A photovoltaic assisted residence with supplemental battery storage : searching for a complementarity

Abstract

A significant mismatch may exist between residential load characteristics and array output from photovoltaic energy conversion systems. This has warranted a closer look at incorporating energy storage as a supplement device. Storage enhances total system energy capture although its weighted benefit is highly sensitive to the particular operating scheme. For utility interfaced systems which include a schedule for utility purchase of excess PV output, the advantage of the additional capture becomes a fairly complex function of the rated price structure, utility buy-back, and the system control logic. The problem arises since photovoltaics and storage each stand as independent investment opportunities for grid interconnected users, thus offering the potential for competition between them. This competition is characterized by a total system value somewhere below their additive stand-alone values. This study includes a search for a system control logic, along with the economic and location-specific conditions, which maximize total system (PV ana storage) value. The latter is defined in terms of the breakeven capital costs at which a user-owner would be economically indifferent toward purchase, given the utility as the sole competitor. Numerous customer-utility relationships are possible in addition to a variety of system configurations. Here, a utility interfaced storage operation without photovoltaics is examined against a tandem (PV-battery) arrangement with a range of utility buy-back policies. No studies were made to assess the value of only photovoltaics or only storage to the utility, though analysis on photovoltaics can be found in both Tatum (8) and Carpenter and Taylor (3). The residence hardware and behavioral simulation were accomplished with the use of models previously developed by members of the MIT Energy Laboratory.