What Size Solar Battery Do I Need for My House - A Guide to Choose the Right Battery
More and more households are installing solar energy and energy storage systems. During the day, solar panels on the roof generate power. At night, most homes still rely on the grid. When a power outage occurs, the refrigerator, internet, and lighting are immediately interrupted. That’s why many people now ask: “What size solar battery do I need for my house?”
Some people are worried that choosing too small is not enough, while others are afraid of buying too big and wasting money. Online calculators, forum advice, and neighbors’ setups may look helpful. But they often don’t fit your own home.
This article will help you understand what kind of capacity you truly need and which power station solutions are more suitable for different household scenarios.
Key Questions to Understand Your Home Battery Needs
Don’t rush to choose a battery based on the kWh number alone. What size battery do I need for my house isn’t determined by a simple formula—it depends on how electricity is actually used at home.
For many households, the focus is less on battery size itself and more on what the power is meant to support, such as greater flexibility at night or better preparation for power outages. Some aim to keep most appliances running, while others prioritise power during critical moments.
Clarify Your Power Goals
solve by installing batteries?
For many families, the initial idea may be:
To store solar energy during the day so that I don't have to buy electricity at night.
To avoid worrying about electricity consumption when turning on the air conditioning or cooking at night.
To keep the home functioning normally during power outages.
After some time, many people realize something important. The only things that cannot be disconnected at home are often the refrigerator, internet, lighting, and mobile phone charging. Washing machines, ovens, and electric stoves can usually wait until daytime or until power comes back.
Therefore, clarifying the purpose of use is a crucial step in determining what size home battery do I need.
High-Load Power Support vs Essential Power Needs
The requirements for battery capacity vary greatly depending on different power supply targets.
Electricity demand for each power goal:
Supporting high-power and multiple appliances requires a larger, scalable battery system, similar to how a home backup generator supports broader daily electricity needs.
Covering essential loads only can usually be achieved with a medium-capacity battery system.
For example, if a household expects to keep the air conditioning on, cook, do laundry, and charge your electric vehicle as usual during a power outage, then the battery system must work like the power grid.
But if the goal is simpler, the battery does not need to be large. Keeping the fridge running, Wi-Fi on, lights at night, and hot water needs much less capacity. This also makes it easier to control your budget.
Think About the Next 1–3 Years Battery Needs
The last often overlooked issue is the future changes in electricity consumption. Many households use "current electricity consumption" to calculate when installing batteries, but the changes within 1-3 years are often faster than imagined:
Install an additional air conditioner
I bought an electric car and started charging it at home
As children grow, they tend to use more electronic devices.
All of these changes will directly affect what size battery I need for my house. Planning some room for expansion makes it easier to adapt—especially if your goal is long-term resilience and to better prepare for power outage at home.
Home Battery Basics Made Simple
When calculating home battery capacity, two concepts are involved. These concepts directly influence how you determine what size solar battery you need for your house.
What Is kWh and Why It Matters
kWh does not decide how many devices you can turn on. It decides how long they can run.
You can think of a battery as a bucket:
The power of electrical equipment is the speed at which you release water
KWh is the total amount of water in the bucket
Assuming you have a 4 kWh battery at home, if it is used only to power essential low-load devices such as the refrigerator, lighting, and router, it can typically support several hours of nighttime use. However, once high-power appliances like air conditioners or electric stoves are turned on, the stored energy will be consumed much faster due to the higher power demand.
That’s why, when considering what size solar battery you need for your house, kWh matters more for determining runtime, while kW defines how many appliances can run at the same time.
Rated Capacity vs Usable Capacity
After understanding how kWh determines "how long it can last", there is a more easily overlooked question: how much electricity you can actually use. Most batteries are labeled with a capacity number, but in actual use:
To protect battery life, the battery will not be depleted to 100% capacity
During the charging and discharging process, there will also be energy loss in the amount of electricity
For example, if you see a battery that says 10kWh, the actual usable one may only be 8-9kWh. Many families fall into this trap here. When calculating, it was just enough, but after installation, it was found that the power started to run out every early morning.
So, when determining what size solar battery I need, it is important to consider "available capacity" rather than just looking at the numbers on the packaging.
How to Calculate: What Size Solar Battery Do I Need for My House
The following three steps are calculation methods that many ordinary families can easily complete. You don't need to score every kilowatt hour accurately, as long as you roughly judge a reasonable range based on your daily electricity habits, it is enough to help you avoid inappropriate battery capacity.
Step 1: Estimate Daily Energy Usage (kWh)
The first step is to understand approximately how much electricity your home uses every day.
The simplest and most reliable method is to check the electricity bill. If the bill shows that you used 450kWh in a month, then on average, it's about 15kWh per day. This number doesn't need to be precise; it's just a reference starting point.
If you recall your daily life, having a refrigerator and router on standby at home during the day, and cooking, doing laundry, turning on air conditioning or heating at night, these combined are actually highly matched with billing data.
For most families, knowing whether they are around 10kWh, 15kWh, or above 20kWh can already provide crucial information for determining what size solar battery they need for their house.
Step 2: Decide How Long the Battery Should Last
The next thing to think about is: how long do you want the battery to support your appliance without sunlight? You can estimate battery capacity using a very simple formula:
Required battery capacity (kWh) ≈ Common equipment power (kW) × Usage time (hours)
Don’t worry about the formula. In real life, this step is very simple. You just need to think clearly: which appliances will you really use simultaneously when there is no sun or power outage?
Here is a reference power meter for a common household (approximate range for a single device):
Household appliances | Common power |
Refrigerator | 0.1–0.2 kW |
Router | 0.01 kW |
Lighting (whole house) | 0.1–0.3 kW |
TV | 0.1–0.2 kW |
Washing machine | 0.5–1 kW |
Electric kettle/stove | 1.5–2 kW |
Air conditioner | 1–3 kW |
If a family needs to keep the following equipment running for 10 hours during a power outage:
Refrigerator (0.15 kW), lighting+router (0.15 kW), TV (0.15 kW). So the total power is about 0.45 kW x 10 hours ≈ 4.5 kWh
At this point, you will realize that the home does not need batteries that can drive the entire house, but rather batteries that can stably drive key equipment. This step will help you determine more clearly what size solar battery do I need for my house.
Step 3: Add a Safety Buffer
The last step, often the most easily overlooked, is to leave room for real life. Because in real life, batteries almost never operate in their ideal state.
So the question is: how much safety margin should be left?
For most families, practical experience suggests adding a 20% -30% margin based on the calculated results
If the capacity matches the calculated value, any small fluctuation in daily life will cause the battery to run out of power ahead of schedule. For example, if you calculate that you need 8kWh, in real use, situations like running the air conditioner a bit longer at night or starting the washing machine may cause the battery to run out.
But choosing a capacity of around 10kWh, these fluctuations can basically be 'eaten up', and the electricity experience will be much easier.
For most families, instead of calculating capacity just right, it is better to focus on whether there is room to cope with fluctuations, which is often more important than precise numbers.
Choosing the Right Battery Size by Household Scenario
After calculating the battery capacity, put these choices back into real-life scenarios. Starting from the two most common types of households, let's take a look at how battery capacity is "utilized" in real life.
Everyday Home – Night Use & Basic Backup
This is the most common and easily overestimated type of family in terms of demand.
During the day, solar energy covers most of the electricity usage, while at night, the battery is mainly responsible for cooking after meals, watching TV, doing laundry, and lighting. During occasional power outages, the priority is usually to keep essential appliances running—such as the refrigerator and internet—so the home doesn’t fall completely dark.
At this stage, many families reach a practical realization: what they really need is a stable, well-managed, and readily available battery system that can take over at night and provide basic electricity. For these types of households, batteries are more often used "every night" rather than as backup power for one or two extreme situations.
In such a living scenario, solutions like EcoFlow DELTA Pro 3 Portable Power Station would appear more in line with practical needs. It is not meant to appear exaggerated in terms of parameters, but rather to better fit the rhythm of 'using it every day'. Nighttime electricity is sufficient, power outages are easy to switch, and there is no need to change lifestyle habits just to manage the system.
So, when asking what size solar battery do I need for my house, if your goal is only to use electricity at night plus basic backup, this "just right" solution is often more reasonable than choosing a larger one in one step.
High-Consumption Homes
Some families also face higher intensity electricity demand from the beginning.
When there is a power outage, not only the refrigerator and internet, but also the air conditioning needs to continue running. The most common problem faced by these households is insufficient battery capacity, forcing them to make choices about electricity usage, and the experience becomes fragmented and tense.
When a home needs to repeatedly calculate whether another appliance can be switched on, or continually adjust daily usage habits due to limited battery capacity, the issue is no longer simply about what size battery is needed. It becomes a question of whether the system is suitable for long-term, high-load residential use.
In this situation, instead of repeatedly struggling with a single capacity, it is better to choose a system that is designed to support expansion and can cover most household power needs. The EcoFlow DELTA Pro Ultra Whole-home Backup Battery is more suitable for households with clear electrical structures and consistently high loads.
Its value lies not in being 'bigger', but in solving real-world problems. When multiple high-power devices are running simultaneously, there is no need for frequent compromises, and household electricity consumption remains continuous and predictable. For such families, choosing the right system is essentially reducing the cost of repeated replacement and remediation in the coming years.
Battery Size for Different Solar System Capacities
After understanding the household electricity usage scenario, many people will naturally continue to search: What size battery do I need for a 5kW solar system? Does a 6.6kW, 10kW, or even 20kW system necessarily require a large battery?
A common misconception is that the larger the solar system, the bigger the battery must be.
But in real life, it's not like that. For example, some households have installed a 10kW solar system that generates a lot of electricity during the day, but most of the time there is no one at home and the electricity cannot be used up; And what we really need at night is just a part of cooking, lighting, and air conditioning. In this case, the task of the battery is not to 'store all the electricity', but to cover critical periods of power consumption.
In areas with good sunshine conditions, medium-capacity batteries combined with reasonable electricity management are often more efficient than buying large batteries at once, and are also more in line with the rhythm of long-term household use.
The table below can help you quickly establish a clear understanding.
Typical Battery Size Guidance by Solar System Capacity
Solar System Size | Common household scenarios | Battery capacity reference range | Suitable usage |
5kW | Ordinary household, with people during the day and basic electricity consumption | 5–10 kWh | Nighttime use and basic backup for essential loads |
6.6kW | Common household configuration, sufficient power generation during the day | 10–15 kWh | Night use with support for critical household equipment |
10kW | Power generation is high, but electricity consumption is concentrated in the morning and evening | 15–25 kWh | Extended runtime and higher-comfort electricity usage |
20kW | Large unit/ high load household/semi off-grid | Modular expansion system | High-load households with scalable, near whole-home support |
In addition, for a 10kW or even 20kW system, it does not mean that you must fully charge the battery capacity at once. Many families choose to start with a capacity that is "currently sufficient" and gradually expand in the future as electricity consumption increases, making it easier to find a balance between cost and experience.
Conclusion
What size solar battery do I need for my house, the real focus is not the number. It is whether the battery fits your family’s daily life.
What truly affects the decision is your electricity usage habits, backup goals, and the potential for change in the next 1-3 years. Whether it's nighttime electricity usage or backup power outages, as long as the scenario is clear, the answer will become clear.
FAQs
How long will a 100Ah battery last off-grid?
A 100Ah (12V) battery provides about 1.2 kWh of nominal capacity, with less usable energy in real conditions. It is commonly used in RVs or small off-grid setups to run low-power devices such as lighting or routers for a limited number of hours. Due to its limited capacity and runtime, a single 100Ah battery is generally not suitable as a reference for household energy storage or for powering appliances like refrigerators or air conditioners.
The larger the battery, the more it saves?
Many people intuitively believe that since solar energy is installed, the larger the battery and the more electricity it stores, the lower the electricity bill will be.
In reality, many families notice something after installation. The battery is only used for a few hours each day.
The bill hasn't decreased much, but the equipment has been "idle" all the time, which is a typical manifestation of choosing too much capacity. For most households, the capacity that covers both nighttime and critical electricity needs is often more cost-effective than buying the maximum at once.
Can a 10kWh battery run a whole house?
A 10 kWh battery can support a household only under carefully managed loads, where high-power appliances are avoided or used separately. For example, when there is a power outage, only the refrigerator, lighting, router, and TV are running, and high-power devices are not turned on at the same time. 10kWh is more suitable for "overnight critical equipment" rather than whole-house operation. But if both the air conditioning and the electric stove are turned on at the same time, it will be difficult to cover all the electricity consumption of the entire house.
How can I determine what size solar battery I need for my house?
There are many online tools that can help estimate what size solar battery you need for your house, providing a quick numerical reference. However, most calculators assume ideal electricity usage and don’t account for variations like family routines, seasonal weather changes, or specific appliance habits. To choose the right size, it’s important to combine these estimates with your real-life electricity consumption and household needs.