Life Cycle Greenhouse Gas Emissions of Electricity Generated from Solar Updraft Towers

The solar updraft tower power plant (SUTPP) is a technology that combines wind and solar energy and has been proposed for future utility-scale installation in arid climates such as the southwestern United States. To assess its potential global warming impact and compare its life cycle greenhouse gas (GHG) emissions against alternative electricity sources, a geospatial life cycle assessment (LCA) was performed for a solar updraft tower energy system for ten different case study locations in five states in the Southwest United States: Arizona, California, Nevada, New Mexico, and Texas. This is the first study to incorporate location-specific solar radiation, ambient temperature, and thermal energy storage in the soil at 1-hour time intervals into an LCA model of this technology to calculate its electricity generation and life cycle GHG emissions. Scenarios were also developed modeling solar photovoltaic (PV) panel coverage on a small percentage of the collector area to determine how much the life cycle impacts vary for a solar updraft tower system with and without PV. Without PV incorporated into the system, the total life cycle GHG emissions ranged from 29.74 g CO2eq/kWh electricity to 33.82 g CO2eq/kWh electricity for the 10 locations, and when 2.0% of the collector area is covered by solar PV panels, the total life cycle GHG emissions ranged from 30.36 g CO2eq/kWh electricity to 34.36 g CO2eq/kWh electricity. The site-by-site comparison demonstrates that the climate change impacts with solar PV were generally slightly higher than the stand-alone SUTPP systems for every studied location. Sensitivity analyses show that the operational lifetime of the system is the single most sensitive variable for both the stand-alone system and the hybrid system. For the stand-alone system, turbine efficiency is the next most sensitive parameter and for the hybrid system, the next most sensitive parameters are performance ratio followed by turbine efficiency. This study suggests that the potential life cycle GHG emissions from SUTPPs can be notably lower than fossil fuel (15 times lower than natural gas and 31 times lower than coal) and so implementation of SUTPPs may reduce global warming impacts of electricity generation in the southwest regions of the US