Abstract: Modular storage systems include load sensors disposed beneath or in association with platforms. The load sensors are pulse-sampled for signals corresponding to loads at time intervals, rather than continuously, in order to conserve electrical power. An item associated with a transaction is identified based on a change in the loads, as determined from the pulse-sampled signals. The platforms are aligned at horizontal or non-horizontal angles, and photovoltaic power sources with banks of photovoltaic cells are mounted to front edges of the platforms. When a user reaches over one of the photovoltaic cells to access an item on a platform, a level of power or voltage generated by the photovoltaic cell is diminished. The item closest to the photovoltaic cell having the diminished power or voltage, or a customer that accessed the item, may be identified accordingly.