Web application users are able to specify power constraints for remote web servers. These may be based on individual performance needs and energy-conservation desires. They enable the user to exercise control over the amount of energy that the web server expends in serving the needs of the user. The invention may employ such features as vertical scaling using power capacity on demand (CUoD) type functionality. The method includes providing a user-interactive interface to enable the user to indicate a preference for power restrictions with respect to its web requests. The user then instructs the web site provider to reduce power consumption in response to the user's request. The user specifies a reduction in overall power consumption for the user's needs, such as instructing the web service provider to use an energy-conserving server to handle the user's web requests, or specifying a acceptable delay or fulfilling the user's web requests.