Leveraging Green Ammonia for Resilient and Cost-Competitive Islanded Electricity Generation from Hybrid Solar Photovoltaic–Wind Farms: A Case Study in South Africa

Abstract

Hybrid solar photovoltaic (PV) and wind generation in combination with green ammonia as a seasonal energy storage vector offers an excellent opportunity to decrease the levelized cost of electricity (LCOE). In this work, an analysis is performed to find the most cost-effective configuration of powerto-ammonia-to-power (P2A2P). In P2A2P, wind and solar resources are combined with energy storage to design a resilient electricity grid. For daily generation, batteries are utilized for energy storage, whereas ammonia is employed to cope with seasonal fluctuations. The costs of energy storage capacity have a significant influence on the LCOE. Therefore, this work studies the effect of solar/wind hybrid generation systems and energy storage capacity on the LCOE. A base case of the region of De Aar in South Africa was selected because this inland location has excellent wind and solar resources. The optimized battolyzer and Haber−Bosch design capacity led to an overall load factor of 20− 30%. At a 30% load factor, a hybrid system with 37% wind-based and 63% solar-based energy generation capacity was the most costeffective configuration, resulting in a LCOE of 0.15 USD/kWh at a 5% annual discount rate. In an optimistic scenario for PV costs, the LCOE achieved is essentially unaltered (0.14 USD/kWh), while the contribution of wind and PV changes to 25 and 75%, respectively. This analysis indicates that appropriate designing of hybrid energy solutions will play a key role in determining the final energy storage capacities needed to reduce the LCOE. While these costs for LCOE are above those reported for coal-powered electricity in South Africa (e.g., 0.072 USD/kWh for businesses and 0.151 USD/kWh for households), a carbon tax of 50 USD/ton of CO 2 can increase these costs to 0.102 and 0.191 USD/kWh, rendering a more promising outlook for the P2A2P concept.

Flexible Green Ammonia Production Plants: Small-Scale Simulations Based on Energy Aspects

“…A trade-off between kinetics and equilibrium is accomplished through the use of temperatures between 320 and 550 • C and pressures between 150 and 300 bars [44]. Sagel et al [45] indicate that for a relatively small-scale process, it is beneficial to work at moderate process conditions: 350-525 • C and 100-200 bar. Employing multiple catalyst beds arranged in series along with an intercooler system is a method that is utilized in the chemical industry to reconcile the trade-off between thermodynamics and kinetics.…”

“…Sagel et al [45] indicated that moderate temperatures and pressures are preferred for small-scale ammonia production plants. Spatolisano et al [24] indicated that when applied to small-scale production plants, NH 3 synthesis has to be performed at lower pressures in order to reduce operating costs, but low pressures negatively affect the chemical equilibrium of the reacting system; consequently, the authors used 200 bar.…”

“…In relation to the energy consumption in each section of the ammonia plant, there are also different values in the literature: Sousa et al [10] reported 11.0 kWh/kg NH 3 when working with an electrolyzer of 1 MW and reported that 88.5% of energy consumption comprises H 2 generation and 10.2% comprises NH 3 synthesis [45]. Lin et al [20] reported very low consumption energies with respect to the NH 3 synthesis loop, which represents 9.1% of the total energy when working with high-pressure reaction-condensation and 3.5% when working with low-pressure reaction-absorption.…”