Our home is located in Suffolk (East Anglia, UK), one of the sunniest and driest parts of the UK. Our house faces 154° South (i.e. 27° to the East of South) and the main roof is inclined at 40°. This means it is pretty much ideally orientated for solar PV energy collection according to this orientation calculator. We undertook our first smart home solar installation project in October 2022 and have been really please with the benefits, savings and improvements to our quality of life.

In 2024 we started planning our smart home extension project and it made a lot of sense to consider adding solar panels to the new roof area that will project out from the rear of our home as this would extend the time we generate useful solar power by several hours.

We decided to install "in roof solar panels" on the new extension roof. This gives a sleeker finish and works nicely with the planned Velux windows.

The East facing roof is big enough for the Velux window and 6 × 405W (2430W) solar panels. It will mean we start generating earlier in the day and generate more during day.

The West facing roof is the same size and it will mean we generate much later into the evening and more in the 'peak rate' period.

These solar panels will be partially shaded at times by the existing roof, so we plan to use Enphase microinverters again.

The main reasons for choosing an 'in roof' solution are the aesthetics and the ability to integrate seamlessly with the Velux windows.

We know that in roof solar panels can be less efficient as they get hotter but, they will not be South facing so this will be less of an issue. In roof solar panels are also more expensive to fit. With an in roof solar system, we do not require any bird protection mesh.

In-roof solar panels still require a 400mm border around them. One challenge with in roof solar installations can be finding panels that fit in landscape orientation.

The GSE in-roof mounting system seems a popular choice. They use plastic trays but, they seem to work with many types and size of panels and they have also partnered with Velux. GSE have a list of panels that they certify to work with their mounting system.

With this system the panels are lifted slightly off the trays and trays work as a gully system for rain. This combined with the large raised holes (4 per panel) allows airflow and hence cooling.

The Viridian in-roof mounting system seems to be very well regarded in the solar Facebook groups but it is more expensive. The Clearline Fusion modules fix directly to the roof structure.

Viridian provided a design based upon six PV-16 405W solar panels and a single MK08 Velux window. Whilst the architects drawings had two windows on each side, this design works better in my view. This provides 2430W of panels on both roof aspects and with Enphase IQ8HC microinverters, each roof could deliver up to 2280W.

It is possible to predict the monthly energy generation for both aspects using the European Union PVGIS service. The numbers generated by this tool do not factor in the shading that occurs due to our existing roof though. For simplicity we have assumed the front of our house is 30° East of South. In reality it is 26°.

For now, I have assumed the peak output of the solar panels on each new roof aspect is 2400W and that each roof will slope at 45°.

In the middle of summer, the sun is rising from 60° at about 6am above our neighbours house, so it hits the East facing roof. The sun is high enough to hit both the East and West roof through most of the day. It sets to the West and hits the horizon at around 9pm and at 300°

In the middle of winter, I don't think the sun gets high enough to directly hit the East & West facing roof aspects during the day but, time will tell!

The PVGIS figures show that the new solar panels would add about 3900kWh per year. Our existing 6.63kW South facing roof generated 7400kWh in 2023.

The combined figure is 11,300kWh and about 53% more than we currently produce over a whole year. We generated 10.6MWh in 2025 (not a complete year with this added solar), so these estimates look a little high. They do not factor in the complex shading though.

The additional solar panels will not just provide more peak power. They will widen our daily generation curve (this one is from July 2023), to start generating more power earlier in the day and to then continue generating more power much later into the day. This means more energy will generated each day and a lot more energy will be generated in the 'peak rate' evening period. The 'tail' currently captured at the end of each day will be filled out. In theory, we could produce more than 70kWh on a good day.

I looked at adding a second Tesla Powerwall to our system, to ensure some of the planned HVAC components can run on cheap rate electricity throughout the whole day. It would also mean we could run our home through longer power outages and the two Powerwalls would be able to handle house loads up to 10kW. Both would charge at 5kW too and take less than 3 hours to fully charge on cheap rate electricity.

These Enphase IQ8HC microinverters fix underneath each panel and deliver 230V ac power from the roof. They are rated at 380W continuous power, which is perfect for the 405W Clearline Fusion panels. They ensure that we extract maximum power at all times, despite the complex shading that occurs on an East and West facing roof with a gable that points North and is behind the main roof to the South.

We have Enphase IQ7A microinverters on our South facing roof as part of our original smart home solar installation project and the performance has been exceptional.

The Clearline Fusion solar panels are held in place by bespoke clips that align with the joists at the top and bottom. Different bespoke clips are also fixed to the battens and stop sideways movement.

The gaps between the panels are filled with a trim piece, to keep a smooth, flat profile.

The East facing roof starts generating energy much earlier in the morning than our South facing roof. In May, all the panels appear to be in direct sunshine for most of the day.

The West facing roof generates energy much later into the evening than our South facing roof. They have direct sunlight nearly two hours after the South facing panels have ceased generating useful power. In May, all the panels appear to be in direct sunshine for most of the day.

The Viridian system is tiled around once the panels and flashing kits have been installed.

The Viridian system is tiled around once the panels and flashing kits have been installed.

With Enphase microinverters you get individual panel monitoring and each installation may also be set up into sub-groups of panels. Within the Enphase Enlighten app microinverters are also grouped into 'strings' with a maximum limit. My 'System' has two parts currently, the main 'South Facing Roof' and the panels in portrait orientation grouped as 'South Facing Roof Lower'.

The lower panels see the sun a tiny bit later in the morning and the panel orientation makes no difference at all to the amount of energy generated.

The app now shows each roof aspect and I can see how much each contributes to the generated power.

I've asked to installer to add another CT clamp to show both solar installations and to enable me to monitor and compare them. This is what the MyEnergi app view looked like before the extension install. The Zappi has only got three CT inputs (+ the EV charger internal input) and as you can see above they were all in use. The 'house' figure is actually calculated based on the other inputs.

I was hoping to add another CT clamp to enable independent monitoring and data collection for both the old and the new installations but, this is not possible. As a work around, I moved the CT3 from the battery to the new solar system and this appeared to work when looking at the measured power level on the Zappi display. Annoyingly though, the app aggregates inputs of a similar type into one icon and associated graph. I also lose the ability to see what the battery is doing but, at least the Tesla app gives a view on this.

I ended up changing my first solar installation type to 'generation and battery' and this allows me to see what both solar systems are generating at any one time. I can only log the data for the new East + West solar system though. This will at least allow me to see how it is performing.

I also asked my installer to add another CT clamp to show both solar installations and to enable me to monitor and compare them. This is what the Tesla app view looked like before the extension install. The Tesla Gateway has 3 inputs but these are for a 3-phase system. To add another CT clamp would require a bespoke Tesla wireless clamp at a cost of £250 + installation + VAT. I passed on this and simply used the one CT clamp to measure the output of both solar systems, so the app view is unchanged but the total solar generation is much higher.

This is our generation history, showing the impact of the new extension solar.