Most of the applications I've encountered in the PC power management software space typically are delivered via a very traditional enterprise software licensing model. But I just came across a managed services provider, New Boundary Technologies, that seeks to offer this sort of service via the cloud.
The company's PwrSmart service is controlled and accessed via a Web browser with a Silverlight plug-in. As the motivator to use its service, New Boundary cites pretty standard industry research and statistics that suggest that using power management features to power down client PCs and notebooks when they are not in use can save about 15 percent on a company's annual electricity budget.
Features include an interactive dashboard that serves up the company's real-time energy savings; auditing capabilities and reports that can be used for energy rebate and other business sustainability initiatives; analytics that help you create graphs and charts showcasing energy cost reduction details; and automation capabilities that let you set power management parameters (and that will override attempts of end users to buck a corporate policy). The software also allows your company to set different policies depending on the role of the user and/or on the time of day.
You can actually try the PwrSmart service for free for up to 30 days. After that, you pay for the software on a subscription basis.