Off-Grid Solar: Costs, Process, and Best Products in 2023 – EnergySage Blog

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The above approach is a great way to review your historical energy usage, though it may not be as helpful to forecast future energy consumption. The second approach, on the other hand, is better at predicting what you may use in the future. Both of these approaches are estimates. If you’re planning to install solar and storage to go off-grid, it may be worth purchasing a home energy monitor or an energy management system to get a more precise estimate of your electricity usage.

How many batteries will you need?

To go off-grid, you need a way to store the electricity produced by your solar energy system at times when you’re not using it. Not every solar battery can operate independently of the grid, even if you feed it solar energy: You specifically need a battery that can “island” or form its own grid so that the panels will recharge the battery daily without a grid connection.

To determine the number of batteries you need to power your house for a single day, you need to know your daily electricity consumption and the amount of electricity stored in a standard solar battery. 

The amount of electricity stored in a battery is called the “Usable Energy,” expressed in kWh. This is the amount of electricity you can get out of a battery after accounting for electrical losses and any energy needed to power it. 

With these two data points in hand, calculating the number of batteries you’ll need is straightforward. For instance, the average American household uses about 30 kWh per day. Given the conversion losses associated with storing electricity, you’ll need enough batteries to store slightly more than what you use per day, likely closer to 32 kWh, depending upon the efficiency of the battery you select.

Two of the most common solar batteries are the Tesla Powerwall 2 and the LG Chem RESU 10H, which store 13.5 kWh and 9.3 kWh of usable energy, respectively. In this example, the average American homeowner would need 3 Powerwalls or 4 RESU 10H batteries to meet a single day’s electricity needs. 

This is just the number of batteries you’ll need to power your house for a single day. In reality, you’ll want enough backup storage capacity to power your home for many days, or even an entire week, to ensure you still have electricity if you have a period of inclement weather or need more than your average daily usage in a single day. 

How many solar panels will you need?

Next, you’ll want to design a solar energy system that’ll supply electricity to your property and a storage setup large enough to fill your battery every day. 

The electricity your solar panel system produces directly results from the amount of sunlight your panels receive. The average home in the U.S. gets an average of 5 sun hours per day, which doesn’t represent the amount of time your panels are in the sun but instead measures the number of hours during which sunlight intensity is 1,000 W/square meter. Learn more about what your average sun hours are depending on your state. Other factors like shade and the angle of your panels relative to the sun also affect the electricity your panels produce.

To determine how many solar panels you need to fill your batteries every day, divide the amount of electricity required (in this case, 32 kWh) by the number of expected sun hours (5 in this example): 

32 kWh / 5 hours = 6.4 kW

Thus, we need a solar panel array of about 6.4 kilowatts to fill up a battery bank with a capacity of 32 kWh daily.

The number of solar panels you’ll need for a 6.4 kW system depends on the power output (in watts) of the solar panels you use, which generally range in wattage from 250W to 400W:

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