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Solar Battery System Sizing

Home battery storage systems are becoming more popular among homeowners installing solar PV (Photovoltaic) systems. It enables them to make the most of the solar energy they create and reduces their reliance on National Grid electricity when the sun isn't shining.

What Exactly Is A Household Battery?

A home battery system is a huge battery that you install at home to store surplus electricity – typically what is generated by your solar PV system and not needed at the time. You can use this surplus energy in your home at a time when power cannot be supplied, such as at night or on days with bad weather.

Your demand on the grid is reduced because your home would use the energy stored in a battery instead. It allows you to save money on your electricity bills while also ensuring that more of the energy you use is renewable.

What Is The Function Of A Household Battery?

A household battery system stores electricity for later usage in your home. Energy needs in the house do not remain constant throughout the day, especially if some or all of the family members are absent. The electricity supplied by their solar panels isn't fully utilised at certain times of the day.

Solar PV can't generate electricity when the sun sets, or the weather is very terrible. You'll have to rely on the grid to power your home. A home battery allows you to store surplus solar energy available until you need to draw from the grid.

Factors Influencing Solar System Battery Size

A few essential elements influence how many batteries you should acquire to meet your solar energy storage needs. The electricity loads you need to power, the size/production capability of your solar panel system, and what you want from a storage system are some of the factors to consider.

Electricity consumption

Anything that consumes power is referred to as a "load." Electricity loads, in the context of solar and home batteries, are equipment and systems that use electricity in your home, such as refrigerators and air conditioners.

Knowing how much electricity you'll need to power your appliances when constructing a storage system is critical. Depending on what you need to power, you'll need more or less storage space.

System size and output

You can either draw power directly from the grid or charge your batteries using solar. Charging a battery with solar energy is generally the way to go, especially if you want to save money on weekly or monthly electricity bills.

As a result, it is critical to know how much power your panels produce and how much they can charge your battery system during the day. You may require more storage capacity than your panels can provide, so you'll need to add more solar panels to get the most out of your solar energy storage system.

Customised requirements

Knowing what you want to gain out of a solar-plus-storage system is critical when determining how many solar batteries you require. Off-grid systems typically require many batteries, whereas systems designed for robustness and savings are much smaller.

How Long Do Solar Batteries In The Home Last?

There are two ways to address this issue regarding house battery systems that are charged by your solar PV system. The battery system's capacity and the charge level will determine how long the solar battery can power your home. The capacity of some home batteries is more than the average daily family electricity demand.

These systems theoretically power your home for more than 24 hours from a full charge. The energy will not last as long while powering your home if it is just partially charged or if you have a rechargeable battery with less capacity. Also, the life expectancy of a home battery system varies based on the manufacturer and model of the battery. The same can be said for how it is used.

These batteries will eventually lose a tiny percentage of their capacity over thousands of cycles. This is so even though they are intended and optimised to be charged and discharged frequently. Professionally installed home battery systems will always come with a warranty, such as the Tesla Powerwall 10-year warranty for 80% of original capacity.

If your battery isn't storing at least 80% of the energy it did when it was new within the first ten years, Tesla will replace it. Based on your personal experience with these electronic goods and the relatively moderate degradation of the batteries used in home battery systems, a home battery system is likely to outlast its warranty. It's the same as any other electronic product: if you buy a TV with a 5-year warranty, you should expect it to last for at least ten years.

Why Buy A Solar Storage Battery?

There are a variety of reasons to consider battery storage for your home. They include:


People generally wish to be more self-sufficient and power their homes with the electricity they generate themselves. You can use solar-generated electricity to power your automobile even if you are out during the day. Similarly, when you go home, store your generated electricity in a house battery and then discharge it into your vehicle.

Minimise environmental pollution

Using a home battery minimises peak electricity demand from the grid. Peak demand also decides how many power plants we need. If we can cut demand during peak times, we won't need as many fossil-fuelled power plants, and thus there will be reduced environmental pollution.

Power back-up during an outage

Solar storage batteries allow you to utilise your saved electricity in a power outage. This is the excess power that you stored during the day or as you used the grid. This gives you access to cost-effective electricity when you need it.

It means you'll always have access to the cheapest electricity available, whether it's from solar or the grid.

How Much Money Can A Home Battery Save You?

It's tough to estimate how much money a home battery will save you because it depends on how much you consume and the quantity that your system generates.

A battery can boost the return of a solar PV (Photovoltaic) system in some cases. You may charge the battery from solar PV for a longer time when the solar PV system is extensive. This will improve the home generation system's overall economics.

The capacity to supplement with cheap grid electricity when solar isn't available significantly boosts the return on investment. Overall, battery paybacks are in the 10 -15-year range. This is longer than a solar system's warranty but is within the range of how long you might expect the system to last.

This is why most people consider battery storage systems a relatively low-cost solution. They enable you to boost your self-sufficiency and reduce your reliance on polluting grid electricity.

How To Calculate The Size Of A Solar Battery Bank

A solar battery bank calculator can help you figure out how big a battery bank you need, how many watts per solar panel you need, and what solar charge controller to buy. Make sure to size it for the month with the least amount of sunlight if you decide to create an off-grid system.

You will have constant access to a suitable amount of energy if you size everything correctly. There are several steps to take when determining your solar battery bank. Let's have a look at them:

Step One: Calculate your daily energy consumption

You should find this information on your electric bill. Your monthly kilowatt-hour usage will typically be printed. To convert your daily kilowatt-hour output to watt-hours, divide the figure by 30, then multiply by 1000.

This equates to one watt of continuous electricity use for one hour. This is the first step in calculating the size of your solar battery bank.

Step Two: Calculate days of autonomy

If you don't have it on hand, you can look up your area's annual average of overcast weather online. This step is critical to ensuring you have year-round solar energy access.

A large solar battery bank is optimal in places with more gloomy days. In areas with abundant sunlight, a smaller solar battery bank should suffice. It is, however, usually better to size up rather than down.

Step Three: Calculate the lowest ambient temperature

You can look up the lowest temperature in your neighbourhood online once more. This step will assist you in precisely predicting your battery bank's capacity. This is important because the temperature will impact your battery set's capacity.

Figuring Out How Many Batteries You'll Need

Every solar and battery system is distinct. This is something to remember when looking for solar and storage choices. It's critical to consider your energy demand profile. Any possible solar installer you engage with can help you with this process.

They'll be able to guide you through the ins and outs of your specific property and how to reach your objectives. Here's how energy storage system sizing calculations can look for three major use cases:

Installing solar batteries to save money

The quantity of electricity you use when the sun isn't shining, i.e., the amount of electricity you can't rely on your solar panels for, is the most critical estimate you need to do for a solar battery system if you are looking to save money.

Installing solar batteries for resiliency

Solar batteries for resiliency are similar to the situation above in that you must first determine what you want to power and the length of time it will be powered. If you run your dishwasher for an hour, you can cover that load with one battery for an hour and a half, which is more than enough to get you through a regular power outage.

Installing solar batteries for self-sufficiency/going off-grid

Staying connected to the grid is less expensive and more involved than becoming utterly self-sufficient with solar batteries.

In general, you'll need to budget for extended periods of low solar electricity production because, unlike keeping connected to the grid, you can't rely on utility-supplied electricity when it's cloudy.

The Times You Can't Generate Solar Power

You may then calculate the electricity consumption from all of the equipment you want to run and the number of batteries you'll need by multiplying the electrical demand of the appliances you wish to power by the number of hours they'll require to run. This isn't perfect as some items, such as a dishwasher, only need to be used once and aren't a continuous electrical load.

You can make an educated guess. If you have a 1,500-watt (W) dishwasher, a 3,000-watt (W) air conditioner, an 800-watt refrigerator, plus lights, Wi-Fi, and other 1,000-watt appliances, you'll need about 6.3 kilowatts (kW) of electricity from a storage system. This is enough for the hour you run your dishwasher and 4.8 kW for the rest of the time. Assume that you are using a four-hour peak price interval as an example.

Creating A Solar Battery System To Save Money

You'll need to know your electricity rate plan if you want to save as much money on electricity as feasible with solar batteries. You'll want adequate storage capacity on a flat-rate structure to rely on the grid as little as feasible. The more energy you can store and use from your solar panels, the more money you'll save in the long run.

A variable-rate plan is the other main option for an electricity rate; in this case, ensure you have the adequate storage capacity to get through the high-cost periods of the day. The key message is that you need enough energy storage to maintain your home self-sufficiently during peak electricity price hours if you want to save the most money with solar batteries.

Peak price hours vary depending on where you reside and your plan. In the end, you'll need about 2-3 standard lithium-ion batteries to avoid utilising grid electricity during peak hours and when your solar panels aren't providing enough power.

Most importantly, this does not imply that you are self-sufficient and do not use the grid; rather, it implies that you are making the most of your solar panel installation and generating as much solar electricity as possible.

What Battery Size Do I Require For My Home?

The size of the house battery system you require is determined by your home's size and energy demands.

A typical home consumes, on average, 8-10 kWh of electricity. Smaller home storage batteries have a capacity of 2.5-5 kWh, whereas bigger systems have a capacity of 13-15 kWh.

When sizing a system, use the following two-step process:

  • The best size for a battery in terms of cost is one that will cover your evening and nighttime usage. By the following day, your electrical usage will have depleted the battery, leaving it with the greatest amount of room to capture the next day's sunshine.
  • After that, compare it to the size of your solar PV system. If your generation is minor, having a large battery is pointless because you'll never be able to fill it.

In practice, some battery storage systems are sized to meet a home's demand, while others are sized to meet the solar PV system's capacity. You should remember that home rechargeable batteries may not receive sufficient energy to charge daily.

With a properly sized rechargeable battery for your home in Australia, you should have enough energy stored to satisfy your evening and overnight demands for the bulk of the year. But you will most likely need to use the grid during winter.

Can A Battery Power My Home At Night?

Removable battery storage systems may not be able to provide enough power for all of your needs all night if your household has very high energy needs in the evenings, especially during the long winter nights.

For example, if you wanted to use numerous 'hungry' appliances at the same time in the evening, such as kettles, microwaves, washing machines, as well as TVs, lights, and refrigerators, your battery would empty considerably faster than in a less busy household with lower energy demands.

The number of electrical appliances that a home battery system can provide at any given time is similarly limited. It's critical to select a battery storage system for your home that is most suited to your demands.

Seek Expert Help When Sizing A Backup System

You'll run out of power if you don't have enough battery capacity. Therefore, you'll need to install solar battery backup and turn on your backup generator. On the other hand, buying too many batteries increases the cost of your system by adding more components, complexity, and upkeep.

One of the first tasks in planning your off-grid system is sizing solar batteries. To size, your backup system appropriately, seek professional help from companies specialising in solar. They can even assist you with getting a solar rebate on your system.