Policy process scholars have expressed a long-standing interest in policy evolution, though such assessments offer a limited understanding of how policy language changes across time. These micro-level assessments of policy design evolution lend insights into substantive aspects of policy adjustment over time. In this paper, we conduct a comparative case study of changes in the text of net metering legislation in four US states.

Specifically, using the Institutional Grammar (IG), we measure policy evolution as: (1) change in policy provisions that define the net metering policy system or regulate behavior, (2) change in different types of provisions (rules), and (3) calibration of policy provisions. Furthermore, we identify the dynamics of policy patching and packaging with these measures, demonstrating more information is revealed about the dynamics of policy evolution at the micro-level.

For scholars and practitioners, our novel micro-level measurement allows discernment of changes in who is being incentivized, in what ways they are being incentivized, and the extent to which they are being incentivized. Furthermore, our approach can assist practitioners in identifying policy provisions and the language of those provisions that are changing more frequently, as we find policy language does not evolve evenly.