Battery Storage Knowledge Bank

Tesla Powerwall 3 - Everything you need to know

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Functionality & Features

Hybrid inverter - Solar capacity
Hybrid inverter - Why 3 MPPT strings?
Hybrid inverter - DNO acceptance likelihood
Size & scalability - Expansion packs
Size & scalability - Single phase
Size & scalability - Three Phase
Backup & Off-Grid support
Octopus integration
Battery chemistry
Round trip efficiency
Storm Watch

Installation & Design


Usable capacity: 13.5 kWh
Starting Price ~£7950
Continuous AC power output: 3.68 kW - 11.04 kW
Round-trip efficiency: 97%
Monitoring: Tesla app
Warranty: All inclusive 10 year warranty. Guaranteeing 80% cell capacity after 10 years.
Mounting: Wall- or floor-mounted.
Location: Indoor or outdoor installation - Flood resistant up to 2ft. IP67 rated.
Weather resistance: -20°C - 50°C
Dimensions: H 1,098.6mm x W 609.6mm x D 193.04mm
Weight: 130.18kg
MPPT strings: 3
Scalability: Up to 44 kW AC output, 216 kWh of storage on a single phase supply.

Headline Features of Tesla Powerwall 3

-Continuous AC output of up to 11.04 kW.

-13.5 kWh capacity.

-"Plug and Play" expansion packs available.

-11.04 kW Integrated hybrid inverter with 3 MPPT strings.

-Integrates with Octopus Intelligent Tariffs.

-LFP battery chemistry.

-Flood, weather and dust resistant.

-Competitive price point.


Tesla Powerwall 3 Price

Tesla Powerwall 3 starts at £7950.

Tesla Powerwall 3 from Spirit Energy currently starts at £7950. However, when installed with solar, this can decrease by up to ~£1500. This is primarily due to the shared inverter, negating the need for a dedicated solar inverter. Additionally, when installed with solar, the labour cost can be shared between the solar and battery installations.

This compares to its predecessor, the Tesla Powerwall 2, which started at £11000 at the beginning of it's production life cycle, and currently is priced at £7100 from Spirit Energy.

Functionality & features

Hybrid inverter - Solar capacity

Tesla Powerwall 3 has an inverter ranted anywhere within a range of 3.68 kW to 11.04 kW. Additionally, Tesla claim that the Powerwall 3 inverter can be oversized up to 170%, meaning that 18.5 kW of solar capacity can be stringed on it. This equates to 52x 430W panels (accounting for 20% clipping).

Inverter Rating (kW) Maximum kWp (20% clipping, kWp) Estimated maximum number of solar panels stringed (430W panels)
3.68 4.4 10
5 6 14
7 8.4 20
8 9.6 22
9 10.8 25
10 12 28
11.04 13.2 31
18.5 (11.04kW 170% oversized) 22.2 52

*For more information on clipping and kWp, please read here - Spirit Energy - Solar PV Clipping, Undersizing and kWp

Hybrid inverter - Why 3 MPPT strings?

With most residential scale solar inverters having 2 MPPT’s, the major advantage of the third MPPT is that it allows you to take advantage of a third roof space without needing an additional inverter. A lot of semi-detached houses in the UK have south, east, and west facing roofs. The third MPPT makes it much easier to use all three roof spaces.

For more information on MPPT's, how they work, and their benefits and limitations, please read here - Spirit Energy - What is MPPT (Maximum Power Point Tracking)?

The third MPPT will also help with shade mitigation. If you have a solar array with a section of panels that are severely shaded, by a chimney, for example, they could be stringed on their own MPPT which will separate them from the rest of the system so they don't affect the output of any unshaded panels. Modern panels do also have bypass diodes in which help with shade mitigation.

For more information on string design an the impact of shading, please read our blog here - Spirit Energy - Solar Panel Shading Analysis

Hybrid inverter - DNO acceptance likelihood

For any PV or battery system with an inverter rating greater than 3.68 kW, a DNO application needs to be done prior to installation (usually G99). Hybrid inverters greatly increase the number of panels that you can have, as well as the amount of battery storage that you can have. The reason being that you don't need a dedicated inverter for the PV and a separate inverter battery storage.

Because the inverter combines the solar inverter and the battery inverter, the potential output of the system will decrease, which increases DNO acceptance likelihood.

This is further aided by Tesla’s versatile range of rated inverter capacities, meaning the same inverter can be sized to best meet both your needs, and the DNO restrictions.

More information on DNO restrictions, and how it can impact your system, can be found here - Spirit Energy - DNO Permission

Spirit Energy - Tesla Powerwall 3 - First Installation

Size & scalability - Expansion packs

Tesla are offering a expansion packs in the size of 13.5 kWh. These can be added to a Powerwall 3, increasing it’s capacity. Up to 3x expansion packs can be added per Powerwall 3, for up to 54 kWh per Powerwall 3.

Fitting an expansion pack is cheaper than installing an additional PW3 because the expansion packs don't need the same technology, and are straightforward to install.

You can stack 3x expansion packs behind a PW3 unit or mount them next to each other on an adjacent wall.

The benefit of expansion packs, in our opinion, would be further advantaged if they were offered in incremental sizes, such as a 5 kWh variant. This would give users more customisation options.

Size & scalability - Single phase

Tesla Powerwall 3 can scale up to 216 kWh on a single phase supply.

For single phase systems, up to 4x Powerwall 3’s can be installed, each with up to 3x expansion packs. This equates to 216 kWh of battery capacity, with full house back up, which is almost unheard of for residential systems.

Size & scalability - Three Phase

Tesla Powerwall 3 can scale up to 162 kWh on a three phase supply.

Powerwall 3 has far superior three phase support than its predecessor, and most other residential battery storage systems for that matter, however, for the time being, it does not support as much storage capacity as it does for single phase systems. Currently, due to only having 80A three phase inverter support, only 1x Powerwall 3 is supported per phase, but each with the full 3x expansion packs, resulting in 162 kWh capacity, with full house back up.

Backup & off-grid support

Tesla Powerwall 3 enables you to continue providing power to your property during power cuts. It also allows your solar PV system to keep running in a power cut.

To learn more about how emergency backup, and off-grid battery systems work, please read here - Spirit Energy - Grid Backup and 3 Phase Systems

You can specify a custom reserve percentage (e.g. 30%) and the system will always keep that percentage of the capacity in reserve for a power cut. Tesla recommend 20% (2.7 kWh) or more.

Tesla Powerwall 3 Powercut Reserve - In App Monitoring
At 30% capacity (4.05 kWh), the Powerwall should power a standard home for 3-4 hours, whilst allowing you to keep the TV, fridge, lights and WiFi on (~ 1100 W).

Appliance Predicted load (W)
Fridge / Freezer 500
Kettle 3000
Oven 3650
Induction hob 1500
Office & Entertainment
Laptop 50
TV 80
WiFi 20
Average load – 4 to 5 bedroom house, all LED 500
Laundry & Dishwasher
Dishwasher 1250
Washing Machine 500
Electric Clothes Dryer 4000


(PW3 - Tesla Powerwall 3
EP - Expansion pack)
Max Capacity (kWh) 30% Reserve (kWh) Time running ~1100 W load (hours)
1x PW3 13.5 4.05 3.7
1x PW3 + 1x PW3-EP 27 8.1 7.4
1x PW3 + 2x PW3-EP 40.5 12.15 11
1x PW3 + 3x PW3-EP 54 16.2 14.7
2x PW3 + 6x PW3-EP 108 32.4 29.5
3x PW3 + 9x PW3-EP 162 48.6 44.2
4x PW3 + 12x PW3-EP 216 64.8 58.9

*Maximum capacity for Powerwall 3 on a three phase supply is currently 162 kWh

A typical schematic is as follows:

Tesla Powerwall schematic

No permanent off-grid support

A drawback of Powerwall 3 is that it will not support full off-grid support, ie. Commissioned and run entirely off-grid. The support has also been removed for Powerwall 2. Tesla claim this is because it is too costly for them to maintain considering how few people use it. This is disappointing, however, in our experience installing Powerwall 2's in the UK, we have installed no full off grid Powerwall 2’s.

Octopus integration

Powerwall 3 is compatible with Octopus Intelligent tariffs such as Octopus Intelligent Flux and Octopus Agile.

"Intelligent Octopus Flux pairs with your battery to optimise your charging and discharging to save you money and help balance the grid" – Octopus Energy

Octopus Intelligent Flux will tell Powerwall 3 to export at the times when it's most profitable to do so, meaning that you'll always get the best export deal. If the battery needs topping up, it will also charge automatically when the import rates are cheapest, helping to maximise your savings.

For a deeper breakdown of SEG tariffs, and which may make the most sense for you, please read here - Spirit Energy - SEG Tariffs


Tesla Powerwall 3 comes with a 10 year warranty, guaranteed for 80% capacity.

Tesla Powerwall 3 has a 10 year warranty, at the end of this warranty period, Tesla guarantee that the battery will have 80% (10.8 kWh) of its initial capacity remaining. Tesla offered the same warranty with their Powerwall 2, and it is still unmatched in its 80% guarantee by any competitors.

Battery chemistry

Tesla Powerwall 3 uses a Lithium Ferro Phosphate (LFP) battery chemistry.

Tesla have opted to use Lithium Ferro Phosphate (LFP) for Powerwall 3, swapping over from the Lithium Nickel Manganese Cobalt (LNMC) cells that Powerwall 2 uses. LFP is widely regarded to have a longer lasting life-cycles and better cell degradation. It is also generally considered to be more ethical and sustainable.

The only downside is the energy density, which has resulted in Powerwall 3 being a slightly larger, and heavier package than Powerwall 2. Though it is important to note that it also contains a high-quality hybrid inverter within its dimensions, which makes up a substantial proportion of the internal area, as we saw in the first Powerwall 3 installation, seen below (battery cells seen in lower two-thirds)-

Tesla Powerwall 3 Internals - First Installation by Spirit Energy

Round trip efficiency

Tesla Powerwall 3 has a round trip efficiency of 97%.

Powerwall 3 has an industry leading round-trip efficiency of 97%. This is the amount of power put in from solar, minus the amount lost before exporting to the grid. What this means for you is that this system will be able to retain more power than any other battery system in the UK market. Tesla likely achieved this with their industry-leading hybrid inverter, which is obviously tightly integrated and tuned for the battery itself.

Interestingly, this is the same efficiency as the Powerwall+, which was never released in the UK, only the US market. The Powerwall+ also has an integrated solar inverter, with 4 MPPT solar strings.

Storm Watch

Storm Watch is a feature that Tesla created to predict power cuts. It monitors local weather stations, and, in the UK, The Met Office, and if it sees a storm on the horizon will start to charge up. In the event of a power cut that's caused by a storm, Powerwall 3 should be fully charged to maximise the amount of time that you can run the house off-grid.


Powerwall 3 is controlled and monitored via the Tesla app. 

If you don't have a Tesla Powerwall and would like to try out the app, there is a demo version available. Just download the Tesla app, open it up and scroll to the bottom of the main page. You'll then be able to demo the Powerwall 3 app and take a look at the different system monitoring and controls available.
Tesla Powerwall 3 App Homepage - In App Monitoring

Tesla Powerwall 3 Installation & Design

Space is a consideration in residential properties, as indeed is aesthetic appearance. Similarly to Powerwall 2, the design is modern and minimalist, designed to be seen, not hidden away out of sight. And the water-resistant enclosure case means that it can be installed outdoors. The ability to install outside is one of the major plus points of the Powerwall.

Tesla Powerwall 3 is rated to IP67 water-resistance, with flood-resistance to 2ft, or 60cm. This is achieved through a laser-welded lower half.

The installation process is similar to Powerwall 2, which Spirit Energy had become exceedingly experienced with. For this reason, installation costs are similar. Tesla have slightly streamlined the installation process, with 2 particularly notable changes. Powerwall 3 now requires a LAN cable for its internet connection. Secondly, Tesla have made a custom dolly for Powerwall 3 installers. This makes installations simpler, faster, and therefore, safer.

The design of Powerwall 3 and the installation process is documented in our video showcasing our installation of the 1st Powerwall 3 performed by an installer -

Battery storage for solar panels: summary page

Interested about finding out about other battery systems?

Read our summary page on battery storage for solar panels.