Dreaming About Storage

..Dreaming About Storage

The California Independent System Operator (CAISO) determined that adding too much wind and solar on their grid would create problems.

They described the problem by using a graphic representation that has become known as the DUCK curve.


CAISO Duck curve with effect of increased solar and wind, beyond 2030, superimposed on the curve.

CAISO Duck curve with effect of increased solar and wind, beyond 2030, superimposed on the curve.

The CAISO DUCK curve shows the effect of adding solar and wind through 2030, which, at the time the DUCK curve was created, was sufficient to reduce CO2 emissions 25%.

The extended belly, in red, establishes the magnitude of the problem when 80% of electricity comes from wind and solar.

California’s new goal is to cut CO2 emissions 40% by 2030.

As solar and wind become a larger and larger percentage of electricity consumed during the day, it blocks out electricity produced by fossil fuels, rendering fossil fuel power plants mostly unusable during the day.

It also creates the situation where, in the evening when the sun sets, the fossil fuel power plants must ramp up very rapidly to meet the evenings peak demand.

This creates the untenable situation of having to retain all the fossil fuel power plants so they can be used to supply the electricity needed during the evening and at night.

In addition, fossil fuel power plants are essential when the sun doesn’t shine and the wind stops blowing.

Fossil fuel power plants can’t be shut down and dismantled, because they must be available to meet the peak demand that occurs during the night, and, also on rainy days when the sun doesn’t shine.

Much of the solar and wind generated electricity is produced by individuals, e.g., PV roof top installations, and by independent corporations, such as wind farm operators.

If utilities are prevented from selling electricity generated by fossil fuel power plants during the day, it’s impossible for them to earn enough money to stay in business.

They will either have to be paid a fee for covering their costs when not being used, or the government will have to take them over. Either increases the cost to businesses and homeowners.

In essence, utilities must be paid for not generating electricity.

The end results are:

  1. Solar and wind displaces fossil fuels, threatening economic viability of utilities
  2. Ramping in evening becomes potentially insurmountable
  3. Higher costs for electricity

The holy grail for partially resolving the DUCK curve problem is to add storage to the grid.

Supposedly, enough storage would dampen the ramp-up in the evening and also replace electricity from fossil fuel power plants when the sun doesn’t shine during the day.

Can storage supply all the electricity needed at night? This is a huge load for an extended period of time: Literally, thousands of Terawatt Hours of electricity. Probably not, which means fossil fuel power plants are needed.

Aside from the improbability of being able to supply the entire load from storage, which, for example, would have to be done on rainy days, there is the question of whether storage can supply enough electricity for the few hours the system is ramping up in the evening.

These are well recognized problems.

Unfortunately, these problems are glossed over by those who promote so-called clean energy, because of their intense desire to eliminate CO2 due to the perceived threat of climate change.

Once again, the root cause of this energy issue is climate change, supposedly caused by CO2 emissions.

We would all be better off if the IPCC would try to identify the cause of global warming, rather than merely assuming it’s CO2.

But, if storage is a partial answer to the DUCK curve problem, what are the alternative storage options?

Here’s a list of storage options:


V2G assumes battery-powered vehicles (BEVs) can supply the grid with power when it’s needed at night. Unfortunately, BEVs will likely be charging at night, so BEVs will be adding to the load, and the problem, rather than solving it. Similarly, vehicles will be on the road during rush hour, so won’t be able to supply electricity to the grid during the critical ramp-up period.

Pumped Storage

Pumped storage is a proven method for storing electricity, but is frequently opposed for environmental reasons, which makes pumped storage problematic.

Currently there is 20,000 MW of pumped storage in the United States, with the potential for an additional 31,000 MW, primarily in the West. While substantial, it still falls short of the storage capacity needed for eliminating a large portion of fossil fuel generating capacity.

Recently, it has been proposed to use abandoned coal mines for pumped storage, but most of these would be smaller than existing pumped storage sites.

Compressed Air

Only two CAES facilities have been built thus far: one at Huntorf, Germany, in 1978, and the second at McIntosh, Alabama, in 1991. Huntorf is rated 321 MW, and McIntosh is rated 110 MW. A third CAES facility, to be rated around 300 MW, is proposed for the Intermountain Power Generation site in Utah.


There are many different types of batteries, some with subcategories. Lithium-Ion subcategories could reflect different electrolytes, or different anodes, or different cathodes.

Other battery categories include:

  • Sodium-sulfur, which are typically large house-sized units.
  • Zinc-air
  • Flow
  • Lead-acid

(A major problem with many of these types is that they must be replaced periodically, possibly as frequently as every ten years.)


  • Digging 50 ft diameter parallel holes in the ground to replicate pumped storage by moving water from one pit to the other.
  • Making Ice for storage when electricity is available from wind or solar to freeze water, and then using the latent heat of evaporation for air conditioning.
  • Installing salt pits for thermal storage at concentrating solar power (CSP) plants, such as the Crescent Dunes CSP plant near Tonopah, Nevada.
  • Using rail cars on an inclined track, moving them up the incline when electricity is in over supply, and then allowing them to fall freely down the incline to generate electricity.
  • Producing hydrogen by using electricity from solar and wind installations, and then using the hydrogen in gas turbines to generate electricity.

Note that these storage options are tiny when compared with the amount of storage needed. Even pumped storage, with the potential to provide MWs of storage, is too small.

There is also the question of cost.

PG&E, a California utility that must find ways to comply with the musings of California bureaucrats, conducted a trial in an attempt to understand the cost implications of battery storage. See, PG&E Storage Appraisal. (May 2 article)

Quoting from T&D World, “A 2MW/14MWh sodium-sulfur battery storage array (PG&E’s Vaca site) cost approximately $11 million ($5,500/KW, $783/kWh) to build.”

The cost per KW was over twice the amount typically mentioned for the cost of storage, i.e., $2,000/KW.

More important was the conclusion that the current cost of battery technology is 27 times higher than what’s needed for battery storage to be economically viable.

The T&D World analysis concluded:

“There has been no breakthrough in electricity storage technology that delivers all the requisite features of high energy density, high power, long life, high roundtrip efficiency, safe handling, and competitive cost.”

The DUCK curve demonstrates the need for storage if solar and wind are to be a viable solution for cutting CO2 emissions 40%, and later 80%, but available storage options are unable to meet the amount of storage that’s required. In addition, the storage options are far too costly.

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5 Replies to “Dreaming About Storage”

  1. Here’s another idea: Avoid much of these costly investments through increasing the direct use of natural gas.

    • Yes, but natural gas emits CO2, so is not a viable solution for those who believe CO2 is the cause of global warming.
      Thanks for the comment, as I agree that natural gas is good for the world.

  2. Keep Diablo Canyon running 24×7. Refurbish San Onofre.
    Much less expensive and effective to reduce CO2.

    • I agree. Unfortunately the powers that be in Sacramento won’t consider your suggestion.