How Many Batteries to Power a House?
🎁 Free Diagrams: https://cleversolarpower.com
📖 My Best-Selling book on Amazon: https://cleversolarpower.com/off-grid...
Recommended Batteries: https://cleversolarpower.com/go/EG448V
In this video, I'm going to show you how to determine how many batteries you need to power a house, whether you're living off-grid or just need a battery backup for grid outages. We'll go through an easy 4-step guide to help you calculate the size of your battery bank.
Step 1: Understanding Your Power Consumption
First, you need to know how much power you are consuming daily. There are two methods:
Off-Grid Load Analysis: If you are off the grid, you need to make a load analysis. Take John, for example. John lists all his appliances and their energy consumption in a spreadsheet. By noting the power of each device and how many hours per day it runs, he calculates his total daily watt-hour usage. John has a daily consumption of 10kWh.
Grid-Connected Analysis: For those who are grid-connected, like Mike, you can use your power bill as a reference. By dividing the total kWh consumed by 30 days, Mike figures out his daily power consumption. The average monthly consumption in the US is about 10,300kWh, which comes down to approximately 30kWh per day.
Step 2: Days of Autonomy
John needs to decide how long he wants to run his appliances. In an off-grid situation, I recommend having three days of autonomy. This means if there's no sun, wind, or generator power, John can still run his house for three days on battery power alone.
For Mike, who is grid-connected, the consideration is how long power outages typically last in his area. If outages usually last just a few hours, one day of autonomy should suffice. Remember, a larger battery will cost more, so Mike needs to balance his needs with his budget.
Step 3: Choosing the Right Battery Type and Voltage
Contrary to popular belief, lithium batteries are now cheaper than lead-acid batteries. Both John and Mike should go with a lithium battery, specifically lithium iron phosphate or LiFePO4.
The battery voltage should be 48V, not 12V or 24V. Using a higher voltage battery reduces the required thickness of your cables, saving you money. For example, a 5000W inverter with a 12V battery will have much more current draw than a 48V battery:
5000W/12V = 416A
5000W/48V = 104A
As you can see, using a higher voltage battery is beneficial not only for discharging but also for charging. You can use a cheaper charge controller and charger. For more details, check out my video on the advantages of using a 48V system.
Step 4: Sizing Your Battery
Now, let’s size the battery for John’s off-grid setup. Using our example of a 10kWh daily load, the formula is:
10kWh×3 days of autonomy=30kWh of energy storage
One 48V 100Ah battery stores 5kWh, so John needs six of these batteries. This setup will cost him $8350.
For Mike’s grid-tied system with battery backup needing only one day of autonomy, the formula is:
30kWh×1 day of autonomy=30kWh of battery storage
This is the same battery requirement as John’s off-grid setup.
Mike can reduce the number of batteries by being mindful of his consumption. During a power outage, he might choose not to run high-power appliances like the washer, dryer, or air conditioning. If he limits his usage to 10kWh for the day, when the grid is down, he will only need a 10kWh battery for one day of autonomy. This approach will be much more cost-effective.