In this study, two novel metal-based microencapsulated phase change materials (PCMs) with melting temperatures of 577 °C (Al-Si) and 520 °C (Al-Cu-Si) are analysed for a next-generation concentrated solar power plant operating at 650 °C. Five storage units with different Al-Si to Al-Cu-Si volume ratios (1:0, 0:1, 1:1, 2:1) and height/diameter ratios (H/D ratios, 3:2, 2:3) are designed and benchmarked under the actual operating conditions, with the charge and discharge cut-off temperatures set for the return loop at 376 °C and 456 °C. The results show that the case with single Al-Cu-Si PCM leads to a higher average outlet temperature of 557.3 °C (8.7 °C higher outlet temperature), while the case with smaller H/D ratios shows higher energy storage capacity (on average 34 % higher capacity) due to smaller surface area of tank shell, resulting in less heat loss.