Home Energy Needs & Solar Battery Sizing
How much Solar Battery back up a home needs is a vital question to answer before you buy an energy storage system. The answer depends on what you want to power when the grid goes out. You can choose to have partial house back-up (link) or if the budget is available, then whole-house back-up (link) is possible. Over-sizing the battery is common if you want to have power waiting for use when needed.
The simplest way to determine the battery size needed is to review the kilowatt-hours (kWh) consumed on a daily basis. The utility power bills can be used as a starting point. Just find the average daily kWh used for the previous year. If the power bill does not show this for you, then add the kWh for 12 months of power bills, and then divide by 365 to calculate the daily average kWh used.
The average home in the USA consumes 30 kWh per day. Therefore you might want a battery that is rated for more than 30 kWh to handle your power needs. If you choose partial house backup, then a smaller battery may just work out nicely.
The chart below can also help guide your solar battery sizing decision. The chart shows the daily kWh used for common household appliances, Below the chart is an example of one family’s decision for their power use when the grid goes out and how that influenced their solar battery backup sizing decision.
Home Energy Use for Common Household Appliances
Typical kilo-watt (kWh) used per day. Actual use may vary.
Applying this kWh use to an example of a family of four who wants to go solar would look a bit like the following. This family is looking to go solar as they experience power outages due to the weather during the summer months to their Grid-Tied home. They do not want to limit their entertainment energy use, so they calculate energy use for their four laptop computers, wifi, one tv, and one game console. These items will use approximately 11 kWh per day.
It is warm where they live during the summer, so when the power goes out, they need a way to cool themselves down. They decide that having AC on during a power outage will use too much energy; they decided to cool down using their six ceiling fans. Since they are making this exchange, they do not want to limit their use of the fans. The ceiling fans will use approximately 1.5 kWh per day,
If the grid goes out, they will plan to wait on washing clothes because the grid has not stayed down for more than two days in a row. They will plan to power their refrigerator and freezer and use their stovetop, microwave, and coffee machines. These items will use approximately 9 kWh per day.
Adding up these three areas of consideration, 21.5 kWh needed for one day of solar battery back up. These calculations do not incorporate the hours that their solar array will be producing power. The family decided to make sure that if the power goes out, and their weather does not produce usable solar energy, they will have power for their needs. Since the power has gone out for two days in a row, they will get a solar battery backup to cover two days worth of energy for their home, 43 kWh. This sum means looking at our 40 kWh Solar Battery Back-up products to get a general cost idea for a battery this size. If they can oversize the battery a bit, just in case, they missed something in their energy use calculations.
Additionally, this example does not calculate variations for Depth of Discharge (DOD) and cold and heat temperature adjustments for your Solar Battery. To learn how to take your Home Energy Use calculations, and incorporate these variations into your Solar Battery Size, see our page Solar Battery Sizing Simplified.