u/DanielLorey — reddlx

Installer recommending to disconnect panels (over voltage)

Background: we had 2x Powerwall 3 fitted in 2025 and added a 16kw solar array in 2026.

The 16kw is split 8kw on the south facing elevation and 8kw on the north facing elevation.

Problem: not long after installation the primary powerwall tripped. The installer came back and split the south array over 2 MPPTs inputs, leaving the north array on the 1 remaining input.

Today: in the midst of a UK heatwave, the solar generation abruptly stopped at 1pm (peak generation) and it tripped the PW.

I spoke to the installer who suggested they miscalculated the load that the north array was capable of. As a result there was an overvoltage on the MPPT which likely caused the trip. Normally they’d split the array over multiple inputs but the PW only has 3. Annoyingly the secondary PW (full featured not an expansion) can’t be used.

Their suggestion: as we still have scaffolding up they’d come back to disconnect 2 of the 515w panels to reduce the voltage on the north array. They offered to refund me the difference of the panels etc.

This makes sense logically as Tesla One is reporting 575v (limit is 600v) but I’m finding it hard to justify given that this weather is very much an exception in the UK (33c).

I’m concerned that I’d be effectively “giving up” 1kw of potential generation all year round (albeit not full because of the orientation, granted).

Do I have any other options? Should I take the hit for the 1 or 2 days where there’s a red weather warning and switch off the north array at the DC isolator if I’m worried, or do I take the hit year-round with the security it’ll never trip?

u/DanielLorey — 13 days ago

▲ 6 r/SolarUK

Rant: why does Tesla insist on doing a calibration at stupid times?

So this morning I woke up to both of our Powerwall 3 units sitting at 98%.

That immediately seemed odd because the system is set to Time Based Control and today has a strong solar forecast. There should have been no reason for it to top up overnight.

I checked the energy graph and realised the system had actually charged the batteries to 100% and then started a calibration cycle. Interestingly, the Tesla app never showed the usual calibration warning. I only spotted it through the NetZero logs.

The frustrating part is that calibration now means the system will dump the entire battery capacity back to the grid.

What makes it even worse is that our DNO export limit is capped at 8 kW. At around 8:30am the system was already generating roughly 3 kW from solar, so the batteries could only discharge at the remaining available export capacity. It is basically like trying to empty a bath while the taps are still running at full flow. At that rate it could easily take all day.

The bigger issue is that as solar generation improves through the day, the export rate from the batteries could reduce even further or potentially stop altogether. Our solar array is 16 kW, which is double the DNO export limit, so during strong generation periods the solar alone can consume the entire available export capacity.

In the end I turned off the solar DC isolators just so the calibration could finish in a reasonable timeframe.
This brings me to the main issue. The only options Tesla gives to postpone calibration are 8:30am or 3:30pm. You can choose a different day, but those are the only time slots available.

What I cannot understand is that the system clearly knows:

The solar forecast for the day
2)The tariff rates when running in Time Based Control

Yet the calibration process appears to completely ignore both of them.

The last time this happened, the system started calibration at around 3:30pm and actually imported electricity during peak rate pricing to charge the batteries from around 40%, only to immediately dump that energy straight back to the grid.

I emailed Tesla asking them to make calibration respect Time Based Control and carry this out overnight when electricity is cheapest, but all I received was a generic “thanks for your feedback” response.

Surely I cannot be the only person who thinks this is an area where the software needs major improvement?

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u/DanielLorey — 2 months ago

▲ 0 r/SolarUK

I had 2x Powerwall 3 installed in April 25 to supplement our small solar setup, which has been working well.

Just before Christmas our roof developed a leak and upon further inspection, it was obvious we needed to remove the solar panels and repair the roof.

As the original installer did a good job the first time, it made sense to go back to them for a quote for a new solar system. In total we agreed on 2x 8kW strings (each on the north and south elevations) and that install was completed today.

To the issue… several hours after completion the PW3 tripped out. I went around the house to troubleshoot and I noticed that the casing of the PW3 seems to have gotten scratched up pretty badly where the Ethernet cable enters.

There’s been a few other issues with the install which I won’t go in to here, but sufficed to say there was already an Ethernet cable that entered this gland previously, but due to poor communication they removed it. How they’ve managed to take out a plastic gland containing the end of a cable and replace it with another plastic gland leaving lots of nasty marks is truly mysterious… but anyway.

I’m worried that the scratches may compromise the integrity / waterproofing of the PW casing. The sensible side of me says it’s not likely to cause a catastrophic failure but then any leak is a ticking clock and I doubt Tesla would honour a warranty if they could pinpoint a leak in that area.

Tl;dr - should I push the installer to rectify this? Realistically the only resolution is going to be a full replacement.

u/DanielLorey — 2 months ago

▲ 6 r/ukheatpumps

So, earlier this week I paid for a heatgeek to come out and conduct a survey for an ASHP.

I literally cannot fault the guy that came out, his knowledge and enthusiasm was top-tier and he was very happy to answer my questions.

That said, after the survey we sat down to discuss the quote. I was happy with the price but the spec is calling for a 3.5kW Vaillant aroTherm. The total surveyed heat loss is 3.67kW.

I understand that it’s designed to -2’c and that it’s only really designed to replace the heat being lost but this to me doesn’t allow much scope for colder winters. I also understand that overspeccing would cause cycling but I’m wondering why they haven’t specced the 5kW Vaillant aroTherm, especially given it’s the same frame size etc.

The quote says that they’ll guarantee the efficiency at 440% but I really wouldn’t want to faff about staring at data and having to query with the installer 6-9 months after install if the house drops too much on the coldest of winters.

For context, we have a 1 year old baby and likely another on the way in the next year so the house dropping more than 1-2c in the winter months would cause stress for the Mrs, which I want to avoid.

Any thoughts? Should I push for the quote to be amended? I know they’re likely to fall back on “trust the algorithm” but I also don’t fancy playing FAFO with our heating system for the sake of a small bump.

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u/DanielLorey — 2 months ago