Ways to Choose the Right Home Battery Size for Your Solar System

This guide walks you through a clear, step-by-step way to choose a home battery size that fits your solar system, usage, and budget. Along the way, the guide will use real-world numbers from public sources and simple math that you can check on your own.

Step 1 – Decide What You Want The Battery To Do

You should first decide what main job you want the battery to handle. Your answer will shape the required size more than any other factor.

Backup Only Essentials

Many homeowners only want the battery to keep key loads running during blackouts, such as:

• One fridge and freezer

• A few rooms of lights

• Wi-Fi and router

• Some outlets for phone and laptop charging

• A small pump or a gas boiler controller

This “essentials only” plan usually needs a smaller battery, often in the 5–10 kWh range, depending on your daily use and your backup time target.

Backup Most Of The Home

Some homes want a more “normal life” during outages, with:

• Most lights

• Fridges and freezers

• TVs and computers

• Some air-conditioning or fans

This plan usually points to a medium battery, often around 10–15 kWh for an average-size home.

Go Near Off-Grid

A few homes want to run almost everything from solar and batteries, even when the grid is down for days. This goal often needs:

• Larger batteries in the 20+ kWh range

• Careful planning for winter sunlight in your area

• A clear list of what you will turn off in long outages

Off-grid and near off-grid plans need the most careful sizing, and many guides suggest planning for the month with the least sun, not the average month.

Step 2 – Work Out Your Daily Energy Use (kWh)

You should next find out how much energy your home uses on a typical day.

Most articles recommend that you:

1. Look at your power bill: The bill usually shows your monthly energy use in kilowatt-hours (kWh).

2. Turn monthly use into daily use: If your bill shows 900 kWh in a 30-day month, you can divide 900 by 30. Your average daily use = 900 ÷ 30 = 30 kWh per day.

3. Check if this number feels right: If you have big loads (pool pump, electric heater, EV charger), your daily use may be higher than the number for a small home. Many guides use 20–30 kWh per day as a rough range for a typical modern family home.

Your daily kWh number is the base for all later battery size calculations.

Step 3 – Choose How Many Days Of Backup You Want

You should now decide how long you want the battery to cover your needs without grid power.

Industry guides often suggest this simple rule of thumb:

• 1 day of backup: Good for homes with stable grids and rare outages.

• 2–3 days of backup: Better for homes in areas with storms, heatwaves, or weak grids.

• More than 3 days: Useful only for off-grid or very remote sites.

For many grid-tied homes, one to two days of backup for essential loads is enough. If you try to run every device for three days, your battery size and cost will grow quickly.

Step 4 – Understand Ah Battery Meaning, Voltage, And kWh

Many homeowners search “ah battery meaning” when they first look at battery specs. You will see both amp-hours (Ah) and kilowatt-hours (kWh) on data sheets, and the terms can be confusing.

You can use these simple points:

• Amp-hours (Ah) tell you how much electric charge a battery can supply at a given voltage.

• Voltage (V) tells you how “strong” that charge is.

• Watt-hours (Wh) = Voltage (V) × Amp-hours (Ah).

• Kilowatt-hours (kWh) = Wh ÷ 1000.

You can see a clear example if you look at a common home unit:

A 48 V, 200 Ah battery has:

• Wh = 48 × 200 = 9,600 Wh

• kWh = 9,600 ÷ 1000 = 9.6 kWh

So the practical answer to “ah battery meaning” is that Ah is just part of the path to kWh. You still need the voltage to know the real energy in the battery. For home solar systems, most planning uses kWh instead of Ah, because kWh links directly to your energy bill and your daily energy use.

Step 5 – Use A Simple Formula To Estimate Battery Size

Many professional and DIY guides use almost the same basic formula for battery capacity.

You can use this version at home:

Battery Capacity (kWh)
= (Daily Energy Use × Days Of Backup × Coverage Factor) ÷ (System Efficiency × Depth Of Discharge)

Where:

• Daily Energy Use is your kWh per day from the bill.

• Days Of Backup is how many days you want the battery to support.

• Coverage Factor is the share of your use that you want the battery to cover (for example, 0.5 for 50% or 0.8 for 80%).

• System Efficiency includes inverter and wiring losses (a common assumption is 0.9 or 90%).

• Depth Of Discharge (DoD) is the part of the battery you are willing to use each day (lithium batteries often use 80–90% DoD).

 

Example – Average Home, Essentials Only

You can walk through a real-world style example:

• Daily energy use: 30 kWh/day

• Days of backup: 1 day

• Coverage factor: 0.6 (you only want to back up about 60% of your normal use, that is mostly essentials)

• System efficiency: 0.9

• DoD: 0.9

Now you can plug the numbers into the formula:

Battery Capacity
= (30 × 1 × 0.6) ÷ (0.9 × 0.9)
= 18 ÷ 0.81
≈ 22.2 kWh

You would normally round this up to a standard size, such as a 20–25 kWh system, or two 10–12 kWh modules.

Example – Small Home, Short Backup Time

A small home might use:

• 15 kWh/day

• 1 day of backup

• 0.5 coverage (only essentials)

• Efficiency 0.9

• DoD 0.9

• Battery Capacity
  = (15 × 1 × 0.5) ÷ (0.9 × 0.9)
  = 7.5 ÷ 0.81
  ≈ 9.3 kWh

In this case, a single 10 kWh wall mounted battery would usually be enough for backup of key loads.

Typical Battery Size Ranges For Different Homes

Home Type Or Use Case	Daily Use (kWh)	Backup Goal	Typical Battery Size (kWh)
Small apartment, lights + fridge	8–15	1 day, essentials only	5–10
Small home, basic loads	10–20	1 day, most key circuits	7–12
Average family home	20–30	1 day, wide coverage	10–15
Average home, 2–3 days essentials	20–30	2–3 days, essentials only	15–25
Large home, high use or mini-off-grid	30–50+	1–3 days, wide coverage	20–40+

Where A Wall Mounted Battery Fits In Your Home

A wall mounted battery is a compact battery pack that sits neatly on a wall instead of taking floor space. This type of battery suits:

• Garages and utility rooms with limited floor area

• Tight urban homes where every square meter matters

• Homeowners who want a clean, modern look next to the inverter and switchboard

Avepower focuses on home backup batteries such as wall mounted battery units built around LiFePO4 (lithium iron phosphate) cells, with a smart BMS (battery management system) and options for modular expansion. These features help you:

• Match one 5–10 kWh module to a small home

• Stack several modules to reach 15–25+ kWh for larger homes

• Keep safety high, because LiFePO₄ chemistry is very stable and works well with deep cycles

A wall mounted battery also makes the cable runs short between the battery, inverter, and main switchboard, which can reduce losses and make the system look more tidy for long-term use.

You can use the formula and steps in this guide to get a strong first estimate of your ideal battery size. You can then talk with an installer or a supplier to refine the number.

Avepower, as a home backup battery manufacturer, can support you and your installer in several ways:

• The Avepower team can review your daily kWh use and your backup goals and suggest a capacity range, not just a single number.

• The Avepower product line includes wall mounted battery models and other formats that cover small apartments up to large homes with higher loads.

• The modular design and wide voltage options help you start with a smaller system and expand later as your needs grow.

If you are planning a new solar system or upgrading an older one, you can:

1. Collect your last 6–12 months of power bills.

2. Decide whether you mainly care about backup, bill savings, or both.

3. Use the formula in this article to find a kWh range.

4. Share this range with Avepower or your local installer to check which battery model and inverter pairing fits best.

If you follow these steps, you will not just buy “a battery.” You will choose a home battery size that fits your life, your roof, and your future plans.