By Tyson Cook, Staff Scientist

For those of us looking forward to a day when we’re less reliant on dirty, fossil fuel-based power plants, it’s important to know the role they serve in the electricity system, and just what we have to do to replace them. One argument that is starting to be used against renewable energy revolves around that very idea: The claim that renewables may not be able to provide the “baseload” power like large fossil-fuel plants.

Which begs the question, what is this “baseload” power, and why does it matter?

The first thing to realize is that so-called “baseload” is not actually a different kind of power; it’s simply part of an engineering concept to visualize electrical demand. Imagine a line graph of the amount of total electricity used in a region over time. The plot would look like a series of waves, with peaks in the afternoon and early evening when everything is running on high, and dips at night and on the weekends when people are sleeping and offices are closed.

You could divide the line graph a lot of ways, but the idea of “baseload” comes from drawing a horizontal line to represent the minimum amount of electricity that is being used, no matter what time or day. The areas above that line are then labeled “intermediate” and “peak” loads. Kind of like this:

From Understanding Base Load Power, October 2008, New York Affordable Reliable Electricity Alliance

In this way of thinking, the “baseload” power demand is met with big generators like old coal and nuclear plants that don’t turn on and off very well. To accommodate electrical needs above the “baseload,” smaller, more responsive plants are used that can more easily follow the demand. Makes sense, right?

The problem with this idea is that it’s not how the electrical grid actually works. In reality, the grid isn’t one uniform pool of power demand, but a huge, sprawling, interconnected web of transmission lines of various sizes and capacities, dotted with producers and users of power. More like this:

From Atlanta Journal-Constitution

The whole thing is controlled by an “independent system operator,” whose job is to make sure the system works right and everyone gets the power they need as cheaply and reliably as possible. This means constantly turning production up and down at various plants and using various mechanisms to manage flow.

So the idea of “baseload” power? Yes, there is always some minimum level of power being used in a particular region of the grid, but it’s certainly not as simple as that old line graph would indicate. And when trying to meet electrical demand, the power can come from any number of facilities at any time of day. For the system operator, the solution to which plants should be running when (and how much) is clear: Whatever makes electricity cheapest at any given time, considering the constraints of the grid. If that happens to be a large coal plant, so be it. If it’s a wind farm or small solar installation, that’s just as good. Even better.