Demand-side flexibility: helping solve solar’s curtailment conundrum


By Peter Bronski, WattTime

For renewable energy—solar PV included—there’s often the question of how to handle surplus generation. What do we do when the wind is blowing and the sun is shining, but there’s not enough grid demand to absorb that generation? How do we manage what the California ISO innocuously calls “oversupply”?

The answer that none of us wants to hear is curtailment. To co-opt a popular phrase, “renewable energy is a terrible thing to waste.” Yet that’s exactly what happens when we curtail perfectly good clean energy, as pv magazine covered regarding California earlier this year.

The grid can handle more solar, if only we enable it to do so.


Diverse approaches to mitigating renewable curtailment

Different markets and different technologies have explored diverse approaches to solving renewable energy’s curtailment problem. For example:

  • Green Dispatch: In China, grid operators have experimented with “green dispatch” (also sometimes referred to as “priority dispatch”) to ensure that renewably generated electricity is fully used before calling upon other traditional fossil-fueled generators.
  • Balancing Interconnections: In regions such as Europe, the continent’s interconnected grid and electricity markets have enabled the “sharing” of surplus renewables across borders, such as when a country like Denmark exports surplus wind to its neighbors. California and neighboring states have been recently exploring a more inter-connected and coordinated electricity market toward similar ends in the Western United States.
  • Energy Storage: As energy storage gets ever more economic, it becomes a viable option for storing surplus solar-generated electricity for later use. From behind-the-meter system to utility-scale solar-plus-storage, this is arguably the biggest disruption since stand-alone solar and wind hit price points competitive with new fossil-fueled generation.
  • Demand Flexibility: Even as energy storage costs—especially for lithium-ion batteries—have come down, it remains a relatively expensive option vs. cheaper alternatives that achieve similar ends. Here is where demand flexibility shines. By shifting flexible demand, the grid can use more renewably generated electricity rather than letting it go to waste. In short, flexibility can cost-effectively allow for more solar on the grid.


From solar load following to absorbing solar surplus

When it comes to demand flexibility and “pulling” more demand under the solar production curve, there’s now a new—and arguably better—frontier for the solar industry to embrace. Absorbing more solar production is now less about simply moving flexible demand to coincide with peak solar production, and much more about shifting demand to times when solar production is on the margin, and thus at risk of being curtailed because of insufficient demand.

This nuanced but incredibly important shift requires a new kind of intelligence in the electricity grid, and more specifically, a software-based signal that can detect the variations in which type of generation is on the margin in five-minute intervals. Smart devices can then use this signal to shift the timing of flexible electricity loads that they control.

At WattTime, we call this Automated Emissions Reduction (AER), since a primary use case for the capability is to sync electricity use with times of cleaner energy and avoid times of dirtier energy. At its core, AER-enabled smart devices—and by extension, the flexible demand they control—can sync their energy use with times when surplus solar is on the margin and at risk of curtailment.


Expanding the solar market through demand flexibility

With flexible demand, solar curtailment no longer needs to be seen as a necessary evil of building more and more solar generation. At least some solar curtailment—and arguably a lot of solar curtailment—can be avoided.

Likewise, net negative grid demand and reverse backflows on grid distribution feeder circuits because of excessive Duck Curve effects can be mitigated, not merely by shifting more demand into the belly of the duck, but also by more subtly shifting demand to those times when solar could be curtailed.

Even further, for existing solar projects, flexibility enhances their economics, since a project’s fixed capital costs can supply more kWh of electricity to the grid. And for new projects, demand flexibility can allow even more renewables to be developed and integrated into the grid, while better sustaining their value and reducing their risk of curtailment.

Perhaps most importantly, the real-time visibility AER offers helps to take curtailment out from behind the curtain and bring it into broad daylight. Once we’ve done that, we can truly start to address curtailment, rather than hoping and guessing for how to use the diverse solar—utility-scale, community, behind-the-meter—that the grid has to offer. And when outlets such as Greentech Media ponder if solar PV can be “too much of a good thing” and curtailment a foregone conclusion, we can confidently answer: “Not yet. Not even close.”


Peter Bronski ( leads marketing and communications for WattTime. He is also director of marketing and communications for the Energy Web Foundation and founder of Inflection Point Agency, a boutique marcom firm that works with cleantech clients.

The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.

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