Sustainability analysis of renewables for climate change mitigation.

Carbon dioxide is a major greenhouse gas (GHG) responsible for climate change. The energy sector accounts for approximately 75 % of the total carbon dioxide emissions in the world. The main options for reducing carbon dioxide emissions in energy systems are energy efficiency, and utilization of renewable energy and nuclear energy. In the present global energy scenario, the share of modern renewables in the total primary energy use is marginal (about 4.5 %). This paper assesses the sustainability of renewables for the world using the criteria of life-cycle cost, net energy ratio, resource constraint and greenhouse gas emissions. Renewable options for electricity generation and hydrogen generation for vehicles are assessed on the basis of these criteria. Life-cycle assessment (LCA) is carried out using SimaPro 6 LCA software. For electricity generation the base case considered is thermal power generation using coal. The options considered are wind energy, solar photovoltaics and biomass gasification. For hydrogen production three methods based on renewables (photovoltaic (PV)-electrolysis, wind energy conversion systems (WECS)-electrolysis and biomass gasification) are compared with the steam methane reforming (SMR) method. The renewable-based technologies seem to be sustainable on the basis of all criteria except the high life-cycle cost. In some cases, e.g., in biomass-based systems, land availability may constrain sustainability. Biomass is likely to be a sustainable solution only if marginal/scrub lands can be used for biomass plantation with adequate yield. However, this option needs to be studied to see if the net energy ratio is greater than one. It is found that hydrogen production by photovoltaic-electrolyzer can be a non-renewable method at low load factor (~0.15) and PV module efficiency (10 %). However, this method is renewable for higher values of load factor and PV module efficiency. The framework developed in this paper can form the starting-point for sustainability analysis. [Copyright &y& Elsevier]