Funicular Power – Newton’s Apple to the rescue

Posted in Uncategorized at 1:23 am by Administrator

If you have been reading entries in the “Black Swan Blog” you should have noticed that they deal with concepts that are somewhat off the mainstream but still very grounded in real world situations and applications.  However, in my introduction to this blog I did warn readers that some of the ideas would be really “out there”.  This is one of those blogs.

From the beginning of widespread distribution of electricity in the 1880’s through to the middle of the 20th century the most common source of electrical power generation has been the hydro-electric dam.  “New Deal” projects like the Hoover Dam in Arizona and the establishment of the Tennessee Valley Authority brought on massive new generation capacity leading in a very real way to the expansion of urban development in the Southern and Western United States.  Other regions, like the Canadian provinces of British Columbia, Manitoba and Quebec as well as Scandinavia rely almost 100% on hydro-electric power.

Most of us have probably never thought about what the true source of energy for a hydro-electric generator is.  It is that most mysterious of forces in the universe . . . gravity.

Water from lakes, rivers, soil and trees as well as the world’s oceans evaporates to form clouds.  These clouds are carried by the wind until they are forced over some mountain or hill causing them to cool, condense, and produce rain.  As a result of this hydrologic cycle rivers and lakes are formed at high elevations.

Anyone that has carried a gallon of water up a set of stairs can tell you that water is a pretty weighty substance.  So the existence of millions of gallons of water in mountain lakes and streams represents a vast amount of what is known in scientific terms as “potential energy”.  Hydro-electric generators work by tapping into this energy as the water makes its way back down to the sea.

As we all know, electricity use varies throughout the 24 hour diurnal cycle.  During peak demand from roughly 5 pm to 11 pm local time, 2-3 times the electricity is required compared to what is needed in the middle of the night.  Therefore during the off-peak hours there is an excess of capacity at most hydro generating stations.  Sometimes it is possible to reduce the flow of water and refill the reservoir (cutting it off altogether would dry up the river below the dam with serious impacts on fish and wildlife).  However, if the reservoir is full that possibility does not exist and all of the potential energy for the water that goes over the dam’s spillways is lost.

There have been efforts to try and recapture some of this energy since the early days of hydro power development.  The most common technique is known as “hydro-pumping”, in which water from below the dam is pumped back up into the reservoir at night. However, there are only a limited number of locations where the geography lends itself to a successful implementation because of the requirement for a significant reservoir below the dam.  And here again, if the upper reservoir is at capacity this technique does not work.

But there is another possible approach to capturing and storing the excess electricity generated at night from hydro (and wind, and even coal-fired plants which must be kept running 24 hours a day).   The concept is to use a purpose-built funicular railway.

The first funicular railways began to appear in the late 19th century.  They are built with the specific purpose of carrying goods or passengers up steep slopes.  In most cases these are relatively short and designed to carry passengers such as the funicular at the St. Regis Deer Valley Resort in Utah, completed in 2008.

However, there is precedent for the industrial use of funicular railways.  For example, the Katoomba funicular in Australia was originally built to carry coal and kerosene shale before it was converted into a tourist attraction.

So imagine if you will a funicular railway over 4 kilometers long constructed up a mountainside at an angle of 35 degrees.  The train built to run on this railway would consist of 20 or more relatively conventional cargo cars loaded with blocks of solid cast iron weighing approximately 300 tons each for a total of 6,000 tons.  The main modification for these cars would be the addition of 3 extra axles so that the cars could carry much more than the normal maximum weight.

A 10 MW electric locomotive engine would be used to haul the train up the mountain at night using relatively cheap “surplus” electricity.  The next day, during peak demand times, the train would be allowed to slide back down the mountain with the electric motor working in reverse to generate 10 MW of electricity.  Given current market conditions this peak demand electricity would sell for approximately $60/MW-Hour more than it cost to purchase it the previous night.  For this configuration the annual revenue would be more than $2 million/year with the potential to increase significantly during the lifetime of the project in step with rising electrical rates.

Assuming a cost of $10 million/kilometer for construction of the funicular rail bed and an additional $8 million for the cars, electric motor, cast iron ballast, and system integration the total project cost would be approximately $50 million.

At $5 million/MW this concept would be competitive with the real cost of wind and solar (because of their low effective yield rates).  The major advantage is that funicular power would be truly available “on demand” at the flip of a switch and as such could help reduce imbalances in regional grids caused by fluctuations in renewable sources such as wind and solar.  And, of course, it is 100% green and could be located anywhere there is a mountain.

A Black Swan – definitely!  But if it could be made to work …

28-Mar-2016 Update: A commercial firm, Advanced Rail Energy Storage has developed a successful pilot project using this approach and has received approval to proceed with a full-scale commercial project.

17-Apr-20 Update: Two firms in Europe are proceeding with promising applications of gravity based energy storage systems. The award winning team at Gravitricity have raised sufficient funds to start building their prototype installation which will involve lowering and raising a large weight in an abandoned mine shaft. Over in Switzerland the Energyvault company is proposing to use a large number of stackable weights to store energy.

Harnessing the power of gravity in different ways could be an important part of our efforts to achieve a truly sustainable energy environment.

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