Large Scale Electricity Storage.

One of the biggest barriers to the adoption of wind and solar electricity generation is the lack of storage technology with the capacity to handle the hundreds or megawatt hours necessary.    

Large scale electricity storage technology also allows utilities to flatten their demand, and defer construction of expensive new generation. 

Here’s a quick rundown of some of the technologies vying to meet this need.  Most of this is information is drawn from the Electricity Storage Association website.

Technology

Description

Comments

$/kWh; efficiency

Investment opportunities?

Pumped Hydro: Reservoir to Reservoir

Energy is stored by pumping water from a low reservoir to a higher one, and recovered by running the water back out through a turbine.  This system can be easily retrofitted into existing reservoirs, but has limitations due to water regulations.  First used in 1890.

The cheapest and most developed technology, pumped hydro is nevertheless limited by the availability of suitable sites.

$3-$50 per kWh;

70% to 85%

The major supplier in the business is private.  Could look for opportunities in utilities that have good potential projects.

Compressed Air Storage (CAES)

Energy stored by compressing air into large underground caverns.  Air combined with natural gas on exit and burned in turbine.  The gas compensates for the cooling as air decompresses. 

Gas used is about 40% of the amount used in comparable peaking turbine.  First built in 1978.

70% to 80% efficient; $30-$100 per kWh

 

Underground Pumped Hydro

As above, but water is pumped between an aquifer and an above ground reservoir.

More sites available, developing application.  Might have some water quality issues.

Costs Low

75% to 85% expected efficiency.

Small turbine/pump makers.

Polysulfide Bromide battery

A regenerative fuel cell based battery technology (aka “Flow Battery.)  Seems have run into difficulties due to the toxicity of the chemicals involved.  

15 MW demonstration project in 2003; more recent projects canceled.

75%, unknown cost;

Regenysis, the owner of this technology, was a subsidiary of
Germany’s RWE.  No recent activity; the program may have been wound down.

Molten Sodium-Sulfur (NaS) Battery

Molten battery technology.  “Safety concerns addressed in

30 sites in
Japan, mostly for peak shaving.  Largest is 6 MW for
Tokyo electric

Cost “High” compares to BrS and hydro/ CAES.

NGK, Japanese power equipment supplier focused.  Can be bought by US investors on the Pink Sheets NGKIF.PK

Regenerative Fuel Cell (Hydrogen)

Fuel cells can be run in reverse for electrolysis, with the hydrogen stored in large tanks.

First pilot project 2004

“much less” than 80%

Fuel cell manufactures: Ballard, FCEL, and others.

All these technologies except hydrogen are dealt with very well on the Electricity Storage Association site.  They have some great technology comparison graphs which deal with a lot more variables than I have here in their technology comparison section.

Cost Comparisions

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Efficiency/Quality Comparisons:

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Of these technologies, Pumped Hydro and CAES are the only ones ready for near term, large scale deployment (with NaS and Flow Batteries applicable in some markets highly constrained markets.)

The major downside for pumped hydro is siting, part of which problem can be solved with the smaller scale reservoir to aquifer option.   For CAES, the downside is the need to use gas to run the turbine, albeit a very efficient one.  One option might be to substitute for the natural gas used in CAES with hydrogen from electrolysis, allowing the system to work at locations remote from natural gas supply, and, for wind energy storage systems, be 100% renewable.

 10/20/06- Article about a flow battery from VRB power systems for an Irish wind farm.

8/5/07: Here’s an article I just wrote about two potential investments in utility scale electricity storage.

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1 Comment

  1. Hello,

    I noticed an interesting note on your website about “Underground Pumped Hydro” in which “…water is pumped between an aquifer and an above ground reservoir.” This sounds like a very interesting concept, and is closely related to some research I am doing as a master’s student at the University of Colorado.

    Do you have any more information on this concept? Maybe we could chat about it sometime?…I’m at 206-280-5722

    Greg Martin

    Master’s Candidate
    University of Colorado at Boulder
    Electrical and Computer Engineering Department
    Power Electronics and Renewable Energy Systems
    206-280-5722 (mobile)

    TK: Hi, Gregory… I’d be happy to chat with you about it, but this is probably your own research coming back to you. I believe I met you at the NREL/CU Energy Initiative Poster session last summer, shortly before I wrote this article.

    PS: I’ve deleted your email in this comment to save you from spam.

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