Transformity dynamics related to maximum power for improved emergy yield estimations

•Environmental accounting is used to estimate the value of ecosystem services.•Energy-based environmental accounting uses multipliers called transformities.•We present a new approach for selecting the most appropriate transformities.•A pulsing system exhibited minimum transformities at maximum empower.•Estimation of emergy yield can be improved by using these minimum transformities.

H.T. Odum originally defined transformity as the amount of energy of one type required to generate a unit of energy of another type with the caveat that the energy production system was operating under competition at optimum loading for maximum power. The caveat has been mostly ignored in emergy evaluations, often because it is difficult to identify when or whether a transformity was produced at maximum empower. We developed the model TechnoPulse to explore the temporally dynamic relationship between transformity and empower. As TechnoPulse cycled through four distinct phases of birth, growth, decline and recovery, maximum empower was accompanied by minimum transformity for the production flow. Conversely, the period of minimum empower corresponded to maximum transformity. After the “birth” of the new energy form, the period of growth saw empower increase as tranformity declined. Since transformity is the reciprocal of efficiency, maximizing empower also increased efficiency. We found that the non-pulsing situation had higher empower than pulsing, but that pulsing maximized power and minimized tranformity (maximized efficiency). We found that the national production of electricity in the US followed the pattern observed from the growth portion of the TechnPulse simulation by maximizing empower and minimizing transformity over the period 1995–2006. A contrast of two methods for estimating the emergy yield of systems (emergy summation based on common practices and transformity multiplication based on using minimum transformity at maximum empower) applied to PV electricity production revealed starkly different interpretations for PV’s role and viability as a primary source of electricity, but more importantly suggested that there is a easy rationale for employing each method. Finally, emergy evaluations can be improved by heeding Odum’s original definition of tranformity and using the minimum tranformity corresponding to maximum empower.