production after the eclipse.

Reasons for excitement for electric industry

Although the energy from solar is currently at low significant levels, the electric industry and the solar industry are both excited about this event. There are two certainties – i) in the long term solar energy will constitute a much larger portion of the energy mix, and ii) there will be another eclipse, or other abnormal events that require a similar balancing of the grid. This Great American Eclipse will provide a rare opportunity to grid operators to prepare and test their grid balancing measures. There might valuable lessons to learn from this experience which can help prepare for similar conditions in the future.