We have developed sensor network using wireless sensor nodes in order to increase the convenience, safety and sustainability of society. We conducted small- and mid-scale experiments and improved the sensor network. To reveal the scale-dependent problems, a large-scale sensor network experiment was important. We conducted a power consumption monitoring experiment using wireless sensor nodes in 1987 convenience stores located in the Tohoku and the Chubu district for three years. The experiment started using 15896 button battery type wireless current sensors. The sensors were installed in stores’ electrical distribution boards and current data were col-lected every ten second. We verified that sensors worked well in real store environments: average battery life was estimated over 550 days, average data receiving ratio was over 0.95. A battery maintenance operation revealed that battery replacement in excess of 10000 sensors was not practical in terms of cost. We developed a novel maintenance free wireless current sensor, which had a rechargeable battery charged via current from clamp type current transformers. All current sensors were replaced and we verified that new sensors worked well. Accuracy of power consumption data were investigated using artificial low data receiving ratio current data, the results showed that the power consumption monitoring network had practical accuracy.