Determining how many batteries are needed to power a house depends on the system type and energy consumption. Let’s break down the main factors:
Key Battery Specifications
Capacity (Wh): This indicates how much energy a battery can store. It’s often expressed in ampere-hours (Ah) but can be converted to watt-hours (Wh) for easier comparison. The formula is:
Capacity (Wh)=Ampere-hours (Ah)×Nominal Voltage (V)
Power Rating (kW): The amount of electricity a battery can deliver. A high capacity with a low power rating supplies less electricity for a longer duration, while a low capacity with a high power rating can power multiple devices but for a shorter period.
Depth of Discharge (DoD): Represents how much of a battery’s capacity can be used without damaging it. For example, a 10 kWh battery with an 80% DoD allows you to use 8 kWh before recharging.
Round-trip Efficiency: Measures how much energy is lost during storage and use.
Off-Grid System: 30 kWh Daily Requirement
For an off-grid system, where the house is entirely dependent on solar energy, you need a robust battery setup. Take Tesla’s Powerwall 2 as an example: it has a 14 kWh capacity, 95% DoD, and 90% round-trip efficiency. Thus, one Powerwall delivers about 11.97 kWh.
Given that an average American home consumes around 30 kWh per day, two Powerwalls (24 kWh total) would get you close to a full day of backup.
Hybrid System: 10 kWh Daily Requirement
Hybrid systems, which are connected to the grid, only need smaller batteries for backup power. Batteries like the Powerwall help store energy during peak times or outages. One unit would be sufficient for a hybrid system.
Backup for Critical Loads
If your priority is powering essential devices (fridge, medical equipment), you can install a smaller battery bank dedicated to these critical loads. To size your battery accurately, list your essential devices along with their power needs (running wattage and surge wattage). Summing these will give you the total peak power required, ensuring your battery’s discharge rate matches this number.
Grid-Tied Systems: Backup Options
While grid-tied systems typically don’t use batteries, you can still add storage options like:
1. AC-Coupled Battery System: Adds a battery with its own inverter to your existing solar setup.
2. Solar Generators: Portable power stations provide backup, though they usually have smaller capacities (200 Wh to 6 kWh).
3. UPS or Power Banks: Useful for keeping smaller electronics, like routers, running for a few hours during outages.
Conclusion
For off-grid systems, around 30 kWh is recommended, while hybrid systems can suffice with 10 kWh. For backup of critical loads, carefully assess your power needs and choose a system that can handle the peak load.
Ready to explore the right battery setup for your home? Sunhub’s team of energy experts is here to guide you through your options and help design a system tailored to your needs. Contact us today to get started on your journey to reliable, sustainable power!