How low do battery prices need to go?

Battery prices already on the decline
LG Chem appears to be one of the companies leading the charge on cost reductions, having recently introduced the next generation of its RESU battery banks. By our estimates, LG Chem’s RESU10, which has a nominal capacity of 9.8 kilowatt-hours (8.82kWh of usable storage), will retail for about $10,000-$12,000 fully installed (about $1,100/kWh). Solar panel manufacturer Trina have also recently introduced a battery bank solution of their own (the Powercube 2.0) with 6.4kWh of (usable) capacity and an ~$8,000 price point (about $1,200/kWh). Alpha ESS, meanwhile, offers all-in-one storage unit (the Alpha-ESS Eco) that rivals even these on price, with 8.64kWh of usable capacity for $8,000 installed (about $925/kWh) according to them. These prices represent a significant reduction from the $1,500-$2,000/kWh figures commonly seen over the last year or so.
We should note that the prices we’re discussing here are for lithium batteries with 10-year warranties and 60% ‘end of life‘ retained capacity – so the comparisons are more or less apples-to-apples. Batteries with better performance specifications are available (e.g. 80% retained capacity at end of life), but unsurprisingly are a bit more expensive.

Battery storage product	Image	Usable storage capacity	Indicative price (fully installed with inverter)*	Indicative price per kWh of capacity (fully installed with inverter)
Alpha ESS Storion-Eco		8.64kWh	$8,000-$10,000	~$900-$1,150/kWh
LG Chem RESU10		8.82kWh	$10,000-$12,000	~$1,100-$1,360/kWh
Tesla Powerwall		6.4kWh	$11,000-$13,000	$1,500-$2,030/kWh
TrinaBEST Powercube 2.0		6.4kWh	$8,000-$10,000	~$1,200-$1,560/kWh

*These prices are our own rough figures based on offers we’ve seen. Actual out-of-pocket costs will vary depending on the company that sells the system. If you have feedback, please email the author.

A note about lithium batteries
Lithium has established itself as the most prolific and widely-used battery chemistry type for residential applications in Australia (and likely the world as well). In fact, of the 20 different battery brands currently included in our Battery Storage Product Performance Comparison Tool, 17 use lithium batteries; of the remainder, two (Redflow & Imergy) are flow batteries and one (Aquion) is a ‘saltwater’ sodium-sulphur battery. At present, we haven’t listed any lead-type batteries mainly because there are so few companies targeting the residential grid-connected system market with lead-based battery banks (Ecoult is one exception, but so far we haven’t been able to ascertain price points or specs on their residential unit).

Are these prices low enough?
Estimating battery system pricing can be tricky, as the components required vary with the circumstances of individual households will differ. For example, are we talking the pricing for just the battery component of a brand new solar PV system, or about a battery retrofit to an existing system? If solar and batteries are being installed at the same time, will they use a single hybrid inverter, or will there be separate inverters for the batteries and the solar panels (a ‘one box’ or ‘two box’ solution)? Or what about if we’re talking about a battery retrofit for an existing solar system that also encompasses the replacement of the existing inverter? These are all important considerations for you as the potential purchaser of a battery storage system.
For simplicity’s sake, however, let’s assume we’re talking about the installation of a battery with a new inverter (this is the assumption we make for pricing in our Battery Storage Product Performance Comparison Tool), so that the prices quotes above – in the $900-$1,200/kWh range – are still relevant to our current investigation. (If you’re contemplating a battery retrofit that doesn’t include a new inverter, you may end up paying less.) How do the returns stack up?
What we’re looking for: The point at which batteries reduce system payback times
All the analysis we’ve done or seen to date indicates that a ‘solar only’ system is usually a better investment than a solar-plus-storage system (e.g. see here and here and here). Although solar power is already quite affordable in Australia, high battery price points mean that batteries have to work extra hard to earn their proverbial keep (ideally cycling more than once per day); the solar panels are the component of the system that delivers most of the savings.
At $1,500/kWh installed, batteries inevitably lengthen the payback period of a solar PV system; typically, the payback for a solar-plus-storage system at this price point will be 10 years+, meaning that the battery owner may not have broken even by the end of the 10 year warranty period. Below this price point, however, things start to get rosier. But at what price point does it make more financial sense to have batteries installed with your solar than not – that is, at what price does a battery storage bank reduce a solar system’s payback time?
Brisbane example
Let’s look at an example from Brisbane to see how reductions in battery pricing affect payback times & return on investment figures. We assume the home has the following characteristics:

• 30kWh/day energy consumption;
• Flat retail electricity tariff of ~$0.24/kWh (ex. GST);
• 5kW solar system for $5,700;
• 6.4kWh battery storage; and
• ‘Double peak‘ energy consumption pattern.

For the ‘base case’ payback period and ROI figures, we assume that the system is capable only of solar charging (i.e. using the solar panels to charge the batteries). We crunched the numbers using PVSell to determine payback periods at a range of battery price points (from $1,500/kWh down to $200/kWh).
The difference in annual savings for the solar only system was about $1,130; addition on the 6.4kWh of battery storage kicked this up to about $1,550 – a difference of about $400. This remained the same regardless of how much they paid for the battery bank.
Once we worked this out, we then did a bit of speculation how additional savings via tariff arbitrage (on time-of-use billing) and/or spot market trading could help to improve payback periods further – assuming either 20% or 30% savings on top of a solar charging only scenario. The results are laid out in the table below.

	Payback period(Solar charging only)	Return on investment (Solar charging only)	Payback Period (+20% savings)*	Payback Period (+30% savings)*
Solar only	4yrs 2mo	20%	n/a	n/a
@$1,500/kWh	10yrs 6mo	10%	~8yrs 9mo	~8yrs
@$1,200/kWh	9yrs 2mo	11%	~7yrs 6mo	~7rs
@$1,000/kWh	8yrs 2mo	12%	~6yrs 9mo	~6yrs 3mo
@$750/kWh	7yrs 1mo	14%	~6yrs	5yrs 6mo
@$500/kWh	6yrs	17%	~5yrs	~4yrs 6mo
@300/kWh	5yrs 1mo	20%	~4yrs 2mo	~3yrs 1mo
@200/kWh	4yrs 7mo	22%	~3yrs 10mo	~3yrs 6mo

*Assumed additional estimated savings from tariff arbitrage on time-of-useplans and/or spot market trading opportunities such as those possible through Reposit Power, carbontTRACK, Redback Technologies or Sonnen(amongst others) on certain retail electricity plans (such as Diamond Energy‘s GridCredits100 or Urth Energy’s Urth Trader). The 20% and 30% additional savings are very rough, and are not based on actual case studies or modelling. Actual savings may be smaller or greater – we’re just trying to paint a picture of possibilities here.
Gallery: Output infographics from each battery pricing scenario (created using PVSell)