Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of photovoltaics has declined steadily since the first solar cells were manufactured, and the levelised cost of electricity (LCOE) from PV is competitive with conventional electricity sources in an expanding list of geographic regions. Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries. The Energy Payback Time (EPBT), also known as "energy amortization", depends on the location's annual solar insolation and temperature profile, as well as on the used type of PV-technology. For conventional crystalline silicon photovoltaics, the EPBT is higher than for thin-film technologies such as CdTe-PV or CPV-systems. Moreover, the payback time decreased in the recent years due to a number of improvements such as solar cell efficiency and more economic manufacturing processes. As of 2014, photovoltaics recoup on average the energy needed to manufacture them in 0.7 to 2 years. This results in about 95% of net-clean energy produced by a solar rooftop PV system over a 30-year life-time. Installations may be ground-mounted (and sometimes integrated with farming and grazing) or built into the roof or walls of a building (either building-integrated photovoltaics or simply rooftop).