Power Density and Its Implications for Renewable Energy

A well respected thinker in the renewable energy space Jigar Shah posted this article on Linkedin for discussion.  The article has a lot of great data and information but I think the conclusion that centralized power is required to support large cities is off the mark.

In summary, the article points out that cities are very concentrated energy users and renewable energy is a dispersed and not dense energy source.  So in the unlikely event that you could completely cover the city with renewable energy it would be insufficient to provide the power for the city.

Second he concludes that the ONLY solution is therefore to provide power from highly concentrated central sources of power.  I strongly disagree with this conclusion.  I would rephrase it to say that a significant amount of the energy must come from outside of the city.  But the need for dense or centralized does not follow logically from the initial premise of the city being a dense user of Power / Energy.

Lets add a little more to the part that makes sense, i.e. that you would not site the majority of a city’s renewable energy in the city.  It is right on and there is a second reason this is true and that is that even if the renewable energy had sufficient density, you would be required to have massive, uneconomical storage to address the intermittency.

There is another solution to the Power/Energy density problem and that is to bring in power from dispersed sources via the grid.  Much as leaves feed a tree.  This also dramatically reduces the intermittency problem as it aggregates decorrelated sources smoothing the intermittency.  As the grid expands, the impact of intermittency diminishes.   This series of posts on the Supergrid looks at this in detail and provides a wealth of current source material.

At this point the state-of-the-art for moving massive amounts of power is High Voltage DC.  This can now be deployed at 800kV and can move power transcontinentally.  Serious plans are under way to do just that and combine it with a more robust network of 765kV AC.   There is some good summary information starting at page 180 of this report.

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