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Environmental impact of renewables

By Dave Elliott

Renewable energy technologies are usually considered to have low environmental impacts compared with conventional energy systems. That seems obvious in terms of direct emissions of carbon dioxide and other greenhouse gases – for most renewables (biomass apart) there are none. Similarly for emissions of radioactive materials – none. However, the use of renewable sources does lead to some impacts, most of them being small and local. How can they be assessed and compared?

Whilst we can use broad, generalized assessment frameworks based on, for example, life cycle carbon emissions, to compare conventional fossil and renewable energy options, these frameworks have their limits, and they are less use in making comparisons between individual low or zero carbon renewables. Given that there are also so many different renewable energy technologies, using very different types of source, it is certainly hard to make realistic comparisons between their total environmental impacts. Many of the impacts seem likely to be site specific and simply totting up individual impacts on some arbitrary score basis clearly has limits: how do you weight the different types of impact?

Well, help may be at hand. As I have mentioned before, Alexander Clarke, at Bath University, UK, has been working on a novel approach to environmental analysis of renewable impacts for some while. It seeks to provide a parametric framework for comparison that is more fundamental, based on basic physical principles, so as to aid policy choices between them. See his interim paper.

Now this work has come to fruition, with the publication by Routledge of Clarke’s major book ‘Rethinking the Environmental Impacts of Renewable Energy: mitigation and management‘. He argues that, historically, the assumption has been that energy sources and flows are incidental to natural processes, and therefore readily available for human use without much impact. However, he says this is not the case: energy flows in nature serve ecosystem functions, and using them will have eco-impacts. His focus is on what happens when natural flows are interrupted – when we extract energy from them. He uses hydro as his main case study, since there is sufficient data on river energy flows and energy extraction impacts to test his model of interactions. But he applies it to the other ‘flow’ renewables – solar, wind, wave, and tidal, as well as biomass stocks, which are indirectly related to solar energy fluxes. In each case he looks in detail at the technical and environmental processes involved and their interactions.

So what are the conclusions? Put, simply when large amounts of energy are extracted from natural flows, you get large eco-impacts, but the scale depends on the energy flux density of the flow, and on the specifics of the extraction technology, as well, of course, on what the energy flux does, or would have done if not diverted, in nature. So wind has quite high flux density (compared with direct solar), but only a small part of the flow is extracted by wind turbines, so extraction does not have significant impacts on the flow or on the environment. Using direct very diffuse solar flows has even less impact, unless very wide areas are covered. Hydro and tidal barrages have probably the most impact – intercepting, and almost completely blocking, high energy flux flows that normally carry out significant eco-system functions. With wave and tidal streams, the impacts are less – only small amounts of energy are abstracted from large flows. Biomass impacts are more complex. The energy input is low flux density solar, but it is collected over large areas and long times in usually very sensitive and interactive environments to produce a medium intensity energy source, which we may then use in a variety of ways. The impacts depend on the type of source used and the environment in which they are produced – clearly biomass has many roles in ecosystems.

The book quantifies these various extraction-related interactions wherever possible and gives an excellent overview of the role of energy flows in the natural environment and the impacts of modifying them. Note that, although it is generalisable to a degree, local conditions will change the results, and this high-level parametric analysis only looks at physical impacts on ecosystems, which may have some significance for wildlife but cannot identify specific wildlife population impacts, or human perceptual reactions, e.g. in relation to visual intrusion. Even so it offers some good insights into the impacts it can identify, and thus also indications of how they might be reduced or avoided. While it is clear that, as with any energy technology, there will be impacts, whereas with fossil and nuclear fuels they are mainly related to emissions and pollutants, in the case of renewables the impacts are more to do with interactions with ecosystems. This study provides a helpful framework for assessing and comparing their scale.

In terms of possible responses to the impacts Clarke’s book describes, it allows us to go beyond simple practical rules of thumb, like that evidently used sometimes by run-of-the-river hydro project designers who say you should not take out more than 10% of the energy in the flow. It gives some indication of how impacts can be reduced or avoided by careful design, location and orientation of extraction technology. That is important since potential impacts are often seen as a major issue for renewables, sometimes without much basis in fact. For example, it’s sometimes claimed that wind turbines will ‘use up all the wind’. Odd since they will have less impact than trees! It is helpful to have a rigorous basis for counter-assertions and a guide for making low impact choices. There are impacts, but mostly they are small and, with the help of studies like this, most can hopefully be dealt with. Recommended.



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