Prospective CO2 emissions from energy supplying systems: photovoltaic systems and conventional grid within Spanish frame conditions

In order to assess the environmental sustainability of a novel wastewater treatment process based on power an electrochemical reactor by photovoltaic solar modules (photovoltaic solar electrochemical oxidation), a life cycle approach was considered to quantify the CO2 equivalent (CO2-eq.) emissions coming from the two supplying power systems to the electrochemical process: conventional grid power or photovoltaic solar power under Spain frame conditions. GaBi 4 software was used to build models to characterize the conventional grid and photovoltaic power generation (corresponding functional unit, 1 kWh). ecoinvent v2.0 was chosen to consider background data. Nine different 2030 scenarios were evaluated versus 2007 reference values to take into account: (a) the progressive change to a greener grid mix in Spain and (b) the improvements in photovoltaic solar technology. The results showed that, under the nine considered scenarios for 2030, the CO2-eq.per kilowatt hour emissions are always lower than the reference values for 2007 (reductions around 60%). Additionally, the results showed that 2030 values for the CO2-eq.per kilowatt hour emissions coming from the use of photovoltaic modules for power generation are expected to be around 60% lower than for 2007 values. In order to power an electrochemical process, the direct use of photovoltaic solar energy will give much lower CO2-eq.per kilowatt hour emissions than the supply from conventional grid. A quantitative study based on life cycle assessment has compared the CO2-eq.per kilowatt hour emissions coming from supplying an electrochemical reactor by conventional grid and by photovoltaic solar modules under Spanish frame conditions and stated that the novel process photovoltaic solar electrochemical oxidation would be a preferred environmental option due to the lower CO2-eq.per kilowatt hour emissions under present and future scenarios. The results would suggest that it is worthy to explore not only the possibilities of this technology but also other electrochemical technologies that can be supplied directly by electricity in order to have a better sustainability performance.