Prosumers are households that are both producers and consumers of electricity. A prosumer has a grid-connected decentralized production unit and makes two types of exchanges with the grid: energy imports when the local production is insufficient to match the local consumption and energy exports when local production exceeds it. There exists two systems to measure the exchanges: a net metering system that uses a single meter to measure the balance between exports and imports and a net purchasing system that uses two meters to measure separately power exports and imports. Both systems are currently used for residential consumption. We build a model to compare the two metering systems. Under net metering, the price of exports paid to prosumers is implicitly set at the price of the electricity that they import. WeThe authors thank the FNRS and the Walloon Region (Grant TECR) for its financial support. They also thank P. Agrell and participants at the Mannheim Energy Conference, the BAAE conference held at CORE/Louvain-la-Neuve, the 65th congress of AFSE Nancy, the Energy Symposium at University of Barcelona, the third FAERE Conference in Bordeaux, the EARIE conference in Lisbon, the IIOC conference in Boston and the workshop on electricity demand at Université Paris-Dauphine for comments and I. Peere for English editing.