Tag Archives: renewable energy

EROI and the limits of conventional feasibility assessment—Part 3: Intermittency & seasonal variation

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In the previous post in this sequence, I developed the concept of power return on investment as a complementary indicator to energy return on investment (EROI) for assessing the viability of wind and solar PV as alternatives to thermal electricity generation. I used as my departure point for this an article in which Ioannis Kessides and David Wade introduce a dynamic approach to EROI analysis.[1] Specifically, I drew on an illustrative example that they present, based on IEA data for coal-fired thermal and wind electricity generation in Japan, showing how the time required for coal and wind installations to provide sufficient energy to emplace additional generating capacity equal to their own can differ by an order of magnitude even where the EROI for coal and wind is identical. Given that the data on which this example was based was from prior to 2002, both the doubling time in Kessides & Wade’s example and the power return on investment in the extended analysis would likely be improved if up-to-date figures for emplacement energy and capacity factor were substituted for those from the IEA study. Unfortunately, this goes only a limited way to mitigating the central issue in terms of “real world” considerations. Continue reading →

A rough guide to visualising energy density

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In concluding the previous post, I pointed out the problem with comparing stock-based energy sources—such as fossil fuels and uranium—with flow-based sources—such as wind and solar radiation—on the basis of their associated energy densities. [Update: strictly speaking, we’re dealing here with the distinction between energy density and power density. While energy density is a straightforward and very useful way to characterise and compare energy storage media such as fuels and batteries, the infrastructure for producing fuels and electricity is often better characterised in terms of power density—the rate of energy transformation or supply per spatial unit. This reflects the more immediate dependence of a particular set of socio-economic arrangements, if it’s to be maintained, on its associated energy supply rates, rather than its energy reserves. For now though, I’ll continue the inquiry based on the concept of energy density, as it is arguably the more accessible concept given the nature of our direct experience with fuels—including our own fuels, the food that we eat!] Just to recap on the previous post, establishing a characteristic energy density for a given source requires that we first nominate an appropriate spatial dimension associated with that source. This is straightforward for stock-based sources involving a given quantity of material such as coal, oil or gas, and we can readily compare the energy densities between different sources. The characteristic spatial dimension is the volume occupied by the source material. Continue reading →