Net green energy potential of solar photovoltaic and wind energy generation systems

"Green energy" is the energy that can be produced while sustaining ecosystem services. Maintenance of the services provided by the ecosystem requires energy, termed the ecosystem maintenance energy (ESME). Including ESME costs in energy accounting enables assessment of an energy plant's ability to produce energy over and above inputs and EMSE costs over the lifetime of the plant. In this work, an assessment of the potential of two renewable energy plants wind and solar photovoltaic to produce "green energy" is undertaken, those were chosen due to their likely dominance of the future energy market. The assessment is done using a methodology that unifies environmental impact assessment, ESME and energy accounting into a single metric termed the green energy return on investment (EROIg). The paper also extends ESME calculation by incorporating ecosystem impacts that were previously unaccounted-for such as: biodiversity loss; delayed ecosystem maintenance; carbon capture by photosynthesis; ozone depletion and formation and ionizing radiation. The solar and wind energy plants considered were sized to produce an equivalent amount of annual energy and were placed at a theoretical location where the capacity factor (CF) is equivalent to the average global utility scale CF for each resource. The study found that onshore wind energy has a greater potential in generating green energy with an EROIg of 17.19. Removal of impacts related to biodiversity loss, which is included here for the first time, is found to play a critical role in plant assessment from both biodiversity and CO2 capture by photosynthesis perspective. Plants needing and providing biodiversity offsets are shown to provide an overall 18%-25% improvement in EROIg. This improvement is triggered by the corresponding CO2 capture by photosynthesis. Some design options were evaluated to determine the sensitivity of the resulting EROIg to the plant design and to the temporal element of the investigation. Those include the addition of battery storage and the delay in action on ecosystem maintenance from a 20-year to a 100-year time horizon which were found to reduce the resultant EROIg by >40% and >87% respectively.