Hitting the solar wall

ISO peak and off peak california


California peak and off peak demand in California. Solar produces power when it’s least needed: from 7 am to 4 pm during Off Peak and Super Off Peak time frames.  Adding more solar power makes the problem worse, requiring even more solar PV power and other plants to shut down more often.

[ California solar generation has reached the point where it’s producing so much power at the time of day when it’s least needed that it has to be shut down during the sunniest time of the year.  This is because year round, solar generates power when there is the least demand, and the least power when demand is highest.

Notice in the figure above that peak demand occurs after 4 p.m., which according to the California ISO, is “when the sun is setting and solar output is declining. During July and August supplies are even more limited during peak hours”. Except for July and August on the weekends, supply surplus occurs during “super off-peak” hours from 10 to 4 PM – which is when solar generation is at its highest. In addition, surplus conditions occur this same time period in March and April weekdays while weather is still mild and there’s no need for air-conditioning.

Because solar PV is so seasonal, it provides from 2% in winter, to 10% in summer of California’s daily needs — but not when most needed, and at times, far more than what is needed, so solar PV and/or other power generation has to be shut down.  Additional solar PV power only makes the problem worse.  Solar thermal with energy storage would help, but it’s mostly “smoke and mirrors”, less than a quarter have storage, and most of the time produce less than half a percent of daily power needs for California.

Alice Friedemann   www.energyskeptic.com  author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer]


July 12, 2016. On the path to deep decarbonization: Avoiding the solar wall. Op-Ed by Sally Benson and Arun Majumdar Co-Directors, Stanford Precourt Institute for Energy.


If California continues to rely mostly on solar resource for meeting the 2030 50% Renewable Portfolio Standard, the total statewide solar-generating capacity would reach 30 to 40 GW under peak production, according to a report by Energy and Environmental Economics Inc. (E3).

Under these conditions, on a sunny day, for most of the year, California would be generating more electric power than it needs during the middle of the day from solar energy alone.

E3 calculates that this large amount of over-generation could be a problem 23% of the time, resulting in curtailment of 8.9% of available renewable energy, with marginal overgeneration by solar PV of 42-65 percent.

In other words, California could hit the solar wall.

And this does not even consider that midday demand is likely to decrease due to the installation of additional residential and commercial solar PV systems “behind the electricity meter.”

Consequences of hitting the solar wall

Just a decade ago it would have been nearly unthinkable that during the middle of the day solar energy could provide more electricity than an economy as large as California’s needs. But supportive policies, rapid scale-up and decreasing costs make this possibility a reality today. While from some perspectives this is very encouraging, in reality, there are consequences for hitting the solar wall. For example:

  • Reliance on so much solar energy would require rapid ramping capacity for more than 10s of GW of natural gas power plants from 4:00-6:00 p.m., when the sun is going down and electricity demand goes up as people return home.
  • Large back-up capacity from natural gas plants or access to other sources of dispatchable electricity would be required for days when the sun isn’t shining.
  • Zero marginal-cost solar generation could squeeze out other valuable low-carbon electricity sources that can provide baseload power. For example, natural gas combined cycle plants, geothermal energy and nuclear power that cannot operate during these times at zero marginal cost.
  • Large-scale curtailment of solar PV during times of overgeneration, which will reduce the value of solar capacity additions to investors.
  • Real-time pricing during times of overgeneration could limit or eliminate the net-metering advantage of PV on residential and commercial-scale installations.

There is no doubt that California’s solar energy potential is invaluable, but we must take steps to avoid the solar wall.

A few of the suggested things to do:

  • Ensure adequate capacity of rapid ramping natural gas plants to provide reliable supply during the morning and evening hours as the sun rises and sets.
  • Increase energy storage to avoid curtailment of solar overgeneration during peak production periods. For now, few financial incentives exist for large-scale pumped-hydropower or compressed air storage projects. Levelized costs of small-scale storage in batteries range from about $300 to more than $1,000/megawatt-hour (MWh) depending on the use-case and the technology. These are expensive compared to pumped-hydro storage at $190 to $270/MWh. For comparison, gas peaker plants have a levelized cost of $165 to $218/MWh. The business case for battery storage will be limited until prices come down significantly. Both R&D and scale-up will be needed to reduce costs.
  • Use electrolysis to produce hydrogen fuel to augment the natural gas grid, generate heat and power with fuel cells, or power hydrogen vehicles. However, compared to storing electricity in batteries, hydrogen-based storage systems that combine electrolysis and  fuel cells are about three times less efficient. In addition, today, these technologies are expensive, and significant cost reductions will be required to make them competitive alternatives.


California ISO  

Issues with renewable power:

  • Short steep rams when the ISO must bring on or shut down generation resources to meet an increasing or decreasing electricity demand quickly, over a short period of time
  • oversupply risk: when more electricity is supplied than needed
  • decreased frequency response when less resources are operating and available to automatically adjust electricity production to maintain grid reliability.

To balance unpredictable, intermittent renewables ISO needs flexible resources that can sustain an upward or downward ramp, change ramp directions quickly, react suddenly to meet expected operating levels, start with short notice from a zero or low electricity operating level, stop and start many times a day, respond for a defined period of time.

For example, figure 1 shows a net load curve for the January 11 study day for years 2012 through 2020. This curve shows the megawatt MW amounts the ISO must follow on the y axis over the different hours of the day shown on the x axis. Four distinct ramp periods emergy.

#1 Ramp of 8,000 MW upward (duck’s tail) starting 4 a.m.

#2 Ramp down at 7 a.m. when sun comes up and solar generation starts (belly of the duck).

#3 At 4 p.m. solar generation ends, ISO must dispatch resources to meet the 11,000 MW ramp up (arch of the duck’s neck)

#4 Finally a ramp down after around 6 p.m. until the next morning

ISO winter duck









Figure 1. Net load – January 11, winter ramp duck

The summer has even more extreme requirements – the system needs to supply an additional 13,000 MW within just 3 hours to replace the electricity lost by solar power as the sun sets.

ISO summer duck











The more renewable energy added to the grid, the more likely it is that more electricity will be generated than needed.  Since the system frequency must be within a very tight band around 60 hertz, solar and wind sudden over or underproduction can cause a blackout if not compensated for.  When there’s too much production of electricity, this drops wholesale prices to zero or even negative, which causes generators to have to paly utilities to take the energy.  This is a situation to be avoided if possible.  The middle of the day is when it is most likely solar will produce too much electricity.  ISO would like to see this electricity exported, more electric cars, encourage users to consume when this happens, and more energy storage.

More California ISO links

Today’s renewables and net demand

Daily Renewables Watch (daily renewable stats back to 4-20-2010)

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2 Responses to Hitting the solar wall

  1. sheila chambers says:

    I see you have found a few more problems with solar energy aside from the fact that it is as “renewable” as your truck, SUV, aircraft etc, is that it produces the most electricity when it’s least needed & there isn’t enough storage to capture that energy to distribute it when it is needed like after 1600.
    Storing that excess energy is a HUGE problem due to the limits in resources needed to build the necessary batteries or to build the pumps needed to pump water uphill into a storage reservoir to run through NONrenewable turbines later. But storage reservoirs need to be ELEVATED to function as energy storage & most parts of the country are too flat or too far from an elevated area that could be used.

    Our greatest problem with these so called “renewables” is not only are they not “renewable” but the raw materials they need for their manufacture are LIMITED & some are getting scarce. The also require VAST amounts of energy for their mining, processing, manufacture & transportation, something we won’t have after the oil age.

    So we spend billions if not trillions of dollars building up this infrastructure for a TEMPORARY source of energy only to have it grind to a halt when some critical material runs out.
    Then what? What’s plan “B”?
    I would do a huge reduction of the excessive human population, disease, war, starvation are not my first choices & it’s too late for education, abortions or birth control to prevent our collapse.
    So collapse it is, a collapse we could have avoided if we had been “wise”.

    Even if “renewable” energy could produce 50% of the electricity we use, there is still the problem of FEEDING a endlessly growing & excessive human population & climate change will reduce our ability to feed ourselves.
    People will be much more concerned about their next meal or drink of clean water & could care less whether the lights are still on. Collapse is still a certain thing in our bleak future, a future we made ourselves.

    I still wish you would stop calling this NON renewable technology “renewable” because anything that needs NON renewable resources is NOT RENEWABLE!

    Websters dictionary = renewable “restored or replaced by natural processes : able to be replaced by NATURE.”

    Yes, the SUN, WIND & MOVING WATER are a renewable SOURCE of energy but the high tech devices used to capture that energy & convert it into electricity are NOT renewable.
    Do you claim that your CAR is “renewable”? If not, why not?
    It’s just as “renewable” as your precious solar panels.

  2. energyskeptic says:

    I don’t care if I scare people. There is no solution to the energy crisis. But there is a solution to climate change: the energy crisis will take care of that. Somewhere between now and 2035 all fossil fuels will be in decline and CO2 go down forever after. Fossils could decline even sooner if there’s war, a financial crash, and so on. And since conventional oil peaked in 2005 where 90% of oil comes from, and on the way to reaching 9% decline rates by 2030, there will be less oil to get coal and natural gas, which could potentially leave a lot in the ground that we consider reserves now.

    The only possible solution to lessen the hard landing ahead is free and easily obtained birth control and abortion, world-wide. But we’re moving the OPPOSITE direction, with right-wing religious groups in the U.S. and elsewhere doing everything they can to prevent women from having control over their own bodies and futures by making abortion pills, abortions, and birth control pills hard to get. If people want to make a difference, they need to stop thinking energy efficient light-bulbs and bicycling are going to save the world and start trying to make birth control and abortion available world-wide, and get organizations like the Sierra Club, who abandoned birth control, back on track. It’s awfully late to attempt this though. It should have started no later than the 1970s.

    The public are big babies, raised on TV shows that always have a happy ending, are more interested in sports than science, and brainwashed to consume, consume, consume. Because most Americans aren’t scientifically educated, the public believes all sorts of nonsense, which James Howard Kunstler writes about in “Too Much Magic: Wishful Thinking, Technology, and the Fate of the Nation”. Michael Shermer also has many excellent books such as “Why People Believe Weird Things: Pseudoscience, Superstition, and Other Confusions of Our Time” and “The Believing Brain: From Ghosts and Gods to Politics and Conspiracies—How We Construct Beliefs and Reinforce Them as Truths”. What Americans believe matters: we’re only 4% of world population but consume 20% of the oil (and out-sized amounts of most other goods as well — see http://energyskeptic.com/2016/limits-to-growth-2016-united-nations-report-provides-best-evidence-yet/).

    Many politicians are aware of the energy crisis – see my summaries of many U.S. House and Senate hearings under category Experts/Government. There are a hell of a lot of scientists and others who know as well. But why aren’t they doing anything? see http://energyskeptic.com/2015/climate-change-deniers/

    The point of my book “When trucks stop running” is that there is no solution. When trucks stop running, civilization ends. If you can’t keep the supply chains going to deliver 8,000 wind turbine parts or get turbines and solar contraptions to their destination, game over.

    Wind and solar MUST be balanced. Right now this is mainly done with natural gas. But natural gas is finite, hydropower is limited, and utility scale battery energy storage is far from commercial, with only sodium sulfur batteries having physically enough material produced to be possible (but nearly all energy storage batteries so far use lithium). If you can’t balance intermittent supply, the electric grid is over. Renewable power is also extremely local – solar and hydro mainly west coast, wind the middle of the country, and in the East, very little renewable energy of any kind, yet that’s where 70% of Americans live. Without a national grid and tens of thousands more miles of transmission (NIMBY! COST! TIME!), there’s no way to share renewables, and wind and solar are very seasonal, with almost all of the U.S. a wind desert in the summer, the South East year round, and the southwest in the winter too far north to provide the nation with solar power.