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Solar System Battery Sizing

Most people purchase batteries to reduce the amount of power they buy from the grid to save money. Others might just care about harnessing solar energy to power their homes, while some desire solar batteries to serve as a backup power source. It is important to size your battery to effectively go off the grid. The creation of solar system battery storage technologies has garnered much interest.

The availability of solar batteries is growing as battery technology advances, and demand for renewable energy sources like solar continues to rise. As a result, it's crucial to understand your alternatives for a battery system, whether you already use a solar panel system or are thinking about shifting to solar energy and also buying solar battery storage.

Australian households consume 16 kWh of power on average per day. Whenever solar panels generate power throughout the day, a typical family may utilise a third of that amount (5.33 kWh), with the other two-thirds (10.67 kWh) coming from the grid.

You would require a battery size with a minimum capacity of about 10kWh if you intend to have a system that does not rely on the grid to meet your household's power needs. Please continue reading to understand more about battery storage and determine how to choose a battery that will meet your demands for electricity.

What Exactly Is A Solar Battery?

A solar battery is a technological device that stores the energy obtained from your solar PV system. The solar panels capture solar energy, which is then transformed into electricity to run your property. Any extra energy is saved in your solar battery, which is gathered and stored so you can use it later. In essence, your solar battery serves as a means of storing extra energy generated by the solar panels.

Determine How Much Battery Storage You Need

Because solar batteries exist in various system sizing, it may be more prudent to determine the capacity, energy, and other characteristics you want and proceed from there. You should consider elements such as your daily energy use, battery specs, and the primary function of your battery storage to effectively determine the appropriate size.

Most individuals use their batteries to hold surplus energy that they will use at night or during periods when the solar panels are not producing electricity. As a result, you will only require enough stored energy for one evening of use.

To determine the type and number of batteries you require, you must first learn some basic information about solar batteries. The following are the primary factors that will influence your decision to acquire a solar battery:

Battery capacity

The capacity of a battery is the entire quantity of electricity it can store. This is expressed in kilowatt-hours(kWh) and denotes the size of the battery. For example, the Tesla Powerwall 2 has a capacity of around 13.2 kWh.

Solar battery power rating

A solar battery's power rating is the quantity of electricity that your solar panels can provide at once. It is measured in kilowatts and directly influences how much power can be pulled from the battery. So, if you need a battery that can power many household appliances and devices simultaneously, it must have a high-power rating.

Depth of discharge (DoD)

The depth of discharge (DOD) of a battery refers to how much energy is cycled into and out of it during a particular cycle. It is usually marked as a percentage of your battery's overall capacity. For example, a battery depleted by around 30% has a 30% DOD and thus retains 70% of its capacity. In what ways does DoD affect the performance of your battery?

A battery's lifespan will be shortened if it is charged and discharged more frequently. Because of this, all batteries require additional power reserves for safety, which are impossible to deliver with very depleted batteries. Due to increased loads, higher temperatures, etc., you'll need more power on certain days, or the energy generated by solar won't be sufficient.

Power usage

Electricity usage in residences is measured in kilowatt-hours. One kilowatt hour of energy is comparable to one hour of one kilowatt or ten hours of a 100-watt device. Your monthly energy bill displays how many kilowatt hours you have used on your property and may also include helpful information from the preceding month.

Life of the solar battery and warranty

Your battery will "cycle" (charge and drain) daily for most of your home energy consumption. The more you run the battery, the less power it has to keep a charge. Solar batteries function similarly to the battery in your mobile phone in this regard: you probably charge your phone every night to use it during the day.

However, as your phone ages, you'll realise that the battery isn't holding charge as well as it did when it was brand-new. For instance, a battery may have a 5,000 cycle or ten years at around 70% of the battery's original capacity warranty. Your solar battery will have lost approximately 30% of its initial capacity to store energy by the conclusion of the warranty.

A warranty includes assurance on the number of cycles of your battery's usable life. Most manufacturers also guarantee that the battery will maintain a specific portion of its capacity throughout the warranty because battery performance naturally declines with time. The short answer to how long your batteries can last is that it relies on the kind of battery you choose and the amount of capacity it will shed over time.

The battery manufacturer

Many businesses are creating and producing solar battery solutions, from automakers to digital start-ups. Although a large vehicle manufacturer joining the energy sector probably has a longer track record of making components, their batteries might not have the most cutting-edge technologies. On the other hand, a tech company may have advanced, high-performing technology but less of a track record to vouch for the battery's durability.

Your priorities will determine whether you select a battery made by a cutting-edge start-up or a seasoned manufacturer. You could get more insight when choosing a battery by analysing each of the warranties.

Roundtrip efficiency

The ability of your energy storage system (battery + inverter) to convert and store power is measured at the system level by a parameter called roundtrip efficiency. Any electrical operation involves losses; thus, when you go from direct current (DC) power to alternating current electricity or recharge a battery, you lose a certain amount of kWh of energy. The roundtrip efficiency of a solar battery dictates how many units of power you will receive out of the battery for each unit you put into it.


All solar batteries must satisfy specific safety standards to be approved for installation in residences and commercial buildings. However, several battery chemistries have undergone safety testing to varying degrees, even exceeding the government-mandated safety standards for batteries, indicating that some battery chemistries are somewhat safer than others. The most crucial thing to consider is that every battery installed in Australia is entirely secure.

Peak power output

The kilowatt peak, or kWp, may also be used to categorise solar batteries. The system's theoretical peak energy output is kWp under ideal circumstances. The max output is less of an absolute unit and more of a comparative metric.

A solar battery's peak power output rating (kWp) determines the maximum amount of electricity it can produce at peak performance—the greater the kWp rating, the superior the battery.


The primary substance utilised to store energy inside a battery is called the battery's chemistry. Since chemistry ultimately influences many of the properties of batteries, it might be the most crucial factor to compare. For instance, some lithium-ion chemistries might be more power dense. They hold more energy in a smaller volume and may cycle better, enabling them to operate at a higher level for more extended periods.

And those are only the variations found within the lithium-ion chemistries; variances exist between lead acid batteries, vanadium flow batteries, and other experimental battery cell chemistries as well. Different solar battery chemistries have varying pricing points, as is typical for most things.

5 kW Off-Grid Solar System Battery Requirement

It all relies on how long you want your device to run on solar batteries without any help. There are many different kinds of 5 kilowatts off-grid solar system inverters on the market; however, the two most common are:

  • Solar panel input below 5000W
  • Solar panel input exceeding 5000W

Solar panel input below 5000W

Assuming your solar system panel is around 3000W, the power produced is around 3kWh each hour, requiring a 48V60AH solar battery to store. If your area receives about five hours of sunlight daily, the electricity generated daily requires a 48V300AH battery to store, which is 15kWh. When the off-grid solar power system you create operates for a day, the energy received from the solar energy will be instantly transformed into AC power for the load.

Your battery is always fully charged and is utilised at night when no direct solar panel energy is available. 15kWh with a load of 1000W may be utilised for approximately 15 hours. This method is inexpensive and functional. The battery's life will be quite long if it is a constructed lithium iron phosphate battery.

Solar panel input exceeding 5000W

This type of design is typically employed in commercial or industrial settings, which consume a lot of power during the day and are essentially unnecessary at night. The solar panel industry has created a 5000W solar panel input that can produce 5kWh per hour, with most of the electricity going straight to the load and a small amount stored in the battery.

It can create 25kWh of power every day, based on calculations for five hours of sunlight, and the size of the battery you need depends on the load used at night. However, since it generates 5kWh of energy per hour, even a 1C lithium iron phosphate battery requires at least 48V120AH.

The Various Kinds Of Solar Batteries

Lead-acid batteries

The gold standard for storing electrical energy is lead-acid batteries since they have been tried and proven over time. They have been around since the 17th century, when they were first created, and are still the most frequently used batteries to store energy. Lead-acid batteries' greatest asset is that they are relatively inexpensive to purchase.

Due to their lower purchase cost compared to the cost of extending the electricity mains grid, they are frequently installed in rural and distant regions. Lead-acid batteries are the preferred option when installing a solar system off the grid. They are incredibly trustworthy, simple to update or replace, and, as already mentioned, reasonably priced.

Lead-acid batteries are the standard for most emergency power backup systems nationwide. Deep-cycle batteries, such as lead-acid batteries, have a consistent output over an extended length of time. Their rate of discharge is constant. Both sealed and flooded versions of these batteries are available.

The same idea underlies how they both operate. However, lead-acid batteries have a dull aesthetic; they are big, unattractive, and heavy. They also need to be put in a climate-controlled shed since they take up a lot of room and operate at temperatures lower than room temperature.

Flow batteries

Flow batteries are sometimes referred to as redox flow and are a brand-new contender in the solar battery market. Vanadium and zinc, bromine, and a water-based solution are all used in these batteries to store electrical energy. Only a few businesses manufacture flow batteries at the moment, with the Australian business Redflow being the most renowned.

Flow batteries are highly scalable. This means that the capacity and output of the battery can be increased or reduced according to the battery size. As such, they differ from the other batteries on this list in that deep discharge has no effect on the performance or lifespan of the battery.

They have a long-life cycle and very low self-discharge. It is also beneficial to note that flow batteries do not heat up during use. Flow batteries are the best choice for applications where the batteries go through several charge/discharge cycles each day. This makes them ideal for application in large-scale installations.

The cost of the fluids (their chemical composition) utilised to create flow batteries is outrageous. Although the concept on which they are based has been available for a long time, few businesses make commercial flow batteries; therefore, these batteries are not widely used among the general public. These batteries contain poisonous and highly corrosive metals like zinc and bromine.

Lithium-ion batteries

Because Li-ion batteries are the preferred power source for producers of electric vehicles, they are growing in popularity. Although they are promising, lithium-ion has not yet been wholly explored as an energy storage medium. However, given how quickly they develop, it won't be long until they overtake other batteries as the preferred method of storing solar energy. The most widely used energy storage system that uses this technology is Tesla's Powerwall battery.

Lithium-ion batteries come in two different varieties. The first is the NMC (nickel-manganese-cobalt) chemical type, which is the most common among electric car makers. The other kind of battery is LiFePO 4 (lithium iron phosphate). Because of its long-life cycle, the NMC-type battery is perfect for off-grid installations. The extreme temperature performance of LiFePO batteries makes them ideal for application in areas with high temperatures.

Li-ion batteries need very little upkeep or none at all. In addition, they have better energy densities. This means that a lithium-ion battery of the same physical size can store more energy than a lead-acid battery. These batteries have a longer lifespan and discharge at a higher depth than their counterparts because they have longer life cycles. With an 80 per cent depth of discharge, a lithium-ion battery could last up to 15 years while delivering between 4,500 and 7,000 cycles.

The automobile sector has become a home for lithium-ion batteries. As electric car makers compete to acquire it, demand for this battery is at an all-time high. The biggest drawback of lithium-ion batteries is their high cost. They can cost up to twice as much as lead-acid batteries with the same energy storage capabilities. Unlike lead-acid batteries, these batteries are also incredibly delicate, necessitating a stabilising circuit to assure safe operation.

Sodium nickel chloride batteries

The sodium nickel chloride battery fiercely rivals the lithium-ion battery. Utilising a particular chemical, this energy storage is completely recyclable. It doesn't release harmful chemicals and doesn't pose a fire or heating risk. Sodium Nickel Chloride batteries don't need expensive cooling systems to function appropriately, unlike lithium-ion batteries.

Sodium nickel chloride batteries are secure and dependable due to their chemistry. Even at severe temperatures of between -4°F (-20°C) and 140°F (60°C), these batteries can operate effectively. Because they do not contain any poisonous or dangerous substances, you may recycle them.

Sodium-nickel chloride batteries are ideal for big solar off-grid power installations and emergency power backup systems. However, they have a short lifetime of around 3,000 cycles and a discharge depth of only 80 per cent. This implies that up to 20% of the stored energy cannot be utilised. Moreover, installing these batteries may be rather expensive, especially for big projects and residential solar systems.

Go Off-Grid By Getting Solar Battery Storage

Solar batteries, as you've seen in this article, are crucial for storing extra power generated by the sun so that your home may utilise it after the sun has set or during cold seasons. Because of this, picking a quality solar battery is also crucial. In general, putting up a solar power system in your house has many fantastic advantages.

In addition to playing your role in environmental conservation, you may make money through the feed-in tariff and take advantage of the solar rebate program. Simply get in touch with a reputable solar installation company if you need assistance choosing the finest solar batteries for your home.

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