Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps. During periods of high electrical demand, the stored water is released through turbines.

According to NMES research, pumped storage is the largest-capacity form of grid energy storage now available.

Run-of-the-river hydroelectricity is a type of hydroelectric generation whereby the natural flow and elevation drop of a river are used to generate electricity. Power stations of this type are built on rivers with a consistent and steady flow, either natural or through the use of a large reservoir at the head of the river which then can provide a regulated steady flow for stations down-river

NMES's assesment relates this technology to be clean, more available locations and cost effective.

Marine current power is a form of marine energy obtained from harnessing of the kinetic energy of marine currents, such as the Gulf stream.

According to NMES research, although not widely used at present, marine current power has an important potential for future electricity generation. Marine currents are more predictable than wind and solar power.

Osmotic power or salinity gradient power is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis (RED) and pressure retarded osmosis. (PRO). Both processes rely on osmosis with ion specific membranes.

According to NMES research, the technologies have been confirmed in laboratory conditions. They are being developed into commercial use in the Netherlands (RED) and Norway (PRO). The cost of the membrane has been an obstacle. A new, cheap membrane, based on an electrically modified polyethylene plastic, made it fit for potential commercial use.

Ocean thermal energy conversion (OTEC or OTE) uses the temperature difference that exists between deep and shallow waters to run a heat engine. As with any heat engine, the greatest efficiency and power is produced with the largest temperature difference.

According to NMES research, this technology has great importance as it is able to produce other benefits other than power generation:

• Air conditioning
• Chilled soil agriculture
• Aquaculture
• Desalination
• Hydrogen production
• Mineral extraction

Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power.

According to NMES research, although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power.

Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example for electricity generation, water desalination, or the pumping of water (into reservoirs).

According to NMES research, Deep water wave power resources are truly enormous, between 1 TW and 10 TW. The useful worldwide resource has been estimated to be greater than 2 TW. Waves are very predictable; waves that are caused by winds can be predicted five days in advance.