Technico-economic assessment of a lead-acid battery bank for standalone photovoltaic power plant

The average minimum and maximum SOC of the battery were found to be respectively, 34.0% and 87.45%, for the monitored period. The incremental cycle efficiency (Ycd) was found to vary between 68 and 90%. A low efficiency is usually observed when either the charge or the discharge durations are small (or the corresponding currents are high). The Coulomb efficiency is marked by a quasi-constant degradation rate of 1.8% per year, and the internal resistance of the battery bank increased from 0.07 to 0.27 Ohms during the 4 year monitoring period. From the monitoring of these parameters, and by using real costs, the levelized cost of storage (LCOS) was determined for various discount and capacity degradation rates as well as battery bank replacement periods. The calculated LCOS was affected by the discount rate and the replacement period of the battery bank. Additionally, the LCOS analysis revealed that for PV standalone systems lead-acid battery is more cost effective than li-ion on the short term. The latter storage technology is expected to be cost effective for medium and long term.