Category Archives: Electricity

Tesla Powerwall Energy Export Option Setting

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The Tesla Powerwall 3 integrated inverter-and-battery system is meant to be ‘smart’ in learning about solar generation and energy usage patterns, but it’s not proven to be as clever as I was expecting – notably in terms of Exporting from the Batteries to the Grid. One downside with the Powerwall is that its control algorithm is very much a ‘black box’ so it’s difficult to check if it’s working correctly – or even what “correctly” is expected to look like.

During the Winter, with modest solar PV generation and heat pumps running in both the House and the Outbuildings – plus all the other usual electrical loads – the Powerwall was effective in fully charging the batteries by Importing from the grid overnight, taking advantage of 6 hours of the Intelligent Octopus Go off-peak import rate of £0.07 per kWh and then using its battery to service all the electrical demand throughout the remaining 18 hours, generally avoiding all peak-rate Imports. Any solar PV generation – which could be significant on a sunny-but-cold Winter day – was Exported to the grid (in real-time).

At the end of March, with the heating off and much more solar PV generation, that model is no longer appropriate. In particular, with the distribution network operator imposing an Export limit of 5.5kW but the potential to generate more than 16kW at Noon, there’s a requirement to temporarily store much of the PV generation in the battery and then export that in the evening – to create the headroom in the battery to accept further solar generation ‘tomorrow’. If that doesn’t happen, the solar PV generation has to be curtailed once the battery gets full.

My expectation was that the Powerwall would have visibility of a solar PV generation forecast for ‘tomorrow’ and choose to Export to the Grid from the Batteries in the evening, since it knew all the generation would never be consumed on-site. But that’s not been happening: the Powerwall never exported any of the energy stored in its battery.

Within the Tesla iOS App, I see options to set the Operational Mode, choosing between:

  • Self-Powered, which “reduces the reliance on the Grid”
  • Time-Based Control, which “uses stored energy to maximise savings”

I’ve also been seeing two Advanced Options:

  • Permission to Export, which can either be Yes or No
  • Grid Charging, also Yes or No

With both Permission to Export and Grid Charging set to Yes, in Time-Based Control mode I saw all the Solar PV Generation being Exported to the Grid (up to the Grid Export Limit of 5.5kW, with additional generation above that limit being used to charge the batteries). However, none of the energy stored in the battery (either from local solar PV generation or from an off-peak import from the grid) was ever exported.

Tesla’s documentation for the Advanced Settings in the Mobile App includes the following text:

Energy Exports

Some energy suppliers allow Powerwall to send energy back to the grid and claim credits during peak times. If ‘Energy Exports’ is not available in the Tesla app, your energy supplier does not allow Powerwall to export energy to the grid for any Time of Use purposes.

How It Works

If your Powerwall is allowed to send energy to the grid, the following energy export options will be available in the Tesla app:

Energy Exports OptionDescription
Solar1Powerwall will only export solar production to the grid during high-cost time periods.
EverythingPowerwall will export both solar production and stored Powerwall energy to the grid during high-cost time periods.

When set to ‘Solar,’ your Powerwall will only use stored Powerwall energy to match your home load consumption when the price of energy is expensive. Use this setting if you want to earn credits while also keeping energy stored in your Powerwall to reduce reliance on the grid.

When set to ‘Everything,’ Powerwall will send both solar and Powerwall energy to the grid and will continue to discharge to your set Backup Reserve. Use this option if you want to maximise savings.

1 Default setting

However, I’ve not been seeing anything that looks like that Energy Exports option in the iOS App and – based on the behaviour I have been observing – the PowerWall has been acting as if that setting was on its factory default of ‘Solar’.

While investigating third-party control options to implement the behaviour I ideally wanted, I installed the Home Assistant integration for the Tesla Fleet API. (I’d tried installing that previously, when the Powerwall was first commissioned, but was thwarted by an obscure error. I finally got around to investigating why it failed and applying a work-around.) Unlike the Tesla iOS App, this integration exposes the Energy Exports options. I actually only spotted that because the setting initially defaulted to ‘Never’ and I was puzzled as to why the normal daytime export behaviour wasn’t working on the day after installing the integration. The names of the Energy Exports options in the Home Assistant dashboard for the the Tesla Fleet integration are slightly different from in the Tesla documentation:

  • Never – which presumably equates to “Permission to Export” being set to No
  • Solar only – which presumably equates to “Solar”
  • Battery – which presumably equates to “Everything”

Initially I was hopeful that changing this setting via Home Assistant would influence the behaviour of the Powerwall, but that wasn’t the case. However, with the benefit of more experience of how the system has been operating and the clarity of the highlighted text in the Tesla documentation, I was fairly certain my unit had been commissioned with the wrong setting.

I contacted my installer, who contacted Tesla (who seem to be the only people able to correct configuration errors made during commissioning) and they changed the setting that was prohibiting export from the batteries. Now I’m seeing a third option under Advanced Settings in the Tesla iOS App, which is giving it permission to export from the batteries.

It looks like that setting was changed about 24 hours ago. As a result:

  • The Powerwall barely charged from the grid during last night’s off-peak tariff period – even in Time-Based Control mode – meaning the battery had spare capacity to accept much of the excess solar generation during the daytime
  • The Powerwall was aggressively exporting all through the early evening, maintaining the maximum permitted 5.5kW of Export even after the solar generation dropped to zero
    • It’s only just now (at 20:00) started reducing the export to maintain enough charge to get it to the next off-peak import time slot (at 23:30) with the configured 20% ‘buffer’ of minimum charge to maintain, in case of a grid outage

So the behaviour has definitely changed – for the better. I’m expecting it to take a few days to re-learn the ideal behaviour and tweak its optimisations.

Tesla PowerWall Backup Gateway Grid Outage Detection – UPS Still Required

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The Tesla PowerWall 3 solar PV inverter and battery storage system provides the ability to automatically disconnect from the grid and power the site from its batteries in the event of a grid outage – including topping up the batteries from solar generation during the outage. The component that handles this is the Backup Gateway 2 which is installed next to the meter, in the outdoor GRP cabinet.

The installation engineer was very positive about the performance of the switch-over from Grid supply to Battery supply, based on their experience testing this by manually triggering a switch-over while the grid connection was still live, with no flickering of lights or resetting of appliances. The official Tesla specifications (which I’m struggling to find to reference here) are much less optimistic and note it can take a few seconds to switch in a real-world power outage scenario – especially when there’s a brown-out rather than a clean break in the supply. Clearly that’s long enough for most appliances to reset.

It’s typical to have a couple of short-duration power outages every year – perhaps as a consequence of the overhead 11kV supply and the way that is connected to the rest of the grid. When the grid power went away for a second or two the other day the Backup Gateway did not react (at all? – there was certainly no message to say it had gone off-grid) and the network switch and router in the Outbuildings lost power for long enough to reset. The equivalent devices in the House are already protected by an Uninterruptible Power Supply (UPS) so stayed online.

That prompted me to add a UPS to the networking equipment in the Outbuildings – something I was planning to do anyway, but I had decided to wait for some real-world experience first (in case the Backup Gateway did react quickly enough after all).

I’ve had good experience with second-hand APC UPS equipment over many years and the smallest and cheapest APC model I could find on eBay was the Back-UPS CS BK350EI which runs from a single 12V 7Ah lead-acid battery (very widely used as backup batteries for alarm systems so readily available and competitively priced). While this UPS is only rated for 210W and won’t run for more than a few minutes at full load it seems perfect for covering a few seconds of outage while the Backup Gateway kicks in, powering the Outbuildings’ network router and network switch (including the CCTV cameras and Wireless Access Points supplied via PoE from that switch).

While a rack-mount UPS would have been nice, those tend to be much more expensive and – importantly – the smaller rack-mount models need much more expensive batteries.

APC Back-UPS CS (BK350EI) located in the network rack in the Outbuildings Plant Room

The UPS was only £17.99 without a battery (including free shipping) and a new Yucel 12V 7Ah battery was only £15.49 from a local electrical wholesaler that specialises in alarm system equipment and hence has a pretty quick stock turnover for those. (The same battery would have been £27.49 from Screwfix/Toolstation, with more risk of getting one that has been in stock for months.)

The APC BK350EI UPS has three IEC 60320 Type F socket outlets (in fact the photo on that Wikipedia page is of an almost identical UPS) – plus another socket that is only surge-protected, not also battery-backed. It was supplied with two Type E to C13 cables which are ideally suited to powering devices like the UniFi network switch which has a C14 plug connector. In order to power devices which demand a standard UK BS 1363 socket (e.g. because they use a power adaptor integrated into a BS 1363 plug) it’s necessary to use an extension lead with a Type E socket. While re-wirable Type E sockets are available (and I’ve used a good quality one successfully before – and struggled with poor quality ones) it’s generally better to cut the C13 connector off the end of a pre-made Type E to C13 cable and wire that to something like a 3-way socket outlet adaptor.

These small APC UPS devices don’t support the ‘SMART’ monitoring network cards which the larger models (aimed more at business deployments) do, but they still provide an option for USB connectivity via a non-standard cable (APC AP9827) with an RJ50 (like an RJ45 but 10-way) plug at the UPS end and a USB Type A connector at the other end. Genuine APC cables are very expensive but much cheaper equivalents are available via eBay. While an 8-way RJ45 plug will physically fit into a 10-way RJ50 socket and only 4 pins are actually wired, those include pins 1 and 10 so it does need to be a 10-way plug.