# Changes

## Solar Photovoltaic Cells for the Kingston Home FAQ

, 02:55, 27 April 2010
Are solar panels environmentally friendly?
Yes, solar panels are environmentally friendly. The main concern regarding the environmental benefit of solar panels is the amount of energy required to manufacture them, in order to address this concern the energy payback time of solar panels has been determined. The energy payback time (EPT) of a technology is commonly defined by the following equation:
:$\, EPT = \frac{EnergyIn (MWMWh)}{EnergyOutput (MWh)}$ [someone please fix units; see discussion]
This equation takes into account the energy required for manufacturing and installation (EnergyIn) and compares it to the annual energy output (EnergyOutput). The EPT of a panel is dependent on many factors such as manufacturing process, the panel efficiency, the amount of carbon in the electricity mix where the panel is manufactured, the geographical location of where the panel is operating along with many other factors. That being said many Life Cycle Analyses have been conducted on solar photovoltaic panels and a range of payback times have been determined, Alsema and Fthenakis found a range of EPT of 1-2.7 <ref>Alsema, Fthenakis"Photovoltaics Energy Payback Times, Greenhouse Gas Emissions and External Costs: 2004 - early 2005 Status", Progress in Photovoltaics: Research and Applications 14, no.3 (2006):275-280</ref> years while the National Renewable Energy Laboratory [http://www.nrel.gov NREL] found EPTs ranging from 1-4 years. An EPT has not yet been determined for Kingston, Ontario however with average panel life times of 20 – 30 years even with higher EPT the solar panels continue to be environmentally friendly.
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