The government has noted the lack of available technological solutions for the transport sector and considers that opportunities for cleaner transport are limited. Electricity is supplied by the government-owned Tonga Power Ltd (TPL), which is regulated by the Tonga Electricity Commission. The rural areas in Tongatapu have grid electricity supplied by TPL and the outer islands have solar power or mini-grids that are operated on a community-based management model. The average residential electricity tariff in 2013 was US$0.52 (Figure 9.5). Tonga has used solar energy since the late 1980s although biomass remains the primary renewable energy source. There is no potential for hydro energy and assessments indicate that geothermal energy is uneconomical.