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The State of Charge is a battery metric you may have heard of, but what does it mean? This measurement helps you understand the battery charge available, but it can be impacted by several factors, ranging from charging habits to things out of your control, like age, natural self-discharge, and weather.
Learn what the state of charge is, how to measure it and find it for your EcoFlow batteries, and what influences this figure.
What is State of Charge?
A solar battery or solar generator’s state-of-charge (SoC) refers to how much charge remains in the battery, usually after use. SoC voltages are influenced by the type of battery used, battery age, weather, and more. Eventually, these influences can reduce the total charge your solar battery can hold, which makes checking the SoC critical to maintaining the battery’s health.
The state of charge can be expressed as a percentage of the battery’s maximum charge that remains after use. Here’s the equation:
Capacity Remaining / Total Storage Capacity x 100 – State of Charge Percentage
So, if you know your battery’s total storage capacity is 2kWh, and you’ve used 0.5kWh, your equation would look like this:
(1.5kWh/2kWh) x 100 = 75% SoC
This metric helps understand the available energy and gauge the system’s overall performance. You can apply this measurement to grid-scale batteries or use it more individually for your residential solar batteries, including EcoFlow Solar Generators, such as those in the compact but powerful EcoFlow RIVER 2 Series.
How Do You Measure the State of Charge of a Solar Battery?
Several methods are used to determine a solar battery’s state of charge, including voltage measurements, coulomb counting, specific gravity measurements, internal resistance measurements, and ampere-hour tracking.
- Voltage Measurement: This method is simple but might not be as accurate as other methods. It involves using the voltage to understand SoC. While voltage and SoC are roughly correlated, SoC is also impacted by things like recent charge/discharge activity and temperature, which this method may not account for.
- Coloumb Counting: Coloumb counting requires tracking the energy current that flows into and out of the battery over some time. While its accuracy is superior to the voltage measurement, it requires an extended monitoring period, leaving more room for errors.
- Specific Gravity Measurement: This is a measurement option for lead-acid batteries and won’t work for lithium-ion or other sealed batteries. You can measure the gravity of the electrolyte within the battery.
- Internal Resistance: In this technique, you calculate SoC by analyzing the battery’s internal resistance, which fluctuates along with the state of charge. You’ll need specialized equipment to take this approach.
- Ah Counting/Metrology: You can also estimate its remaining charge by analyzing how many ampere-hours (Ah) are added or removed from a battery. This method is similar to coulomb counting.
For EcoFlow DELTA Series Solar Generators like the EcoFlow DELTA Pro + 400W Solar Panel, we make it easy to understand your battery’s state of charge by providing it either on the battery’s LCD screen or conveniently in the EcoFlow app, where you can view and manage SoC and other metrics.
State of Charge vs. State of Energy vs. State of Health
Don’t confuse SoC with the measurements of state of energy (SoE) or state of health (SoH). While SoC measures the percentage of battery capacity remaining, SoE represents its remaining energy under certain conditions, such as temperature variation. SoE is more dynamic and easily influenced by context, while SoC is more straightforward.
SoH assesses the battery’s overall condition and aging process as a ratio of its current maximum charge capacity to its out-of-the-box rated capacity. SoC is an immediate measurement, while SoH considers long-term degradation over time and helps predict a battery’s lifespan.
All of these terms and measurements are used for batteries, whether powered by renewable solar energy or nonrenewable energy, like the electricity from the grid, primarily powered by fossil fuels.
Factors That Affect State of Charge
The state of a battery’s charge can be primarily influenced by factors such as charge/discharge current, voltage, temperature, battery type, degradation, and more.
Charge and Discharge Current
If a battery is discharged quickly, such as when paired with a fast-charging cable to increase your phone’s battery, the SoC will deplete faster. On the other hand, a rapidly recharged battery will increase the SoC quickly.
Charging Voltage
The electrical potential (voltage) applied to the battery during charging can also impact it. Higher volts increase SoC quickly, but only when the voltage is within safe limits, as it can otherwise cause overcharging, which can harm the SoC.
Type of Battery
A battery’s chemistry and the elements that make up its power can determine its voltage profiles and capacity, affecting its SoC behavior.
Temperature
Extreme temperatures, including scorching and cold conditions, can damage the battery’s SoC. Temperature monitoring features (like the iPhone’s overheating warning) help the battery stay cool or warm to avoid such harsh temperatures, which can reduce the overall SoC.
Degradation and Age
As batteries degrade and age, they can hold less charge. The maximum SoC of an old battery will almost always have less capacity than the maximum SoC of a brand-new battery.
C-Rate
C-rate measures the charge and discharge rate relative to the total battery capacity. A higher C-rate (which represents rapid charging and discharging) can make an SoC estimate less accurate.
Self Discharge
Batteries can self-discharge some of their power if stored for an extended time and unused. This proves that even under ideal charging conditions, battery SoC can degrade over time due to self-discharging, which is out of human control and, unfortunately, a drawback of renewable energy batteries.
DoD, Overcharging, and Discharging
If you’re deeply discharging a solar battery every time, you can reduce the battery’s capacity and impact battery performance and behavior. You also want to avoid charging a battery beyond its capacity (leaving it connected to a charging cord after the battery reaches 100%), as it can make SoC less accurate.
Final Thoughts
Understanding your solar battery’s state of charge can help you see how your charging behaviors and battery usage impact its maximum capacity. We make it easy to find your EcoFlow Delta Solar Generator’s SoC by displaying it clearly on the battery’s LCD screen and featuring it within the EcoFlow smartphone app.