Parabolic dish stirling engines - Devices that concentrate sunlight at a single focal point via a parabolic dish to produce electricity, and can track the sun along two axes by automatically adjusting the direction of the dish.

Parabolic troughs - Solar thermal energy collectors that consist of a long parabolic mirror and a Dewar tube running its length at the focal point that absorbs energy from the sunlight which is converted into electricity.

Particulate matter (PM) removal systems - Systems that remove particulate matter (harmful fine particles) from flue gas.

Passive design - Building design that takes advantage of the local climate to provide some or all of the heating, cooling, lighting and ventilation needs of the occupants.

Peak load capacity - Maximum electrical load capable of being handled by transmission equipment in a given time period.

Physical wastewater treatments - Treatment methods that usually treat suspended (as opposed to dissolved) pollutants. The process often involves simply allowing suspended particles to float to the top of a container or settle at the bottom, but may also use mechanical means to assist in the settling/floating process.

Point-of-use solutions - Water monitoring or treatment solutions that are installed at the point where water is actually used (such as apartments, commercial and industrial facilities).

Power towers - Type of solar power plants that uses a tower and a high heat capacity component to receive the sunlight focused by an array of flat movable mirrors and convert it into electricity.

Pressure swing adsorption - Application that seeks to separate certain target gases from a broader mixture of gases using specialized adsorptive materials. Typically used to remove carbon dioxide and hydrogen sulfide to increase the quantity of methane, a key component of natural gas.

Pressurized fluidized bed combustion (PFBC) - Developed to further improve efficiency levels in coal-fired plants, it replaces the conventional combustion chamber of the gas turbine with a pressurized fluidized bed combustor. The end result is that the products of combustion pass through a hot gas cleaning system before entering the turbine.

Primary treatment solutions - Solutions used primarily at the sedimentation stage, where the solids are separated from the wastewater stream.

Process waste - Waste that result from the process of converting raw materials into final products (e.g., scrap metal, slag, mine tailings, etc.).

Process-redesign - Redesign and/or systems optimization of the operation with the purpose of increasing resource use efficiency and minimizing pollution.

Pumped hydro storage - Method under which energy can be stored by pumping water into a high reservoir and then releasing it back into a lower reservoir to generate electricity when passing through power generating turbines.