In this paper we study the energy efficiency of hybrid high altitude platform (HAP) and terrestrial communication systems in the uplink. The applications of HAPs in the recent years have gained significant interest especially for telecommunications. A cooperative relay based communication strategy on the ground with a single source-relay pair is considered for the hybrid HAP-terrestrial system. We show that cooperation on ground between the terrestrial terminals could improve the energy efficiency in the uplink depending on the temporal behavior of the channels. Thus by having cognitive context aware capabilities in the ground terminals one could exploit the spatial domain to improve the energy efficiency. The energy efficiency can be further improved by means of proper power allocation between the terrestrial source and relay nodes. We consider the decode and forward based cooperative system for our study with a constraint on the overall bit error probability to achieve a predefined quality of service. Results show that considerable gain in the energy can be attained by exploiting the spatial domain by means of cooperation.