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Detailed reviews and information of the best solar panels, inverters and batteries. Plus hybrid and off-grid solar system reviews and information articles on how solar and battery systems work.

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Reviews and information of the best Solar panels and inverters from SMA, Fronius, SunPower, SolaX, Q Cells, Trina, Jinko, Selectronic, Tesla Powerwall, ABB. Plus hybrid inverters, battery sizing, Lithium-ion and lead-acid batteries, off-grid and on-grid power systems.

Complete Solar Battery Review

Jason Svarc

Battery storage Review 2.2 2018.jpg
  • Released - Nov 2015

  • UPDATE 1 - May 2016 - price reductions and specification changes

  • UPDATE 2 - July 2016 - Powerwall specification changes.

  • UPDATE 3 - Aug 2016 - Powerwall warranty and LG chem spec update. Cost per kWh comparison now includes battery efficiency.

  • UPDATE 4 - Oct 2016 - New LG chem RESU, new pricing and warranty.

  • UPDATE 5 - Nov 2016 - Tesla Powerwall 2 announced, double capacity.

  • UPDATE 6 - Feb 2017 - Powerwall 2 pricing and specifications

  • UPDATE 7 - Mar 2017 - Powerwall 2 available as AC only - No DC version! PylonTech new battery model US2000B, was Extra2000

  • UPDATE 8 - May 2018 - Price updates (Tesla & LG) Added Simpliphi LFP and SonnenBatterie. Removed Powerwall 1

  • UPDATE 9 - June 2018 - Added battery capacity loss over lifetime. Updated battery efficiency specs including inverter losses.

Background

Home battery systems combined with rooftop solar have being touted as an energy revolution, a game changer, or simply as a way for people who are sick of paying high electricity prices to lower their bills. In Australia there is a great incentive to store solar energy as the feed-in tariff has been reduced to as little as 5c per kWh or less, while the cost to purchase electricity is an average of 28c per kWh and rising. This has become a driving force and great incentive to store solar energy rather than send it to the power grid for little return.

Batteries for energy storage in buildings have been around for a long time in both stand-alone (off-grid) and commercial back-up (UPS) power systems, however over the last few years domestic energy storage in the form of hybrid solar systems have started to gain momentum, even with the relatively high cost of batteries.

Another main driving force for battery storage is energy security. With the increase in severe weather events due to climate change causing regular blackouts in some locations, a battery system can provide instant back-up power for your home or business. Residential battery storage systems also enable energy independence and provides a means to generate and store your own renewable energy.

Home battery storage - Want to know which solar battery is best suited to your home? See our guide to Selecting and sizing a home solar hybrid system.


New Battery Types available

Traditional hybrid and off-grid solar systems used Gel or AGM deep cycle lead-acid batteries however over the last few years lithium batteries have really started to take hold with many large companies such as LG and Samsung releasing lithium based battery systems. Of course the biggest boost in interest came with the announcement of the Tesla Powerwall, this was when home storage batteries hit the mainstream. But will the Powerwall 2 be able to meet these high expectations, especially with growing competition from well established companies such as LG chem, BYD and Narada in China, BAE in Germany and the well established US manufacturer Simpliphi power?

A direct comparison is not as easy as it sounds as each battery chemistry behaves differently under different conditions which can either prolong or decrease the life of the battery.

The Battery Comparison

To do an accurate comparison we lined up the Tesla Powerwall 2 with the LG Chem RESU lithium battery which considered the leading competitor to the Powerwall, together with the well known and widely used lithium iron phosphate (LiFePO4 or LFP) battery systems from US manufacturer Simpliphi Power, German manufacturer Sonnen and the large Chinese manufacturer Pylon Technologies.

In this review the various lithium batteries are compared against the leading gel lead-acid based batteries from BAE and lead-carbon battery released by Narada. There are also many new batteries technologies currently being developed but few are suitable for residential applications or have moved to the high-volume production level required to become price competitive.

Selected battery systems

 

SonnenBatterie - Lithium LFP - Germany

Tesla Powerwall 2 – Lithium NMC - USA

LG Chem RESU – Lithium NMC - Sth Korea

PylonTech US2000B – Lithium LFP - China

Simpliphi PHI - Lithium LFP - USA

Narada – Lead-Carbon - China

BAE – Gel Lead-Acid - Germany

 

Summary charts of the estimated results below - Full details in conclusion

 (1) Estimated capacity loss based on 1 cycle per day - 80% DOD for Lithium, 30% DOD for Lead-acid.

(1) Estimated capacity loss based on 1 cycle per day - 80% DOD for Lithium, 30% DOD for Lead-acid.

Battery cost comparison chart above and life cycle chart below

** The rate of capacity loss over time depends on a number of variables including internal cell temperature, cell chemistry, depth of discharge, rate of charge and discharge. Full details and explanation in summary section below. (Click to enlarge)

Lead-acid Vs Lithium Batteries

In this article we compare both new and traditional battery technologies using a number of criteria. A direct comparison is not as easy as it sounds as each battery chemistry behaves differently under different conditions which can either prolong or decrease the life of the battery. The primary aim is to determine each batteries storage capacity measured in kWh (kilowatt hour) over the cycle life of the battery, but we will also try to highlight the key advantages and disadvantages of the various types available.

We will not be looking at unsealed (flooded) lead-acid batteries, as these require high levels of maintenance and any cost savings can be outweighed by regular maintenance work required throughout the life of the battery. As highlighted in the conclusion Lithium batteries have several advantages over traditional lead-acid especially in regards to usable capacity, weight, storage space and life cycle performance. However for larger off-grid systems lead-acid batteries are still one of the most trusted options as they are a well proven technology with a correctly designed system typically lasting 10-15 years.


Deep cycle lead-acid battery options

  Deep cycle sealed lead-acid batteries  are available in sizes from 200Ah up to 4500Ah

Deep cycle sealed lead-acid batteries are available in sizes from 200Ah up to 4500Ah

Advanced tubular gel deep cycle batteries are a proven technology with 15+ year design life. There are many well established companies manufacturing very high quality tubular gel lead-acid batteries (VRLA), such as Sonnenschein, Hoppecke and TAB but we selected the well known German BAE solar PVV battery to represent the sealed lead-acid batteries.

 

Battery Comparison Criteria

To accurately compare all the leading battery technologies and brands currently available we used several key criteria listed in order of importance below - Comparison criteria for smaller capacity hybrid/off-grid systems:

  1. Price per kWh (upfront cost)

  2. Depth of discharge (DOD) – usable energy

  3. Cycle life – Number of charge cycles

  4. Power output – Max continuous and peak output

  5. Round trip efficiency – Charge/discharge losses

  6. Size and Weight – Energy density

  7. Sustainability and enviromental impact

Price per kWh

1. The first key criteria is the upfront price per kWh, since upfront cost and payback time is one of the most important aspects for many consumers. Due to some battery chemistries having higher rates of degradation and lower efficiency, the real cost over time (payback) may be higher. This difference is highlighted in the conclusion.

Depth of discharge and cycle life

2 - 3. The second and third criteria really go hand in hand as battery life is almost always directly proportional to the depth of discharge (DOD). This means that the further a battery is discharged the shorter the battery life. The available energy or DOD on a daily cycle (charged and discharged every day) is usually specified by the manufacturer and the cycle life in years is based on this DOD value. However, the end of life (EOL) of a battery is not always clear as a battery doesn't just suddenly stop working after a certain number of cycles.  Almost all battery technologies new and old slowly loose capacity over time and the industry standard for Lead-acid is to determine the EOL once battery capacity has dropped to 80%. However more recent lithium manufacturers such as LG and Tesla are warranting their batteries to lower EOL values of 60 or 70%. Remember the battery is still usable after this, it just doesn't hold as much energy.

To complicate this further in real world conditions there are many variables including temperature, rate of discharge and incomplete charge (partial state of charge) so the performance and life of a battery system can be significantly altered. As a general guide the newer lithium and sodium based batteries are designed to be discharged up to 70-90% total capacity while the traditional lead-acid (gel & AGM) batteries are generally not discharged lower than 50% unless in emergency backup situations. For those in the industry this is a relatively standard assumption. See our battery article for more specific information.

Battery Power Output

4. Following this we have the continuous and peak power output. This can be very important depending on the type of inverter you are using and the application, for example off-grid installations will usually require a higher peak power output as you do not have the grid available to assist in high load (high power draw) situations.

Round Trip Efficiency

5. Next is round trip efficiency, this is the charging and discharging efficiency or losses during cycle use. Unfortunately, due to the laws of physics the transfer of energy from one form to another (in the case of batteries from electrical to chemical energy) will always result in some losses. Generally, charge/discharge losses from a lead-acid based battery is close to 20% while most new lithium based batteries can be as low as 2% but generally in the 5-8% range.

Size & weight

6. You may be surprised but I have put weight or energy density last. This is simply because I consider it rather irrelevant in a stationary situation, however if this comparison was for electric vehicles it would probably be on top of the list.

Sustainability - Environmental impact

7. Of course there are other important factors which should be considered such as recyclability, temperature tolerance and safety. Sustainability with become increasingly important as more and more battery systems are installed. Plus recyclability will over time become a major issue. This topic is covered in detail towards the end of this review.

Battery Details and Specifications

Note: The cost per kWh figures are based on the price of the battery from various distributors. Due to variable Australian dollar we have used the standard US dollar. 

The battery prices can vary from different distributors and from country to country. Also prices do not include the cost of the solar array, inverter/s installation and other associated costs such as rewiring switchboards, additional AC cabling and solar DC cable installation.

Tesla Powerwall 2

 The Tesla Powerwall 2

The Tesla Powerwall 2

The Tesla Powerwall 2 has double the 'usable' capacity of the original Powerwall, now at 13.5kWh and being an AC battery it comes with an integrated 5kW DC-AC inverter. The integrated inverter will make installation simplier but will still require a solar inverter to function with a solar array, plus an additional gateway box will be required to enable backup power (UPS) during a grid outage.

The Powerwall 2 uses a lithium nickel-manganese-cobalt (NMC) cell chemistry developed in collaboration with Panasonic as the battery cells are similar to the batteries used in the Tesla electric vehicles. The unit features an integrated battery management systems (BMS), liquid thermal management, and DC-AC inverter/charger. The new Powerwall 2 will have the capability to work in parallel with up to 9 units for homes/businesses with greater energy storage requirements.

COST: US$7500 - Australian listed price AU$9500 inc GST

  • 13.5kWh usable for 3500 cycles - estimated 70% retained capacity

  • DC-AC Inverter included

  • Power output (AC) – Continuous = 5.0kW, Maximum Peak= 7.0kW

  • Round trip efficiency (claimed) = 89% including inverter losses

  • Powerwall = US$6000 (AU$9500) – Cost per usable kWh = US$521

  • Warranty is 10 years - See warranty certificate for more details.

See the complete Tesla Powerwall 2 review


LG Chem RESU

LG chem RESU battery review vs Powerwall

LG Chem offer a much larger range of RESU (Residential Energy Storage Unit) batteries in various sizes from 3.3kWh up to 9.8kWh in two voltage options, 48V and 400V. Previously just the single 6.4kWh RESU6.4EX lithium battery was available. The latest 48V range includes RESU3.3, RESU6.5 and RESU10 units with an option to combine different units using an adapter for up to 19.6kWh of total storage. More about the new range of new RESU batteries here.

LG chem use lithium polymer pouch with lithium nickel-manganese-cobalt (NMC) cell chemistry. The RESU batteries are housed in compact weather rated (IP55) enclosures with integrated BMS and are warranted to 10 years life, but this is to minimum 60% retained capacity (EOL). Based on current performance estimates it is expected the capacity after 10 years to be in the range of 70-80%.

  • RESU10 - 8.8 kWh usable for 3500cycles to 60% retained capacity (EOL)

  • Power output – RESU10 48V = 5.0kW, Maximum Peak = 7.0kW

  • Round trip efficiency (claimed) = 96%

  • New 9.8kWh LG RESU10 = US$4200 (AU$6000) – Cost per usable kWh = US$509

  • Warranty is 10 years - See warranty certificate for more details.

See the complete LG chem RESU review


PylonTech

The Pylon Technology lithium iron phosphate (LiFePO4 or LFP) batteries were some of the first modular lithium based batteries available which enclosed both the lithium cells and battery management/control system in a simple rack mounted unit. The first Extra2000 has now been replaced by the US2000B and Phantom-S series (pictured) which has a more aesthetic enclosure and more robust battery cable connections. Available in the same standard size 2.4kWh modules (previously with a touch screen interface) allows easy setup and monitoring together with connections for multiple units in parallel. Now also available in high voltage modules for commercial applications.

The pylontech battery modules are often re-branded and used by several large solar manufactures and distributors including SolaX, Canadian Solar and Redback Technologies.

Lithium ferrous phosphate (LFP) is generally considered the most stable of all the lithium battery chemistries especially at elevated temperatures above 40 degC (common in Australia) which is highlighted by the high battery cut-off temperature of 50 degC. Cycle life is also quite high at a claimed 6,000 cycles at 80% depth of discharge, although it is unknown what the end of life (EOL) retained capacity is after this number of cycles?

The warranty is for 5 years and specifies 80% EOL capacity or 60% EOL capacity with the extented 10 year warranty. Note the previous warranty states no more than 360 cycles per year. Based on this the new battery performance will remain the same and we can assume 3,000 cycles at 80% DOD. The battery module operates at the nominal voltage of 48V and now has a higher peak power output of 5kW (previous model was 2.2kW) over a short discharge duration of 60 sec. The updated US2000B battery retails at the same price as the previous Extra2000.

  • 1.92kWh (80%) usable for 3000 cycles to 70% retained capacity (EOL)

  • Power output – Continuous @ 48V = 2.4kW, Max Peak 4.8kW (1 min)

  • Round trip efficiency = 94% - tested

  • Extra2000 = US$1200 (AU$1350) – Cost per usable kWh = US$520

  • US2000B - Warranty: 10 years (after online registration) to 60% retained capacity. Refer to warranty document here

See full detailed PylonTech battery data sheet and manual here


Simpliphi PHI

Simpliphi PHI battery review.png

Simpliphi Power is a US based battery manufacturer which has been a leading developer of Lithium-ion batteries since 2002. Initially developed for durable remote military and mobile power systems the Simpliphi PHI batteries are well known for their extremely high cycle life, safety and stability.

The Simpliphi PHI range of Lithium Ferro Phosphate (also know as Lithium Iron Phosphate or LFP) batteries are rather unique in the home battery market being one of the only fully modular battery systems available. Unlike most residential lithium battery systems which are a fixed capacity or limited to 2-4 modules in parallel the PHI range is fully scalable and only really limited by the inverter and solar array capacity available. With the built in BMS or battery management system in each battery Simpliphi claim the PHI batteries do not require ventilation, cooling or thermal regulation. Considering Lithium LFP is the most stable lithium chemistry available and the proven track record, the PHI range appear to be one of the most robust battery system available on the market and are one of the only 'drop in' replacements for lead-acid batteries.

SimpliPhi also offer the best warranty of any battery on the market with an impressive 10,000 cycle / 10 year warranty (at 80% DOD) and a 3500 cycle / 10 year warranty at 100% DOD. However like all battery warranties there are conditions, in this case they main warranty conditions are the battery operating temperature range (0 - 43 degC) and charge /discharge rate no greater than 1.6kW (PHI 3.4battery) as specified in the warranty document.

  • 3.5kWh 100% usable for 3500 cycles to 80% retained capacity (EOL)

  • Power output – Continuous = 1.6kW (3 x units = 4.8kW), Maximum Peak = 3.0kW per unit

  • Round trip efficiency (claimed) = 98%

  • 3.5kWh module = US$3300 (AU$4000) – Cost per usable kWh = US$719

  • Warranty is 10 years - See warranty certificate for more details.

See full SimpliPhi PHI battery specification data sheet details


Narada Lead-Carbon

ZHEJIANG Narada Power Source Co. is a Chinese based company primarily focused on power system and energy storage solutions. The REXC series Lead-Carbon based battery technology uses a nano carbon material with high capacitance and highly conductivity on the negative electrode. The company claims this combines the advantages of both lead acid batteries and super capacitors to enable faster recharge. The lead carbon battery technology provides not only a higher energy density, but also high power, rapid charge and discharge, and longer cycle life than traditional lead-acid batteries. However, the batteries are only currently available in large 6V and 12V modules so multiple strings of batteries would be required for usable capacities above 6kWh which is not ideal for large system but suitable for most domestic hybrid setups. Also the rated capacity can only be obtained at a very slow discharge rate of 100 hours (C100) which is not optimal for a hybrid situation with full discharge more likely to be over 12 hours or less.  Although the claimed cycle life of 3000 cycles can be obtained at high temperature of 40degC so in theory they should last longer at lower temperatures. Warranty 5 years - See Warranty certificate

  • 48V bank = 4 x 12V 200Ah (C12) = 4.0kWh usable for 3000cycles to 80% retained capacity (EOL)

  • Power output – Continuous @ 48V bank = 5.0kW, Peak up to 10kW

  • Round trip efficiency (estimated) = 82% (based on 12 hour discharge rate - C12)

  • 4 x 12V 200Ah batteries = US$2600 (AU$3600) – Cost per usable kWh = US$650

See full battery specification sheets here - Narada Power


BAE Gel Lead-Acid

BAE_Secura_PVV_battery_review.jpg

BAE Gel Secura batteries are high quality German made lead-acid based batteries designed specifically for off-grid and hybrid installations. BAE manufacture a wide range of batteries of various sizes and voltage configurations but for this review we will focus on the Gel Secura PVV solar (tubular Gel) range.

BAE have been manufacturing lead-acid based batteries for more than 100 years and the latest Gel Secura PVV battery design uses an advanced tubular-plate electrode with woven polyester gauntlet and solid grids in a corrosion-resistant lead-calcium alloy.  The fully sealed maintenance free battery design utilizes the VRLA technology and have been proven to perform in harsh conditions and elevated temperatures.

The BAE Secura PVV batteries are single 2V cells therefore require battery configurations of either 12 or 24 batteries in series to create a battery bank nominal voltage of 24V and 48V respectively, refer to our battery article for more information. The secura range like most VRLA batteries are available in a vast range of sizes ranging from 140Ah up to a massive 4940Ah which in turn enables a wide variety of battery bank capacities up to a 235kWh or higher. For this review we selected the smaller 770Ah (C25) battery for the comparison (610Ah @ C10). BAE batteries are capable of deep discharges to a maximum of 80% total capacity but for the purpose of this article we will use a DOD of 50% which according the specifications will provide 3000 cycles to end of life (EOL). Warranty: 5 years

  • 48V bank = 24 x 2V 610Ah = 14.6kWh usable for 3000cycles to 80% retained capacity (EOL)

  • Power output – Continuous @ 48V bank = 5.0kW, Peak 9kW or higher**

  • Round trip efficiency (estimated) = 82% (based on 10 hr rate - C10)

  • 24 x 2V 350Ah batteries = US$9300 (AU$12800) – Cost per usable kWh = US$635

See full BAE Secura PVV Battery specifications

**Unlike Lithium based batteries Continuous and Peak power output of a lead-acid battery bank depends on battery capacity chosen, up to (235kWh @ 48V) and so power output could be rated as high as 100kW.


SonnenBatterie ECO

SonnenBatterie ECO review.png

Sonnen is the leading Germany lithium battery manufacturer and is the largest residential lithium battery system company in Europe. Until recently Sonnen had deployed the largest amount of home battery systems globally surpassing Tesla and LG. The SonnenBatterie ECO range is much like the Tesla Powerwall 2 in that it is an AC battery with built in DC-AC inverter but it still requires an additional solar inverter to function with a solar array.

There are two main differences between the Sonnen and Tesla AC batteries, the first being that Sonnen ECO is available in a range of different sizes with capacities from 3.3kWh up to 16kWh and the second is Sonnen use Lithium Ferro Phosphate or LFP battery chemistry as opposed to Lithium NMC of Tesla. Lithium LFP batteries are regarded as the safest and most stable battery chemistry with the longest life of up to 10,000 cycles.

Possibly the only real disadvantage of the SonnenBatterie ECO over other lithium battery systems is the limited inverter power rating which is a maximum of 2.5kW for all single phase and 3.3kW for all 3-phase systems.

See full SonnenBatterie ECO specification data sheet here

  • ECO10 - 10kWh usable for 3500cycles to 80% retained capacity (EOL)

  • Power output – Continuous = 2.5kW, Maximum Peak = 2.6kW

  • Round trip efficiency (estimated) = 92% including inverter losses

  • 10kWh ECO = US$8500 (AU$10500) – Cost per usable kWh = US$772

  • Warranty is 10 years - See warranty certificate for more details.


Battery comparison Results

 

Upfront Cost per kWh - usable capacity

* Based on wholesale US prices, may vary significantly in other regions & Counties - Est AUD*1.35

 

Battery cost per kWh per year over 10 years #

(1) Estimated capacity loss based on 1 cycle per day - 80% DOD for Lithium, 30% DOD for Lead-acid. Including battery efficiency factor - Round trip efficiency of the battery during charging and discharging in which some energy is lost.

Note: Simpliphi and Sonnen LFP battery estimated lifetime greater than 15 years according manufacturers specific operating criteria - see battery life chart.

 

Battery capacity loss chart - Estimated Battery life

** All batteries lose capacity over time. The rate of capacity loss depends on many variables including temperature, cell chemistry, depth of discharge and rate of charge/discharge. (Click to enlarge)

* Estimated capacity loss values shown are based on several criteria including manufacturers performance data detailed in each battery section, active or passive cooling, cell chemistry and discharge rate.

High grade cyclindrical Lithium Ferro Phosphate (LFP) batteries are known to have the most stable chemistry, greatest temperature tolerance and longest life of all batteries however they are also the most expensive. LFP batteries also contain no Cobalt and are considered the safest and most sustainable lithium battery chemistry.

# I have used 70% as a hypothetical cut off point where individual battery cells may not be holding charge and 'tripping out' under higher discharge rates. Battery cells may still be functional but BMS, sensors, electronic control systems can also become degraded or fail over time.


Conclusion

A comparison based purely on cost per kWh over a 10 year period show the Tesla Powerwall 2 and LG chem RESU as neck and neck with the PylonTech lithium close behind. However over a life greater than 10 years the SimpliPhi PHI and Sonnen ECO systems will no doubt out last both LG and Tesla due to the high performance LFP chemistry with leading warranty conditions. Generally LFP chemistry, if managed correctly, will result in lower capacity loss and longer life so long as charge/discharge rates are maintained as specified. The PylonTech LFP batteries are not expected to perform as well as the other LFP's due to very high discharge/charge rates allowed which accelerates degradation.

It is important to note there are several assumptions used and true performance in real world conditions may vary. Also this comparison is focused on smaller capacity (hybrid) systems used for residential applications of less than 20kWh capacity. For larger capacity and off-grid applications lead-acid deep cycle batteries would be much more competitive.

The Tesla Powerwall 2 includes a 5kW battery inverter and is the best value for money but it doesn't incorporate a solar inverter or back-up capability so like other battery systems additional equipment will be required which adds to the installation cost. The Powerwall is the only system to incorporate a liquid cooling system which may prove to prolong battery life over time. The SimpliPhi PHI battery range may have a higher up-front cost but due to the very high efficiency, low rate of degradation and range of battery sizes to choose from ends up as one of the best options, especially if considering upgrading an older system from lead-acid to lithium batteries.

Power Output

 PylonTech & Simpliphi are modular lithium batteries - More modules = higher cont & peak output

PylonTech & Simpliphi are modular lithium batteries - More modules = higher cont & peak output

Continuous power output of the lithium batteries can be limited as highlighted in the above chart, although in some cases multiple battery modules can be linked together in parallel to provide greater power output. Unlike Tesla and LG the SimpliPhi battery is fully scalable and not limited in this way. However for most residential applications the 5kW continuous output of the Tesla and LG batteries is more than adequate.

Generally for higher capacity above 20kWh, or high power output systems above 5kW then SimpliPhi PHI, Gel lead-acid (BAE), Narada, or any of the other well known lead-acid manufacturer would be the best option. The Sonnen ECO range is rather limited when it comes to power output as the maximum is 2.5kW continuous output due to the fixed inverter size.

Battery Efficiency

 * Tesla and Sonnen efficiency values include inverter losses AC-DC-AC (charge and discharge).  ** Estimated based on various charge/discharge rates - Typical discharge duration of 2 hrs for Lithium NMC & LFP, 10 hrs for VRLA (Narada & BAE).

* Tesla and Sonnen efficiency values include inverter losses AC-DC-AC (charge and discharge).

** Estimated based on various charge/discharge rates - Typical discharge duration of 2 hrs for Lithium NMC & LFP, 10 hrs for VRLA (Narada & BAE).

The round trip efficiency is the charging and discharging efficiency or losses during use. Unfortunately due to the laws of physics the transfer of energy from one form to another results in some losses and in the case of lead-acid this is normally as high as 20%. The newer high density Lithium batteries can achieve extremely high efficiency with as low as 2% losses, which over time means the performance and return on investment is much better for lithium system.

Another problem with lead-acid or lead-carbon battery systems is the much longer charge time when compared to lithium systems. The Lead-acid charge cycle can take several hours which means during bad or intermitent weather the charge efficiency will be very low and a full charge may not be achieved. In contrast Lithium batteries can charge very quickly (1 - 2 hours) and can efficiency absorb charge at much lower rates.

 Gel lead-acid deep cycle batteries are available in a huge range of sizes

Gel lead-acid deep cycle batteries are available in a huge range of sizes

 

Inverter Compatibility

Besides the cost per kWh figure there are many important factors to consider when selecting a battery storage system such as compatibility with the hybrid or off-grid inverter and adaptability with your existing solar setup (if installed). The Powerwall 2 and Sonnen ECO being AC coupled batteries are very flexible and can be added to most new or existing solar systems however the communications are not compatible with most solar inverters and separate monitoring systems are generally required.

In contrast the LG chem RESU batteries being DC coupled are compatible with almost all well known hybrid and high-end interactive/off-grid inverters so this gives much greater system flexibility. LG chem RESU 48V batteries are compatible with almost all the leading solar hybrid & off-grid inverter brands. The list now includes Selectronic, Solax, Sungrow, Schneider Electric, Ingeteam, GoodWe, Redback and Victron Energy.

Another important consideration is some hybrid and off-grid inverters are optimised for charging lead-acid batteries and some lack the compatible communications to charge/monitor a lithium battery management system (BMS). This is where the SimpliPhi 'drop in' replacement is a real bonus as long as the battery inverter/charger settings can be adjusted to suit a lithium battery.

PylonTech are also compatible with many leading hybrid inverters including Redback, Solax, TrinaBESS and Imeon. Although the communications used by the PylonTech are not compatible with many off-grid inverters. See here for full hybrid/off-grid inverter details and reviews.  For this reason it is recommended to use a hybrid kit (battery and inverter combo) which is known to be compatible. Some examples are:

There are also many all-in-one systems with built-in battery storage such as Alpha ESS, Solax-Box, and TrinaBESS systems.

 

Battery size and weight comparison

 Battery weight comparison table - * Sonnen and Tesla values include inbuilt inverter weight

Battery weight comparison table - * Sonnen and Tesla values include inbuilt inverter weight

LG batteries are one of the lightest and most compact coming in at close to half the size and weight of the Powerwall, and the new range are able to be expanded up to 19.6kWh capacity. If a smaller system is required and space is an issue then either the SimpliPhi, LG chem or Pylon Tech batteries would be the best option.

Weight isn't generally an important factor for most installations but if wall mounting is required or a very limited area is available then this might become more critical, especially for the lead-acid batteries which are very heavy and can take up a considerable amount of room.


Best Batteries for Off-grid systems

Whilst lithium batteries seem to be the most cost effective solution and excellent for most hybrid grid-connected applications if you are setting up an off-grid system then high quality sealed gel lead-acid or lead-carbon batteries are still one of the most trusted options. Lead-acid batteries are a well proven technology and still advancing, in most cases with a correctly designed system you can expect a life of 10-15 years.

Lithium battery options for off-grid

The US manufactured SimpliPhi PHI and Australian made GenZ lithium LFP batteries are some of the only 'drop in' replacement lithium batteries which can operate with most of the leading off-grid inverters. These unique scalable battery modules are able to be easy linked up to provide adequate storage capacity or continuous/peak power output for larger off-grid system from 10 to 200kWh.

The Tesla Powerwall 2 and Sonnenbatterie ECO AC battery systems are not designed for off-grid use as the in-built (transformerless) inverters are not capable of handling very high surge loads and do not incorporate any back-up (black-start) features. Also the warranties will not cover them for off-grid use.

From our knowledge the LG chem RESU and SimpliPhi PHI batteries are the only lithium batteries certified for off-grid installations when used with the high end Selectronic SP PRO off-grid/hybrid inverter. For more information see our technical guide to selecting an off-grid or hybrid inverter.

Off-grid system Review - Selectronic SP PRO multi-mode inverter and 48kWh Gel battery bank

For information about designing a solar powered home refer to the building off-grid guide on our other site. You don't have to build an 'earth ship' made from recycled materials to have a solar powered off-grid home. Although looking at the newer housing developments we definitely need more unconventional and intelligent/passive home designs.

How much does it cost to go off-grid?

To learn more about selecting an off-grid or hybrid solar system for your home and the costs involved see our guide to selecting a home solar battery system.


Battery Recycling and Sustainability

With an ever increasing number of battery installations around the world comes the inevitable problem of recycling the batteries once they have reached the end of their usable life. In the case of lead-acid based batteries this is not an issue as the infrastructure and recycling collection centres are already in place in most countries, enabling the Lead, plastic and electrolyte to be extracted and recycled relatively easily. In fact approximately 96% of all lead-acid batteries are recycled.

The Aquion Sodium-ion (salt water) battery system is possibly the only battery which has been designed with sustainability in mind. With a unique non-toxic chemistry they are the first battery manufacturer to have met all the stringent criteria to obtain cradle-to-cradle certification for sustainability. Also since Aquion batteries are manufactured using abundant materials they are not be likely to suffer any material shortages due to high demand.

Lithium batteries on the other hand are more difficult to recycle with some manufacturers not yet capable of 100% recycling the lithium cells. However there have been several breakthroughs in recent months by independent groups which are developing advanced recycling techniques specifically for complex lithium based batteries. American Manganese Inc is one of the many new companies developing lithium battery recycling facilities around the world. There are also some unique battery recycling methods being developed to simply extract the compounds (battery elements) to be manufactured into new batteries.

Of all the lithium battery chemistries available the Lithium Ferro or Iron phosphate (LFP) batteries are the least toxic as they do not contain Cobalt. LFP batteries are also considered the safest chemistry with the longest life and lowest risk of thermal runaway if damaged or overheated.

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Re-using old electric vehicle batteries in homes

In the case of electric vehicles the Australian startup Relectrify has developed a clever way to extent the life of EV batteries by re-assembling them into a stationary unit for use in homes and businesses. Since most EV batteries still have a retained capacity of 60% or more at the end of life, this will give a new life to old lithium batteries for an additional decade or more extended use.

Since most large lithium batteries are still in use there is no real push on recycling until the batteries reach their end of life over the next 5-10 years. The recycling difficulties lie in the complex lithium chemistries being manufactured of which there are several variations. Some cells are in powder form, others coated onto metal foil, all of which must be separated. At present the safest Lithium combination is lithium iron phosphate (LiFePO4 or LFP for short) which is one of the lithium batteries which can be more easily recycled. Lithium cells are also much smaller and often incorporate electronic management systems and thermal sensors which will also need to be disassembled. There is still abundant quantities of lithium minerals available but it is a finite resource so this will lead to greater incentives to develop more ways to recycle lithium batteries as the raw material cost will no doubt rise as demand increases.

 

FURTHER INFORMATION AND REVIEWS:

For more information to help you understand hybrid inverter technology and select the appropriate inverter or battery for your installation, see our introduction to solar & hybrid inverters

For more reviews on hybrid solar - Hybrid inverters and energy storage systems

The complete battery comparison chart - Lithium battery systems