What is baseload?
Baseload power is defined in multiple ways1 . In general though it refers to a class of power generating equipment that is used for meeting the general trend in power use by a population. This means that it fulfills a complementary role to that of ‘peaking’ power supply. Peaking power plants are turned on to match sudden spikes in electricity demand.
The characteristics that define baseload are that they generally have cheap cost per watt delivered and are nominally on all the time. That is, these plants are generally running if they are functional, but they are sometimes down due to maintenance, refueling, or repairs. Technically a wide variety of energy sources are capable of being part of meeting power demand of this type, but in common usage ‘baseload’ often refers to only coal, nuclear, certain types of natural gas, and sometimes hydroelectric power. This is not accurate because baseload generators can also be geothermal, solar thermal (with storage), and biomass to name a few.
We want reliable power
What people really want is reliable power. We don’t want to end up freezing in the dark. Electricity is important enough to our society that our energy security is of great importance to us. This is a fundamental issue that all technically advanced nations have to face.
It would be a mistake to equate baseload with reliable. Baseload power sources still have to turn off sometimes. The downtimes for the big thermal plants such as nuclear and coal are between 10% and 20% of their lifetimes, although these downtimes are generally planned well in advance. If our power grid were based off of only baseload sources of this type we might see rolling blackouts now and then unless we built extra power plants to cover the downtime.
Dispatchable sources are the key
Luckily this isn’t the way it works. When a baseload source has to go down, power utilities will ramp up other forms of generation capacity. Quite often these other sources are not baseload. They are dispatchable sources such as hydro, natural gas, and biomass. This is definitely the case when a baseload source goes down suddenly. Dispatchable sources are fired up as soon as possible to cover the source that is going down. Before the dispatchable sources can come online, the power utility may have to import power, signal industrial customers to reduce demand, or send sections of their grid into blackouts.
For an in-depth look at dispatchable power, see our article on how we can create dispatchable power from renewable energy sources.
Dispatchable sources are the systems that make reliable power possible. With enough dispatchable power, it is possible that you may need no baseload generation at all. For example, imagine a power grid that has to provide 100 MW of power constantly. If this grid can dispatch 110 MW of dammed hydroelectric power at one time, then it can in theory meet its needs with just its hydroelectricity. This is not necessarily the only constraint however, since there is not an infinite amount of water behind the hydro dams. Eventually the water might run out if you use only that for your power grid. To reduce the amount of water you use, other energy resources can be used. Wind power is such an energy resource. If you have 80MW of wind turbines, you might only need 20 MW from your hydro sources if the wind is blowing hard. If you had built more wind than you can use, such as 120 MW, then you can sell power to your neighbors when the wind is blowing hard, or you can try to store the energy using pumped hydro storage. If we don’t have this much available dammed hydroelectric power, we can use other dispatchable sources such as natural gas and biomass. The environmentalist in me would of course like to see us maximize our use of our hydro reserves before turning to the more expensive and carbon-intensive natural gas.
Baseload still needs backup
This was a simple example, but I believe it demonstrates a point. We can build a power grid without baseload sources. This is important because many of the renewable forms of generation are not baseload. Those people that are pushing for coal or nuclear often tout them as reliable when renewable energy sources are not. This is a statement deliberately designed to hide the truth. All forms of power require backup, and that backup has to be dispatchable so that we can get it when we need it. Power grids deliver different amounts of power at different times. They turn on dispatchable power to meet increases in demand as well as failures of other sources.