The best solar storage batteries: Tesla Powerwall and 17 others put to the test


An independent trial compared 18 batteries in lab conditions, and not all survived.

Solar battery storage trial results


If you've got solar panels on your home, or you're considering getting them, then you're probably wondering if you should get a storage battery as well – and if so, which one is best?

An independent trial of 18 solar power batteries has been running in Canberra since 2016 to see how well they meet their performance claims over time. Batteries from Tesla, LG Chem, Alpha ESS and others were put to the test by ITP Renewables, and not all survived. 

Here's a summary of results from the three-year trial.

In this article:

Key findings from the solar battery trial

  • Several batteries failed in testing.
  • Solar storage is a rapidly evolving technology and industry, with some battery companies having collapsed or exited the industry already.
  • Several batteries performed reliably and look likely to meet their claims.

Possibly the major lesson for CHOICE is that running a battery test is just as challenging and fraught with unexpected outcomes as we thought, and we're very glad ITP did it instead.

Faulty and discontinued products

The battery trial encountered a number of technical challenges. Not the least is that several batteries developed faults and had to be removed or replaced. Some models are no longer available, as companies collapsed or withdrew from the battery market. This illustrates how new this technology and industry is. The industry has already matured significantly since the battery test began and we expect this will continue, and new entrants and new technologies are also appearing.

Inverter integration

Integrating batteries with suitable inverters also proved problematic in many cases, in particular with the battery-inverter communications interface. (Learn more about inverters in our solar inverter buying guide.)

The trial has also demonstrated how difficult it is to devise a single test regime that covers several different battery chemistries, as they each have different performance limitations. It's likely that the test regime works better for lithium-ion batteries than for lead-acid, for example.

Lessons for people thinking about buying solar battery storage

The key lesson is that storage battery technology is complex and is still evolving. There is a risk that a battery purchased today will be obsolete within a few years (not a problem in itself if the battery keeps on working as claimed), and that the manufacturer or distributor might not be around to honour warranty claims.

Apart from the possible technical issues, it's still the case that batteries don't yet make full economic sense for most households, though we expect that to change in the next few years.

If you do go ahead and get a battery, it's important that it is installed by experienced technicians who are familiar with the individual requirements of the product. Good warranty support is also essential, so we advise sticking with major brands who you can expect to be around in five or 10 years.

See which solar panels perform best in our lab tests:

See our expert product reviews.

Solar panel reviews

Summary of the solar battery trial results

  • Six have operated without any major problems (BYD B-Box, GNB Sonnenschein Lithium, Pylontech US2000B, Samsung AIO10.8, Sony Fortelion, Tesla Powerwall)
  • Two appear to be operating OK but have had some operational issues (CALB CA100, GNB Sonnenschein Lead-Acid)
  • Six had problems and had to be replaced, with the replacement samples either not yet installed or not running long enough to draw any conclusions (EcoUlt Ultraflex, LG Chem RESU 1, LG Chem RESU HV, Redflow Zcell, Tesla Powerwall 2, Alpha ESS M48100)  
  • Four had major failures (with either the battery itself, or essential manufacturer support) and are effectively out of the test (Ampetus Super Lithium, Aquion Aspen, Kokam Storaxe, Simpliphi PHI 3.4).

Overall, that's a disappointing outcome, and again it is a reflection on how new these products and this industry are.

Top performers

Models that demonstrated superior performance:

  • The Sony and Pylontech battery packs have so far demonstrated superior capacity retention; that is, their claimed capacity didn't significantly diminish over time.
  • The Sony, Samsung, Tesla Powerwall, BYD and Pylontech have shown high reliability.
  • The Samsung and BYD have shown consistently high efficiency. This is a measure of how much of the energy put into the battery is actually stored and able to be extracted for use again. Most of the batteries have efficiencies around 85% but these two achieved about 95% efficiency.

Individual problems and results for each battery are detailed below.

 Tesla  Samsung batteries
Tesla and Samsung batteries showed high reliability in the solar battery trial.

Solar batteries in the test

Phase One of the test started in 2016 with eight batteries that were available at that time, and Phase Two added another 10 models in 2017. Most of the batteries are lithium-ion – the most common battery chemistry available – but some other types such as lead-acid and flow batteries are included.

Battery Trial phase Country of origin Chemistry Total Installed Capacity (kWh)
CALB CA100 One China Lithium Ion (Lithium Iron Phosphate) 10.24
EcoUlt UltraFlex One USA Lead Acid Carbon 14.8
GNB Sonnenschein Lead-Acid One Germany Lead Acid 15.84
Kokam Storaxe One Korea Lithium Ion (Nickel Manganese Cobalt) 8.3
LG Chem RESU 1 One Korea Lithium Ion (Nickel Manganese Cobalt) 9.6
Samsung AIO10.8 One Korea Lithium Ion (Nickel Manganese Cobalt) 11.6
Sony Fortelion One Japan Lithium Ion (Lithium Iron Phosphate) 10.24
Tesla Powerwall One USA Lithium Ion (Nickel Manganese Cobalt) 10.24
Alpha ESS M48100 Two China Lithium Ion (Lithium Iron Phosphate) 9.6
Ampetus Super Lithium Two China Lithium Ion (Lithium Iron Phosphate) 9
Aquion Aspen Two USA Aqueous Hybrid Ion 17.6
BYD B-Box Two China Lithium Ion (Lithium Iron Phosphate) 10.2
GNB Sonnenschein Lithium Two Germany Lithium Ion (Nickel Manganese Cobalt) 13.6
LG Chem RESU HV Two Korea Lithium Ion (Nickel Manganese Cobalt) 9.8
Pylontech US2000B Two China Lithium Ion (Lithium Iron Phosphate) 9.6
Redflow Zcell Two USA Zinc Bromide Flow 10
SimpliPhi PHI3.4 Two USA Lithium Ion (Lithium Iron Phosphate) 10.2
Tesla Powerwall 2 Two USA Lithium Ion (Nickel Manganese Cobalt) 13.5

How each storage battery performed

Products are listed below in alphabetical order. Typical problems encountered include:

  • Operational failures such as the battery shutting down unexpectedly.
  • Lack of manufacturer support for technical issues.
  • Accelerated capacity fade: the capacity of the battery is how much energy it can store. It's expected to decline in an orderly fashion over several years, but for some models their capacity faded faster than it should.
  • Poor performance during summer temperature tests. Batteries don't generally like extreme temperatures but these models should be expected to cope with a wide range of climates.

Alpha ESS M48100

The battery did not perform as expected during the 2018/19 summer temperature tests, with the battery cycling at a reduced charge and discharge rate. The manufacturer stated this was abnormal and took the test battery away for their own analysis in March 2019. We don't yet know the outcome of that.

Ampetus Super Lithium

ITP had difficulties in commissioning this battery (i.e. setting it up and getting it running with a connected inverter). The battery pack had issues with reliability and shut itself down frequently. The Chinese manufacturer Sinlion would not honour the product warranty for this fault, which apparently occurred with other samples as well, and ultimately Ampetus, the Australian company selling the batteries, went into receivership. 

Aquion Aspen

This interesting battery is not lithium-ion or lead-acid; rather it uses a salt water electrolyte. Unfortunately, ITP wasn't able to get this battery fully set up and running with an inverter, as Aquion went bankrupt in early 2017 and could not provide the final support needed. The company has since been bought out but is not supporting products purchased before the bankruptcy, and it's not clear what presence they now have in Australia.

BYD B-Box

This battery has run without problems, and demonstrated high efficiency, though its capacity fade appears to be accelerating over time.

CALB CA100

The CALB is the only battery system in the trial with an external battery management system (or BMS, which controls and protects the cells) from a different manufacturer to the battery itself. A faulty cell was replaced early on, and since then there have also been issues with cycling, possibly due to another weak cell or poor management by the BMS. Although test data indicates that this battery appears to be performing efficiently and is reasonably likely to meet its lifetime claims, the operational issues reduce the reliability of this data.

EcoUlt UltraFlex

This advanced lead-acid battery has had a number of operational problems relating to integration of the battery with the inverter, some of which may have been exacerbated by the accelerated cycling program. EcoUlt replaced the original batteries. Since then, EcoUlt has advised ITP that the replacement product currently on test has been permanently damaged and will also be replaced. No conclusions can be made from the data collected. ITP says that this is a demonstration of how essential it is to get the battery/inverter integration just right, rather than a problem with the EcoUlt battery itself.

GNB Sonnenschein Lithium

This battery has run without problems, though some inconsistent data for energy discharged each cycle suggest a possible fault. However, the manufacturer has said there is no fault apparent with the battery.

GNB Sonnenschein Lead-Acid

The Sonnenschein lead-acid batteries have had several problems in the test. Their overall capacity has reduced; and the SMA inverter has struggled with accurately estimating the state of charge of the battery, resulting in the batteries not being fully charged and discharged as often as they should be. The test program may be exacerbating the battery's decline, as lead-acid batteries are not as suited to accelerated cycling as lithium batteries.

Kokam Storaxe

This battery developed a fault early in the test, when it apparently entered a low-voltage protection mode and shut down. However, it appears to have continued powering its internal components, to the point where its charge had reduced too far for it to be safely recharged again. No conclusions could be made from the small amount of data obtained.

LG Chem RESU 1

This early model LG Chem battery shut down multiple times during the 2018/19 summer temperature tests, suggesting a problem with operation in hot weather, though this has probably been exacerbated by the accelerated cycling program. Up to this point it had shown high reliability and had achieved among the highest number of cycles in the test. LG Chem batteries have comparatively high energy density and therefore can't dissipate heat as readily as other models. In normal operations they are less likely to have problems in hot weather than shown in the test. Ultimately LG Chem decided to replace this sample as it had developed faults. The replacement is a newer model RESU 10 as the older model is no longer available. The RESU 10 has not yet been installed.

LG Chem RESU HV

This battery operated OK for nearly one year, until September 2018 when it would not restart after a scheduled outage. Inspection determined that the battery voltage had dropped too low and that had resulted in swelling of the battery cells. The battery was replaced with a new sample in October 2018 but there's not enough data collected for the new sample to draw any particular conclusions.

Pylontech US2000B

This battery has had no problems in the test, and so far is showing very good capacity retention.

Redflow Zcell

The Redflow battery is another interesting non-lithium battery, using a pumped zinc bromide electrolyte to store and release charge. Unfortunately, the tested samples have suffered several electrolyte leaks or contamination and the battery has been replaced four times over the course of the trial. Redflow identified manufacturing and transport issues as the cause of these problems and have modified procedures since then, and expect the problem will be avoided in future. Due to the various failures, there's not enough data collected for this battery to draw any particular conclusions.

Samsung AIO10.8

This battery has proved very reliable and has had no operational issues. It's showing excellent efficiency so far. The battery is now sold under the brand name Hansol (a Samsung partner).

SimpliPhi PHI3.4

After this battery had been cycling for approximately one year, Simpliphi advised that their recommended inverter settings had changed from the original set-up, and that the discharge cycles had drained the battery too far. They collected the tested battery but decided to issue a refund rather than a replacement, so this brand is no longer in the test.

Sony Fortelion

This battery has had no problems in the test, and so far is showing excellent reliability and capacity retention. Unfortunately, it appears to no longer be available in Australia.

Tesla Powerwall

This sample of the first-generation Tesla Powerwall has proved challenging to control for testing purposes, as it is not compatible with the SMA inverters used in the test lab. A Solar Edge inverter was used instead. While ITP is able to control the Powerwall to some extent, their only option was to have the Powerwall charge and discharge at its maximum rate, which is not ideal and may be accelerating its capacity fade. Nevertheless, so far this Powerwall has performed reliably and in line with its claims, with no operational problems. This model is superseded by the Powerwall 2.

Tesla Powerwall 2

Similar challenges were encountered as with the original Powerwall above. Also, a fault occurred with the first sample delivered to ITP; this was replaced by Tesla. The new sample has been on test since November 2018. There's not enough data to comment on its performance to date.

About the battery storage trial

SMA Inverters
SMA inverters were used in the test of solar battery storage.

Our solar battery buying guide explains the general details of what to consider and whether a battery is likely to be cost-effective. But does a Tesla Powerwall beat an LG Chem battery? Should you go with other brands, or non-lithium types like Redflow? And do they all really meet their performance claims? Sounds like we need a comparative test under controlled laboratory conditions! Unfortunately, while CHOICE labs excel at product testing, a test of these batteries is far too complex and expensive for us to undertake.

Fortunately, someone else has done the work. ITP Renewables, a renewable energy consulting and project management company, has been running a battery trial in Canberra since 2016. With major funding grants totalling $870,000 from the Australian Renewable Energy Agency (ARENA), they built a test facility and have been testing 18 batteries to an accelerated program designed to measure performance and reliability under typical Australian conditions.

How the solar battery trial is run

A climate-controlled fire-proof test room was built and the batteries installed inside it, connected to inverter units on the outside. Power is supplied from the mains grid. The aim is to cycle (charge and discharge) each battery three times each day, which over the three-year trial is roughly the equivalent of nine years of use in a typical setting.

This is more cycles per day than the batteries would experience in normal use, but the program isn't designed to stress the batteries unnecessarily. That said, the accelerated test program may have affected some batteries more than others.

If you're curious what the lab looks like, you can take a virtual tour.

The full reports for each stage of the trial can be found here.

Will the trial continue?

ITP Renewables sees merit in expanding the trial to include a new set of batteries, and possibly new battery technologies, as well as continuing the trial for some of the current products. We agree that the trial should continue and we would continue reporting on future phases, which hopefully will allow us to recommend specific brands and models to our members.

Acknowledgement

Our thanks for the assistance of ITP Renewables in producing this summary.


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