Baseload is a myth
There are only loads and generators
One of the recurring meme’s in electricity is ‘baseload’, the idea that there is a consistent minimum level of load that should be matched up against big generation plants to maximize efficiency.
This idea is archaic, once rooted in fact but now obsolete. Its persistence skews otherwise productive conversations about the future of energy, and we need to retire the term like the coal plants that originally powered it.
But let’s back up, where does the term come from?
It originates from two things: the minimum amount of load (energy) that is always needed on the grid, and the operating characteristics of traditional thermal power plants (like those run on coal).
First, it is true that there is a stable level of load that is basically always needed for a given region.
In the chart below, the green line shows the number of hours where a given load was needed in California. There are effectively no hours below ~18 gigawatts—the baseload level in red. At least this much load was needed during every hour of the entire year.
This part is still true, a meaningful amount of load is always required somewhere on the grid.
The gap in understanding comes with the second factor: belief that it is inherently more efficient to match this load with big thermal generation.
This comes from a historical contingency, where large stable loads matched very well with traditional coal-fired and nuclear power plants. These burn coal (or fission) to heat water, creating steam that then drives a turbine to generate electricity.
In both cases, getting the water up to temperature can take hours, and these plants do not handle fluctuations in demand well. They are much more efficient running steadily at a given rate. But, when operated at that steady rate, these large plants were historically some of the most cost effective available.
As a result, in most places a layered system of generators was built with large, slow-but-efficient coal and nuclear plants designed to serve the ‘baseload’ that would always be required. On top of this, faster-but-more-expensive gas, oil, and hydroelectric generators were layered.
Thus, baseload became a design shorthand within the power system, born from the economic and operating characteristics of specific generation technologies.
But that set of characteristics no longer holds.
For one, we are well on our way to phasing out coal:
In the US, this has been an economic story more than anything else: natural gas has been world-historically cheap for the last 20 years. It has become cheaper to build and run a new combined cycle gas plant (CCGT) than continue to operate an existing coal plant. Power generation has shifted accordingly.
Big coal-fired and nuclear plants are no longer the lowest cost power, requiring a stable base to operate effectively.
Modern generation technologies are also much better at ramping to match fluctuations in load.
Combined cycle gas plants can achieve partial output quickly based on simple combustion of gas, even if they still heat water to reach their full output. Nuclear reactors have also gotten better at safely following fluctuations in load. Batteries are quickly proliferating as responsive tools for managing fluctuations on the grid.
This has significantly reduced the efficiency penalty from ramping up and down in non-coal generators.
So why are we still talking about baseload?
This myth has persisted because it is satisfying.
A certain type of person will look at the distribution of load above, and think:
There is always 18 gigawatts of load, it just feels most efficient to match that with a big set of generators that run all the time.
Wouldn’t it be so much simpler and aesthetically pleasing, if we kept this layered system of load-following and peaker plants to handle loads above 18 GW?
We can design it with certainty, and be confident the generation will be there when we need it. We could even match up big zero-carbon nuclear with this base load!
But you have to actually check the relative costs, and aiming for lowest cost overall increasingly leads to a messier mix of resources.
Say you have a single 100 megawatt (MW) combined cycle gas turbine plant that serves a constant 100 MW of load (e.g., a datacenter training a model to write non-rhyming poetry).
The gas plant has fixed costs of ~$150,000 per megawatt-year (e.g., capital costs, financing, overhead), and variable costs of ~$35 per megawatt-hour (e.g., fuel, maintenance).
If the plant runs at full capacity for the whole year, it would accrue total cost of ~$45.6M. Spreading this across the 876,000 MWh of energy produced, and we get an effective cost of $52.12 per MWh.
Now, say that we look into adding a 100MW solar plant into the mix. The solar plant produces ~100MW for 6 hours each day at a levelized cost of ~$20 per MWh.
The result looks like this:
Interestingly, the average cost for energy from the gas plant goes up from ~$52 to ~$57 per MWh, even as the overall cost goes down to ~$49.
This occurs mechanically because we are spreading the fixed costs over fewer megawatt-hours. This is something people seem to point at as ‘renewables undermining baseload’ resources, but the overall cost is lower and the gas plant still gets paid enough to operate. The solar plant should be built, even as it intrudes on stable ‘baseload’.
This leads to a broader point: If the levelized cost of a new generator is below the marginal cost of the existing generators, adding it to the system can lower average costs. This holds even if the headline cost of the existing generation goes up.
As a result, with new cheap generation technologies like solar, baseload is no longer a useful frame. In sunny regions, solar can be cheaper than the marginal costs of even low cost gas plants. The same holds of wind farms in places like west Texas.
To be sure, this won’t be the case everywhere, and there will be an important role for gas, nuclear, and geothermal generation as we seek to decarbonize. But it will be because those are less expensive in specific regions, not because there is some slug of baseload that needs to be served.
Instead of the layered metaphor of baseload, we need to think about a tapestry of generators that weaves in and out throughout days and seasons. This will not be deterministic–solar and wind cannot be ramped up at will–but a probabilistic tapestry.
The system will appear messy, with more volatility in pricing and more complexity in long-term resource planning, but the end result is lower cost, more abundant energy for everyone.
Clinging to the myth of baseload will not help us get there.
Further reading:
Brattle Group - Advancing Past “Baseload” to a Flexible Grid
CleanTechnica - Elon Musk Harpooned Baseload Power
Been really enjoying your writing. Keep it going!