If you’re considering a solar battery system to complement your home’s solar panels, you’re making a smart move toward energy independence, security, and efficiency. However, choosing the right size battery for your home requires careful consideration of your energy usage, backup needs, and solar production. This cheat sheet will guide you through the essential steps to properly size a solar battery system for your home because let’s face it…it’s confusing and complicated.
Why Choose a Battery Backup?
Many homeowners opt for battery backups to achieve greater control over their energy usage. Here are the main reasons why a solar battery backup is a valuable addition:
- Energy Independence: Reduce reliance on the grid by storing and using your own solar power.
- Backup Power: Maintain power to essential appliances during outages.
- Avoid Utility Buyback Rates: Maximize the value of your energy by using it yourself, especially in markets with low buyback rates for excess solar power.
- Time-of-Use (TOU) Optimization: Avoid high electricity rates during peak hours by relying on stored energy.
- Maximize Solar Value: Ensure excess solar energy is stored and used efficiently, even when production exceeds daytime needs.
Step 1: Understand Your Energy Usage
To size your solar battery accurately, you first need to evaluate your household’s energy consumption.
Key Metrics to Gather:
- Monthly Energy Usage: Review your utility bills to find your average monthly kWh usage.
- Peak Usage Times: Note the hours during the day when your energy consumption peaks.
- Essential Loads: Identify appliances and devices you’d prioritize during a power outage, such as:
- LED lights
- Refrigerator
- Wi-Fi router
- Fans or small heaters
- Microwave or electric stove
Tools for Monitoring:
- Smart energy meters or apps can provide real-time data on your energy usage patterns.
Step 2: Decide What to Back Up
Solar batteries can back up your entire home or just specific circuits. Your choice depends on your budget and needs.
Options for Backup:
- Whole Home Backup:
- Requires a larger battery system, typically starting at 20 kWh.
- Supports high-energy appliances like air conditioning, electric vehicle chargers, or well pumps.
- Recommended for homes with high energy consumption or frequent outages.
- Partial Home Backup:
- Targets essential appliances and circuits.
- Typically requires 10-15 kWh of storage.
- More cost-effective and prolongs battery life.
Why a Single Battery Can’t Start an AC Unit:
Air conditioning units and other high-power appliances require significant startup power (known as inrush current), often exceeding the capacity of a single battery. Multiple batteries are needed to handle such loads, especially if they are running simultaneously with other appliances.
Examples of Backup Scenarios (Average home usage):
- 10 kWh Battery: Supports LED lights, refrigerator, microwave, fans, TV, and internet for one day.
- 20 kWh Battery: Adds a dishwasher and garage door to the above list.
- 30 kWh Battery: Includes well pumps and air conditioning for moderate usage.
Step 3: Compare Battery Options
Choosing the right battery involves evaluating capacity, output, efficiency, and features. Here’s a comparison of popular options:
| Feature | Enphase IQ Battery | FranklinWH aPower X | SolarEdge Energy Bank | Tesla Powerwall 2 | Tesla Powerwall 3 |
|---|---|---|---|---|---|
| kWh Capacity | 10.0 kWh | 13.6 kWh | 9.7 kWh | 13.5 kWh | 13.5 kWh |
| AC Continuous Output | 7.64 kW | 5 kW | 5 kW | 5 kW | 11.5 kW |
| AC Peak Output (10 sec) | 12.28 kW | 10 kW | 7.5 kW | 7.2 kW | 11.5 kW |
| Round Trip Efficiency | 90% | 85% | 94.5% | 90% | 97.5% |
| Battery Chemistry | Lithium Iron Phosphate | Lithium Iron Phosphate | Nickel Manganese Cobalt | Nickel Manganese Cobalt | Lithium Iron Phosphate |
| Warranty | 15 yrs (60%) | 12 yrs (70%) | 10 yrs (70%) | 10 yrs (70%) | 10 yrs (70%) |
| Self Consumption Mode | Yes | Yes | Yes | Yes | Yes |
| Backup Standby Mode | Yes | Yes | Yes | Yes | Yes |
| Load Shifting (TOU) | Yes | Yes | Yes | Yes | Yes |
| Wall/Floor Mount | Wall/Floor | Wall/Floor | Wall/Floor | Wall/Floor | Wall/Floor |
| Weight (Single Unit) | 146.1 lbs | 408 lbs | 267 lbs | 251.3 lbs | 287 lbs |
| States Available | Nationwide | Nationwide | Nationwide | Nationwide | Nationwide (except PR) |
Step 4 (optional): Explore Self Consumption Mode
In markets like California (CA) and Texas (TX), Self Consumption Mode can be a useful feature for maximizing energy independence and savings.
What is Self Consumption Mode?
Self Consumption Mode prioritizes using stored solar energy to power your home instead of exporting it to the grid. This mode is particularly beneficial in areas with high time-of-use (TOU) rates or limited net metering options.
Benefits of Self Consumption Mode:
- Reduced Grid Dependency: Use stored solar power during peak hours or at night.
- Cost Savings: Avoid high TOU grid rates by relying on your own energy.
- Energy Security: Maintain control over energy consumption during outages or periods of high demand.
- Cheaper to Install: The batteries and installations designed for self consumption are typically cheaper than a backup system.
Step 5: Calculate Solar Production and Battery Storage Needs
The size of your solar system directly impacts how much energy you can store in your battery. Use the following guidelines:
General Solar Production and Battery Sizing:
- 3,000-5,000 kWh Annual Solar Production: Requires 5-10 kWh of battery capacity.
- 10,000-20,000 kWh Annual Solar Production: Requires 20-30 kWh of battery capacity.
- 30,000+ kWh Annual Solar Production: Requires 40 kWh or more of battery capacity.
Example Calculation:
- If your solar system produces 10,000 kWh per year and your essential loads require 15 kWh daily, a 20 kWh battery system is ideal to store enough energy and handle outages or peak usage.
Step 6: Plan for Installation Requirements
Installing a solar battery involves more than just picking the right size. Consider these factors:
Main Panel Upgrades:
- Some homes may require a new or upgraded main service panel to handle the battery’s backfeed.
- Sub-panels can be backed up if all loads within them are supported.
Battery Placement:
- Install batteries in weather-protected locations such as a garage or covered exterior wall.
- Avoid direct sunlight or placing batteries within 3 feet of windows and doors.
Step 7: Consult with Experts
Every home is unique, and professional consultation ensures your system meets your needs and complies with local regulations. A solar consultant can:
- Perform a site survey to assess your home’s energy needs.
- Recommend the best combination of solar panels and batteries.
- Handle permitting and installation requirements.
Conclusion
Sizing a solar battery system for your home involves understanding your energy usage, solar production, and backup needs. By carefully evaluating these factors and consulting with a trusted solar provider like Eagle Mountain Solar, you can design a Solar+Storage system that maximizes efficiency, savings, and energy independence.
For expert consulting and customized Solar+Storage solutions, contact Eagle Mountain Solar today. Our team is ready to help you achieve your energy goals and make the most of your solar investment.