Friday, October 3, 2014

Principle: use the lowest form of energy possible

This post is part of a series on the principles of energy reduction.

Some kinds of energy are harder to get/make than others. High-grade energy, such as electricity and petrol, are very hard to produce and thus have great effects on the natural systems that support us. Thus, it's beneficial to use low-grade energy where possible, and avoid high-grade energy.

An approximate heirarchy is, from lowest (on the left) to highest (on the right) grade:
Heat << Fuel << Movement << Electricity
This means that it takes a lot of heat energy to make movement energy [1], and a lot of movement energy to make electricity (ie. a lot of energy is wasted at each stage. Generally speaking, a lot of heat energy has been use to make the electricity we have in our homes. If we then use that electricity to produce heat, we have wasted a lot of energy.

How to optimise this

We can use heat energy to heat. An excellent example of this is solar hot water which uses heat from the sun to directly heat water (a process that otherwise uses considerable amounts of fuel or electricity). Similarly, heat from the sun can be used to heat our houses (using either passive-solar [2] or active solar space heaters [3]) -- this saves a lot of fuel and/or energy. Solar heat can also be used directly for cooking via a solar oven [4].

A more subtle point is that if you have solar-heated hot water, and want a cup of tea, put solar hot water in the kettle and boil that.

[1] For example, the internal combustion engine in our car uses fuel to create movement. It does this at about 25% efficiency [5]. This means that it takes for units of fuel energy to produce one unit of movement energy.

This post was written by Angus Wallace, and first appeared on


  1. Have you seen Howard Odum's work on energy hierarchies? Definitely recommend "A Prosperous Way Down" by him if you haven't come across it already...



  2. Thanks Nat, no I haven't heard of him -- will check it out!
    Cheers, Angus


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