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What does embodied energy mean?

Posted by Alex Barrett on 9 January 2017 at 1:30 pm

We often worry about how much energy it takes to use an appliance or gadget. We can save a considerable amount of energy by being careful how we use our devices, but domestic energy use is just one part of a much larger problem. What about the energy it takes to make that gadget in the first place? How much fuel was used to ship it to our part of the world? What is the total cost of its existing on the environment?

What is embodied energy?

In order to determine our full carbon footprint we need to consider embodied energy. This is the total amount of energy that it takes to produce all of the components of a product, assemble them, ship them, use them and ultimately dispose of them. This can be quoted either in terms of the energy cost, or the amount of CO2 equivalent emitted in the process. In the latter case it is usually called embodied carbon.

Figuring out how much energy has gone into making something is often easier said than done. Consumer items are rarely manufactured locally, but how far something has been transported is not always made clear when you purchase it. Some businesses are reticent to publish details of their manufacturing processes, and complex devices may have components from a wide variety of sources.

In order to work out the full cost of making something requires a Life Cycle Assessment (LCA). This process examines the energy costs at each stage of the production process, from “cradle to grave”. The cost of extracting the raw materials is determined, as is the cost of manufacturing each component. The transport and assembly costs are factored in as well as the cost to use. Finally the energy required to dispose of an item is factored in.

Clearly you cannot do an LCA analysis on your own, it requires the cooperation of industry at every stage of the production process. However more and more studies are being conducted to work out the average cost of producing different appliances, gadgets and importantly, energy generation technologies.

Net energy gain

It is very important to understand how much energy went into making a wind turbine or solar panel. If a generator requires a lot of energy to make then it has to produce much more energy over its lifetime in order to break even.

This is determined by working out the Net Energy Gain (NEG) of a generator. This is calculated by subtracting the energy required to produce and operate a device, from the amount which it will ultimately return. For conventional energy sources you have to put in energy to mine coal, or refine petroleum. For renewables the cost of building a solar panel or wind turbine must be taken into account.

The circular economy

Reducing the embodied energy of our possessions is obviously much harder than reducing our personal energy usage is. The best way to do so is through recycling. It requires less energy to recycle material than to refine or manufacture it from scratch. Even when new material has to be added to the recycled stream to ensure it meets the correct quality there will be a saving.

Reuse is even more energy efficient than recycling. It takes a lot less energy to refill a bottle than it does to break one down, recover the materials and use them to make a new one.

One way to encourage reuse is with modular construction systems. These work in a similar way to LEGO. Components are designed to be interchangeable so that they can easily be reused in other projects or devices. You use a lot of energy demolishing a machine and extracting the constituent materials. If it is easily dismantled then the components can be far more easily reused.

Photo: SuperHomes


The Energy Collective: Net Energy Gain Life Cycle Assessment and Embodied Carbon

Circular Ecology: Embodied energy and carbon footprint database

Waste and Resources Action Programme: The Circular Economy

Low tech Magazine: Modular construction systems

If you have a question about anything in the above blog, please ask it in the comments section below.

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