The Treehouse Blog


Power vs. Energy

by on Apr.08, 2010, under Science, Technology

I’m trying to catch up on some reading, and am working through a number of articles concerning energy sources, the power grid, and so forth.  One almost constant source of annoyance I find in these articles is that the difference between power and energy are either ignored, misused, or left hopelessly ambiguous.  The writers are not totally to blame, since our vocabulary for discussing these concepts is weak and it takes a lot of effort to clearly convey the correct meaning.  Consider the following example:

The U.S. electric system has 2.5 gigawatts of pumped hydro storage capacity.

“Capacity” when used to discuss an energy storage apparatus can have two meanings.  It could mean the power capacity of the system, which is the amount of energy that can be released from storage and converted to electricity instantaneously.  For pumped hydro storage, this would be determined to a large degree by the size of the turbines, generators, and penstocks.  This quantity represents, for instance, the number of lights a plant could handle without dimming – it says nothing about how long it could keep them lit.  A common unit of power capacity is gigawatts.

The other type of “capacity” is the energy storage capacity of the system.  For pumped hydro storage, this is the value related to the size of the water reservoir.  This is the quantity that represents how long a plant could keep a given number of lights lit, for instance.  A common unit of energy capacity is gigawatt-hours.

Assuming the author chose the units correctly, this quote tells us that the power capacity of US pumped hydro is 2.5 GW.  Unfortunately, something isn’t right, because the Energy Information Administration says the number is actually 20 GW.

Consider another example:

The Norton project could store 2.7 gigawatts of power in an abandoned limestone mine.

I’m afraid this one is beyond redemption.  You don’t store power, you store energy.  But the units given are for power, and from further research in other articles, the power capacity of the plant is expected to be 2.7 gigawatts.  I was not able to find a source that estimated the plant’s energy storage potential.

Any time you read the words “power,” “energy,” or “gigawatt” in an article, read it very critically.  The commonly cited statistics for power plants are always their power capacity, and even for energy storage plants, storage capacity is seldom stated.  One likely reason is that power capacity is relatively easy to determine – it is likely written on a nameplate on the generator somewhere.  Calculating the energy capacity of a storage facility would be more challenging, and might not be a number required by regulators – and hence one that is seldom available.

Both quotes are from this article, but many articles discussing energy storage have the same problem.

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Climate Change

by on Dec.28, 2009, under Politics, Science

I’ve been giving some thought recently to educating myself about the studies behind climate change.  It’s a very charged issue and one that could have profound impacts through either its effects or the effects of trying to combat it.  It’s also one that’s difficult to discuss.  The term “global warming” has lost its literal meaning and now connotes the heat-death of the world with dead Polar Bears and permanently flooded coastlines.  But what are models really predicting and with what certainty?  What data are these models based on, and with what accuracy?  I’ve just about concluded that I can’t trust anyone but myself look at the primary sources and not the distilled summaries, but that sounds like a massive undertaking.

It was brought to my attention recently that the late Michael Crichton had given a speech about his skepticism of “global warming” (the non-literal term) and I had to give it a read.  In case you don’t know, he’s the author of books such as Jurassic Park (ad) which I thoroughly enjoyed for their technical detail.  Not to mention he was working on the movie adaptation of his book The Andromeda Strain (ad) while still in medical school, if I remember correctly – so a pretty gifted guy.  While I think his speech makes some oversimplifications (just as Al Gore’s An Inconvenient Truth (ad) does – yes, I have seen it), there is one point he makes that I emphatically agree with: “I [regard] science as the business of testing theories with measured data from the outside world. Untestable hypotheses are not science but rather something else.”  If I do manage to do some reading on this, that sentiment will be the standard I measure against.

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