Storage for Solar

While there are many options when it comes to what to do with excess solar power, at present the major storage option for solar is certainly batteries. In recent years the market has shifted massively away from lead acid batteries to lithium ion batteries. This is mostly due to the rapidly falling costs and much longer lifetimes of lithium ion batteries. Lithium batteries are able to give long life, using all of their energy in each cycle (i.e. using a ‘depth of discharge’ close to 100%). Lead acid batteries, on the other hand, can’t tolerate such deep cycling and must be cycled using only half their energy or less.

While batteries are certainly booming, they are still relatively expensive. Unless there is a particular situation such as off-grid living (learn how to size off-grid solar systems), or high demand charges in industry, in normal use you will do well to break even on the cost of the battery. Of course, many users do not want to use solar panels directly without batteries and want the independence and higher certainty of electricity price that a battery can provide.

Lithium Ion Battery Prices

Which Brands are Good?

In a rush to capture a slice of the booming lithium ion battery market, many companies have sprung up and pushed battery products into the market. There are currently over 300 battery companies in China. Unfortunately, the skills and expertise required to set up a high quality battery manufacturing plant are pretty rare and many companies simply don’t have this expertise.

The problem with battery manufacturing is that tiny faults in the battery can cause major problems such as failure of the battery or even worse, dangerous fires. Battery plants can produce more than 1 million batteries per day, day after day, week after week, year after year. Sophisticated quality control systems are needed to guarantee consistent quality and safety in so many cells.

The problem is: how is the ordinary homeowner supposed to know which solar batteries are the best? Fortunately there is some help available. The Australian government has helped fund a test centre for home battery units: the Australian Battery Test Centre. This centre has been charging and discharging a large number of batteries in conditions that simulate real life, for a number of years. The troubles they have had with getting many systems to work properly, and the wide range of performance quality they have found, reflect the current state of the lithium ion battery market very well.

The reports from the battery test centre give a very good idea as to which systems can be relied upon to give trouble-free operation, and which systems give good lifetime. As a guide, a good lithium battery should have a 10 year warranty and to be able to cycle at least 4000 times and still maintain about 80% of its’ original energy.

Lithium Ion Batteries

Which Type of Lithium Ion Battery?

There are quite a few types of lithium ion batteries, mostly distinguished by the type of cathode material. Different cathode materials are nickel-cobalt-aluminium (NCA) of Panasonic/Tesla fame, nickel-manganese-cobalt (NMC) and lithium iron phosphate (LFP).

LFP has inherently longer life and better safety than NMC and NCA however there are more consumer products available using NMC cathodes than LFP. This is because the battery makers have been heavily focused on the electric vehicle industry. Cars need more energy density than homes or industrial sites, therefore the car industry uses NMC and NCA materials. Since the battery companies are so heavily committed to these chemistries they are also used for energy storage systems for home and industry.

NMC and NCA work pretty well when managed properly. When not managed properly they can give poor lifetime and can potentially be dangerous. Even Tesla’s Powerwall 1 product performed poorly at the Australian Battery Test Centre (Powerwall 2 is performing much better).

Safety is Paramount

Lithium ion batteries have been around for about 30 years and billions of cells have operated without any issues. When done properly, it is a very safe and reliable technology. However, when not done properly, lithium ion batteries are potentially very hazardous and therefore should not be taken lightly. In today’s booming market there is a risk that products will be pushed into the market before they are really ready.

There have been many safety incidents with lithium batteries that have been very well publicized. A good example was the lithium ion battery system in Boeing’s Dreamliner aircraft, which was released in 2013. During its first year of service, five incidents in five days prompted the US Federal Aviation Authority (FAA) to ground the entire fleet, the first such grounding since 1979. The plane was reported to have had two major battery thermal runaway events in 52,000 flight hours and these were not contained safely. Boeing had predicted one event in 10 million flight hours. The Dreamliners used batteries from a leading Japanese battery company, GS Yuasa.

Another high profile example was the Samsung Galaxy Note 7. On 19 August 2016 Samsung released its new Galaxy Note 7 product. Less than three weeks later, Samsung issued an informal recall, after fires resulted from excessive heat in some products. A formal recall was announced in the US on 15 September, and Samsung recalled the Note 7 worldwide on 10th October, not even 2 months after its release. Credit Suisse estimated this incident cost Samsung up to $17 billion in revenue.

More recently, Hyundai has been hit with the most expensive vehicle recall in history because of fires in their LGChem batteries. Batteries will be replaced in 82,000 cars at a cost of $1.13 billion.

So when choosing a battery it’s a good idea to stick with known brands, and do a bit of homework on safety. If there are lots of safety incidents with a particular brand it might be worth a re-think.

What’s in the Future?

Lithium ion batteries are dominating the residential market at the moment and that isn’t going to change anytime soon. Battery prices will continue to fall, which is great for homeowners. Battery lifetime will also continue to improve. Sony can already make batteries with a 20 year lifetime, giving them a lifespan almost equal to that of the solar panels they’ll be storing energy from. Both these things will continue to drive better economics for batteries. You might also want to read our article to learn the expected duration of solar panels.

Hydrogen is starting to make some inroads into the market but more in the commercial/industrial sector. Companies such as GenCell (Israeli) and Lavos (Australia) have medium-sized storage options available using hydrogen. Hydrogen is finding a place as a much cleaner option than diesel generators, particularly in remote areas.

One interesting produce from GenCell is a hydrogen fuel cell that runs on ammonia. Ammonia is converted to hydrogen by the system itself. This seems a major step forward, as ammonia is the second largest chemical product on earth, and very large volumes can be exported and stored easily and safely. This product is due for commercial release next year: it will be interesting to see how it goes.

Flow batteries such as vanadium redox and zinc bromide are also being offered by a number of companies. They have potentially very long life however are costly and have had reliability issues. Flow batteries have found it hard to penetrate the market. They do not have the long history behind them that lithium batteries have and therefore present a riskier technology option. Perhaps in coming years they will be able to make their mark.

Very Large Scale Storage

When the scale of storage gets very large – as with offshore wind farms, solar farms ( read our article titled overview of solar farms), or the very largest solar array complexes in the world – things get interesting. There are a number of new technologies emerging that could change the game.

Energy Vault is a Swiss company that stores energy by literally building a high-rise structure by lifting and dropping large bricks. When energy is available the bricks are lifted into place. When energy is needed the bricks are allowed to drop and the energy is captured.

Other companies are also looking at gravity. Gravitricity is a UK-based company that uses abandoned mineshafts to lower and raise heavy weights. Again the weights are lifted when energy is available and dropped when needed.

Azelio stores energy using molten aluminium. The aluminium is melted using solar, wind or solar thermal power to melt the aluminium. The heat is then converted to power using a Stirling engine. This technology is available in a wide range of sizes.

This is a fascinating area and it will be very interesting to see if any of these technologies can make the grade into full commercial options.

Read also: Estimate of Solar Panel Costs


Currently the storage market is dominated by lithium ion batteries and this will remain the case in the foreseeable future. However there are many different types and brands of lithium batteries available, with a wide range of quality and safety. It will pay the buyer to do some homework before purchase.

Into the future hydrogen and flow batteries may play a larger role particularly in industrial/commercial.

It certainly is an exciting time to be involved in storage.

Frequently Asked Questions

What sort of storage should I use in my home?

The vast number of home energy storage systems are lithium ion batteries and this will continue for the foreseeable future.

Is storage worth it?

In particular situations, such as off-grid, or in industrial and commercial applications where demand charges may be high, storage can be a good economic investment. For normal residential use you will do well to break even on storage.

What’s coming in the future?

Lithium ion batteries are expected to dominate the market into the future, however costs will drop and lifetimes will be extended. Hydrogen is starting to replace diesel generation and may continue to expand.

Which battery should I buy?

Sticking to known brands with good track records on safety is a wise choice. The Australian Battery Test Centre has good data on most of the home battery brands currently available.

Editorial Contributors
avatar for Geoff Edwards

Geoff Edwards

Geoff Edwards has worked in the renewable energy sector for more than 15 years, initially at the forefront of lithium ion battery technology, and more recently in solar power combined with energy storage. He has over 15 patent applications in various fields. Geoff has a degree and PhD in engineering from the University of Queensland in Brisbane, Australia.

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