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Solar battery and energy storage comparison

Be prepared: a solar battery and inverter will set you back $8,000 to $15,000.

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By

Sam Baran

Updated

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Aussies have only recently started incorporating deep-cycle batteries into their home solar array. But are they worth the hefty price tags and if so, what are the costs and which one should you get?

We've broken it down for you below so you know if you're getting your money's worth.

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Can solar batteries actually save you money?

Home batteryCycleskWh per cycle Total kWh produced Total cost (AUD) $ per kWh used
Tesla Powerwall 5,0005.828,980$10,151,42$0.35
Tesla Powerwall 3,2855.819,040$7,108.84$0.37
Tesla Powerwall 5,0005.828,980$4,265.30$0.15
Tesla Powerwall 5,0005.828,980$5,118.36$0.18
AGL Power Advantage5,0003 15,000TBATBA
Aquion Energy S20P3,00025,430$1,642.14$0.30
Iron Edison 24V Lithium Battery2,0002.765,530$3,925.50$0.71

Should I get a solar battery?

For the majority of home customers, the answer is probably no. While the price of batteries has decreased over time, a battery and inverter will still set you back $8,000 to $15,000. This is the kind of investment that is unlikely to be recouped over the effective lifetime of the battery.

However, if you are planning to invest in a home battery for storage or potentially backup, you should ensure that you get a strong warranty on it to protect your investment. You may be able to take advantage of government rebates or renewable schemes in your state or territory, especially VIC, SA, the ACT and QLD.

Just keep in mind that if you're funnelling power into your storage battery you aren't feeding it back into the power grid, meaning that you won't be able to benefit from solar feed-in tariffs for that energy.

Pros

  • Can work as a backup. Depending on your battery and set-up, you may be able to disconnect your house from the grid in the event of a blackout and rely upon stored energy from your battery to power your appliances.
  • Save power for later. With a battery, you can take advantage of almost all the solar energy you produce. Alternatively, you could change to a time of use tariff on your power plan and use your stored energy during peak hours.
  • May be able to take advantage of tariff rates. Some retailers pay higher feed-in tariffs for battery users with stored energy when the power grid is experiencing a shortage.

Cons

  • Price. While there has been a drop in prices of home batteries over time, don't expect one to come cheap even now. The price of a 7kWh Powerwall is around $3,800 and the 10kWh model sells for around $4,435.
  • Tariff loss. A unit of energy spent charging your battery is usually a unit of energy you don't feed back into the grid. You may end up losing out on some solar feed-in tariffs, especially on low-efficiency batteries.

How to compare solar batteries

  • Capacity/power. Capacity is how much electricity a battery can store, while power is how much energy a battery can provide at a specific point in time. High capacity alone doesn't mean your battery will last a long time, since a higher power output could mean it lasts for a shorter duration but can power many devices at once.
  • Depth of discharge (DoD). Dropping some batteries below a percentage of their maximum charge – their DoD – will damage their ability to function. A higher DoD means you can tap into more stored energy safely.
  • Round trip efficiency. This is the percentage of useful energy you get out of a battery as a fraction of how much you put in to charge it. For example, if you get 9kWh out of a battery charged with 10kWh of power, it has a 90% round trip efficiency. A higher efficiency means you get more out of your battery with each charge.
  • Battery life and warranty. Batteries become less and less efficient over time. Your battery will be rated for a certain number of cycles of charging and discharging. Warranty on your battery will often guarantee a certain capacity after a period of use, such as 80% of its max charge after 3,000 cycles.

Which battery type is the best?

There are three types of batteries that can be used for solar installations: lead-acid, lithium ion and saltwater. Of the three, lithium ion currently performs best, though the others may be considered for cost purposes.

  • Lithium ion. This is the most common battery type, consisting of a mix of lithium and other metals to form a cell. They have a high depth of discharge and a long expected lifespan of thousands of cycles. The main drawback is their price and the fact that they can be difficult to recycle.
  • Lead-acid. This is a tried and tested battery technology that's been in use for ages in cars and other heavy devices. Unfortunately, they don't offer nearly as long a lifespan or high efficiency as lithium ion cells. They are far cheaper, but are slow to charge.
  • Saltwater. These contain no toxic chemicals and are totally safe, containing saltwater as their only ingredient. While they're fairly efficient and can last a long time, they have a really low power output and are extraordinarily bulky. On top of that, they're not particularly environmentally friendly, either. Saltwater batteries are currently only made by one company, Aquion Energy.

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