A financial model for lithium-ion storage in a photovoltaic and biogas energy system.

• A novel cash flow model was created for Li-ion battery storage in an energy system. • The financial study considers Li-ion battery degradation. • Frequently using Li-ion (thus reducing lifetime) can be financially attractive. • Using Li-ion is unprofitable unless it participates in grid services. Electrical energy storage (EES) such as lithium-ion (Li-ion) batteries can reduce curtailment of renewables, maximizing renewable utilization by storing surplus electricity. Several techno-economic analyses have been performed on EES, but few have investigated the financial performance. This paper presents a state-of-the-art financial model obtaining novel and significative financial and economics results when applied to Li-ion EES. This work is a significant step forward since traditional analysis on EES are based on oversimplified and unrealistic economic models. A discounted cash flow model for the Li-ion EES is introduced and applied to examine the financial performance of three EES operating scenarios. Real-life solar irradiance, load, and retail electricity price data from Kenya are used to develop a set of case studies. The EES is coupled with photovoltaics and an anaerobic digestion biogas power plant. The results show the impact of capital cost: the Li-ion project is unprofitable in Kenya with a capital cost of 1500 $/kWh, but is profitable at 200 $/kWh. The study shows that the EES will generate a higher profit if it is cycled more frequently (hence a higher lifetime electricity output) although the lifetime is reduced due to degradation. [ABSTRACT FROM AUTHOR]