Battery systems play a crucial role in maximizing the benefits of solar installations and other energy solutions. In this article, we cover key technical concepts and the differences between various types of battery systems, including AC- and DC-coupled batteries. This is the first part of a two-part series that covers everything from fundamental concepts to more advanced applications of battery technology.
Key Technical Concepts
Capacity
Battery capacity is typically expressed in ampere-hours (Ah). A battery with a capacity of 15 Ah can deliver 15 amps for one hour. To convert this to watt-hours (Wh), you need to consider the system’s voltage. For example, a battery with 53 Ah and 3.2V delivers 169.6 Wh, which is equivalent to 0.17 kWh. The qapasity Arctic Series consists of 32 such cells connected in series within each battery module. This formula can help calculate how much energy a battery can deliver.
The Arctic Series offers relatively high capacity compared to similar systems on the market, with a modular design that can be scaled from 10.84 kWh to 37.94 kWh, from 2 to 7 modules.
State of Health (SoH)
The State of Health (SoH) indicates how much of the battery’s original capacity remains after use over time. For example, a battery with an initial capacity of 10 kWh may retain only 8 kWh when the SoH decreases to 80%. Degradation occurs naturally due to chemical reactions in the battery.
C-Rate
The C-rate describes how quickly a battery can be charged or discharged. A C-rate of 1 means the battery’s full capacity can be charged or discharged in one hour. For example, a 5 kWh battery discharged in one hour has a C-rate of 1, while a 10 kWh battery discharged over two hours has a C-rate of 0.5. A higher C-rate allows for faster charging and discharging, which is important for handling power peaks. The qapasity Arctic Series has a C-rate of 1, enabling rapid charge and discharge cycles.
Depth of Discharge (DoD)
Depth of Discharge (DoD) indicates how much of a battery’s capacity is used. A fully discharged battery has a DoD of 100%. Lower DoD reduces battery stress and extends its lifespan but also decreases usable capacity. More on this in section “Cycle life and energy throughput” below.
State of Charge (SoC)
State of Charge (SoC) measures the battery’s current charge level, where 100% indicates full charge and 0% indicates full discharge. SoC is an important parameter for monitoring and optimizing battery performance.
Cycle Life and Energy Throughput
Cycle life refers to the number of complete charge and discharge cycles a battery can endure. For example, if a battery is charged from 15% to 75% SoC and then discharged back to 15%, that counts as one cycle. Factors such as charge rate and operating temperature affect cycle life. Another measure of lifespan is energy throughput, which indicates the total amount of energy that has passed through the battery. The Arctic Series is designed for over 6,000 cycles, ensuring a long service life.
Efficiency
Battery efficiency measures how much energy can be stored and retrieved relative to the amount of energy input. Some battery types have higher efficiency than others, which is an important consideration when designing an energy system. Losses in the system should always be accounted for to create realistic expectations, such as when calculating the payback period.
Battery System Configurations
AC-Coupled Systems
In an AC-coupled system, there are two inverters: one to convert DC from the solar panels to AC and another to manage battery charging. This architecture generally results in higher energy losses due to multiple conversion steps. However, AC-coupled systems are flexible and can be used without solar panels, making them suitable for applications where energy is drawn primarily from the grid. These systems are a good option for installations where the existing inverter is not battery-ready.
DC-Coupled Systems
A DC-coupled battery charges directly from the DC output of solar panels, eliminating the need for conversion before storing energy in the battery. These systems typically use a single inverter to manage both solar production and battery charging, offering a simple and efficient solution with minimal energy losses. DC-coupled systems are popular as they often have lower installation costs and fewer components.
Hybrid Systems
Hybrid systems combine the functionality of both AC- and DC-coupled systems. They are connected to the grid for normal operation but can also function off-grid during power outages. Hybrid systems are ideal for applications that require high reliability, such as hospitals or other critical infrastructure where downtime can have severe consequences. Hybrid systems often include UPS (Uninterruptible Power Supply) functionality to ensure uninterrupted power.
Off-Grid Systems
Off-grid systems are fully independent of the electrical grid and are often used in remote locations such as summer homes or RVs. These systems typically operate on 12V, 24V, or 48V battery configurations. When AC power is needed, a combined charge controller and inverter can be used. Larger off-grid systems may integrate solar panels with other energy sources like wind or diesel generators to create a microgrid.
Conclusion
Choosing the right battery system depends on your needs and expectations. DC-coupled systems are ideal for maximizing efficiency, while AC-coupled systems offer greater flexibility. Hybrid systems provide a balance of both worlds, and off-grid systems are perfect for isolated applications. By understanding the basics of battery technology and key concepts, you can make an informed decision to future-proof and optimize your property’s energy system.
