PADD: See Petroleum Administration for Defense District (below).
Parallel Path Flow: As defined by North American Electric
Reliability Council, this refers to the flow of electric power
on an electric system's transmission facilities resulting from
scheduled electric power transfers between two other electric
systems. (Electric power flows on all interconnected parallel
paths in amounts inversely proportional to each path's
resistance.) Particulate Matter (PM): Unburned fuel particles
that form smoke or soot and stick to lung tissue when inhaled. A
chief component of exhaust emissions from heavy–duty diesel
engines. Passive Solar Energy: Use of the sun to help meet a
building's energy needs by means of architectural design such as
arrangement of windows and materials such as floors that store
heat, or other thermal mass. Passive Solar System: A solar
heating or cooling system that uses no external mechanical power
to move the collected solar heat. Peak Demand: Peak demand is
the maximum electric load or deman