PG&E Storage Appraisal

Storage is seen by many as the savior of unreliable renewables, yet it would seem that the additional costs of storage, both the initial and perpetual costs, are enormous and that current technologies aren’t viable.

In 2016, Pacific Gas & Electric reported on an 18-month trial of storage on the grid.
The following details are from T&D website, operated by Penton Information Services:

  • “The trial encompassed 6 MW of storage split between two sites, both integrated to function as dispatched by the California Independent System Operator (CAISO) that manages operations of the state’s grid and wholesale power market.”
  • “The specific storage hardware examined was sodium-sulfur batteries, which are at the high end of the technology maturity scale and the low end of the cost spread for storage options of similar performance, having been used at utility scale in several nations for 25 years.”
  • “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 report included two external studies that found that cost of battery storage must come down to about $800/kW to achieve economic break-even.”

Sodium-Sulfer Battery Trial by PG&E

Sodium-Sulfur Battery Trial by PG&E


Here are some of the conclusions from the T&D analysis.

  1. Costs must actually come down to $200 / KW to achieve break-even. This is 27 times below the costs of the trial.
  2. Actual battery life will be 10 years and storage capacity must be 30 minutes, not 15, as used in the original analysis.
  3. Energy arbitrage revenues barely covered expenses. Arbitrage consists of selling power when prices are high and storing power when prices are low.
  4. Frequency regulation is most lucrative use of batteries. However, this requires maintaining the battery at a 50% charge, so as to be available to store or discharge at a moment’s notice. This usage harms the cells and hurts battery life. Revenues barely covered the cost of the asset.
  5. Dispatcher must know the battery’s state of charge (SOC) at all times if the grid operator is to use batteries successfully. Attaining this for a multitude of batteries is virtually impossible, even with the best of technologies and use of algorithms.
  6. Parasitic losses complicate dispatch.
  7. Battery location is dependent on usage, limiting their flexibility. For arbitrage, as defined in item 3, they should be located near the intermittent sources, i.e., wind or solar, but for frequency regulation they should be located near their loads.
  8. Other battery technologies are inferior to the sodium-sulfur batteries used in the trial.

PG&E reached the following conclusion:

“If revenues from market participation are to be the key driver of evaluating the cost-effectiveness of battery storage, it is recommended to be conservative in the forecasting of those revenues. With California Assembly Bill 2514 and its requirements that utilities procure 1.3 gigawatts of energy storage, California ratepayers could expect to pay billions of dollars for the deployment and operations of these resources.” (Emphasis added.)

Quoting the T&D analysis:

“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.”

Batteries must be replaced every 10 to 20 years, while a natural gas power plant can last for 60 years.

Clearly, batteries of any type are not a viable method for storing electricity. They are not a substitute for fossil fuel power plants.

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11 Replies to “PG&E Storage Appraisal”

  1. Thank you again Mr. Dears.

    I will again mount my horse and carry you additional news on the impossibility of achieving a reduction in CO2 emissions enumerated in the UN Paris Climate Agreement.

    Daniel Kahnemann illustrated, in his book Thinking: Fast and Slow, why nearly all people, Doorman to PhD, will not read nor change their mind. Simply, it is too difficult to read and think. It’s human in fact to just go with what is first learned, provided it is simple.

    But, like you, I will keep on keeping on. May success favor you myriad efforts.

    • Thanks for your comment. Yes, it’s hard to get people to learn something about which they have already formed an opinion, but it’s worth trying.

  2. How does the use of 2 reservoirs compare….ie, pumping water uphill when power is cheap and generating power when demand is high. hey do this in the Fresno area . How poorly does this type of physical system work??

    • Pumped storage is excellent, and the most efficient storage. It’s been used for over a century.
      Even so, it can’t handle all the storage that’s needed if California decides to cut CO2 emissions 80%, as they plan on doing.

  3. How absurd. 5MW? That’s power, not energy. How many hours before the batteries poop out? What’;s the pollution footprint of the battery builds, operation and decommissi9oning?

    Our descendants expect better of us.

    PG&E’s Diablo Canyon delivers >2 billion Watts 24/7 at a fraction of the cost of wind/solar/storage. And, like hydro & geothermal, nuclear is storage — any atom not fissioned remains ready to do so for millions of years.

    California is on track to illustrate why our educational stature is so far down the list in relation to advanced countries.


    Perhaps see what someone learns from studying facts…

    And, more. professionally..

    • Excellent. There’s no question that our education system is failing the country. As your referenced videos suggest, an important failure is instilling the ability to think critically about issues.
      How much copper is needed? etc., are fundamental questions that must be answered. Without some idea of resource requirements, it’s impossible to judge whether wind and solar are viable to the extent needed to cut CO2 emissions 80%.

      • Gentlemen,

        While this is not a specific discussion on climate changes, I have an idea about that which I would appreciate some comments on. Anyone interested may send an E-mail to and I will send a PDF.

        Kjell Danielsen

    • Thanks. I’ll look at the report and see if there is something I can comment on.