Electric Grid Energy Storage

Storing electricity

Electricity can’t be stored. It has to be converted to something else.   Nearly all of the electric grid storage (95%) comes from pumping water up to a reservoir so the water can fall again and generate electricity. But dams have a finite lifetime just like fossil fuels – they silt up within 50 to 200 years, and there aren’t many places to build more dams.  Second most common is compressed air storage, but that is also geographically limited to areas with suitable underground caverns.

The electric grid can  handle at best 30% of intermittent energy resources like wind and solar before the grid becomes too unstable — it’s so fragile that it needs to be kept within 2% of 60 Hz. There’s no safety net, what keeps the electric grid from falling off the wire into cascading failures is the stability provided by Natural Gas Combined Cycle (NGCC) plants that kick in when the wind dies or the sun sets, and the constant hum of coal and nuclear power plants that provide 24 x 7 baseline power.

The irony is that the more wind and solar you add, the more NGCC plants you need to add for stability.

The Los Angeles Times (Halper) reports that wind and solar are making the  grid less stable because:

  • The role of the grid is to keep the supply of power steady and predictable. Engineers carefully calibrate how much juice to feed into the system as everything from porch lights to factory machines are switched on and off which requires painstaking precision. A momentary overload can crash the system.
  • Energy officials worry about the stability of the massive patchwork of wires, substations and algorithms that keeps electricity flowing.
  • “The grid was not built for renewables,” according to Trieu Mai, senior analyst at the National Renewable Energy Laboratory.

Meanwhile, the electric grid is falling apart

Seventy percent of transmission lines and power transformers are over 25 years old, and 60% of circuit breakers are more than 30 years old (Fitch).  The American Society of Civil Engineers gave the electric grid a D+ in their 2013 report card. The Pew Center said “In short, the present U.S. electric grid will not work on any scale–local, state, national or international—at the higher loads and more diverse generation sources required in the future.”

Nuclear power (19%) and fossil fuels keep the lights burning (coal 40% & natural gas 27.5%).  The maximum amount of electricity we can store is only 2.3% of the total 25 GW electric production capacity.

The Current State of Energy Storage (GES)

So of course if we keep adding more NGCC plants we’re not lessening our need for fossil fuels.  We need to store energy if we’re to wean ourselves off of them.  But we’re still a long way from figuring out how to make low cost, high energy density, fast response, safe storage devices.

Electric Grid Energy Storage Options Peter Singer

Source: Peter Singer. 2011. Energy Storage Crucial Step for Renewable Electricity, Says APS. EnergyStorageTrends.Blogspot.com.

Pumped Hydro: 1) Geographically limited 2) Environmental impacts 3) High overall project cost

Flywheels 1) Rotor tensile strength limitations 2) Limited energy storage time due to high frictional losses (1-2 hours).

Flywheels spin at very high speeds, up to 20,000 rpm, which makes them very unsafe when fragments of a broken flywheel spin off.  for safety, they’d need to go underground (or expensive thick-walled enclosure), which greatly increases their cost.

Superconductive magnetic energy storage: 1) Low energy density 2) Material and manufacturing cost prohibitive

Electrochemical capacitors: Currently cost prohibitive

Thermochemical energy storage: Currently cost prohibitive

Compressed Air Storage:  1) Geographically limited and a lack of suitable caverns, 2) Lower efficiency due to round-trip conversion, 3) Slower response time than flywheels or batteries, 4) Environmental impact


There are many issues, see “Why Killed the Electric Car” for details.  But the deal killer is the cost –$100-200/kWh — at least as expensive as generating electricity.  And scale: the energy density of batteries is so low that you’d need a LOT of batteries, and the the billions of tons of materials to make them would likely exceed known mineral reserves and drive the cost of batteries even higher, with dire environmental consequences if their cadmium, lead, nickel, and so on were released (Pew).

There is significant uncertainty about the usable life of batteries, and concerns about their safety as well.

It takes a long time to bring a battery to market. The sodium–sulfur battery, conceived by the Ford Motor Company back in 1967 was finally commercialized over 40 years later (Whittingham).

Lead Acid: 1) Limited depth of discharge 2) Low energy density 3) Large footprint 4) Electrode corrosion limits useful life

NaS: 1) Operating Temperature required between 250°-300° C (482°-572° F)   2) Liquid containment issues corrosion and brittle glass seals

Li-ion: 1) High production cost – scalability 2) Extremely sensitive to over temperature, overcharge and internal pressure buildup 3) Intolerance to deep discharges

Flow: 1) Developing technology, not mature for commercial scale development 2) Complicated design 3) Lower energy density

Too complicated?

One of the main reasons societies collapse is they grow too complex (Tainter).  Not only is each of these storage devices complex, we need a dozen different kinds of energy storage to meet the different needs of the complicated electric grid:

1) Off-to-on-peak intermittent shifting and firming. Charge at the site of off peak renewable and/ or intermittent energy sources; discharge energy into the grid during on peak periods.
2) On-peak intermittent energy smoothing and shaping. Charge/discharge seconds to minutes to smooth intermittent generation and/or charge/discharge minutes to hours to shape energy profile
3) Ancillary service provision. Provide ancillary service capacity in day ahead markets and respond to ISO signaling in real time.
4) Black start provision. Unit sits fully charged, discharging when black start capability is required.
5) Transmission infrastructure. Use an energy storage device to defer upgrades in transmission
6) Distribution infrastructure. Use an energy storage device to defer upgrades in distribution
7) Transportable distribution-level outage mitigation. Use a transportable storage unit to provide supplemental power to end users during outages due to short term distribution overload situations
8) Peak load shifting downstream of distribution system. Charge device during off peak downstream of the distribution system below secondary transformer); discharge during 2-4 hour daily peek
9) Intermittent distributed generation integration. Charge/Discharge device to balance local energy use with generation. Sited between the distributed and generation and distribution grid to defer otherwise necessary distribution infrastructure upgrades
10) End-user time-of-use rate optimization. Charge device when retail TOU prices are low and discharge when prices are high
11) Uninterruptible power supply. End user deploys energy storage to improve power quality and /or provide back up power during outages
12) Micro grid formation. Energy storage is deployed in conjunction with local generation to separate from the grid, creating an islanded micro-grid


(BES) Basic Research Needs for Electrical Energy Storage. 2007. Report of the Basic Energy Sciences workshop on electrical energy storage.

EIA. Table 1.1. Net Generation by Energy Source: Total (All Sectors), 2004-February 2014. U.S. Energy Information Administration.

Fitch Ratings, “Frayed Wires: US Tr ansmission System Shows Its Age,” 2006

Friedemann, A. 2014. Electric Grid Overview.  www.energyskeptic.com

Fridley, David. 2010. Electric Energy challenges. Post Carbon Institute.

GES. December 2013. Grid Energy Storage. U.S. Department of Energy.

Halper, E. Dec 2, 2013.   Power struggle: Green energy versus a grid that’s not ready. Los Angeles Times.

Pew Center. 2004. The 10-50 solution. Technologies and Policies for a Low-Carbon future. The National Commission on Energy Policy.

Whittingham, M. S. April 2008. Materials Challenges Facing Electrical Energy Storage. Harnessing Materials for Energy  www.mrs.org/bulletin vol 33.

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