The operating time of a 300Ah battery in off-grid systems depends on the system efficiency and load power. For instance, in the 12V system, its total energy capacity is 3.6kWh (300Ah×12V). With 80% discharge depth and 90% inverter efficiency, the available energy is 2.59kWh. With a 200W continuous load connected, the theoretical operating time is 12.95 hours. However, actual test results show that due to voltage drop and temperature influences, the median tested life of lead-acid batteries is 11.3 hours ±8%, while for lithium iron (LiFePO4) batteries, it is 13.6 hours ±3%. The United States National Renewable Energy Laboratory (NREL) in 2023 declared that the overall efficiency loss of off-grid systems is 18%, mainly due to line loss (5%) and battery self-discharge (the lead-acid battery monthly self-discharge rate is 3% against the lithium battery rate of 0.5%).
Ambient temperature has a significant impact on the performance of batterie. At -20℃ low temperature, the capacity aging rate of lead-acid battery is 40%, while that of lithium battery is merely 15%. At 45℃ high temperature, the cycle life of lead-acid battery degrades from 1,200 times to 600 times, while that of lithium battery drops from 3,000 times to 2,700 times. Experimental results of German TESVOLT Company show that its commercial 300Ah lithium battery energy storage system can supply a 1.5kW air conditioner (COP3.0) to run continuously for 6.2 hours in a condition of constant temperature at 25℃, 127% longer than that of the lead-acid battery solution. A sample of case study for an off-grid solar project in Africa shows that a 300Ah battery system in combination with a 600W photovoltaic panel has the capability of providing uninterrupted power supply to the refrigerated cabinet of a clinic (average daily energy consumption of 1.8kWh) for 72 hours based on an average of 4.2 sunlight hours per day.
Load management practices can achieve optimized battery longevity. Using the dynamic power regulation technology, the peak load reduces from 2kW to 1.2kW, which has the potential of boosting the runtime of 300Ah batterie by 43%. The results of the data gathered by Victron Energy’s smart Energy management system in the UK show that synchronizing the refrigerator (with a periodic load of 150W/40%) and LED lighting (with a continuous load of 50W) resulted in the system’s battery life being increased from 9.1 hours to 14.8 hours. In 2024, Tesla Powerwall 3 load-following algorithm boosted the 300Ah equivalent battery’s off-grid operation efficiency to 94%. In the average home with a daily usage of 10kWh, it can produce 34 hours of self-supplied power.
Cost-benefit analysis indicates that the upfront investment in a 300Ah lithium battery system amounts to around 3,600 US dollars. Calculated over a 10-year lifetime, the cost per kilowatt-hour is 0.17 US dollars /kWh, which is 55% lower than a diesel generator (0.38 US dollars /kWh). Although the initial cost of lead-acid batteries is only $1,800, due to their cycle life of 500 times (3,000 times for lithium batteries), the total cost per kilowatt-hour over their entire lifetime comes to $0.32 per kWh. China Tower Corporation’s 2023 off-site operation data show that after substituting lead-acid batteries with 300Ah lithium batteries, maintenance expenditure decreased by 62%, and the rate of power failure dropped from 5.3% to 0.7%.
Innovations in technology continue to shatter the limitations on the battery lifespan. The third-generation sodium-ion battery that CATL will launch in 2024 has increased the volume energy density of the 300Ah specification to 160Wh/L, with a capacity retention rate of 92% at -30℃. With an intelligent thermal management system, it can increase the off-grid working time by 28%. The Tesla Megapack 2 battery pack-level optimization technology expends 7.2% more usable energy on the same 300Ah capacity by reducing connector loss (from 3% to 0.8%). Industry forecasts predict that, by 2030, 300Ah solid-state batteries’ off-grid lifespan will be 2.3 times longer than conventional lithium batteries with a cycle life of more than 20,000 times, driving off-grid energy systems’ return on investment to 19.8%.