In the debate around solar photovoltaic (PV), the concept of ‘grid parity’ has emerged as the dominant benchmark for competitiveness, while some even argue that it will determine the point in time after which the PV industry will boom. But more recently, others have called into question the usefulness of the grid parity concept. Yet despite its pervasive use and increasing contestation, the grid parity concept has not been systematically interrogated to date. This paper makes two contributions towards that: first, to show how the grid parity concept emerged and how it is calculated and second, to explore the role of the grid parity debate in the solar PV field. The first contribution takes the form of a literature study of grid parity studies. To arrive at a meaningful estimation of the grid parity point, assumptions made in each step of the calculations have to be articulated and carefully evaluated. Nevertheless, this is almost never done: the grid parity studies, presentations and reports we reviewed invariably used the simplest representation available. We argue that their authors chose a simplified model for strategic reasons, e.g. to obtain (material and/or non-material) resources. This assessment leads to our second contribution: a discourse analysis of the grid parity debate. We distinguished ten key storylines and six discourse coalitions, comprised of actors who share a specific set of these storylines. Analyzing these storylines and coalitions, we show that while these actors share a common goal of PV up-scaling, they can have drastically different ideas about strategies to achieve this goal. Opening the black box of grid parity thus reveals tensions about preferred strategies in an otherwise seemingly homogeneous PV discourse. Keywords : Photovoltaic; Grid parity; Calculation methodology; Discourse analysis; Up-scaling strategies