Curtailment of electricity occurs when there is not enough demand for the available supply. In the absence of some sort of grid storage strategy, whether batteries, pumped hydro, or other technology, the excess energy is simply wasted.
The California Independent System Operator keeps track of such things. Its latest figures show approximately 3.5% of all renewable energy generated within the state so far this year has been curtailed. That’s more than prior years primarily because there is more renewable energy available this year than previously.
That gets a lot of renewable energy detractors fired up, as if curtailment has never happened before in the utility business. The Union of Concerned Scientists has taken a look at the issue and found there are two primary causes of curtailment — system wide oversupply and local transmission constraints.
According to CAISO, the majority of that curtailed electricity is attributable to local transmission constraints, which UCS describes as follows. “This kind of curtailment occurs when there is so much renewable electricity in a local area that there is insufficient transmission infrastructure to deliver that electricity to a place where it could be used. A great example of this is in Texas, where wind energy curtailment fell from 17% in 2009 to 0.5% in 2014 mostly due to construction of additional transmission lines to move that wind energy out of local pockets to places where it could be used.”
Renewable energy critics react angrily to the cost of building new transmission infrastructure. Oddly, though, there is never a peep of protest from them when transmission lines are constructed for new coal, gas, or nuclear facilities.
CAISO has proposed 8 strategies for putting excess renewable energy to work, strategies that are endorsed by UCS. These ideas basically center on constructing a smarter, more resilient grid that uses the available supply of electricity more efficiently. Electric cars can play an important part in that process if the charging infrastructure provides for powering chargers with excess electricity whenever possible.
According to UCS analyst Mark Specht, curtailment, if managed properly, is an opportunity not a problem. “[W]e need to be smart about how we approach the ‘problem’ of curtailment,” he says. “Every year, California sets a new record for the amount of renewable energy that’s curtailed. But that doesn’t mean you can use up all that energy by plugging in a battery at any old place on the grid. This means that, when investing in resources such as storage, we need to be smart about where we are making those investments, because putting it in the right place could increase the amount of excess renewable energy that’s available for the storage to soak up.”
To sum it up, utilities and system operators need to build grids that support the renewable energy future. The days of running coal powered generators constantly 24 hours a day are over. Nuclear cannot easily be ramped up or down to reflect variations in demand and older natural gas plants are less efficient when changes in output are called for.
An interactive grid that allows utilities a measure of control over such demand centers as heating, air conditioning, and EV charging via the internet of things is the best way to put all the power available from renewable sources to work. Pricing signals such as time of use tariffs will incentivize utility customers to make use of excess renewable energy whenever possible.
As battery storage prices continue to fall, adding grid scale storage to soak up available supply for use later will become the first choice of utility companies rather than building new fossil fuel powered plants. That trend is already apparent in the decision by 8minute Solar and NV Energy to build a combined solar power plant with 540 MWh of battery storage in Nevada. The cost of electricity from the facility will be $35 per MWh — far below the cost of energy from any other source.
Curtailment is an issue to be managed not feared. It is certainly not the bugaboo renewable energy critics make it out to be. Not everything can be like it was in 1920 no matter how dearly some may wish things good go back to the “good old days.” Sometimes we have to be dragged kicking and screaming into the future. Low cost electricity will help ease the pain of that transition.
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