Transactive energy has been proposed to facilitate integrated economic and technical scheduling, dispatch and control of DR resources as increasing levels of intermittent renewable energy resources begin to challenge the economic viability, security and reliability of bulk electricity systems. This letter presents an important relationship between the elasticities of energy demand, capacity demand and ramping demand. The implications of this relationship are briefly examined in terms of technology development, utility and aggregator business models, and regulatory oversight with particularly emphasis on retail competition and retail tariff design. Show Partial Abstract