Selection of Battery Type
Main Contents
With the rapid development of battery technology and the fast decline in costs, lithium batteries have become the mainstream choice in household energy storage projects due to their high efficiency, long cycle life, accurate battery data, and high consistency.
Four Common Misunderstandings in Battery Capacity Selection
Misunderstanding 1
Selecting battery capacity based only on load power and electricity consumption
Load conditions are indeed the most important reference factor in battery capacity design. However, the battery’s charging and discharging capacity, the maximum power of energy storage machines, and the electricity consumption period of the load cannot be ignored. Therefore, it is necessary to consider comprehensively instead of only considering the load power and electricity consumption when selecting battery capacity.
Misunderstanding 2
Treating the theoretical capacity of the battery as the actual capacity
Usually, the theoretical design capacity of the battery is marked on the battery manual, which is the maximum amount of electricity that the battery can release from SOC 100% to SOC 0% under ideal conditions.
However, in actual applications, the actual capacity of the battery will be different from the design capacity due to factors such as temperature and service life. In addition, in actual applications, in order to extend the battery life, it is generally not allowed to discharge to SOC 0%, and a protection electricity quantity will be set, which makes the actual available electricity quantity less. Therefore, when selecting battery capacity, these factors need to be excluded to ensure that there is sufficient battery capacity available for use.
Misunderstanding 3
The larger the battery capacity, the better
Many users may think that the larger the battery capacity, the better, but we also need to consider the battery utilization rate in the design. If the photovoltaic system capacity is small or the electricity consumption of the load is small, the demand for battery capacity is not so great, which will also cause waste of battery cost.
Misunderstanding 4
The battery capacity is just equal to the load electricity consumption
Sometimes, in order to save costs, the selected battery capacity is almost equal to the load electricity consumption. However, due to process losses, the battery discharge amount will be less than the battery storage amount, and the electricity consumption of the load will also be less than the battery discharge amount. Ignoring efficiency losses may cause insufficient power supply.
How to Desigh Battery Capacity?
Battery Capacity Design in Different Application Scenarios
This article mainly introduces three common battery capacity design ideas in different application scenarios: self-use (high electricity charges or no subsidies), peak and off-peak electricity prices, and standby power (unstable power grid or important loads).
① “Self-use”
Due to high electricity prices or low subsidies for photovoltaic grid connection (no subsidies), installing a photovoltaic energy storage system can reduce electricity expenses.
Assuming that the power grid is stable and not considering off-grid operation, photovoltaic is only used to reduce the electricity consumption of the power grid. Generally, there is sufficient sunlight during the day.
The ideal state is that the photovoltaic + energy storage system can completely cover the household’s electricity consumption. However, this situation is difficult to achieve. Therefore, considering the investment cost and electricity consumption, we can choose the battery capacity based on the average daily electricity consumption (kWh) of the household (assuming sufficient energy supply from the photovoltaic system). The design logic is as follows:
Battery Capacity Design in Different Application Scenarios
This article mainly introduces three common battery capacity design ideas in different application scenarios: self-use (high electricity charges or no subsidies), peak and off-peak electricity prices, and standby power (unstable power grid or important loads).
① “Self-use”
Due to high electricity prices or low subsidies for photovoltaic grid connection (no subsidies), installing a photovoltaic energy storage system can reduce electricity expenses.
Assuming that the power grid is stable and not considering off-grid operation, photovoltaic is only used to reduce the electricity consumption of the power grid. Generally, there is sufficient sunlight during the day.
The ideal state is that the photovoltaic + energy storage system can completely cover the household’s electricity consumption. However, this situation is difficult to achieve. Therefore, considering the investment cost and electricity consumption, we can choose the battery capacity based on the average daily electricity consumption (kWh) of the household (assuming sufficient energy supply from the photovoltaic system). The design logic is as follows:
“If we can accurately collect the rules of electricity usage and combine them with energy storage management settings, we can maximize the utilization of the system.
②Peak and valley electricity
Peak and valley electricity prices have a structure where 17: 00-22: 00 is the peak period of electricity usage. During the day, electricity usage is low (photovoltaic systems can basically cover it). During the peak period of electricity usage, at least half of the electricity should be supplied by batteries to reduce electricity expenses.
Assuming the average daily electricity usage during peak periods is 20 kWh, the design concept is as follows:”
If the user’s text language is English, the translated text will be the same as the original text without any changes.
Calculate the maximum demand value of battery capacity based on the total electricity consumption during peak periods. Then, based on the capacity of the photovoltaic system and the return on investment, find the optimal battery capacity within that range.
③ Unstable power grid area – Backup power
Mainly used in unstable power grid areas or scenarios with important loads.
For example, the application site can install about 5-8KW components, with important loads including 4 ventilation fans, each with a power of 550W. The power grid is unstable, with occasional power outages lasting up to 3-4 hours. The application requirements are that the battery is charged first when the power grid is normal, and the battery plus photovoltaic system ensure the normal operation of important loads (fans) when the power grid is out.
When selecting the battery capacity, the key consideration is the amount of power required when the battery is supplying power alone (assuming there is no PV during a power outage at night). The total power consumption during off-grid and the expected off-grid time are the most critical parameters. The design can be based on a power outage expected to last up to 4 hours.
Two Important Factors in Battery Capacity Design
① Photovoltaic System Capacity
Assuming that the battery is fully charged by photovoltaic charging, and the maximum power of the energy storage machine charging the battery is 5000W, with 4 hours of sunshine per day.
Then:
In the mode of battery backup power supply, the effective capacity of an 800Ah battery, when fully charged under ideal conditions, requires an average of:
800Ah/100A/4h=2 days
② Battery Redundancy Design
Due to the instability of photovoltaic power generation, line loss, ineffective discharge, battery aging and other factors causing efficiency losses, a certain margin needs to be reserved in the battery capacity design.