Embodied energy
Paul Reeve (below) explains what embodied energy is and why it is important.
Embodied energy or ‘embodied carbon’ is becoming an increasingly important factor in working out the true 
environmental impact of a product or technical solution.
Building services contractors and system designers are being encouraged to take this ‘hidden’ environmental cost into account when specifying equipment. It is a key element of the overall lifecycle cost and impact of a project.
Studies of embodied energy look at the total (fossil) energy required to make a given piece of equipment. As well as the energy that goes into making the product, there can be transport and waste recovery issues to consider as well.
Embodied energy has become one of half a dozen parameters for assessing the overall environmental impact of electrical and electronic equipment (EEE). The others are:
direct energy use (or generation)
allowing for a full useful life through ease of maintenance
providing an optimum output (light, heating, other energy)
re-use and recovery at end of life of the installation
quantity and materials consumed during the life of the installation.
Ideally, embodied energy studies would take a rigorous approach, but much of the work is still semi-quantitative because all the necessary data is unavailable. This means the method usually requires assumptions, estimates and ‘trade-offs’.
However, for equipment that aims to directly or indirectly reduce fossil energy use (rather than just consume energy) embodied energy is a fundamental factor. After all, the main rationale for energy-efficient or renewable equipment is to reduce fossil energy use during its lifecycle.
Reliable studies on the embodied energy in manufactured goods rely on the co-operation of manufacturers. Clearly, manufacturers will make judgement calls on whether such studies are in their interests.
Some examples…
One embodied energy study looked at the ‘energy payback’ of photovoltaic (PV) cells1. This was a literature review of PV lifecycle modelling, including embodied energy analysis. It concluded that the likely ‘energy payback’ of a typical domestic sized rooftop grid connected PV cell is around four years (for both mc-Si and thin-film modules).
However, the error bar means the real figure could be between 2-8 years because of difficulties in determining credible, agreed energy conversion factors and even the energy value of human labour. In addition, the available energy resource (sunlight) has to be assumed. Even so, it concludes that: “small-scale roof mounted PV systems have a positive energy payback”.
Wind turbines
There has been considerable interest in the embodied energy of wind turbine equipment2. Again, energy payback for wind turbines varies, notably due to the available wind resource, but it is generally held that the ‘energy payback’ for wind turbines is good.
The energy used to produce, install, maintain, and decommission some wind turbines can be generated by the turbine in around three months plus of operation (ref: UK Sustainability Commission).
It is important to note that ‘energy payback’ (when the operation of the equipment starts to realise a net saving in carbon emissions compared to those to make and install it) is not the same as financial payback, which is how energy saving and renewable installations are often assessed. Financial payback can vary along the supply chain, with elements like economies of scale, ease of installation etc. all having an impact.
The numbers do not take into account any cultural value of installing green equipment. For example, the sight of renewable technology may reinforce the message that it is important to take action to combat climate change.
Conclusions
Embodied energy studies on EEE:
- are still quite rare and the technique is in its infancy
- have many limitations and caveats
- are potentially very important for future installation strategies.
They do, however:
- provide extra insight into the ‘energy credentials’ of equipment during its entire lifetime
- depend on manufacturers’ data
- are good at highlighting salient energy benefits and downsides, if these exist.
References
1 16 Jun 2006 Energy Bulletin
2 Some graphics on the embodied energy of various renewable technologies are available by clicking here.
Studies of basic materials
Up to now, initial embodied energy studies have mainly looked at basic materials, where the data and variables are relatively simple. Assessing embodied energy is harder for manufactured products, and ‘simplifying’ assumptions are used.
The University of Surrey is studying the “systematic life-cycle estimation of carbon inventories in different industrial sectors", including carbon footprints and embodied carbon in the plastics and construction sectors.
The universities of Bath and Oxford are evaluating the energy used in producing basic building materials (e.g. bricks) on a ‘whole life’ basis. This is part of the £3.1 million ‘Carbon Vision’ Buildings project, jointly funded by the Carbon Trust and the Engineering and Physical Sciences Research Council.
For more information about Paul Reeve and to ask him a question click here.