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Storing Electricity

December 6, 2011

Storage of electricity is the holy grail of renewables. Without the ability to store electricity, renewables will remain uneconomic.

Electricity must be generated as it is consumed, unless there is a way to store excess electricity for use at a later time – referred to as time-shifting renewables.

The storage issue isn’t a one size fits all issue.

Renewables require the ability to store very large quantities of electricity.

Uninterruptable power supplies, on the other hand, only require storing enough electricity to provide a buffer until back-up supplies can be brought on-line. The nature of the buffer depends on the required quality of the electricity supplied by the storage medium, in terms of voltage stability, interruptible cycles and frequency.

There are storage devices covering the spectrum between these two extremes, for doing such tasks as smoothing transmission and distribution to provide better quality in terms of voltage regulation, power factor correction and integrating distributed generation.

The real storage issue relates to renewables.

Electricity can be stored as chemical, thermal or mechanical energy.

Batteries utilize chemical storage.  These include lead-acid, Lithium-ion, Sodium-Sulphur and flow batteries.

Salt pits at concentrating solar power (CSP) plants are a form of thermal storage. Using ice in cooling systems is another method of thermal storage.

Pumped storage, where water is pumped uphill to a reservoir, is a form of mechanical storage. Compressed air is another form of mechanical storage. Flywheels, such as those produced by Beacon Power Corp., which recently went bankrupt, is another method for mechanical storage.

Another approach is to use hydrogen as a storage medium.

Storage becomes a critical element of grid operation as the impact of renewable portfolio standards (RPS) or renewable energy standards (RES) become more pronounced. Specifically, as the percentage of electricity from renewables grows from a few percent to 20% or more.

In California, where RPS has been taken to an extreme, regulators are in the process of requiring utilities to equip their systems with increasing amounts of storage. This, of course, will increase costs and the prices paid by consumers for electricity. (Assembly Bill 2514 directs the California Public Utilities Commission to determine energy storage procurement targets.)

In attempting to explain the value of energy storage, the CPUC avoids the financial cost of storage by including societal benefits in the cost equation, such as avoiding use of fossil fuels and greenhouse gas (GHG) emissions.

All of the storage mediums described above, have limitations.

Pumped storage, which is a proven technology, requires building expensive dams and reservoirs, while incurring objections from environmental organizations.

Most batteries have limited storage capacities. Those that could store large amounts of electricity, such as Sodium-Sulphur, are very large and expensive.

Compressed air storage requires a large space, with sufficient volume in which to store the compressed air.

In summary, we currently lack the ability to store large quantities of electricity at low cost.

Until this changes, renewables will remain a very costly and inefficient method for generating electricity.


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10 Comments leave one →
  1. December 6, 2011 10:35 am

    Morning Donn,

    It will be interesting to see how Premium Power’s energy storage works out for SMUD- who received some funding for a few projects as noted- www web

  2. December 6, 2011 10:43 am

    Thanks for the additional information.

    • December 7, 2011 12:27 pm

      Morning Donn,

      It appears that MIT is suggesting that Smart Meters be leveraged to move to dynamic pricing as summarized here www. web site

      The full report is here- web site

      Sooner or later someone is going to have to pay for more expensive alternative electrical energy power generation (and storage of it- or the costs of the idling fossil fuel plants needed to have reliable service). Up till now the added costs have been hidden from most residential customers by the rather inexpensive existing hydro, nuclear and natural gas generation plants (with the major fuel cost declines of the last few years) that make up the largest portion of the allocated generation costs on their (mine included) bills. I have a time of use meter with some self generation (PV) so I am fully aware of the intermittent, non scalable, nature of most forms of RE. It costs me dearly (closer to the true cost to deliver electrical power to me) at peak times in the summer if I use electrical energy from the grid.

      It is going to be a difficult time for Public Utility Commissions, in those states that are adding in lots of RE to the generation mix, in the upcoming years trying to come up with a politically acceptable way to allocate the increased costs that are going to have to be paid by someone.

  3. Reinhard Fischer permalink
    December 10, 2011 9:32 am

    You mentioned hydrogen as a storage medium. But you didn’t write about its limitations. What do you think about that?

  4. December 10, 2011 10:31 am

    I commented on hydrogen for use in cars early last year.
    For cars “The four major problems with using hydrogen are: storage on the vehicle; producing hydrogen; transporting hydrogen to service stations; and the extremely high cost of fuel cells.”
    Overall, hydrogen has important limitations. The talk now is of using wind to produce hydrogen with electrolysis, storing it, then using the hydrogen to generate electricity.
    Every step results in the loss of energy, so wind which is already very inefficient, becomes even less efficient.

  5. Reinhard Fischer permalink
    December 10, 2011 11:12 am

    I agree. The efficiency is really low. But we have learnt from our daily use of gas for our cars, that efficiency is not the only issue. Would you give the otto engine a chance nowadays? 36% efficiency? Paying three times as much for gas?

    Another issue is, how much electricity needs to be stored? If you analyze the wind production in Germany during the last twelve months and if you consider, that because of the low efficiency of 15% there is about a 7 time over-capacity needed (in future we can expect 25% efficiency, still meaning 4 time over-capacity) then you can conclude, that 70% of 1/7 of the installed capacity could be used directly. So, there is a gap of 30% which other sources are needed for, which is solar, hydro, biomass, geothermal, … and some storage medium.
    The target is 80% renewables by 2050 in Germany. I think this can be done without a storage medium.
    The real challenge is to have power plants running as soon as there is no wind and sun. Enough power plants (pump storage, gas fired stations which use either fossile or renewable gas, …) to supply most of the german energy demand.

    • December 10, 2011 11:24 am

      The cost of wind and solar generated electricity is very high; much higher than for natural gas or coal-fired generated electricity.
      From my perspective, it makes no sense to use these renewables. Why should consumers pay much more for their electricity? It’s bad for consumers and bad for the economy.

  6. Reinhard Fischer permalink
    December 10, 2011 12:14 pm

    9 ct/kWh (Euro) for onshore wind, the best developed renewable source right now. And there is still lots of progress in the reduction of production costs.

    • December 11, 2011 3:57 pm

      I don’t know the source of your quoted cost for wind generated electricity, but I do know that the estimates for the cost of wind generated electricity are closer to 20 cents/kWh than 10 cents/kWh (US$).
      And these don’t include the cost of natural gas power plants spinning in reserve to replace wind generated electricity when the wind stops blowing – or the cost of dedicated transmission lines.
      It’s useful to compare the actual cost for building various types of power plants.
      For example, land based wind costs about $2,000 per KW while NGCC plants cost around $1,200 to build, and this is before adjusting for the effect of capacity factor on the cost per KW for the electricity these units can actually produce.
      LCOE’s can be misleading, if that’s what your cost is based on. Adjusting for time cost of money and the period used in the formula, can distort the answers.
      The LCOE assumptions need to be known before making comparisons.

  7. Reinhard Fischer permalink
    December 11, 2011 5:22 pm

    We need to distinguish between the costs of onshore and offshore wind generation. According to the german EEG (renewable energy law) offshore wind generation is heavily subsidized: 15 €ct/kWh for 12 years (19 €ct/kWh for 8 years if the power plant is completed by 2018). After this time period it will be reduced to 3.5 €ct/kWh. 9 €ct/kWh is the current price of onshore wind generated power.
    The additional gas power plants is what I think are the real challenge: How economically can we run a gas power plant, which is used for less than 1000 hours/year?

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