Net metering and net billing are electricity policies that enable grid-connected customer-generators (homes or businesses that own a PV (photovoltaic) or other generation technology connected to the grid) to offset some or all their electricity consumption and get paid for excess energy injected into the grid. There are many policies of net metering and net billing used by different countries. In this paper we propose a modified definition of some of the modalities that can be applicable to the two drafts of the royal decree for the Spanish regulation. Also we show, for the first time, the mathematical formulation of a comprehensive methodology for the assessment of the different modalities of net metering and net billing used in different countries. We compare several cases, taking into account the actual two Spanish drafts, the two models proposed by the Spanish National Energy Commission in its reports about the drafts and other modalities used in other countries, concluding that the first Spanish draft would have been a superior regulation for PV net metering; however, the second draft impedes the profitability of the PV so no user will install a grid-connected PV system if this second draft is finally approved. (C) 2015 Elsevier Ltd. All rights reserved.