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Energy storage problem dates back to the ol mill pond

  • Apr 16, 2018

Major changes to the electric power industry will impact our lives.

There is a mill pond in New England that probably looks now much as it did more than 200 years ago. Hikers sometimes stop there for a break in their trek through the surrounding hills. And on a late-spring morning, they are rewarded with an idyllic view. Soundless except for the occasional soft plot of a float cast by a boy fishing at one end, and its response by the reigning bullfrog, the pond is at peace with itself and its environment.

It is difficult to imagine that this idyllic mill pond could come to symbolize the forces that are gathering to change our lives, but it does.

Mill ponds are not natures work. They were created by dams across creeks and streams or, in many cases, dug with picks and shovels for one purpose: to store energy. In the days before electricity was understood, controlled and in widespread use, grain harvested by farmers was ground into flour by hand or at a mill. In areas blessed with rivers, streams and creeks, the energy to power the mills was provided by water flow.

Mill ponds were dug and filled with water to provide energy storage that could operate the mill when lack of rainfall lowered the water flow.

Artificial lakes behind huge dams and hydroelectric power plants have replaced the mill ponds, but the problem they were constructed to solve remains the same: energy storage. Electricity is a big improvement but storing electrical power is expensive enough to be impractical on a large scale.

The electric power situation today is a bit different, but in one crucial element it is the same. At the supply, or production, end, electric power cannot be stored.

What can be stored is power generating capacity. This concept predates the effective use of electricity, and mill ponds trace its history.

Modern mill pond equivalents were made on a massive scale by building huge dams to block and control a rivers flow creating a large lake of stored electricity generating capacity behind the dam. Many of these lakes are multi-purpose, of course, and their uses sometimes include fishing and recreation, drinking water supply, and river flow control to reduce flooding damage.

The lakes and dams can help to even out the flow of electricity during periods of low river flow, but they do not help with the problem of coping with the peaks and valleys of electricity demand. Without electric energy storage, that requires excess generating capacity, and while hydroelectric dam projects are usually high-output, that output is fixed, and very, very expensive to expand if that is even physically possible.

Much the same economic picture faces fossil fuel-generated power. The cost of installing generating capacity to meet peak demand is very high, and economically inefficient. An industrial strength generator carries an awesome cost and to have it sitting idle is a wasted investment like owning a cargo ship that sits idle at a dock.

The partial solution to that problem is the national power grid. As the earth rotates, clock time advances taking peak demand along with it. Early evening is a peak demand time each day the diurnal cycle and as demand rises in the west it is winding down in the east.

By sending electricity at high voltages to reduce transmission losses, the grid allows power companies to even out their production by purchasing its needed kilowatts from companies selling its surplus energy to companies that need it all parties seeking to maximize the returns from their investment in production facilities.

The national power grid is not without some problems. There is always the weakest link issue in any network, and the grid has on occasion proven vulnerable to human error in dealing with unexpected outages. It is also believed to be vulnerable to hackers, and this could develop into a serious problem.

The grid also serves as a free market for electric energy. In todays world, along with the usual power company customers it attracts entrepreneurial ventures that are producing alternate-source electricity solar, wind, etc. and selling it to grid market participants.

The same problem that the national grid solved is duplicated on the supply side with solar power. A solar power plant faces a daily cycle of light and dark, and every night both its output and its capacity are reduced to zero. Without energy storage, a solar power plant faces the price uncertainty of having to purchase its total capacity on the open market every night.

Economics, engineering and demand combined to produce the mill pond, and these same powerful forces are bearing down on the energy storage problem today. Their impact will bring major changes to the electric power industry and to our lives.


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