The Powerwall lithium battery system from Tesla Energy has made a big impact in the solar world and pushed home energy storage into the mainstream. Tesla took the energy storage world by surprise with the release of the first generation Powerwall 6 years ago. This unique DC-coupled battery had a much smaller 6.4kWh capacity and was the first high-voltage battery for home use. In comparison, the second generation Powerwall 2 released in 2016, which has over double the storage capacity and includes an integrated battery inverter-charger giving it much more power and flexibility. The latest iteration in the Tesla home battery series is the new Powerwall+ (plus), The new Powerwall+ is essentially the Powerwall 2 battery system with an integrated solar inverter making it a complete all-in-one solar energy storage system.

Powerwall Plus main features and specifications

• 13.5kWh usable storage capacity

• AC-coupled battery with integrated inverter/charger and Solar Inverter

• 7.6kW Solar Inverter with 4 MPPTs = Max solar capacity 12.9kW

• On-grid power rating = 5.8kW continuous, 7.6kW peak output rating

• Off-grid power rating = 7kW continuous, 10kW peak output rating

• Advanced liquid thermal management system

• 10-year warranty with a minimum 70% retained capacity*

• Price: US$12,800 – TBC – Plus backup gateway may be required**

• Available in the US only, not available in Australia or the EU

 ** Subject to change. Does not include installation, solar panels, or additional components.

See the full Tesla Powerwall+ (plus) specification datasheet

Battery Inverter Included

The Powerwall is an AC battery, meaning it has an integrated AC to DC inverter-charger; this has several advantages and disadvantages. One main advantage is the ability to be easily retrofitted to homes with an existing solar installation. Since it has an inbuilt inverter, another advantage is that it can be installed without solar and used solely for backup power purposes.

The base Powerwall has a moderately high power rating of 5kW continuous and a peak output of 7kW, while the Powerwall Plus is slightly higher at 5.8kW continuous with a 7.6kW peak. The power output is generally well suited to meet the requirements of an average home, which often has several high-powered appliances running simultaneously. The 7kW peak power rating is reasonable, but it can only maintain the peak output for 10 seconds; this means it’s only suited for brief power (startup) surges and not well suited for off-grid installations.

Increased Power output via software update

Earlier in 2021, Tesla announced a new software update that can increase the continuous and peak power rating by up to 50% on some later model Powerwalls. However, the increased power is only available at ambient temperatures up to 30C. This was enabled after analysing years of operational data and determining there were no detrimental effects. Several competing battery systems above 10kWh can output up to 8kW continuous and 10kW+ surge, so it’s not surprising the Tesla Powerwall had some hidden capacity available.

Liquid-Cooled

The Tesla Powerwall is still the only battery system on the market to incorporate a liquid thermal management system that enables it to operate in a wide range of temperatures from -20 to +50°C. Although, like most lithium battery systems, it is still likely to derate or reduce its power output at ambient temperatures above 40°C. Power derating is common for most lithium-ion based batteries, but Tesla’s liquid cooling enables the Powerwall to expel more heat under high loads and during rapid charging, which should result in a longer life span and better performance at higher temperatures.

Low-temperature performance

Tesla’s thermal management system also enables the Powerwall to charge at temperatures below freezing which is when many other lithium batteries suffer from severely reduced charge rates. Lithium battery cells cannot charge properly below 5°C due to reduced diffusion rates on the anode. Thanks to the unique thermal management system, the Powerwall is able to preheat its cells at low temperatures, known as preconditioning – “When temperatures are below freezing, preconditioning turns on and heats the Powerwall to improve charging performance”. The Powerwall will generally use grid power to preheat the cells, although, in a blackout, it can also use some of the stored energy to heat the cells. Note, this may be problematic if the battery is in a low state of charge.

Multiple Powerwalls for greater storage needs

For larger capacity systems, the Powerwall can be set up in split or 3 phase configurations with up to nine Powerwalls linked together. Although, the additional Gateway unit is required for these complex installations. The maximum capacity per phase is 3 Powerwalls which provides an impressive 40.5kWh of total storage capacity, which is more than enough for most standard households. However, considering EV charging from home can use in excess of 50kWh, it has the potential to charge an EV primarily using stored energy.

Additional Solar Inverter Required

The Powerwall 2 is an AC battery (AC in and AC out), so in order to function together with a solar array, the Powerwall system requires a separate solar inverter (Refer to the diagram below). One advantage of this is the solar inverter can be ‘almost’ any model since it operates independently of the Powerwall.

AC-coupled battery systems like the Powerwall can be easily retrofitted to homes with an existing solar installation, but they are slightly less efficient compared to the common DC-coupled battery systems. This is due to losses in the conversion from DC to AC power – first, the DC solar energy is converted to AC by the solar inverter, then back to DC to be stored in the battery, and finally back to AC when it is needed by the appliances (with typically 3-4% losses in each conversion). This adds up to approximately 90% round trip efficiency compared to around 95% efficiency with a common DC-coupled battery.

Tesla Powerwall 3

While it’s not called the Powerwall 3, the new Powerwall+ (Plus). The all-in-one systems make installation much easier and require less space to install. For example, Redback Technologies, Sonnen, Senec and Alpha ESS supply all-in-one systems with backup power and additional pass-through power as standard. I would expect the next generation Powerwall 3 to move in the same direction and offer a complete solar/battery/backup solution”

Powerwall Plus Solar Battery System

After a teaser a few months ago, Tesla has officially listed the new Powerwall+ (Plus) on the US Tesla website with some impressive features. The successful Powerwall 2 has been on the market for five years with a few minor tweaks to the available capacity and weight. It’s not surprising the new Powerwall+ is built on the Powerwall 2 platform with an integrated Tesla solar inverter to create a complete all-in-one system. While the storage capacity remains the same at 13.5kWh, the power rating has increased substantially to cater for dedicated off-grid and backup use. The power ratings are up from 5kW continuous and 7kW peak, to 7kW continuous and 9.6kW peak in off-grid mode. On-grid power ratings have also increased slightly to 5.8kW continuous and 7.6kW peak.

The inbuilt solar inverter is essentially the same as the 7.6kW inverter described earlier but repackaged to fit the Powerwall form factor. The solar inverter features four individual string inputs or MPPT’s which operate with four different strings of solar panels. Based on the specifications, we determined the inverter could potentially operate with a sizeable 16kW rooftop solar array using up to forty modern 400W solar panels, or ten panels per string. However, the Tesla datasheet specifies the maximum solar DC to AC ratio is 1.7, which equates to a maximum of 12.9kW.