The technical potential for renewable energy sources in PNG is enormous, but many of these resources are in remote locations with limited demand, and are not readily exploitable.Geothermal energyThe Geothermal Energy Association estimates PNG’s geothermal potential at 21.92 terawatt-hours; the association also categorises the country as an economy that could, in theory, meet all its electricity needs well into the future from geothermal sources alone. Installed geothermal capacity in 2010 was 56 MW.HydropowerPNG has significant hydroelectric potential. Its land area includes nine large hydrological drainage divisions (basins). The largest river basins are the Serpik (with catchment area of 78,000 sq km), Fly (61,000 sq km), Purari (33,670 sq km), and Markham (12,000 sq km). There are other catchments of less than 5,000 sq km, in areas that are very steep. On the mainland, the mean annual rainfall ranges from less than 2,000 mm to 8,000 mm in some mountainous areas, while the island groups receive a mean annual rainfall of 3,000–7,000 mm. The gross theoretical hydropower potential for PNG is 175 TWh per year. There is little economic potential for the expansion of large hydro, due to the lack of substantive demand near supply sources. However, greater potential exists for developing smaller hydro schemes, with over 10 new small hydropower schemes deemed as feasible in the 2009 Power Development Plan. Combined capacity for these new schemes exceeds 20 MW.Ocean Thermal Energy Conversion (OTEC)There is very limited knowledge of PNG’s potential for OTEC, tidal energy or wave energy. Near Port Moresby, the tidal range is 2.7 metres, compared to 1.1–1.6m in much of the country. Reportedly, there is a 6m range in parts of the Torres Strait. There have been very preliminary proposals to tap tidal currents (peaking at 7–11 km/hour) at Buka Passage, near Bougainville.Wind energy There have been no systematic estimates of wind energy potential since the 1970s, when the best potentials were assessed in portions of Central, Western, Milne Bay and New Ireland provinces, and the Port Moresby area. A pilot wind energy project is being installed in the Duke of York islands, jointly funded by the Papua New Guinean and Chinese governments.Solar energySolar energy is among the largest potential sources in PNG. Average insolation in much of the country is 400–800 W/m2, with 4.5 to 8 sunshine hours a day. Of 23 locations assessed, Port Moresby has the largest resource, with 2,478 sunshine hours per year. The lowest is Tambul, Western Highlands, with 1,292 hours. The best locations for solar PV are the offshore islands, and in the southern regions of the country. As of 2008, no electricity-producing installations were present in the country, although a solar home systems project for schools is in place, with help from the Sustainable Energy Financing Project from the World Bank/GEF.Biomass energyAlthough two thirds of PNG are covered with forest, much of it is inaccessible or unsuited for energy use. 58% of land is subject to strong or severe erosion, and 18% is permanently inundated or regularly flooded. The main practical biomass energy potential is in areas such as logging and agricultural production, using either the crop output or residues. Log exports are roughly 2 million m3 per year, but very little is processed locally, leaving only small amounts of biomass for energy production. There are 18 major wood-processing facilities, but the amount of residue produced and it's availability for energy use is unknown. Traditional rural use of biomass is still relatively high, due to the low level of electricity access for cooking, lighting etc.