A Beginner’s Guide to Home Energy Storage Systems: Grid-Tied vs. Off-Grid – How to Choose? Money-Saving Tips with Time-of-Use Electricity Prices
I. Grid-Tied vs. Off-Grid Systems: Core Differences and Suitable Scenarios
Core Differences: A grid-tied system must be connected to the public power grid and cannot operate independently off the grid; an off-grid system is equipped with an independent battery pack and can supply power completely independent of the grid. Tests show that for grid-tied and off-grid systems with the same capacity, the initial installation cost of the former is 30%-40% lower than that of the latter. However, the off-grid system can still ensure basic electricity supply during power outages.
Suitable Scenarios for Grid-Tied Systems: Ideal for urban residences with stable power grids and reliable power supply. For example, in urban communities with normal power supply, a grid-tied system can sell excess electricity generated by solar panels to the grid (known as “electricity sales”). Tests indicate that a household with a 5kW grid-tied energy storage system can sell an average of 800-1200kWh of electricity to the grid annually, offsetting part of the electricity bill.
Suitable Scenarios for Off-Grid Systems: Suitable for remote areas with weak grid coverage (such as rural villas, mountainous residences) or households with extremely high requirements for power supply stability. Taking a remote village as an example, an off-grid system paired with a 10kWh battery pack can meet the continuous power supply needs of daily household lighting, refrigerators, and small household appliances (with a total power not exceeding 2kW), ensuring basic daily electricity use without grid access.
II. Saving Money with Time-of-Use Electricity Prices: Practical Operation Tips for Energy Storage Systems
Core Principle: Utilize the price difference between peak and off-peak electricity. Charge the energy storage battery with grid electricity during off-peak price periods (e.g., 23:00 at night to 7:00 the next day) and use battery power during peak price periods (e.g., 10:00 to 18:00 during the day) to reduce grid electricity consumption during peak hours. Tests show that in areas with a 0.5 yuan/kWh price difference between peak and off-peak electricity, a household equipped with a 5kWh energy storage system can save 150-200 yuan on electricity bills per month.
Key Operation Points: Select an energy storage system that supports the “automatic charging and discharging during peak and off-peak periods” function. This function allows presetting charging and discharging times via an APP, eliminating the need for manual intervention. For example, a certain brand of home energy storage system can be set to automatically charge during off-peak hours (0:00-6:00) and discharge automatically during peak hours (8:00-22:00). Tests show that the accuracy error of its charging and discharging can be controlled within 10 minutes, ensuring efficient use of the electricity price difference.
Capacity Selection: Determine the energy storage capacity based on the household’s electricity consumption during peak periods. An average three-person household consumes approximately 3-5kWh of electricity per day during peak hours, and a 5kWh energy storage system can cover more than 80% of the peak electricity demand. If the household has high-power appliances (such as electric ovens and air conditioners), it is recommended to choose an 8-10kWh energy storage system to avoid insufficient battery power that requires additional use of high-priced grid electricity.
III. Matching with Solar Panels: Improving Energy Utilization Efficiency
Advantages of Matching: Electricity generated by solar panels is prioritized for household use, with excess electricity stored in the energy storage battery. If the battery is fully charged, the remaining electricity is sold to the grid (for grid-tied systems), realizing “self-generation for self-use, surplus electricity storage/sale”. Tests show that a 5kW solar panel paired with a 5kWh energy storage system can increase electricity utilization efficiency by 40%-50% compared to using solar panels alone, reducing reliance on grid electricity.
Matching Requirements: The power of solar panels must match the capacity of the energy storage system. Generally, the ratio of solar panel power to energy storage system capacity is 1:1 (e.g., a 5kW solar panel paired with a 5kWh energy storage system). If the ratio is unbalanced (e.g., a 10kW solar panel paired with a 3kWh energy storage system), a large amount of electricity generated by the solar panels cannot be stored in a timely manner and can only be wasted or sold to the grid at a low price, reducing economic benefits.
IV. Safety Protection: Key Details of Home Energy Storage Systems
Battery Safety: Prioritize energy storage systems using lithium iron phosphate batteries. This type of battery has better thermal stability than ternary lithium batteries. Tests show that lithium iron phosphate batteries can remain stable in a high-temperature environment of 200℃, while ternary lithium batteries may experience thermal runaway at around 150℃. At the same time, the energy storage system must be equipped with overcharge protection, over-discharge protection, and short-circuit protection functions. When the battery voltage exceeds the safe range (e.g., charging voltage exceeds 3.65V per cell), the system will automatically cut off the circuit within 0.1 seconds.
Installation Specifications: Installation must be carried out by personnel with professional qualifications. The installation location should be far from water sources and fire sources, and a heat dissipation space of at least 30cm should be reserved. Tests show that an energy storage system installed in compliance with specifications has a maximum shell temperature of no more than 45℃ during operation. In contrast, a system installed in violation of regulations (e.g., close to heat sources) may have a shell temperature exceeding 60℃, increasing safety risks.
Industry Standards: Select products that comply with IEC 62133 (battery safety standard) and UL 9540 (energy storage system safety standard). These standards have strict requirements for the electrical safety, fire resistance, and electromagnetic compatibility of energy storage systems. Products that pass standard certification have an 80% or more lower probability of safety issues during use.
