You’re in the market for a solar battery. You’re after greater energy independence from the grid, blackout protection, lower electricity bills and protection from escalating electricity prices.

This blog provides you with a 10-point checklist to use to help you choose the best home battery for your home.

1. Battery technology

Until 2015, the main battery technology was lead acid.  This needed a dedicated room (normally a shed) and regular maintenance.  Since then, advances in lithium-ion technology have resulted in lithium-ion dominating the home battery storage market.  Here’s why:

• Superior performance (better power output and depth of discharge)
• Set and forget, maintenance-free
• Longer warranties
• Smaller and lighter

Because of this, most home batteries use lithium-ion technology.  There are two main types of lithium-ion battery chemistry – Lithium Nickel Manganese Cobalt (NMC) and Lithium Iron Phosphate (LiFePO4). Both are well-suited for residential use.

2. Storage capacity

We’ll cut to the chase; the minimum size battery most Australian homes need is 10kW. That’s 10kW of usable storage capacity (not nominal storage capacity which is a bit more).  This advice applies if your electricity usage meets the typical profile of most Australian homes, i.e.:

• Your home requires 16-20 kilowatt hours (kWh) of electricity in a typical 24-hour period
• Around 60 per cent of that usage in the evening and overnight (i.e., 9.2 kWh to 12 kWh)

Of course, every household uses electricity differently.  If you’d like us to accurately size a battery to meet your home energy requirement, get in touch.

3. Power

Continuous power output is the amount of power that can be delivered while the battery has enough charge.  If your home needs 7kW and your battery provides 5kW, you will need to buy the extra power from the grid or purchase another battery.  Most batteries have a maximum continuous power output of 5kW (although some have less which is something to watch out for).

Maximum/peak power is the most power that the battery can deliver at any given moment, but this burst of power is usually only delivered for short periods. For example, kettles have a high peak power requirement, as do toasters and induction cooktops.  The more appliances you have with high peak power requirements, the more important this feature will become in your choice of battery.

It is important to be aware of the power needs of your home when choosing a battery.  If you’d like help, get in touch and we can work out your battery power needs based on your actual usage.

4. Depth of discharge

This is like petrol in your car.  If you run down to empty, your car won’t go.  It’s the same with most batteries.  The higher the depth of discharge, the more battery power you can draw on when the sun’s not shining.

Most batteries need a maintain a minimum amount of charge to avoid damaging the damage the battery. With lithium-ion technologies, this is around 80 to 90 per cent.  With lead acid batteries, the depth of discharge is only around 50 to 60 per cent.  This is a drawback with lead acid batteries as you can’t run them down as far as a lithium battery.

The main point to remember about depth of discharge is the higher the better. All other things being equal, a battery with 90 per cent depth of discharge is preferable to one with 70 per cent.

5. Battery back-up

There are different levels of back-up that batteries can provide.

• Some batteries don’t provide any back-up (we recommend avoiding these).
• Some provide reduced back-up but won’t charge the battery from the solar panels when the grid is down. This isn’t useful if your home is without power for more than a day.
• The best batteries provide a seamless switch to back-up power when the grid goes down, and charge from your solar panels indefinitely.

If you’re serious about having a high level of blackout protection for your property, we recommend you ask for a battery that charges from your solar panels when the grid is down.

6. Efficiency

In a perfect world, you’d get the same amount of power out of your battery as you put in.  But unfortunately, it doesn’t work that way.  There is always a loss of power when you charge and discharge a battery.

That’s why it’s important to select a battery that minimizes the loss of power in the charge/discharge process – and that’s what the battery efficiency rating tells you.

A quality lithium battery should have an efficiency of at least 90 per cent.  The higher the efficiency rating, the better the battery.

7. Degradation

Like the battery in your smart phone, solar batteries also degrade with use. The annual degradation of a lithium solar battery is between 3 to 4 per cent a year for the first 10 years.

You can work out the annual degradation rate by looking at the battery warranty; this should state the percentage storage capacity of the battery after 10 years.  Tesla Powerwall has 70 per cent warrantied capacity after 10 years, compared to day 1.  This works out at 3 per cent degradation per year.

The lower the annual degradation rate, the better the battery!

8. Thermal runaway

Thermal runaway can cause a fire in the battery. The best way to avoid thermal runaway is to choose a quality battery with an excellent reputation and make sure it is installed by a fully accredited Clean Energy Council battery installer.  A cheap battery, installed by an inexperienced installer, isn’t worth the risk.

9. AC vs DC coupling

There are two ways of connecting batteries to a solar panel system:

• AC-coupled
• DC-coupled

AC-coupled batteries

• Can be retrofitted to virtually any existing solar panel system
• Lower efficiency (around 88%)
• Some local electricity networks may not let you add a battery to your solar panel system if that takes the total inverter capacity over 10kW
• Example: Tesla Powerwall 2

DC coupled batteries

• Require a single inverter for the solar panels and battery (called a hybrid inverter)
• Higher efficiency (up to 95%)
• Must be installed with a compatible inverter (this is not a problem if you are installing solar and a battery at the same time)
• Avoids common system sizing limits for single-phase properties set by some local electricity networks
• Example: SolarEdge Home Battery

At SolarRun, we know the system sizing rules for every network distributor in Australia.  If you want to know what the rules are for your area, get in touch.

10. Battery warranty

The key points to check with a battery warranty are:

• What is the warrantied capacity of the battery at the end of the warranty period?

Most lithium batteries are warrantied for at least 60 per cent battery capacity after 10 years.  Anything higher than this is a sign of a good quality battery.

• Is there a limit to the number of times you can cycle the battery per day?

Some battery warranties are voided if you cycle the battery more than once a day.  In most cases you’ll only be wanting to cycle the battery once a day.  But if you decide to join a Virtual Power Plant [link to blog] to get paid a higher rate for your stored solar energy, you may want the facility to be able to cycle the battery twice a day.

• Does the warranty just cover you for the battery? Or does it cover the electronics as well?

As home batteries are electronically highly complex, it is a good idea to ensure the warranty covers you for both.

• How stable is the manufacturer?

Most battery warranties are for 10 years.  It’s therefore important to find a manufacturer that’s financially stable and likely to be around to honour any warranty claim.  Big name companies with established Australian support offices are definitely a safer bet than batteries that have been imported with no Australia office.

Find out more

At SolarRun, we supply brand-leading solar battery systems and recommend the Alpha ESS battery and SolarEdge Home Battery for residential and commercial installations.

Alpha ESS SMILE5 battery is a high-performance battery which can be as big or small as you need, with capacity options from 10.1kWh, 13.3kWh, up to 30kWh for residential installations and up to 60.6kWh for commercial systems. Built using lithium iron phosphate chemistry – the safest battery chemistry on the market – Alpha ESS batteries have an excellent safety record.  It’s a great choice for anyone looking to add battery storage regardless of whether you’ve already got solar panels or you’re after a brand new solar and battery system.

The SolarEdge Home Battery is particularly well-suited for households who are interested in making their home fully electric. It’s a technologically advanced storage system that’s ready for the world of home EV charging and smart energy management.  With SolarEdge, you can reduce your reliance on grid energy to the absolute minimum and enjoy near-zero power bills for years to come.

Get in touch for a quote and consultation about the best battery storage system for your home or business.