5 vs 10 Solar Panels with Battery from Octopus – Advice Needed for Future EV & Heat Pump

NedS

Sam3007 said:

Thank you. I am now more inclined to get the bifacial ones with the Tesla powerwall 3 but I still have a few questions please 

If the space on my roof is limited , Is it better to space 10 bifacial panels with gaps to boost rear-side gain, or just install 12 panels close together (6 on each side)?

Almost certainly going to be more beneficial to maximise the number of panels. I don't know exact figures, but I'm guessing that the vast majority of generation is going to come from the front of the panel and additional gains from the rear bifacial aspect will be relatively small. I'm sure there are some studies out there as to the relative benefits of roof mounted bifacial panels.

Sam3007

Just wanted to post an update and big thanks to @Screwdriva for the excellent advice and for recommending an installer. After a lot of research (and questions on here!), I finally had my system installed and thought I’d share the setup and experience after almost a month for anyone considering something similar.

System Details:

• Solar array: 10 panels (south-west facing) 10 panels (north-east) = 10kwh

• Inverter & Battery: Tesla Powerwall 3

• EV charger: MyEnergi Zappi 2

• Tariffs: Octopus Intelligent Go + Octopus Outgoing (winter)

• Heating: Gas (so system mainly for electricity, EV charging, and self-consumption)

Setup Goals (winter):

• Maximise use of solar and off-peak electricity

• Charge EV overnight on cheap rate

• Export surplus 

Solar Generation:

Since installation, the system has been generating around 9 kWh per day in October, with top days exceeding 10–11 kWh when there’s decent sunshine

Initial Issues (and Fixes):

• Zappi scheduling conflict: Originally, my EV charged at peak times despite scheduling in both Zappi and Octopus apps. Removing the charger from Octopus and setting schedules directly in Zappi fixed this after the installer came back to fix a problem with clamps.

• Tesla not exporting from battery: Initially, only solar was being exported. Adjusting Permission to Export and Energy Export = Everything resolved that after trying different peak, off peak and mid peak settings.

• Colour difference on one panel: Raised with the installer/ manufacturer advised it should blend over time, but I opted for a partial refund instead of replacement.

Performance & Observations:

• Powerwall discharges at ~10 kW (DNO) and can recharge fully from the grid in roughly 3 hours at off-peak rate (7.5p/kWh).

• I’ve experimented with forced discharges to take advantage of export.

• The system comfortably covers evening loads with minimal grid import.

Next (future project in the coming two years):

Looking into adding a Mitsubishi split air-conditioning system for efficient summer cooling (mainly one downstairs and two upstairs units) to integrate with the system.

Overall, I’m pleased with the setup. Hopefully, this helps anyone considering a similar system.

Thanks again to Screwdriva and all members who helped guide me through the setup process!