By late in 2019, the combined electricity produced by grid-connected wind and solar photovoltaics represented 10% of the total production. And the share of these intermittent but sustainable energy sources continues to grow. Energy production from coal is in free fall, despite the current administration’s attempts to favor it.
A constant refrain from detractors is intermittent sources such as wind and solar require expensive backup when the wind isn’t blowing or the sun isn’t shining, and therefore can’t be a serious part our electricity production until such batteries or other energy storage systems are available. That however is just not the case. It is estimated that a national network of electricity production and distribution can utilize up to about 30% wind and solar without the need for additional storage to back up the intermittency.
Consider what happens when one of our local nuclear reactors goes down to refuel. Is there another reactor on stand by to make up for the power not produced during the refueling? No, of course not, there is plenty of “slack” in the system to make up for that not produced during the refueling.
Other factors help balance the power from wind and solar. Solar is well matched to demand. Demand is higher during the day when solar panels are producing, and lower at night when the power from solar panels isn’t needed. Without the input from solar panels, a power company may have to buy power from sources that are on standby. Some power companies utilize time-of-day pricing, charging less at night when power is relatively abundant, and more during the day when demand is higher.
Wind and solar also balance each other seasonally. As sunlight passes through the atmosphere light is scattered and less reaches the earth. The lower the sun angle the more atmosphere it must pass through. Solar panels are more productive in the summer due to the the higher sun angle. A higher sun angle means less scattering of the light and more sunlight striking the panels.
Conversely, wind turbines are more productive in the winter. There are two reasons. Wind is generated by temperature differences between locales and the differences are greater in the winter, hence higher wind speeds. Additionally, colder air is denser. More power will be generated by the denser air at a given wind speed.
One final balance is that the sun shines during the day (duh) so solar power is available during the day, but wind speeds are greater at night. Wind and solar are both intermittent but complementary, both daily and seasonally.
As intermittent energy sources grow there will be a need in the future for energy storage and that constitutes a huge area of research. Electrochemical batteries, pumped water storage, other gravitational energy storage systems, compressed air, flywheels, and on and on. The future will be powered by the wind and the sun, cleanly without the need for fuel, and without waste disposal issues.
Dr. Bob Allen is Emeritus Professor of Chemistry, Arkansas Tech University.