Fig. 2: Performance trade-offs of the most efficient strategic national-scale river basin–power system designs.

a–c, The results for the three intervention strategies. Note, black rectangles on some axes of panels b and c serve as filters of Pareto optimal solutions shown in panel a, thus highlighting some optimized designs (the non-greyed out solutions) based on their performance levels. The first four axes from left to right in a to c correspond to objectives (that is, optimized design metrics), and the remaining four axes show three decision variables of the design problem and one tracked metric (agricultural benefit). The top of panels of a–c is the direction of preference for each metric; a straight line across the top of the y axis would indicate a ‘perfect’ WEFE intervention portfolio. Crossing lines between axes represent trade-offs among metrics, whereas a roughly horizontal line joining two metrics indicates a synergy. ako., Akosombo; US$mln, US$ millions. d, The spatial distribution of infrastructure expansion for one selected efficient compromise solution of strategy three (the bold black line in c), which includes significant levels of infrastructure expansion in Ghana’s northern region (for example, a capacity increase of 0.8 GW, corresponding to 76% of the total new bioenergy generation plants installed in the country for the compromise solution). Hydropower providing flexibility services can support high levels of intermittent renewables integration (up to 6.3 GW) and improve power system performance. However, this new role for hydropower would increase hydrological (Hydro.) alteration and decrease agricultural yields up to 5% annually, reducing the agricultural sector’s economic revenues by US$169 million per year, strategy one. A mix of intermittent renewable generation and bioenergy technologies can meet electricity demands while improving all-round system performance and decreasing intersectoral conflicts. That is why the red lines (representing the more diverse energy mix of intervention strategy three) are higher up the y axis—they simply enable better performance. vRES, variable (intermittent) renewable energy sources.