Power curtailment is often viewed as a limiting factor of renewable energy, as intermittent cycles of generation can lead to excess electricity on the grid during peak production. Curtailment is the deliberate reduction in output that otherwise could have been produced, and typically occurs when supply exceeds demand.
The California Independent System Operator (CAISO) curtailed 1.5 million MWh of utility-scale solar in 2020, representing 5% of total production, according to the Energy Information Administration (EIA). Solar is by far the most dominant source of energy that undergoes curtailment in the state. EIA said 94% of power curtailments in 2020 involved solar energy.
While curtailment is often viewed as a bad thing, the National Renewable Energy Laboratory (NREL) said based on its research and modeling of the grid of the future, it may be time to reframe our thinking about power curtailment.
“(Curtailment) can happen not just in cases of oversupply but also when there’s a lack of system flexibility, which could mean congested transmission lines, other power plants being unable to reduce their output safely or economically, or other constraints,” said Kerrin Jeromin, NREL correspondent in a video on the subject.
“Think about it like buying a cable package for your TV—or a subscription to any of the streaming services out there. Buying that package knowing you can’t possibly watch all of the thousands of programs available to you isn’t all that different from building more renewable power plants, knowing we won’t always be able to use all the energy they produce. The point is, you have it for the shows you can’t miss, and the package gets you the best value in the end. We’re going to need a lot of wind and solar in a super-high-renewable future. And the best strategy might be to max out our renewable energy “package,” so we have enough power when we really need it, and get comfortable with curtailing some of it sometimes, to maximize its value at other moments.” National Renewable Energy Laboratory
Power curtailment is nothing new, as the grid has always had more power plants than are used. It is essential to reserve backup power for times of peak demand to keep the lights on. Currently, solar energy is serving that role in Texas, where fossil fuels are struggling to meet demand during summer heat peaks.
Curtailment comes with a particularly negative connotation because it represents lost opportunity. But as the cost of grid-scale renewables continues to decline, so does the cost of that lost opportunity.
“Curtailed electricity can be used to help make the grid more flexible and reliable, making these solar and wind systems more valuable in the end. It’s happening today: Xcel Energy can actively curtail wind generation to support reliability in its US power systems. And First Solar’s large-scale PV plant in Chile uses curtailment as a tool to help the grid respond to changing system needs, letting grid operators turn the system’s output up and down as needed,” said Jeromin.
NREL concluded that creating regulations that discourage curtailment could create barriers for renewable energy buildout, thereby limiting the many benefits it can offer.
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This is a great article. While the CPUC says that curtailment losses must be passed onto rooftop solar customers as fees or taxes on the Sun, this article says that “The California Independent System Operator (CAISO) curtailed 1.5 million MWh of utility-scale solar in 2020, representing 5% of total production, according to the Energy Information Administration”.
I have two 8,000-watt solar systems on my home. One going to the grid or “On-Grid” and the other going to batteries and then going directly to my home or “Off-Grid”. The off-grid system charges batteries and later in the day, the charge controllers, that modulate the power going to the batteries “Curtail” the solar panel output and switch to “Pulse modulation” to top off the batteries at a reduced output. So even off grid systems use curtailment to protect and enhance the battery investment giving longer life to the batteries.
. If grid tied systems, like my Tesla Solar Glass Roof, cannot provide some the power as “usable power” because of curtailment, then whatever the system wide curtailment is, in this case 5%, the value of the energy, produced by the rooftop homeowner, should also be discounted by 5% that use the power grid as their battery, at true up each year. As more solar is installed on the system and curtailment rises to say 15%, then the power provided over and above what a home uses should also be discount by 15%. If energy storage soaks up the excess power, curtailment will be modulated into the storage and relied on when needed and there will be far less loses. Under the CPUC NEM-3.0, they wanted to discount the value of roof top home solar by 80% on all new rooftop solar even though the utilities could sell 95% of the energy produced at retail to other customers even with the 5% curtailment.
On my off-grid solar panel plus battery system, the more battery storage I build into it, the less curtailment is needed by my charge controllers so let the same thing happen with the on-grid excess solar power. Build in more storage or energy conversion to hydrogen so the energy can be released at peak times rather than start up Peaker Plants running on fossil fuels for short periods of time. Curtailment may be good; but storage and release would be better.
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