Further Notes on Energy Density

To follow up the previous video lesson, here are a few further brief thoughts around energy density, along with some useful references on the topic.

Energy Density – Important? Or Not?

You’ll find significant disagreement over the significance of energy density and land use as a barrier in the transition to new electricity supply mixes or to new energy applications (such as electric vehicles). In my experience the debate boils down to these main points:

  • It is a physical fact that energy sources such as sunshine, wind and biomass are less energy dense than “fossil” sources such as coal, oil and gas; and even further removed from the energy density of nuclear fuels. So to replace significant amounts of the latter, we’ll need to collect lots of the former. There’s no point trying to pretend otherwise.
  • However it’s also a physical fact that we can collect sufficient energy to meet our needs from what look like relatively small percentages of the earth’s land area. (In the next lesson, we’ll look at some simple calculations, in order to apply some numbers to this point). So in theory, we don’t have a long-term problem.
  • One practical problem is that the best areas of natural energy resource often don’t coincide with where energy is needed: populations tend not to congregate in deserts, wind-blown plains (or thick forests, or the sides of volcanoes etc.). Whereas we can build a fossil power plant close to a city and transport fuel to it, if we build a solar farm in a remote desert, we have to transport the electricity to where we need it. That means long and expensive grid lines, potentially making projects less economic.
  • If we decide instead to build power projects closer to centres of demand (i.e. to people), we often find that land is already being used for other purposes: housing or agriculture or leisure, and so on. So land may simply be unavailable, or may be expensive to access when different uses come into competition. If it isn’t being used already, there are often reasons why: it is environmentally or visually sensitive, for example.

The practicalities are, as is true so often in this business, dependent on the market you are considering. What “quality” (density) of resources does a country or region have and where are they? Where is electricity demand located? How much land is already being used, and for what? Who owns it? And so on…

There is no one-fits-all answer to the debate!

(The next lesson will explore the land use issue again, by applying some numbers to the “problem”)


(1) If you’re particularly interested in solar power, then this report (pdf) provides an interesting insight into real-life land use of solar farms.

(2) The requirement for large areas of land for some renewable power projects can have direct impacts on project cost and trigger public or strategic policy debates over the best (or most socially acceptable) uses of land. It can also lead to delays, legal or other problems for project developers and their investors where the need to secure more land increases the risk of objections, ownership or other disputes. This news story gives an example of land use issues arising over a wind farm in Kenya.

(3) Land use is obviously a bigger issue in countries which have less of it, or where what they have is more crowded. The UK is a prime example of a country with high energy use but low land availability and high population density. It’s therefore not surprising to find that one scientist who spent a lot of time highlighting some of the practical difficulties in scaling new energy sources to replace conventional fossil ones, was from the UK. His name was David MacKay, a Professor at the University of Cambridge. Here’s a TED talk of his about “how the laws of physics constrain our sustainable energy options”, including land area constraints.

(4) Where the energy sources themselves are diffuse and distributed, one logical outcome of this is to build a system where energy collection/generation is distributed too; rather than a “traditional” system of large, centralised power plants. This is happening (see image below) and I’ve written about it elsewhere: https://greycellsenergy.com/articles-analysis/dist…

(source: http://www.brooksidestrategies.com/resources/30-be…)