Freshwater in off-grid islands is sourced from rain, groundwater, or mainland imports, which are unreliable, limited, and expensive, respectively. Sustainable freshwater generation from desalination of abundant seawater is another alternative worth exploring. Model-based techno-economic simulations have focused on reverse osmosis desalination due to its low energy consumption and decreasing costs. However, reverse osmosis requires frequent and costly membrane replacement. Other desalination technologies have advantages such as less stringent feedwater requirements, but detailed studies are yet to be done. In this work, a techno-economic comparison of multi-effect distillation, multi-stage flash, mechanical vapor compression, and reverse osmosis coupled with solar photovoltaic-lithium ion-diesel hybrid system was performed by comparing power flows to study the interaction between energy and desalination components. Optimization with projected costs were then performed to investigate future trends. Lastly, we used stochastic generation and demand profiles to infer uncertainties in energy and desalination unit sizing. Reverse osmosis is favorable due to low energy and water costs, as well as possible compatibility with renewable energy systems. Multi-effect distillation and multi-stage flash may also be advantageous for low-risk applications due to system robustness.

Renewable energy (RE) utilization is expected to increase in the coming years due to its decreasing costs and the mounting socio-political pressure to decarbonize the world’s energy systems. On the other hand, lithium-ion (Li-ion) batteries are on track to hit the target 100 USD/kWh price in the next decade due to economy of scale and manufacturing process improvements, evident in the rise in Li-ion gigafactories. The forecast of RE and Li-ion technology costs is important for planning RE integration into existing energy systems. Previous cost predictions on Li-ion batteries were conducted using conventional learning curve models based on a single factor, such as either installed capacity or innovation activity. A two-stage learning curve model was recently investigated wherein mineral costs were taken as a factor for material cost to set the floor price, and material cost was a major factor for the battery pack price. However, these models resulted in the overestimation of future prices. In this work, the future prices of Li-ion nickel manganese cobalt oxide (NMC) battery packs - a battery chemistry of choice in the electric vehicle and stationary grid storage markets - were projected up to year 2025 using multi-factor learning curve models. Among the generated models, the two-factor learning curve model has the most realistic and statistically sound results having learning rates of 21.18% for battery demand and 3.0% for innovation. By year 2024, the projected price would fall below the 100 USD/kWh industry benchmark battery pack price, consistent with most market research predictions. Techno-economic case studies on the microgrid applications of the forecasted prices of Li-ion NMC batteries were conducted. Results showed that the decrease in future prices of Li-ion NMC batteries would make 2020 and 2023 the best years to start investing in an optimum (solar photovoltaic + wind + diesel generator + Li-ion NMC) and 100% RE (solar photovoltaic + wind + Li-ion NMC) off-grid energy system, respectively. A hybrid grid-tied (solar photovoltaic + grid + Li-ion NMC) configuration is the best grid-tied energy system under the current net metering policy, with 2020 being the best year to deploy the investment.

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