Building an Off-Grid Nanogrid System Using Sodium-Ion Batteries

Jisoo Lee Ph.D.

Fairbuild LLC

W: www.fairb.com

E: [email protected]

Introduction

With advancements in solar technology and falling costs, solar energy has become one of the most cost-effective renewable energy sources available today. The increased efficiency of solar panels and the availability of incentives have made it easier for homeowners to adopt solar power. Additionally, sodium-ion batteries are emerging as a viable alternative to traditional lithium iron phosphate (LFP) batteries, offering benefits such as improved safety, better performance in extreme temperatures, and potentially lower costs in the future. Although sodium-ion batteries currently have a higher cost per cell, their advantages make them an interesting option for off-grid nanogrid systems.

Sodium-Ion Batteries vs. LiFePO4

Sodium-ion (Na-ion) batteries are gaining attention as a promising alternative to Lithium Iron Phosphate (LiFePO4) batteries for energy storage systems. Here’s why Na-ion batteries might be an interesting option:

Safety:

• Non-Flammable: Sodium-ion batteries are inherently safer as they are non-flammable and have a lower risk of thermal runaway compared to lithium-based batteries.
• Temperature Tolerance: They perform well in a wider range of temperatures, maintaining charge retention and efficiency in freezing conditions as low as -10°C, which is beneficial for outdoor installations.

Cost:

• Raw Material Abundance: Sodium is abundant and cheaper than lithium, which can potentially lead to lower costs as manufacturing scales up. This makes Na-ion batteries an economically viable option for large-scale energy storage.

Environmental Impact:

• Less Resource Intensive: The extraction and processing of sodium are less environmentally damaging compared to lithium, reducing the overall ecological footprint of the batteries.

Performance:

• Cycle Life: Both Na-ion and LiFePO4 batteries offer a high cycle life, with up to 4000 cycles for 80% retention, ensuring long-term usability.
• Energy Density: Although Na-ion batteries have a slightly lower energy density than LiFePO4, advancements in technology are closing this gap, making them competitive for stationary storage applications.

Operational Temperature Range:

• Sodium-ion Batteries: They can charge and discharge at lower temperatures without significant degradation, which is advantageous in colder climates.
• LiFePO4 Batteries: These batteries generally require thermal management systems to maintain performance in extreme temperatures, adding complexity and cost.

Hypothetical At-Home Design Example of Nanogrid System

Solar panels are the primary energy generation component in a nanogrid system. They convert sunlight into electrical energy that can be stored in batteries or used directly.

Solar Panels

Solar panels are the primary energy generation component in a nanogrid system. They convert sunlight into electrical energy that can be stored in batteries or used directly.

Key Considerations:

• Efficiency: Higher efficiency panels convert more sunlight into electricity, which is crucial for maximizing energy production, especially in limited space.
• Durability: Solar panels must withstand various weather conditions, including rain, hail, and high winds.
• Warranty: Look for panels with long-term warranties (25 years) to ensure reliable performance.

Example Setup:

• Product: High-efficiency monocrystalline panels (400W each)
• Quantity: 10 panels for a total of 4 kW

MPPT Charge Controller

A Maximum Power Point Tracking (MPPT) charge controller optimizes the power output from solar panels by adjusting the electrical operating point of the modules. MPPT Ensure that the charge controller can accommodate the voltage and current characteristics of Na-ion batteries.

Key Considerations:

• Voltage and Current Ratings: Ensure the MPPT can handle the total voltage and current from the solar array.
• Efficiency: Higher efficiency controllers reduce energy loss during conversion.
• Compatibility: The MPPT should be compatible with the battery type and system voltage.

Example Setup:

• Product: Victron EasySolar-II 5kVA MPPT 250/100 GX
• Specification: Capable of handling up to 250V and 100A

Sodium-Ion Batteries

Batteries store the energy generated by solar panels for use during periods without sunlight. Sodium-ion batteries are an emerging technology offering safety and cost benefits.

Key Considerations:

• Capacity: Sufficient storage capacity to meet daily energy needs and provide backup power.
• Cycle Life: High cycle life ensures long-term usability.
• Temperature Performance: Ability to operate in a wide temperature range.

Example Setup:

• Product: Apexium 230 Ah Sodium-Ion Batteries (Qty: 24 for 16.6kWh)
• Product: Seplos 48V 280Ah LFP Battery Pack DIY Kits Set Case (Qty: 2)

Battery Management System (BMS)

A BMS monitors and manages the charge and discharge of battery cells, ensuring optimal performance and safety. The BMSmust be configured to handle the specific charge and discharge profiles of Na-ion batteries, including voltage settings and thermal management.

Key Considerations:

• Customization: Ability to configure for specific battery chemistry (sodium-ion).
• Protection: Overvoltage, undervoltage, overcurrent, and thermal protection.
• Communication: Integration with other system components for real-time monitoring.

Example Setup:

• Product: Lynx Smart BMS with customized configuration for Na-ion cells using Victron Connect app

Smart Shunt

A smart shunt measures the flow of current in and out of the battery, providing accurate state-of-charge information. Integrate smart shunts and monitoring systems to provide real-time data on battery health and performance, enabling proactive management.

Key Considerations:

• Accuracy: High precision for reliable battery monitoring.
• Integration: Compatible with the BMS and other monitoring systems.
• User Interface: Easy access to data via apps or display units.

Recommendations:

• Product: Victron SmartShunt 500A/50mV

Finally, as with any electrical system design, one has to implement basic safety measures, including fuses to isolate faults within each core system and manual switches which are useful when installing or maintaining the system.

MPPT and BMS Customization for use with Sodium Ion Battery

Once the electrical systems are connected, both MPPT and BMS need to be customized in order to properly charge and manage sodium-ion batteries. It should be noted that the following  is only an example settings for a specific model of sodium-ion battery and the specific voltage and current settings from the cell manufacturer must be used in the actual setup.

Configuring the MPPT Charge Controller

• Voltage Settings: Adjust the MPPT to handle the lower nominal voltage of sodium-ion batteries (3.10 V) compared to typical LiFePO4 batteries (3.20 V).
• Charge Cut-Off Voltage: Set the charge cut-off voltage to 3.95 V to prevent overcharging.
• Discharge Cut-Off Voltage: Configure the discharge cut-off voltage to 1.50 V to avoid deep discharging the sodium-ion batteries.

Setting Up the BMS

• Charging Parameters: Customize the BMS to follow the specific charging profile of sodium-ion batteries:
• Constant Current Charging: 0.50 C (max)
• Constant Voltage: 3.95 V with a cut-off at 0.05 C
• Temperature Monitoring: Ensure the BMS includes temperature sensors to manage charging and discharging based on the temperature constraints of sodium-ion batteries.
• Safety Features: Implement overcurrent, overvoltage, and undervoltage protection tailored to sodium-ion characteristics.

Integrating the Smart Shunt and Relays

• Smart Shunt: Connect the shunt to monitor the battery state accurately. It should integrate with the VictronConnect app for detailed battery performance analysis.
• Relays and Fuses: Install DC relays and fuses rated for the system’s voltage and current to ensure safe operation and protection against short circuits and overcurrent situations.

Technical Considerations for Energy-Intensive Loads

To utilize the DC current from the sodium-ion battery which has a steep voltage discharge curve, a DC/DC voltage conversion will likely be required to match the input DC voltage requirement of the load device such as a DC air conditioning unit. A buck-boost DC converter is used to adjust the voltage levels up (boost) or down (buck) to match the requirements of the load or storage device. 

Configuring the MPPT for Peak Load Reduction

Hybrid MPPT such as Victron EasySolar-II GX or Victron Inverter RS Smart Solar allows scheduled charging of battery from grid electricity thus allowing for an effective load shifting strategy. Load shifting is the use of battery storage to shift energy consumption from peak demand times to periods when grid use is less expensive or more readily available.

By also configuring specific hours for the DC load, one can schedule time-of-use schedule to avoid use of grid-electricity when its cost is the highest. A example of time-of-use feature that is often used in charging electrical vehicle overnight when the grid electricity cost is the lowest.

Comparison Table: DIY vs. Commercial Solution

There are several commercial options available for at solar panels and energy storage. A quick comparison of the DIY solution versus off-the-shelf commercial solution is shown below.

Going with off-shelf commercial solutions such as Tesla Solar and Powerwall option is the easiest given that the professional installers perform all the necessary tasks. The cost for a Tesla Solar with one 14kW Powerwall appears to be around currently around $24,000 for California residents with all the Federal and State level incentives applied.  

Summary

Implementing an off-grid nanogrid system using sodium-ion batteries is feasible with the right components and customization. While there are technical and cost challenges, particularly for DIY setups, the benefits of energy independence and sustainability are significant.However, understanding how all of the electrical systems needs to be integrated together can be challenging and obtaining permit to DIY setup can be particularly problematic. This is where the commercial solutions such as Tesla Solar and Powerwall can have advantages if there are government programs that can offset the installation costs.

If you are a California resident, by leveraging both federal and state incentives, such as the Federal Investment Tax Credit (ITC) and California's Self-Generation Incentive Program (SGIP), homeowners can significantly reduce the cost of these systems. However, the DIY approach requires careful planning, customization, and a thorough understanding of the technical aspects to ensure a successful implementation.