We compare the leading AC batteries from Tesla and Sonnen against the popular DC coupled batteries from LG chem and BYD. A direct comparison is not easy as each battery type has different advantages depending on the application and what energy storage capacity is required. Other factors include the location (indoors or outdoors) or whether the battery is being retro-fitted to a home with an existing solar. The full battery comparison criteria is explained in detail in the complete solar battery review.
Tesla Powerwall 2 and Sonnen ECO
The Tesla Powerwall 2 and Sonnen ECO are AC batteries meaning they have inbuilt inverters and chargers. Solar panels still require an seperate solar inverter to operate but the benefit is that AC batteries can be retro-fitted to any home with solar already installed. The Powerwall 2 is a weather rated system which means it can safety be installed outside, although as with any battery system it is better to install it in a sheltered location out of direct sunlight. The Sonnen ECO on the other hand can only be installed outside within a special enclosure which adds to the cost.
In terms of life span and warranty the Sonnen ECO battery use longer life Lithium LFP (Lithium Ferro Phosphate) battery cells and come with one of the best warranties on the market with an estimated 88% retained capacity after 10 years of use. The Powerwall 2 on the other hand uses the Lithium NMC cells similar to those used in the electric vehicles. The lithuim NMC batteries used by Tesla have a high discharge rate which equates to higher power output at 5kW continuous compared to a maximum of 3kW from the Sonnen ECO.
LG chem RESU and BYD B-Box
Both the LG chem RESU and BYD B-Box are the common DC lithium batteries which must be connected to a hybrid inverter or a more powerful multi-mode inverter for off-grid installations. Whie they are both DC lithium batteries they have several important differences including cell chemistry, design and configuration options. The BYD is very modular system being comprised of multiple smaller capacity 2.5kWh battery modules while the LG chem batteries are single large battery module. Another key difference is LG chem uses Lithium MNC pouch cells while the BYD uses the more common Lithium LFP cylinder cells. Despite these differences both batteries have similar performance characteristics and expected lifespan which is highlighted in the complete solar battery review.
AC Vs DC coupled systems
For more details about AC and DC coupled solar systems see our detailed comparison including the four main solar battery system types. It may sound confusing as DC batteries can be connected to inverters in AC or DC coupled systems depending on the installation type. Generally grid-connected homes use DC coupled systems while more advanced off-grid and larger scale systems use AC coupled systems.
Tesla Powerwall 2
The Tesla Powerwall 2 with 13.5kWh of 'usable' storage capacity is an AC battery as it comes with an integrated 5kW DC-AC inverter/charger. AC batteries can be fitted to home with existing solar installations which can make installation simplier, but still require a solar inverter to function with a solar array, plus the additional Tesla gateway box is 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: Approx $10,500 inc GST, excludes backup gateway
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
COST = $10,500* (US$8,500) – Cost per usable kWh = AU$768
Warranty is 10 years - See warranty certificate for more details.
Cost excludes backup gateway
LG Chem RESU
LG Chem offer a large range of RESU (Residential Energy Storage Unit) batteries in various sizes from 3.3kWh up to 13kWh 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 and just released RESU13 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%.
COST - RESU H 10kWh - Approx $8500 inc GST
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%
LG RESU10 = AU$6000 US$4800 – Cost per usable kWh = AU$642
Warranty is 10 years - See warranty certificate for more details.
BYD is the largest Chinese manufacturer of rechargeable lithium batteries and has dominated the Chinese electric vehicle and energy storage market for some time, however BYD is still relatively new to both Australia and north America. BYD manufacture a wide range of lithium energy storage systems for both commercial and residential applications using LFP or Lithium Ferro Phosphate cells which are considered the safest and most stable battery chemistry.
The BYD B-Box Pro range of low voltage (48V) batteries have become very popular due to the extremely competitive pricing and compatibility with many of the leading inverter brands. BYD also offer a range of HV or high voltage (400V) battery systems compatible with the emerging and popular hybrid solar all-in-one inverters for grid-connected homes.
The B-Pro Pro or Professional range of battery systems are made up of multiple 2.56kWh units and are available in a range of sizes from 2.5kWh (single unit) up to 10kWh with 4 battery units in a common steel enclosure. Additionally the largest B-box Pro module has 13.8kWh capacity (using two larger 6.9kWh units) and is fully scalable using up to 32 boxes in parallel.
The warranty is 10 years and specifies 60% EOL capacity or a minimum throughput energy as specified in the warranty document. The battery modules operate at the nominal voltage of 51V and have a high peak power output of 5.12kW over a short duration of 30 sec.
2.56kWh (100%) usable for 10 years to 60% retained capacity (EOL)
Power output – Continuous @ 48V = 2.56kW, Max Peak 5.12kW (30 sec)
Round trip efficiency = 95.3%
BYD B-Box Pro 10 = AU$6000 – Cost per usable kWh = AU$608
Warranty: 10 years to 60% retained capacity. Refer to warranty document here
See the full BYD B-Box battery specification sheet here
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 3kW for single phase and 3.3kW for 3-phase systems.
See full SonnenBatterie ECO specification data sheet here
ECO10 - 10kWh usable for 3500cycles to 80% retained capacity (EOL)
Power output – Continuous = up to 3kW, Maximum Peak = 3.3kW
Round trip efficiency (estimated) = 92% including inverter losses
10kWh ECO = AU$9,800 (US$8,500) – Cost per usable kWh = AU$912
Warranty is 10 years - See warranty certificate for more details
Battery comparison Results
Upfront Cost per kWh - usable capacity
Results include all eight batteries from the complete solar battery review.
See the full results in the compete solar battery review article