Devil Horns and Duck Curves: Renewables Reshaping Grid in California, Elsewhere

May 14, 2018

The Duck curve about to get Duckier.


California just mandated that nearly all new homes have solar, starting in less than two years. Now, it’s going to have to figure out what to do with all of that extra energy.

Already, the state is flooded with so much solar power during the day that it has to turn off some of its sun-fueled plants at times and often needs to ship excess green energy to neighboring states. The phenomenon has produced what state grid operators have been calling the duck curve — that’s when net power demand craters during daylight hours and then ramps up after sunset and natural-gas generators fire up to meet customer demand.


It’s an unintended consequence of the Golden State’s effort to slash greenhouse gas emissions and get half of its electricity from renewable sources by 2030, and has vexed the state’s grid operators. California’s top utility regulator warned last week of a looming energy crisis if the region doesn’t start planning for a future with more people either generating their own power or getting it from suppliers besides the big utilities.

“As the amount of renewables on the system grows, grid operators need increased visibility into behind-the-meter resources,” said Steven Greenlee, a spokesman for California Independent System Operator Corp., which runs the state’s power grid. Grid operators will need more visibility into how these home systems are working, he said.


To put it another way, “it has the potential to make the duck curve duckier,” said Ethan Zindler, a Washington-based analyst for Bloomberg New Energy Finance.

Business Green:

Germany’s renewables sector produced more than 100 per cent of the nation’s electricity demand yesterday, pushing wholesale power prices into negative, the latest government data shows.

The surge in clean energy generation on May Day in Germany produced around 50GWh of renewable power, including around 27GWh from wind energy and 20GWh from solar, according to the federal government’s live energy market data.

The achievement was partly a result of favourable weather conditions and lower demand due to May Day being a public holiday in Germany.

Fossil fuel generation, meanwhile, dropped below 1.5GW of generation, pushing wholesale electricity market prices down to almost -€36/MWh, with the surplus power exported to neighbouring countries.

As a result, Czech Republic, Slovakia, Austria and Switzerland also enjoyed negative power prices yesterday, according to analysts.


Europe’s power traders have a colorful name for the way the rise of solar power is distorting the electricity industry: devil horns.

That’s the shape formed by intraday power prices that increasingly having to adapt to greater flows from solar farms in the middle of the day. As photovoltaics feed more supplies to the grid, power prices crash and then rise as the sun sets, leaving a distinctive formation in charts like the one below.


More than an amusing oddity, the dramatic swings indicate the scale of the challenge grid managers are facing in smoothing out supplies from plants that only generate when the sun shines or the wind blows. The pattern is becoming increasingly familiar across Europe, especially in Germany, where it translates as “Doppel Knick.”

As solar capacity has surged more than ten-fold in the past decade in Germany, it’s leaving utility executives wondering if they should switch off coal and natural gas plants for a few hours when the photovoltaic facilities deliver their peak yield.

“Thermal plants are struggling a lot with having to ramp up and down fast when they are needed,” said Hanns Koenig, a project leader at Aurora Energy Research Ltd., which is based in Oxford, England, and advises utilities, investors and governments. “To ramp up quickly uses extra fuel and may not be economical so currently a lot of plants run through solar’s production peak.”

As much as 38 percent of Germany’s power came from wind and solar farms last year. That’s making it difficult to estimate how much supply will feed into the grid at certain times of day as some of it will also feed local distribution networks. It’s a dramatic change from a decade ago when the deep price dip occurred in the middle of the night as reactors were humming even as demand was low.

Storage and charging of electric vehicles will eventually help to even out the sharp within-day price swings, but short-term it will continue to have a negative effect on operations, said Magnus Hall, chief executive officer at Vattenfall AB, the Swedish utility. The company on Thursday reported fewer running hours from its German coal and gas plants in the first quarter, even as cold weather increased demand.

“We are building a system that in the long term have the capability to even out prices,” Hall said by phone. “In the short-term perspective it has this effect that is hard to quantify, but it is a negative effect.”

The impact on the grid from renewables is now so great that supply at times exceeds demand and pushes power prices below zero. The trend has also undercut the economics of replacing some of the oldest traditional plants, with some forms of renewables mature enough to compete in the market without subsidy.

In the past year alone, solar developers in Spain and offshore windfarms in Germany and the Netherlands won tenders for plants without guarantees for higher-than-market power prices.

Even the U.K., with its rainy image, is expanding solar and the technology can now meet as much as 39 percent of peak summer demand.

That’s so much that National Grid Plc is preparing measures to avoid overloading of the network. The grid manager may need to curtail renewable energy production and also ask coal, gas and nuclear plants to rein in output during certain hours.


11 Responses to “Devil Horns and Duck Curves: Renewables Reshaping Grid in California, Elsewhere”

  1. dumboldguy Says:

    Use the excess electricity to generate heat Store the heat in molten salt during the day. Use it to make steam to turn generators at night. No natural gas needed. Seems simple enough. (?)

    • rhymeswithgoalie Says:

      “Use the excess electricity to generate heat Store the heat in molten salt during the day.”

      A curve like that gives market impetus to have *someone* pull the cheap electricity off the grid and store it for later. The cheaper it gets, the less efficiency you need to make money off of it, but eventually market gamesmanship should move to more efficient tricks to make money off this resource.

    • J4Zonian Says:

      ““it has the potential to make the duck curve duckier,” ”

      Anyone who knows anything about ducks would know to say just the opposite.

    • J4Zonian Says:

      Batteries. Seems simpler.

      Deep offshore wind turbines with capacity factors up to 65% and still growing seem pretty simple. Ready for production within 2 years; blade testing this summer for turbines more than 5 times more powerful than anything in operation today seem pretty simple. (Well, not so simple, but worth putting the money in to make them operational in the next 3 years. The Off-Manhattan Project)

      Passive and active solar houses with built-in storage, annual cycle energy systems, clothesline paradox energies that remove demand from the grid entirely seem pretty simple. Been doing them since before the rise of Ur.

      The rest of it is not a problem with renewable technology or batteries; it’s a problem with an economic system that says it’s worse to give away power to those who need it and worse to build batteries and retrofit buildings before it “makes economic sense” than it is to sit and watch television until civilization violently and chaotically collapses around us. The economic system has to go anyway, why not let this little challenge take out its part of it and replace it with one that views survival and the public good as paramount?

      That’s not a real question, the answer is obvious. There are a few people with poor self esteem who are addicted to the current economic system to give them constant jolts of money-shaped shots of it. Like all addictions, diminishing marginal returns makes them seek ever-larger shots, the end of which with heroin is a single death, the end of which with economics is countless decillions of deaths. We need to treat the addiction while engaging in whatever harm reduction is called for, while we build batteries as fast as Musk’s and the Chinese and whatever other factories we can build can churn them out, and PAY ABSOLUTELY NO ATTENTION WHATEVER TO THE PRICE!

      How insane do you have to be to prioritize making rich people richer over the survival of tigers and edelweiss?

  2. Sir Charles Says:

    Electricity to hydrogen could be part of the solution. AFAIK efficiency is only at some 60%.

    => Swedish steel boss: ‘Our pilot plant will only emit water vapour’

    A new pilot facility under construction in northern Sweden will produce steel using hydrogen from renewable electricity. The only emissions will be water vapour, explains the CEO of Hybrit, the company behind the process, which seeks to revolutionise steelmaking.

  3. Gingerbaker Says:

    Interesting discussion about hydrogen in the comments here:

    the tl;dr :

    * electrolysis getting more efficient, cost of electrolysers falling like solar panels

    * There is another tech even more efficient – solar thermal cracking. Excess RE -> produces heat -> makes hydrogen plus heat and/or methanol using CO2

    * hydrogen is by no means “dead”, in fact, will likely be seeing a big resurgence because of its ability to store excess RE, its ease of use, transport as methanol, its ability to be burned as carbon-neutral heat (heating as still a big problem for those of us who live where there is winter), and its potential to be used to combine with CO2 scrubbed from the air.

    * Remember, these bits of “info” are comments on a blog.

  4. Solar energy and wind energy are not alternatives for a coal or gas generated power station. They are just suplementary.

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