# 4. GROWTH POTENTIAL WITH ALTERNATIVE INFRASTRUCTURES UNDER AN ENERGY PLOWBACK CONSTRAINT

In this section we examine the dynamics of growth of electricity supply under the constraint of energy plowback for several representative technologies: coal, oil, gas, nuclear, hydro, wind, and PV. Our analysis is limited to a few representative technologies for which the data needed for our calculations are available. CCS is a promising technology for reducing the heavy carbon footprint of coal-...red generation (Stephens and van der Zwaan, 2005). However, it is clouded by large uncertainties regarding the speed of implementation and the ultimate feasibility of large-scale application. Moreover, CCS is doubly capital intensive, both in terms of the extra equipment to handle the carbon dioxide and the lowered e¢ ciency of the overall plant. Thus its performance metrics (EROI and �1) are likely to be inferior in comparison to traditional coal-...red plants. There is also considerable excitement surrounding the development of concentrated solar power (CSP). The parameter values of both CCS and CSP remain speculative.

Using the idealized model developed above and literature values of the relevant parameters– EROI; T; ';and �1–it is possible to identify the essential constraints on feasible rates of growth of alternative technologies. For illustrative purposes, we ...rst employ the parameter values reported in one speci...c study (IEA, 2002). Subsequently, we utilize values reported in more recent studies that take into account the impacts of technological innovation on plant performance and the energy parameters of alternative infrastructures.

It is important to acknowledge up-front the limitations of the data reported in the IEA study. First, these data re‡ect the operating experience of existing plants as well as engineering estimates for hypothetical installations of electricity generation systems in Japan. As such, they might not be representative of global options. In particular, the single source of data does not adequately take into account the site-dependent nature of renewable energy performance. Capacity factors and consequently net energy returns for wind and solar can vary dramatically across di¤erent locations. Clearly, the wind and solar resources of Japan are not necessarily comparable to those found in the best sites around the globe. Second, we must recognize that some of the values of the parameter estimates reported in the IEA study might be considerably outdated. Wind and solar power have experienced signi...cant technological advances in recent years. On the positive side, since the estimates come from a single study they are likely to su¤er less from problems of methodological inconsistency than the updated estimates we employ that are based on di¤erent studies. Moreover, the estimates reported in the IEA study permit us to back-calculate the two subcomponents of EROI: E the initial capitalization expenditure of energy Pnp'T<sup>and the ongoing variable expenditure</sup> h: To do so with the updated parameter values requires some additional assumptions.

The goal of our illustrative analysis is not to de...ne the most accurate point estimates or representative values of net energy parameters. Instead, we seek to: (i) evaluate the e¢ cacy of postulated symbiotic mixes of infrastructures for attaining sustainability goals; (ii) determine the bounds on the self-sustained growth rate for each category of infrastructure; and (iii) assess the impacts of technological change on the relevant parameters.

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