The Supreme Court has granted cert to review a challenge over FERC's efforts encourage "demand-response" policies. As incredibly dry as that sounds, this is a significant deal in energy/environmental area. The NYT article linked above actually gives a pretty decent summary of the issue, but I'll give my own quick take.
"Demand-response" refers to policies which give consumers price breaks when they consume electricity at off-peak times (as opposed to those times when energy usage is highest, like mid-day). In of itself, this doesn't "save" energy -- it just shifts usage around -- but it matters from an environmental standpoint because of the way power dispatched. Electricity supply and demand must be matched perfectly and instantaneously -- we produce exactly the amount of power that we need to consume. Functionally, that means that certain base generators are (more or less) always on, and then as demand rises additional generators come online to meet peak demand. Typically, these peak generators are older, more expensive, and dirtier than the base load generators -- hence the environmental benefits of demand-response. It also comes with reliability benefits -- reducing the peak electricity spikes means lessening the chance that the system will be overloaded. The losers, of course, are the operators of the expensive and dirtier peak-load plants.
The legal challenge here has to do with how the regulatory authority over electricity is allocated between the federal government (FERC) and the states. The Federal Power Ac, the main federal statute on the matter, grants FERC the authority to regulate wholesale (sale-for-resale) power transactions while preserving retail regulation to the states. Demand-response intuitively is more retail than wholesale -- it relates to when end-use consumers use their power -- but FERC attempted to structure its regulation in such a way that it created a wholesale-based demand-response framework. The D.C. Circuit didn't bite, ruling 2-1 that the program was actually impermissible retail regulation, and that is the decision under review by the Supreme Court.
Hence, as a legal matter this is less an "environmentalism: yay or nay" case than it is a "federalism/administrative law" case. Still, ideologically speaking the Court often has a left-right breakdown regarding the extent of federal power and the degree to which the judiciary ought defer to federal agencies. On that note, one encouraging sign for FERC is that Justice Samuel Alito is recusing himself from the case.