This paper presents a methodology to evaluate the technical and economic performance of a grid-connected system with storage under a time-of-use (TOU) electricity tariff. The storage can help smooth demand, reducing peak demand from the grid and, in some cases, also reducing the electricity bill for the consumer. The methodology is valid for any kind of storage, but it has been used for lead-acid or Li-ion batteries, technologies that could be applied in any kind of building (residential, commercial, or industrial). This kind of system could make sense with a TOU tariff: each day, electricity would be bought during off-peak hours (at a low price) to charge the batteries, and during peak hours (at a high price), the batteries would be discharged to supply the whole load or a part of it. We focus on the storage system's profitability for the electricity consumer, analysing the total net present cost (NPC) of a system with storage and comparing it with a system without storage. The results show that even given a Spanish TOU special for electric vehicles (with a great difference between on-peak and off-peak prices of 0.135 (sic)/kW h), at the present cost of battery storage (battery bank + bidirectional inverter + control), the storage system is not profitable for the consumer. For the battery system to be economically profitable, the costs of batteries would need to be reduced to about 0.05 (sic)/kW h(cycled) in the case of low-efficiency lead acid batteries (with bi-di converter of 700 (sic)/kW) or to 0.075 (sic)/kW h(cycled) in the case of efficient Li-ion batteries (with bi-di converter of 300 (sic)/kW). The most critical parameters are the acquisition cost of the battery bank and the number of cycles to failure, which determine the acquisition cost of the battery bank per kW h cycled. (C) 2014 Elsevier Ltd. All rights reserved.