Joseph Daniel at the Union of Concerned Scientists explains why variable renewables like wind and solar are not forcing coal plants to cycle (ramp up and down). He presents data from the U.S. that clearly shows it’s straightforward variable demand that’s doing it, because demand has always varied considerably throughout the day. So stop blaming the arrival and growth of wind and solar for this “inefficiency”, he says. These renewables have plenty of growth left in them before they impact on coal’s cycling. But they will one day. That’s why the market should be re-shaped to accommodate and respond to that variability, and it should be tech-neutral to minimise system – not plant unit – costs. We need smart flexible demand and pricing to expose the real inefficiencies, says Daniel. He’s betting that coal will come out the loser as clean energy deployment has proven itself a driver of innovation and efficiency.
Integrating renewables into the current mix of resources sure does get a lot of attention these days. Sadly, the issue has been thrown up as an unnecessary barrier to the development of wind and solar. One of the most pervasive arguments I’ve heard suggests integrating variable resources (like wind and solar) is costly and sometimes physically impossible. But data recently analysed by UCS adds to the growing body of work that undercuts such arguments.
In this blog, we’ll explore why the premise of this argument is not only deeply flawed but its entire framing ignores the basic principles and intentions as to why states joined wholesale power pools in the first place. It is also worth noting that we do need flexible resources and that fossil fuels aren’t the best positioned to provide that flexibility.
Before we get into all that, I want to take a special moment to thank UCS Associate Analyst Ashtin Massie for her indispensable contributions to this analysis.
Integrating variable renewables is inefficient? A deeply flawed premise
Coal-fired power plants are ramping up and down over the course of the day, but some analysts seem content with presuming that wind and solar are the culprits to coal cycling.
The latest research from UCS looks at the Midcontinent Independent System Operator (MISO) which spans from North Dakota to Michigan and down to the Gulf states of Louisiana and Mississippi. There is a fair amount of wind in MISO, with more coming online every year.
The variability in output from wind is far less than the variability in demand, which in any given moment has to be met with the mix of resources available on the grid. This relationship has long pre-dated wind or solar adoption and will continue (at least until we are better able to store electricity at scale).
The below graphic represents the 24-hours of an “average” day in MISO in 2018 for each of the four seasons. The sum-total of all resources in a given hour reflects the electricity demand in that hour.
![](https://energypost.eu/wp-content/plugins/lazy-load/images/1x1.trans.gif)
Credit: Ashtin Massie. Processed using data made available by S&P Global Market Intelligence
In MISO, on an average summer day, coal-fired and gas-fired power plants ramp up and down over the course of the day in fairly substantial ways. The data confirms that coal-fired power plants’ output cycles over the course of the day.
However, a close examination of the data shows it’s not in response to wind.
Coal cycling follows everyday load, not wind’s shortfall/oversupply
Coal (and gas) aren’t cycling to follow the output of wind; they are cycling to follow load!
The variance in coal (or gas) output over the course of the day far exceeds that of wind, which wouldn’t be the case if coal was only cycling to back up the variability of wind power. The coal and gas output cycle corresponds to large swings in demand. In the summer, that comes from the air conditioning load to keep homes, office buildings, and industrial facilities cool. In the future, that demand could very easily be met with solar.
In MISO today, coal is no longer a baseload resource and it is this economic reality that is driving many changes in coal plant operations. Demand drives prices, and when coal plants do end up cycling, it is out of response to those price signals.
In the future, flexible demand will also be able to respond to price and will work in concert with renewables and storage to meet our reliability needs.
Right now, growing variable power isn’t a problem. But it will be
The data show that at least for grids with wind adoption at the levels MISO is presently seeing, wind integration really isn’t a problem for coal-plant operators. But both wind and solar adoption are on the rise. Nearly 90% of new capacity in MISO is going to be from wind, solar, or storage. It isn’t impossible to imagine a future where wind integration might create challenges someday.
Minimise system costs, not individual costs
Yet some already assert that integrating renewables has become an “inefficiency.” Such an assertion only appears valid if you look at this issue from the glasses of the plant manager. Not even the lenses of the utility or system operator would produce such a myopic vision.
What the grid operators are supposed to optimise around is the lowest system costs, not the lowest unit costs. And sometimes unit cost minimisation doesn’t result in system cost minimisation.
There is a fundamental problem with framing wind integration as a “cost” or “inefficiency.” When the owner of a unit won’t shut it down (out of a desire to avoid shut down costs) the system is deprived of lower cost, more efficient resources. What UCS, Sierra Club, and many others have shown: turning down or off coal-fired power plants actually lower costs and increasing efficiency.
For example, an NREL study found that increased wind adoption in the west might increases costs at some individual power plants but that for every $1 in ‘integration costs’ there would be $45-$200 of system benefits.
Arguably the introduction of new resources has allowed coal plant operators to go long periods of time without relying on coal. See this glorious visual from a guest blog by one of our Stanford fellows last summer.
![](https://energypost.eu/wp-content/plugins/lazy-load/images/1x1.trans.gif)
Each row corresponds to a year and each stripe within that row corresponds to a day. Pure black indicates the maximum [coal] during these years (in ISO-NE’s case, about 21% of that day’s generation coming from coal). Lower percentages are linearly scaled to some shade of gray. Indigo indicates days with zero coal generation within ISO-NE. / Credit: Emma Spellman, Union of Concerned Scientists
Need for market rules that are flexible, fuel neutral
At the end of the day, we do need an electric grid that is flexible. Demand for electricity is not constant and so we need a grid that is nimble enough to meet those needs. Competitive markets, that often dictate the economics of our grid, might very well need market products for flexibility, but those market rules should be available on an equal basis to all resources and not set up the way capacity markets were set up that resulted in fairly substantial biases.
If a competitive market was developed for a flexibility product, and it was done agnostically, coal isn’t going to be able to offer that service at a lower cost than other resources. Wind, solar, storage, flexible demand, and gas will all beat out coal.
More clean energy deployment has always driven change, innovation
Trying to solve a problem before it gets out of hand is admirable but manufacturing a problem out of fear of the unknown, not so much. Simply put: the current rhetoric of renewables scapegoating is unjustified. We’ve been ramping up on renewables for some time now and every year we seem to learn new ways to cost-effectively integrate higher levels of wind and solar. Deployment of clean energy technologies has led to innovation which has led to more deployment and then more innovation. I’m skeptical that the virtuous cycle is suddenly going to stop.
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Joseph Daniel is a senior energy analyst with the Climate & Energy program at the Union of Concerned Scientists
This article is published with permission
It does not seem wise for me to take general conclusions from a particular example. In fact, the electrical systems have to be in perfect balance between power production and load and we have three solutions: to adapt the demand side to production (we shall promote demand flexibility, but we need to recognise this is a limited contribution from ordinary loads); to change economically the aggregated power generation to match the load (this is the traditional and flexible way); doing both (demand side management will have a larger role in the future due to investments in storage – this a controllable during charging and a controllable power source during discharging). So, variable renewables are not controllable and do not add flexibility to the system. In contrary, they are a new burden to firm and flexible capacity, where thermal plants are included. The resulting lower usage of fossil thermal plants (the objective of renewable investments) makes difficult to recover their fixed costs, being the European systems a good example of this.
Of course, with a low penetration of variable renewables the back up (when there is no wind or no sun) and additional ancillary services they impose to the system do not represent a major impact, regarding load profile and its uncertainty. This is not the case in systems with a high share of renewables, where even other problems are arising (as is the case of insufficient inertia in Ireland and UK systems and the risk arising from the unbalance between power and load, with very fast frequency change and consequent automatic load shedding).
It is necessary to design fair market solutions to promote the environment and the overall system economic optimisation (and not each technology) and the respect of a low system loss of load probability. But power generation investment has been managed using an administrative solution for wind and PV facilities (PTC in USA and subsidies in UE) and a competitive market for traditional power plants, which makes unfair the comparison with the coal power plants. Thinking in a system CO2 neutral, the dream of battery storage has new costs and only solves the daily cycle problem (for example, to transfer daily PV excess energy to be used during the night period). For coping with longer period mismatches (for instance, transfer PV excess energy from summer to winter): or it is better to limit variable renewable penetration (avoiding energy in excess, with the creation of negative spot prices in Europe…) and using nuclear power (to give room for an economic load share); or it is necessary to subsidise hydrogen production (easier to store in large amounts) and new thermal plants using “power to X” solutions! In reality, present thermal producers are paying a cost arising from the lack of coordination between the market and administrative solutions.