California has too much coal and nuclear

“Texas and California have too much renewable energy,” writes Technology Review this month. “California has too much solar power,” chimes in. Nonsense, says Craig Morris, a political arrangement is being passed off as a technical issue. Stop protecting nuclear and coal; get rid of baseload.

Windmills in California with a sunset in the background.

Is there too much wind and solar power in California? (Photo by Tony Webster, modified, CC BY 3.0)

In Germany, renewable power now regularly cuts into medium-load conventional plants and sometimes even offsets baseload capacity. The result can be negative power prices. Easter weekend is a case in point.

A graphic which shows the electricity production and spot prices in week 12 of 2016

Here, we see that peak power demand (around 60 GW on from Monday to Thursday) dipped to 40 GW from Good Friday to Easter Sunday. When wind and solar power production picked up on the weekend, conventional generators were pushed down to 10 GW in terms of demand; around 10 GW of exports (the purple area below the baseline) rescued these plants, whose actual must-run level is closer to 20 GW. Power prices (the red and blue lines) plummeted and briefly went negative. During those hours, conventional plants were paying buyers to take power off their hands.

Why would they do that? It has to do with the must-run level. Think of your car. When you turn it on, the tachometer probably reads around 800 rpm. That’s your car’s must-run level. Hit the gas, and it goes up to 2,000-3,000. But if, for some reason, you wanted your engine to drop down to 600 rpm, you’d be out of luck; without revamps, it won’t work. Coal and nuclear plants have a relatively high must-run level.

A bar graphic which schows the capacity of solar PV, installed in Germany.

The US grid could accomodate 19 times more photovoltaics before it reaches the German level.

Look at the California data, and we see that the complaints cannot be technical in nature. “On March 27… some solar farms had to shut down because there was more power on the grid than Californians were using,” writes KQED Science. But compare the German chart above to the California chart below, and you may notice some differences.

Energy use

Let’s take a look at the “residual load” (demand minus renewables) in the chart from the bottom:

  • Nuclear power does not react to demand at all.
  • Natural gas, which ramps the best, moves from around 4 GW to 6 GW; it can easily do more from a technical standpoint.
  • Likewise, hydropower remarkably moves very little, ranging only from roughly 5 GW to 6 GW. Europe aims to use hydropower in Norway and Switzerland as a “battery” to store renewables; when a lot of wind and solar are generated, hydropower production in these two countries would slow down – and pick up again as need be.
  • Imports react the most at between 5 GW and 9 GW.

At Vox, David Roberts concludes that California “needs another grid to share with.” The chart shows the opposite. If California had more wind and solar, imports could drop, so less (!) interstate grid lines would be needed. California mainly imports coal power, and imports made up 27 percent of the state’s power supply in 2015 (PDF). More green power in California means lower demand for coal power.

Clearly, California is curtailing renewable power before its conventional fleet has reached the must-run level, a technical limit. I suspect renewable power is being curtailed when the market value drops below 1.0, meaning that conventional power becomes cheaper on the spot market than renewables (the expenses are called “system costs.”). Shedding green electricity at a market value below 1.0 is a political decision, not a technical necessity. Germany has made a political decision to go 80 percent renewable for power by 2050, and the Germans understand that this transition will entail such system costs and ruin the profitability of coal and nuclear – in fact, that’s the goal.

A graphic that shows the demand and residual demand in winter 2020.

Bernard Chabot’s calculation of demand and the residual load (demand minus renewables) for 2020 in California. His conclusion: “There is ample room for much more wind and solar production in California without risks of RE oversupply or urgent needs for RE curtailments, storage, or exports.” Note that a study by Eric Martinot from November listed numerous options in addition to grid expansion. (Source)

Two graphics side by side, the left is showing the power demand over a week in 2012, the right is showing the estimated power demand in 2020 in Germany.

Originally produced in 2010 by Prof. Volker Quaschning, this chart shows that the Germans have long understood that the residual capacity for wind and solar will need to be as flexible as possible.


No one doubts the general analysis in these articles from the US:

  • wind and solar will always require backup generation capacity at the full level of peak demand;
  • gas turbines are technically optimal for that purpose;
  • storage will eventually be needed; and
  • grid expansions help.

But the specifics from California show that Americans overlook the need to shut down baseload. Roberts mentions how Denmark uses the grid to manage excess wind power without mentioning that France needs exports to keep its baseload nuclear fleet from ramping down at low levels of demand. IRENA pointed out in 2014 (PDF) that the early retirement of baseload plants precedes storage. Get rid of baseload, and you reduce must-run capacity, making space for wind and solar.

So does California have too much solar or too much baseload? The answer is political, not technical. If you want solar and wind, call for an end to baseload.

Craig Morris (@PPchef) is the lead author of German Energy Transition. He directs Petite Planète and writes every workday for Renewables International.


Craig Morris (@PPchef) is co-author of Energy Democracy, the first history of Germany’s Energiewende.


  1. S. Herb says

    “If California had more wind and solar, imports could drop, so less (!) interstate
    grid lines would be needed. ”
    The peak imports are at 9 pm. The grid capacity must match the peaks. More solar won’t help here, more wind, sometimes. Maybe with more solar and wind, California could start making its neighbors noon-day offers they couldn’t refuse, putting pressure on baseload generation there also. I find the idea of state by state self-sufficiency very dubious. More dependency and interaction between the state systems will help in shaking up the system.

  2. Hans says

    To understand the motivation behind the unnecessary curtailing it is useful to know how the utilities in California are organised. Are they vertically integrated? Who owns the renewables. There might be some conflict of interest going on.

  3. Hans says

    There is something strange about the figure about Californian production: Hydro seems to be used as baseload. A first internet search did not give any hard numbers, but I get the impression that most hydropower in California comes from plants with a reservoir. Especially in these times of drought it is strange that the peak solar power is not used to reduce the water flow through the hydro plants and to save the water in the reservoirs for later.

  4. heinbloed says

    @ S.Herb:

    East-West facing panels would cover morning and evening peaks very well in California.
    Think about facade mounted panels in the household sector.
    A remunerating FIT scheme acknowledging the delivery of peak-demand could help to propel the installations into this direction.
    But batteries would do so as well.

  5. Bronwyn White says

    ## Can you tell me if this company was interviewed in the Documentary “CATCHING THE SUN ” and the name of the companies Founder …

  6. Shawn Perry says

    It is urgent for all of us to realize that renewable resources are our future for sustaining us with the electricity. Southern California’s solar companies are emerging day by day. I myself used the services of LA Solar Group, thus switched to the consumption of much desirable renewable sources of energy.

  7. Where exactly did IRENA point out in the 2014 report that the early retirement of baseload plants precedes storage? I spent quite some time scanning through the pdf but couldn’t find it.

  8. Miklós, thanks for writing. You are right that REmap not explicitly say that “early retirement precedes storage,” but it is implicit in the numbers. Figure 3.1 — the centerpiece of the report — has early retirement as its own category, equivalent to around 10% of all RE. Now look at the meagre numbers for storage, such as in Table 6.1. Elsewhere, the report says ” a large increase in medium and seasonal storage will
    be expected especially after 2025″ (p. 93). So yes, storage is coming, mainly later. Disclaimer: I was technical editor of that report.

  9. Lmao. I’m Californian. If we have SO MUCH solar energy that we’re selling it to other states, why was there a rolling blackouts and flex alert? Why are energy bills over 400 for a 2 bedroom house? What a joke.

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