  In the Internet of Things (IoT), thousands of devices can be deployed to
acquire data from the environment and provide service to several applications
in different fields. In many cases, it is desirable that devices are
self-sustainable in terms of energy. Therefore,the research community is
exploring the possibility of employing battery-less devices, where the energy
is derived solely from external and/or environmental sources, such as solar
panels. In this work, we propose an ns-3 model of a (super) capacitor, which
can be used as the storage of the harvested energy in a battery-less IoT
device, and add the support for the intermittent behavior of devices, turning
off/on according to their energy level. To exemplify the use of the model, we
apply it to a LoRaWAN node, and compare the simulation outcomes with results in
the literature obtained with mathematical analysis, confirming the accuracy of
the implementation. Then, we show the importance of analyzing the interaction
between energy availability and communication performance, paving the way for
more accurate and realistic simulations in the field. The implemented code is
made available as open source.
