Battery energy storage, represented by lithium-ion batteries and sodium-ion batteries, has an absolute advantage in terms of cost-effectiveness compared to traditional pumped hydro storage, flywheel energy storage, and compressed air energy storage.
This is mainly because battery energy storage has advantages such as wide applicability, flexible deployment, and on-demand configuration of power and energy, and can play an important role in different parts of the new power system.
On the power generation side, battery energy storage systems can smooth out power output fluctuations, track and economically dispatch power processing, and participate in power frequency and voltage regulation. On the transmission side, battery energy storage systems can participate in grid frequency regulation and optimize grid distribution, thereby improving system stability. On the distribution side, battery energy storage systems can optimize the energy management of the distribution network and ensure the safe and stable operation of DC microgrids.
Currently, the mainstream energy storage battery technology is lithium-ion battery, represented by lithium iron phosphate battery. Lithium iron phosphate battery has a market share of over 90%, and mostly uses graphite as the negative electrode, resulting in poor low-temperature performance and safety.
In comparison, lithium carbonate batteries, which use lithium carbonate as the negative electrode, have a stable discharge voltage, are less prone to electrolyte decomposition, and are safer. At the same time, under high-rate charge and discharge conditions, lithium titanate batteries also have a significantly improved cycle life, and their charge and discharge rate, battery internal resistance, and polarization characteristics are superior to those of sodium-sulfur batteries and vanadium batteries.
In terms of specific performance, comparing the number of cycles at room temperature (1C), lithium titanate batteries can cycle 30,000 times, lithium iron phosphate batteries only 3,000 times, while NCA, NCM, lead-carbon, and lead-acid batteries can cycle 1,500, 2,000, 1,500, and 400 times respectively, which is incomparable.
In terms of low-temperature performance and temperature range, lithium titanate batteries have an operating temperature range of -40℃ to 60℃. In comparison, lithium iron phosphate batteries, NCA, and NCM batteries have an operating temperature range of -40℃ to 60℃, while lead-acid batteries and lead-carbon batteries have an operating temperature range of 5℃ to 35℃. In other words, lithium titanate batteries have much better low-temperature performance and a more suitable operating temperature range than other lithium batteries.
However, lithium titanate batteries have a major problem: their specific energy is only 90Wh/kg, which is higher than lead-acid and lead-carbon batteries (40Wh/kg), but far inferior to lithium iron phosphate batteries (140Wh/kg), not to mention NCA (240Wh/kg) and NCM (200Wh/kg).
How to enhance the profitability of lithium-ion batteries such as lithium titanate is an important issue of concern in the market.
Researchers used different lithium titanate battery capacities and depths of discharge as independent variables, and annual profits and losses as the dependent variable, utilizing data from Fuzhou.
The study of power grid data in a certain urban area yielded relevant annual profit and loss results.
Studies have found that the cycle life of lithium-ion batteries, such as lithium titanate batteries, decreases exponentially with increasing depth of discharge. When the depth of discharge of the energy storage system is large, at 70%-80%, the cycle life of the battery decreases rapidly, the battery replacement cost increases, the annual cost of the energy storage system increases, and the economic efficiency is poor.
However, when the discharge level is controlled within a relatively small range such as 50%-60%, the shallower the discharge depth, the stronger the profitability. At the same time, under suitable discharge depth conditions, the larger the battery capacity, the higher the returns and the better the peak shaving and valley filling effect.
In the long run, with the further development of battery technology, continuous innovation in battery materials, and gradual improvement in battery internal resistance and polarization issues, battery charging and discharging efficiency will be further improved, and the profitability of energy storage systems will be further strengthened.
