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 power-to-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 cost-effective 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 CO₂ can increase these costs to 0.102 and 0.191 USD/kWh, rendering a more promising outlook for the P2A2P concept.

Figure 1

Designing and modeling approach employed for the determination of the P2A2P techno-economics for De Aar region in South Africa.

Figure 2

Conceptual process flow diagram for P2A2P, using a battolyzer, pressure swing adsorption (PSA), and AE-HB. This figure was reproduced with permission from ref (24). Copyright 2023 Elsevier, Ltd.

Figure 3

Average energy demand per (a) month and (b) hour in South Africa scaled to 1% of the total demand data reported by Eskom in 2021.

Figure 4

Average net capacity factor of solar/wind hybrid systems on a (a) seasonal scale and (b) hourly scale, together with the effect on the (c) annual net capacity factor.

Figure 5

Charging rate data for a 50% wind/50% solar hybrid design using real data for January 2021 with the (a) maximum charging rate at full design capacity together with the real charging rates and (b) maximum charging rate at 30% charging capacity compared to full design capacity together with real charging rates. (c and d) Panels a and b, respectively, for June, per reference.

Figure 6

Monthly energy generation patterns and end use of the given energy generation for a 50% wind and 50% solar system at 30% battery and HB capacity compared to the full-scale design.

Figure 7

(a) Net capacity factor and LCOE at 30 and 100% battolyzer + HB plant capacity together with (b) average HB load and maximum HB capacity at 30 and 100% battolyzer + HB plant capacity.