How Many Solar Batteries are Needed to Power a House?

A solar system can save you money on electricity bills, but how much you save also depends on getting the right number of solar batteries for your home…  After all, you wouldn’t want to overbuy and spend more than necessary, right? That’s not really saving! In this article, we’ll break down how many solar batteries are needed for your home, the factors that affect this number, and how you can calculate the right amount based on your own energy consumption. 

How many solar batteries are needed to power a house?

In most cases, a single 10kWh battery is enough to power a house. This is because many homeowners rely on net metering agreements, which reduce the need for multiple batteries

A study by the Lawrence Berkeley National Laboratory even found that one 10 kWh battery could keep a house running for up to 3 days, provided only essential household items are to be used.

But of course, every household has unique energy needs and goals. You can use the ballpark numbers below as a starting point to help you determine the right number of batteries for your specific situation.

Two (2) Solar Batteries for “Load Shifting” Purposes

Load shifting is when you’re storing solar energy during the day (or using the much cheaper off-peak energy from the grid) to power your home during peak hours – usually around late afternoon to evening when household energy usage spikes.  

Likely, your goal is to save money by avoiding paying for the more expensive time-of-use (TOU) rate during these peak hours.

Two 10 kWh solar batteries should comfortably be enough to meet your energy needs for about 5 to 6 hours daily.

Alternatively, you could choose a consumption-only battery. It functions like a regular solar battery but doesn’t provide backup power during outages, making it a more budget-friendly choice if backup capabilities aren’t a priority for you.

Three (3) Solar Batteries for Backup Power

The same study by Berkeley Laboratory earlier shows that 30 kWh worth of stored energy is enough to power essential household appliances, including cooling and heating.

This means that having three 10 kWh solar batteries should give you the confidence that your home will stay fully powered – almost as if the outage never happened.

Nine (9) Solar Batteries for Full Off-Grid Application

If you’re planning to go 100% off the grid, you’ll have to think beyond your daily energy use. You’ll also need to account for power inefficiencies, occasional peak loads, and unpredictable weather conditions.

Let’s take the US Energy Information Administration’s data on the average household energy use: roughly 30 kWh per day. 

Following off-grid best practices, your system should have enough stored energy to last an extra two days without charging. This bumps your total energy requirement to 90 kWh.

Considering typical lithium-ion batteries have a capacity of about 10 kWh, this means you would need about 9 batteries (90÷10). To be on the conservative side, you might decide to go with 12 batteries in total.

Factors That Affect Solar Battery Quantity

Calculating your exact energy consumption is far better than relying on our estimates earlier. To get accurate results, though, you first need to understand the key factors that influence the quantity.

Your Household’s Energy Usage

When we talk about household energy usage, it’s more about how energy-intensive your appliances are than the number of people in your home.

Are you only powering essentials like a refrigerator and a few small devices? Or do you have larger energy demands, such as electric heating or a pool pump? Homes with higher energy needs will naturally require more storage.

Size of Your Home

Instinctively, the larger your home or property, the more energy it will consume. But beyond that, it also affects how much solar energy you can harness, produce, and store…

With more roof space or open land, you can fit more solar panels and produce more energy. 

On the other hand, a smaller roof or limited space leads to a smaller solar panel system, putting a cap on the amount of power you can generate.

In this case, installing multiple batteries or a large one is only a waste of money if you can’t produce enough energy to charge them or use their full capacity.

Battery Capacity

Battery capacity is essentially how much energy a single battery can store.

If you need 30 kWh of stored power, it’s logical to choose a single 30 kWh battery. However, you could go with three 10 kWh batteries, which would give you the same total capacity and work just as well.

Ultimately, it boils down to how big your storage space is (more on this later).

Utility Electricity Rate

Your electricity rate arrangement can alter your energy goals, which in turn affects how many batteries you’ll need.

If you’re on a flat-rate electricity plan, you’ll want to store as much energy as you can to reduce your grid electricity bills.

For a variable-rate plan (like time-of-use), you’ll need enough storage to avoid high rates during peak hours, like evenings. 

If you happen to live in one of the states supporting net metering programs, you may be thinking of “selling” any excess energy back to the grid. In this case, you may want to invest in more battery storage.

How to Calculate the Number of Solar Batteries for Your Home

Calculating based on your specific energy consumption should help you avoid overestimating or underestimating your needs and give you a better sense of your investment. Here’s how to do it in 3 steps:

Step 1: Determine Your Energy Consumption

Begin by recalling your energy goals.

If you’re looking to use solar batteries to avoid expensive time-of-use rates or as backup power for short outages, you’ll need to perform a load analysis:

• List all the appliances you plan to use, including their power ratings (in watts).

To help you with this, here’s a guide on typical wattage estimates for common household appliances. If you have an energy monitoring system, this can give you more accurate appliance-specific data.

• Note how many hours you will use each appliance.
• Calculate the watt-hours by multiplying wattage and hours.

Say, peak hours or outages last for 5 hours. You might come up with something like this:

If you plan to go off-grid, you can use the same load analysis method to calculate your daily energy consumption. Alternatively, you can check your past electricity bill for the total kWh used in a month and divide that by 30 (days).

Once you have that number, multiply it by the number of days you want your system to last without recharging.

For example, if your bill shows 900 kWh for the month, your daily usage is 30 kWh. So, for 3 days of autonomy, you’ll need 90 kWh (30 kWh x 3 days) of energy storage.

Step 2: Choose a Battery Size

Basically, you need to at least, match the total kWh requirement from your load analysis.

In our earlier analysis, the total consumption is 2,285 W (2.3 kWh). A single 5 kWh would easily cover this. Although, a 10 kWh would provide extra capacity and further reduce your reliance to the grid.

Now, one thing you must never overlook in this step is your battery’s depth of discharge (DoD) or usable energy (you should find this info easily in the battery’s cut sheet). This percentage tells you how much of the battery’s total capacity you can safely discharge.

Let’s take a scenario with a much larger energy need, say 24 kWh. 

If you choose a single 24 kWh battery with 100% DoD, it will meet your energy requirement perfectly.

However, if the battery has an 80% DoD, it would only provide you with 19.2 kWh (24 x 0.8) of usable power – not enough for your 24 kWh requirement.

In this case, you’d need a larger battery, like one with 30 kWh capacity. With 80% DoD, that would deliver exactly 24 kWh of power.

Step 3: Consider Storage Space for Your Batteries

Lastly, when deciding the size of your battery, make sure your batteries physically fit into your storage area.

Let’s go back to our scenario earlier with a 24 kWh energy requirement. Here, you have two options:

• If you have limited storage space: Opt for fewer, higher-capacity batteries. In this case, you can install one 24 kWh battery.
• If you have ample storage space: Use multiple solar batteries, like two 12 kWh batteries or three 8 kWh batteries. This can sometimes make your system more modular and easier to expand later.

Can I start with fewer batteries and add more later if needed?

Generally, you can start with fewer batteries and add more later, provided that:

• Your existing solar setup is compatible with the additional batteries and can handle it without significant modifications (e.g. major rewiring, inverter upgrades, etc.).
• New batteries are added early in the lifespan of the existing ones (ideally within the first 1/3 of their lifespan), to avoid issues with natural degradation.

It’s best to consult with a professional solar installer in such cases. Better yet, have everything set up completely from the start to minimize the need for future adjustments.

Professional Solar Design to Power Your Home

At Avail Solar, you won’t have to worry about manual calculations – our experts will assess your home energy goals and handle all the details, from battery sizing to system integration.

Contact us today to speak with one of our solar experts.