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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.

Tesla Powerwall 2 review - Solar AC battery system

Jason Svarc

  • UPDATE: March 2017 - Powerwall 2 only available as an AC battery. The DC version is no longer available.
  • UPDATE: May 2018 - Price changes and tariff charging feature added

 

The highly anticipated Tesla Powerwall 2 battery from Tesla Energy is finally here. The first generation Powerwall with 6.4kWh capacity was released almost 3 years ago and in that time the engineers at Tesla managed to develop the second generation Powerwall with double the storage capacity at close to half the price including an integrated DC-AC inverter.

The Powerwall 2 (PW2) with 13.5kWh storage capacity and an integrated inverter had a recent price increase of around 8% from AU $8800 to $9500 (US$7200). However with the first Powerwall costing around $7200 for only 6.4kWh of storage capacity this is still a 35% price reduction per kWh.

New Lithium NMC battery cells

The remarkable cost reduction was achieved due to the enormous Tesla manufacturing facility known as the Gigafactory in Nevada which is now up and running. Both Powerwall’s use lithium NMC (Nickel-Manganese-Cobalt) battery cells developed in collaboration with Panasonic and are similar to the cells used in the Tesla electric vehicles, although the new generation, larger 2170 lithium battery cells are used in the Powerwall 2.

 Powerwall 2 battery Competitors - See how the Powerwall 2 compares to other battery technologies including the new range of home lithium batteries by LG chem

The new Powerwall 2 has been completely redesigned to be more compact, easier to handle and install. Gone are the sleek curves, giving way to a more practical rectangular shape with venting either side for cooling and a bright green LED strip. Interestingly it also has a simple on/off switch on one side. Still weighing in at 120kg it is definitely not light, although thankfully the PW2 can now be ground mounted as well as wall mounted. The IP rating (weather rating) remains high at IP56 although it is still recommend installing in a reasonably sheltered location such as carport or garage and out of direct sunlight if possible. Heat and batteries just don't go well together.

Battery Inverter included

The AC Powerwall 2 includes an integrated AC-DC inverter/charger which gives it an advantage over the competition. Inverter power is reasonably high with a continuous output of 5kW and peak of 7kW, compared to 3.3kW (DC output) for the previous model. The higher power output is much more suited to the typical loads of an average home which can have several high powered appliances running simultaneously. Although the 7kW peak is not as high as similar sized dedicated battery inverters, plus it can maintain 7kW for only 10 seconds which means it is only suited for brief power surges and not designed for modern off-grid home installations.

Liquid cooled

The Powerwall 2 is still the only battery system on the market to incorporate liquid cooling which enables it to operate in a wide range of temperatures from -20 to +50 degC. Although like most lithium battery systems it is likely to de-rate or reduce its output once above 40 degC. Power de-rating is common for most lithium based batteries but the Tesla's liquid cooling should enable the PW2 to release more heat under high loads and rapid charging which should result in longer life span and better performance at higher temperatures.

For larger capacity systems the PW2 will have the ability to be setup in split or 3 phase installations with up to 9 battery modules able to be linked together in series, however the additional Gateway unit is required in these more complex installations.

See the full AC Powerwall 2 specifications / datasheet here

Additional Solar Inverter Required

Since the Powerwall 2 is an AC battery (AC in / AC out) in order to function together with a solar array the Powerwall 2 requires a solar inverter as well (Refer diagram below), although the solar inverter can be 'almost' any model since it operates independent of the Powerwall.

AC battery systems are becoming more popular due to the simple installation although they are not as efficient as more common DC systems when used with solar. 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 3-5% losses in each conversion).

Tesla Powerwall 3

Many hybrid solar systems currently available have incorporated both a solar inverter and battery inverter in one complete unit which makes installation much easier and requires less space to install. Redback Technologies, Solax and Alpha ESS for example have systems which can also provide back-up 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/back-up solution. There has been no official announcement from Tesla about the new Powerwall 3 but based on the previous development timing would likely be announced late 2018 or early 2019.

Backup Power

The PW2 cannot function as a backup power supply or UPS without additional components. To enable backup power in the event of a blackout an optional Backup Gateway will need to be installed at additional cost. The rather large Gateway box, which is not as aesthetically pleasing, communicates with the Powerwall over wifi and simply put it's job is to isolate the house from the grid if it detects any issues with the electricity supply. For those who were hoping to purchase a Powewall and go off-grid, it can operate in off-grid (back-up) mode but it is not designed to function as an dedicated off-grid power system. I would recommend reading this first before considering disconnecting from the electricity grid.

 Typical system layout with the Powerwall and solar inverter feeding power the home.

Typical system layout with the Powerwall and solar inverter feeding power the home.

DC VERSION - No longer available - Since the Powerwall's operate at the higher voltage 350-450V DC range they require a dedicated high voltage hybrid inverter to function. The are several inverters which are capable of doing this including Fronius Symo hybrid (3 phase) and SolarEdge StorEdge (single phase) which are both regarded as two of the leading solar inverter manufacturers.

Controversy

Tesla is a disruptive and innovative company which has had several last minute changes to its products before release. This may be due to a number of reasons including raising public interest through its clever PR strategies, but there is also likely to be unforeseen technical and engineering difficulties which need to be ironed out before release. This has caused some issues, especially in the case of the Powerwall 2 as some solar installers have installed DC Powerwall compatible systems only to be told the DC coupled version will no longer be released.

Tesla Energy’s aim is to focus on safety, quality and customer service. A business model that has enabled Tesla to become one of the largest companies in the world without actively promoting their products other than through product launches. The customers and press simply promote it for them. Quite clever really.

  We review the best solar panels from leading manufacturer's LG, Sunpower, REC, Trina and more.

We review the best solar panels from leading manufacturer's LG, Sunpower, REC, Trina and more.

Warranty

The warranty for the PW2 is 10 years with 70% minimum retained capacity (solar self-use and back-up use only). This is much better than the original Powerwall 1 warranty but if it is charged using solar and also low tariff (off-peak) energy, a feature which has just been enabled as of May 2018, then the number of 'daily' cycles could be greater than 1 and this will likely reduce capacity at a higher rate. This is where the warranty details comes into effect in regards to 'Operation Limitation' (see image below).

Keep in mind all batteries reduce capacity over time as they are charged and discharged. This is part of the normal aging (degradation) of a lithium (NMC) battery and the min 70% retained capacity after 10 years is reasonable. Other lithium battery chemistries have a lower degradation rate but usually a higher upfront cost so it's a matter of balancing the cost/benefit. See the full Warranty details here

 First section of the Warranty - Powerwall 2 (DC version)

First section of the Warranty - Powerwall 2 (DC version)

Wrap up

 Powerwall 2 monitoring app

Powerwall 2 monitoring app

The Tesla Powerwall 2 is a huge leap forward from the first generation Powerwall and has overcome many of the issues highlighted by customers and installers, in particular the limited solar inverter compatibility. Tesla overcame this by developing the PW2 as an AC battery which operates independently of the solar inverter and is thus compatible with most new or existing solar systems. However unlike many hybrid inverters the built-in inverter does not have the ability to isolate or island itself from the grid during a blackout and requires the additional 'gateway' to function as a back-up power supply. Also it is not designed for off-grid installations.

In our complete solar battery review the Powerwall 2 came out as one of the best value battery systems on the market, with a large 13.5kWh storage capacity it is well sized for most large modern homes. Also it is the only battery to incorporate liquid cooling which may mean it outlasts other batteries especially in hotter climates. With a 10 year warranty and building on experience from the durable Tesla electric vehicle batteries it is a well engineered system and has so far proven to be a very high performing battery. Although with the current supply issues you might have to wait 3-6 months to get one.

Alternative battery options

There are many other 'hybrid systems' available which include batteries and are also very good value for money, plus many include a solar inverter and back-up function in one complete hybrid unit. For off-grid installations it is recommended to use on of the well known, dedicated DC or AC coupled off-grid inverter systems which incorporate a number of features designed specifically for off-grid installations.

 

Commercial size Tesla Powerpack

 Large Tesla 100kWh Powerpack module

Large Tesla 100kWh Powerpack module

Tesla Energy also has large scale Powerpack modules available for utility scale and commercial energy storage. The 100kWh Powerpack (ref image) is simply made up of multiple smaller battery units and available in a modular system which can be easily linked together to create several MWh of energy storage. With each Powerpack costing around AU$40K this is a breakthrough price for large scale storage.

 

Recycling

Recycling the complex Lithium based batteries used in the Powerwall poses several challenges compared to common lead-acid batteries which are easily recycled, although much research and development is underway. A recent breakthrough by American Manganese Inc or “AMI” has shown very good results in extracting the raw materials from Lithium NMC batteries for re-use. The Lithium NMC batteries used in the Powerwall are difficult to recycle but Tesla claim it will be feasible once the volume increases; since most Tesla lithium batteries are still in use and are expected to last 10+  years there are simply not enough used batteries available yet to refine the recycling process.

 

The Powerwall 2 Vs LG chem RESU and SimpliPhi PHI

See the complete battery storage comparison and review here - The Powerwall 2 compared to leading lithium based batteries LG Chem and SimpliPhi, plus proven lead-acid and advanced lead-carbon batteries.