Calculating the Energy Return on Energy Invested (EROEI or EROI) for Spain’s Solar Photovoltaic Energy

Abstract

Neither an organism in nature nor human society can live without energy. Gaining that energy, whether it is solar, food, wood, coal, oil, natural gas, hydropower, wind, solar PV, or anything else, requires specific systems devoted to obtaining that energy. These systems in turn require both financial and energy investments, both initially for their construction and over time for their maintenance and repair. The energy returned by a system able to deliver energy to society (called ER or E _out) divided by the energy input required to get it (EI or E _in) is called the energy return on investment (EROI or sometimes EROEI, with the second E used to refer to the use of energy in the denominator). The term is related to “net energy” (e.g., White 1949; Odum 1973; Hall and Cleveland 1982) and some aspects of “life cycle analysis” but is more explicit. It was derived originally from thinking about fish migration as an energy investment (Hall 1972), and its first use for societal energy was in Hall et al. (1981) and Cleveland et al. (1984). Usually this relation is derived either as a year by year average (typical for a nation’s oil production) or from costs and gains over the life span of a particular or typical individual well or unit. The latter depends upon a key variable: the expected duration time, or so-called life cycle, during which it is producing energy, either theoretically or, ideally, measured. In photovoltaic systems, this period is usually considered 25 years from the point of installation. We explore this in detail in the following chapters.