Guide to Buying Solar > 3. Battery Storage
In this article:
Should you get a home battery?
What size battery should I get?
Related ‘battery storage’ articles:
Batteries for solar energy storage are evolving rapidly and gradually becoming mainstream as the transition to renewable energy accelerates. Until recently, battery systems were mostly used for off-grid solar but the huge leap forward in lithium battery technology has seen an immense amount of interest in people wanting to store excess solar energy, increase self-consumption and become more energy independent. Additionally, with frequent extreme weather events causing grid-wide blackouts, households and businesses are looking for ways to ensure they have a reliable electricity supply during prolonged electricity supply disruptions.
In this article, we explain some of the advantages and disadvantages of home battery systems, provide a battery cost guide, present some alternative options to using batteries, and present a detailed comparison of the leading battery storage systems used in both off-grid and on-grid solar systems. For those new to solar, you can learn more about the basics of solar and the various energy systems including grid-tie, off-grid and hybrid battery systems.
Types of battery systems
The wide range of battery options and energy storage systems can be overwhelming for many people and the rapid pace of technology has resulted in some confusion over which type of battery is best suited to individual needs. Adding to the complexity are the many different battery types and configurations now available. Often the best way forward is to get advice from a solar professional but this isn’t always reliable as many companies have had limited experience with battery storage. This is where we can help. The team behind Clean Energy Reviews have been installing and monitoring energy storage systems since 2014 and have some extremely insightful tools and detailed reviews to help you understand what type and size battery is best suited to your needs.
The 3 main types of batteries
Lead-acid batteries - Traditionally used for off-grid power systems
Lithium-ion batteries - Now the most common type of battery and advancing rapidly
Flow batteries - Generally used for larger energy storage applications and gradually evolving
Traditional battery systems were made up of deep-cycle lead-acid batteries, however, over recent years different variations of lithium-ion batteries have dominated due to the many benefits over lead-acid batteries including; lighter, modular, improved efficiency and longer life. Large companies such as LG and Samsung began releasing lithium-ion battery systems back in 2015, but the biggest boost in interest came with the announcement of the Tesla Powerwall; this was when home storage batteries really hit the mainstream.
Best battery systems - See our detailed review of the most popular solar battery systems.
Should you get a Home battery?
There is a lot of debate about whether a battery system is cost-effective. The high upfront cost and low return usually means they are not a great investment. However, as solar feed-in tariffs (credits you get for feeding excess solar into the grid) reduce, the numbers start to stack in favour of batteries. Our free solar and battery calculator can give you a good insight into the costs and savings of various battery systems.
For many people, economics is not the primary driving factor for purchasing a battery. There are many other valid reasons for households and businesses to invest in battery storage from the feel-good factor to providing backup power in the event of an emergency. In our opinion, self-sufficiency and energy security are both valid reasons. A battery can significantly increase energy independence using solar and help accelerate the transition to a renewable-powered electricity system.
Advantages of home battery systems
Reduce emissions - reduce pollution and demand from coal and gas power plants
Be blackout safe - Have power available during a blackout or emergency
Reduce cost - save money by using less energy from the grid
Become energy independent - store your excess solar energy to reduce your overall grid usage
Reduce peak demand - Supporting the grid during peak times and help supply grid stability services
Disadvantages of home battery systems
Higher upfront cost - Adds much more to the total system cost
Complexity - Requires a hybrid inverter or additional monitoring equipment
Space - Requires more room and should be installed in a safe area out of the direct sunlight
Solar Vs Battery
Using solar alone, many average households can easily cover 50% or more of their electricity needs. Without a battery, this can even be increased to 75% or higher by changing habits and using simple timers or ‘smart’ controls to turn on high consumption appliances during the day to be powered by your solar directly. This includes things like electric hot water systems, heating/cooling systems, pumps, dishwashers, dryers and even cooking using ovens or slow roasters. After maximising self-consumption, a battery can enable you to become almost entirely energy independent. By almost, we mean you can generally cover 100% of your average daily electricity requirements using solar and an appropriately sized battery, but there will always be times during poor weather when you cannot generate or store enough energy to cover your daily requirement. Another factor to consider is the possibility of additional energy consumption from charging an Electric Vehicle (EV), is this situation and with the current technology it will be very difficult for the average household to generate enough electricity year-round to power a house and charge an EV in you travel long distances.
What Size battery should I get?
Before we get into too much detail you should first understand the basics. Battery capacity is measured in kilowatt hours (kWh) and modern (lithium) battery systems are typically modular and scalable so you can generally get a battery sized to suit your needs. Note, the old sizing terminology used with Lead-acid batteries was Amp-hours (Ah) but this is now mostly superseded with kWh being the industry standard for modern lithium batteries. See more information about solar and battery sizing here.
The next point you should know is roughly how much electricity your household or business consumes over an average 24 hour period. Electricity is also measured in kWh and your bill will usually give you a good starting point. Generally, an average household consumes around 20kWh per day, but this might be much higher or lower in mid-summer or mid-winter, depending on your local climate. Another factor to consider is how much electricity you use in the peak evening and morning periods which is generally when the cost of electricity is at its highest. Over the years of installing and monitoring home battery systems, we have found the most economical battery size for an average home is typically 6kWh to 10kWh. However, for modern all-electric homes and those with home electrical vehicles chargers, the optimum battery size for maximum self-consumption is increasing. Every household is different and there is no one-size-fits-all solution, but luckily this is where our free solar and battery sizing calculator can help.
Can a battery be added to an existing solar system?
Yes, a battery can be added to any grid-connected solar system using an AC coupled battery such as the Sonnen ECO and Tesla Powerwall. Retrofitting a battery can also be achieved using a special type of hybrid inverter designed for AC coupled batteries. One such popular option is the SMA Sunny Boy Storage inverter which can be used to retrofit the popular LG Chem battery. Soltaro and Goodwe also supply AC coupled battery inverters.
What is a battery ready system?
A battery ready system is really a marketing term used to describe a solar system that uses a hybrid inverter rather than a common solar inverter. A hybrid inverter is essentially a solar inverter with battery connections and controls built-in which makes installing a battery much easier if you decide to add one in the future. The problem is ‘battery ready’ or hybrid inverters are typically 30% more expensive than a standard solar inverter and due to the rapid evolution in battery technology finding a compatible battery may be difficult after a few years.
How much does a Home battery system cost?
The cost of a home battery system depends on the battery size or capacity which is measured in kilowatt-hours (kWh) and type of solar or hybrid inverter used. Household batteries typically cost anywhere from $3000 for a smaller 3 to 4kWh battery up to $15,000 for a larger 12 to 15kWh battery depending on the type of battery, installation location, backup power requirements and type of hybrid inverter used. On average, energy storage batteries cost around $1000 per kWh installed - our solar and battery calculator will help give you a clearer insight into the cost of the most popular battery systems.
Home Battery Backup options
Most hybrid (battery storage) inverters are able to provide emergency backup power for simple appliances like lights, fridges and TV’s, however, if you require a high-powered backup system or need instantaneous backup power (like a UPS system without a delay), the best option is an advanced multi-mode inverter which are used for off-grid systems - In Australia, we would recommend the Selectronic SP PRO or Victron Multiplus inverters, while in the USA we would recommend the Outback Radian or Sol-Ark inverters. These high powered inverters are designed to operate in both on-grid and off-grid modes and can power large appliances like heating systems, pumps, and compressors. These powerful inverters are also compatible with many of the leading off-grid battery systems.
An increasing number of economical ‘hybrid’ solar inverters are available with UPS capability for instantaneous backup power. These include the Sungrow SK5H-30, Goodwe ES series, Soltaro hybrid and Huawei SUN2000L1.
Batteries for off-grid solar
There are many lithium battery systems used for off-grid applications but not all lithium batteries are really suitable for off-grid use. For smaller capacity systems there are several 48V options from LG chem and BYD. However, for higher capacity off-grid systems the modular lithium batteries from manufacturers such as Simpliphi in the US, or GenZ and Powerplus energy in Australia offer a more reliable, flexible choice. These modular LFP rack mount battery systems, known as self-managed lithium batteries work with many of the dedicated off-grid multi-mode inverters.
See our detailed review of the leading off-grid solar battery systems here.
Battery configurations - AC and DC coupled systems
Over the years manufacturers have developed a multitude of battery options and configurations to suit different applications and types of installations. This includes AC coupled batteries like the well known Tesla Powerwall and Sonnen ECO which can be easily fitted to homes with an existing solar system and DC-coupled battery options which work in conjunction with a hybrid or off-grid inverter.
DC-coupled batteries - Require a compatible hybrid or off-grid inverter to operate
AC-coupled batteries - Contains a battery together with an integrated inverter-charger
With any type of energy storage system, there are many important features to consider when selecting and sizing the various components. For installers and professionals, we have also created the technical guide to hybrid and off-grid energy storage systems, highlighting the key features and specifications which should be considered.