Carbon Abatement of Photovoltaic (PV) Electricity at the Margin
Introduction: Conventionally CO2 abated by generating photovoltaic electricity has been evaluated using average grid fuel mix profiles at various scales. However at low capacity PV installations it is only the peak-load resources that are displaced from the conventional grid as opposed to the entire average of base intermediate and peak load sources. We develop a novel methodology to evaluate the CO2 abated at the margin by PV electricity in a load zone (ERCOT ISO)(1) and compare the results to the abatement evaluated using average national regional and state fuel mix profiles for the same location.
Methods: The annual hourly data for solar radiation (2) and the load (3) were obtained for ERCOT to model the PV electricity output and demand. The list power plants available for dispatching to meet demand and their characteristics (fuel type CO2 emission factor capacity and capacity factor) were obtained (4). We developed a visual basic excel code to determine the dispatching order in the load zone based on the hourly demand. Using CO2 emission factor with the amount of grid electricity displaced (by PV electricity) from each power plant at the margin the marginal CO2 abatement was evaluated.
Results: Due to utilization of a number of natural gas plants at peak loads the CO2 abated by PV electricity (at eight different capacities from 1 to 1000 MW) was consistently lower when compared to the average fuel mix cases. In the case of ERCOT ISO 95% of electricity displaced at the margin was generated from the less carbon intensive natural gas the marginal fuel uses less coal than the national (51%) regional (23%) and state (38.5%) cases. Over the range of PV installations CO2 was reduced between 329 – 327800 tons for the marginal case compared to average mix cases. Hence carbon abatement using renewable technologies can be significantly different using a marginal displacement approach this study presents one such case using PV technology.
1. An Independent System Operator (ISO) co-ordinates controls and monitors the operation of electrical power system in a region by dispatching power plants to meet demand every hour of the day. ERCOT ISO serves 85% of the Texas’ electricity demand.
2.National Renewable Energy Laboratory (Renewable Resource Data Center) 2008. Solar Radiation Data
3.Federal Energy Regulatory Commission (FERC) 2008. Annual Electric Balancing Authority Report
4.Emissions and Generation Resource Integrated Database (E-Grid U.S. EPA). 2008