Standalone sensors and sensor networks have an important impact in meeting environmental challenges. Sensor applications in multiple fields such as smart power grids, smart buildings and smart industrial process control significantly contribute to more efficient use of resources and thus a reduction of gas emissions and other sources of pollution. Nowadays, the most topical researches pertaining to wireless sensor networks are grounded on the new optimization of structure of network transmission protocol, the routing optimization in transmission network, optimization of network structure, as a result of which the lifecycle of wireless network sensors is possible to increase. This paper describes the conditions of the distribution of network nodes and determines the basic coefficients that affect the overall life expectancy of a wireless sensor network. The methods for calculating the lifecycle of the main nodes in a wireless sensor network are analyzed and a method for assessing the life expectancy of a wireless sensor network is proposed taking into account the operating range of the network elements as well as the load of the transmitted information.