Working Principle of Residential Energy Storage Systems

A residential energy storage system typically consists of three main components: a photovoltaic (PV) power generation system, an energy storage subsystem, and electrical loads. The PV system converts solar energy into direct current (DC) electricity. The energy storage subsystem includes a battery bank and a bi-directional inverter, responsible for the two-way conversion between DC and alternating current (AC) as well as battery charging and discharging management. The electrical loads are various household appliances that consume the AC power output from the system.

During operation, the DC electricity generated by the PV arrays is first converted into AC by the inverter to power the household appliances, with the surplus energy stored in the battery bank. During night-time or periods without solar irradiation, the battery bank discharges, and the electrical energy is converted into AC by the inverter to continuously supply the household loads. In case of a power deficit, the system can also purchase electricity from the utility grid as supplementary power. This system efficiently utilizes solar power generation, reduces peak loads on the grid, saves electricity costs, and can be regarded as a "micro-power plant" embedded in the household.

This integrated system, combining solar power generation, energy storage management, and intelligent energy utilization, is a feasible and promising direction for future residential energy applications.

Battery Technologies for Energy Storage Systems

The battery bank is the core component of an energy storage system. The main battery technologies and their working principles are as follows:

Lithium-ion Batteries

Lithium-ion batteries employ lithium metal oxide/lithium metal oxide or lithium metal oxide/carbon materials as the positive and negative electrode materials. They feature high energy density, long cycle life, and no memory effect, making them the current optimal choice for residential energy storage applications. Lithium-ion batteries are also widely used in electric vehicles, laptops, and other applications.

Lead-acid Batteries

Lead-acid batteries are a relatively traditional type of secondary battery, using lead and its oxides as the positive and negative electrode materials. While lead-acid battery technology is relatively mature and low-cost, it has a relatively low energy density, short cycle life, and requires periodic maintenance and electrolyte replenishment. Lead-acid batteries are primarily used in automotive start-stop systems, telecommunication base stations, and data center backup power supplies.

Lead-carbon Batteries

Lead-carbon batteries incorporate carbon-modified materials into the positive electrode of traditional lead-acid batteries, reducing self-discharge rates during standby and improving high-rate discharge performance. However, their overall performance parameters are comparable to lead-acid batteries, and they also suffer from short service life and large footprint.

All-vanadium Redox Flow Batteries

All-vanadium redox flow batteries utilize two different oxidation states of vanadium in liquid electrolyte solutions as the positive and negative active materials, with energy stored in the liquids rather than the electrode materials. Their key advantages include long cycle life (>10,000 cycles), full charging and discharging capability, and environmental friendliness, making them a potential candidate for residential and large-scale energy storage applications.

Sodium-sulfur Batteries

Sodium-sulfur batteries use molten sodium and molten sulfur as the negative and positive electrode materials, respectively, operating at high temperatures of 300-350°C. Their exceptional high-temperature performance makes them suitable for energy storage in tropical regions, but their drawbacks, such as rapid self-discharge, low cycle efficiency, and safety concerns, have limited their large-scale deployment.

Solid-state Batteries

Solid-state batteries replace traditional liquid or gel electrolytes with inorganic solid or polymer solid electrolytes, offering higher thermal stability, safety, and volumetric energy density. They are considered a future direction for high-energy-density batteries and are currently primarily used in micro-scale wearable device power sources.

Applications and Prospects of Energy Storage Technologies

Energy storage systems are a key technology for enabling the energy transition and increasing the utilization of renewable energy sources. For intermittent renewable energy power plants, such as solar and wind, the electricity generated during daylight or windy periods cannot be consumed immediately, requiring energy storage systems to store the excess power. During night-time or periods without renewable generation, the stored energy can be discharged to supply the loads, effectively balancing the temporal and spatial distribution mismatch of energy resources.

Commercial Applications

In the commercial sector, the main applications of energy storage systems include:

Peak shaving and valley filling:

By charging the batteries with low-cost electricity during off-peak periods and discharging during peak demand periods, effective electricity cost management can be achieved.

Load shifting:

By utilizing energy storage systems to meet a portion of the load demand, the impact of peak loads on the grid can be reduced, allowing for lower contracted electricity capacity and basic electricity cost savings.

As energy storage technologies advance and battery system prices decline, commercial-scale energy storage systems are gradually becoming economically viable.

Residential Applications

In the residential sector, cost-effective home energy storage systems make the application of distributed solar PV and other renewable energy systems more feasible. Traditionally, a major drawback of solar power generation has been the mismatch between daytime energy production and nighttime energy demand. With the integration of energy storage systems, solar energy generated during the day can be efficiently stored, and the stored energy can be utilized to continuously power the household at night, enabling around-the-clock utilization of solar power generation.

Practical Applications

The ultimate goal of energy storage technology development is to provide support services for large-scale grid systems. With the aid of large-scale energy storage, the electricity generated by intermittent renewable sources such as wind, solar, hydroelectric, and tidal power plants can be efficiently stored and dispatched as regulating power into the grid, replacing traditional fossil fuel-fired power plants and promoting the low-carbon and clean transition of the energy industry. The development and application of energy storage technologies will lay the foundation for widespread utilization of renewable energy sources and the eventual complete replacement of fossil fuels.