The graph below shows typical hourly and daily US electricity demand fluctuation for a typical week earlier this year. Pity the poor power grid managers who have to meet these ever-changing needs with today’s combination of electricity generation technologies.
Power demand fluctuates according to weather and season, of course, but the more immediate challenge is the hour by hour variation as people sleep, rise, go to work, come home, and operate different kinds of electric devices (stoves, air conditioners, tools, machines, etc). Add in loads like air conditioning, heating, or EV-charging needs and you have a complicated, ever-changing problem for grid operators to solve.
On the supply side of the equation, operators have to work with inherent limitations of different kinds of electricity generation technologies. It takes a long time to ramp up or ramp down a nuclear or coal-fired plant, so while they may be efficient and effective when carrying a steady base load (or demand), neither provides practical answers to dynamic loads. Gas-fired power plants, hydroelectric plants (and possibly geothermal plants) can be designed and operated to meet changing power needs in a matter of minutes, but only if gas is readily available and if the hydro projects are not hamstrung by prolonged drought. And of course solar panels and wind turbines can provide steady power, but only when sun shines and wind blows. Add it all together, and gas and hydro make up the bulk of the demand-driven power generation, simply because they can be turned on and off relatively quickly and as needed.
Looking beyond power plants, the article mentions three additional options for managing the dynamic nature of power needs: energy storage, demand management, and additional transmission lines.
Energy storage technologies are a natural complement to intermittent power sources like solar panels or wind turbines, but large-scale storage projects (e.g., hydroelectric pumped storage, compressed air energy storage, or large-scale battery installations) have not yet solved the grid management challenges. There are only so many available sites that are both acceptable and suitable for pumped storage or compressed air energy storage, even if the technology efficiencies are up to the job. Battery technologies are attractive, particularly for a dispersed or distributed system for energy storage (think of putting a battery in every garage or basement, perhaps next to the water heater). However, a full life-cycle accounting reveals downsides that include scarce materials; energy-intensive processing and manufacturing; sketchy geopolitics of who owns which resource; and sometimes even child labor for mineral extraction.
Demand management can provide some relief if electricity uses are flexible enough to take advantage of excess power when it is available. However, some power grid loads are driven by need (e.g., lighting at night, air conditioning when the weather is hot, etc) and are not easily shifted to level out the peaks and valleys on the power demand chart. That leave us with the idea of building additional transmission lines to move electricity from where surplus generation capacity is available to where it is needed. However, this might involve moving power from one region of the country to another, rather than just from one county to another, so transmission losses start to become a more significant factor. Not to mention public resistance (pardon the pun) to constructing new transmission lines.
All of this is meant as a short primer on some of the challenges facing our electric utilities or, to the extent government takes over various parts of the utilities, the challenges facing our government agencies. When we hear about energy-related issues in the news, see them at the ballot box, or experience them with blackouts and brownouts, this will help us understand the issues a little better.
2 thoughts on “Power Grid Dynamics”
Back when I had a reason to occasionally stop by the control room at Rocky Reach Dam, one of my favorite things to stare at was a strip chart recorder that graphed load-following information. The recorder continuously drew two curves: demand from the grid, and output to the grid. Both were constantly changing, with demand leading by a few seconds and output following closely. Most generation methods do not lend themselves to this sort of rapid adjustment, but hydroelectric generation does it very well.
One time I was in the HQ office suite for Georgia Power. It was a hot summer day, and they had a set of displays showing power demand across their grid, the status of interconnects with Alabama Power, Florida Power & Light, Tennessee Valley Authority, and other adjacent power companies. The displays also included the status and output of all of their generating plants, including hydro, coal, and nuclear. Everything was maxed out, trying to keep up with demand, and they had a number of gas-fired turbines coming on line to try to stay ahead of the peak demand for the day. This scenario played out day after day, unseen by the public.