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. 26° 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 in 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 this new roof area that projects out from the rear of our home, which faces North.

We are investigating the use of 'in roof' solar panels to cover the new extension roof. This will give a cleaner more integrated look and the solar solution we are looking at is designed to integrate with our planned Velux windows too.

Image shown is by our architect, RAG Designs and modified by me to show the new roof aspects.

The East facing part of this roof is big enough for 2 Velux windows and >2800W of solar panels. It will mean we start generating earlier in the day and generate more during the summer days.

The West facing part of this roof is also big enough for 2 Velux windows and >2800W of solar panels. It will mean we generate much later into the evening and much more in the peak rate period.

These extra solar panels will mean we generate more energy though the summer days but, both aspects can be shaded by the existing roof in the winter months, so we plan to use Enphase microinverters again, to integrate with our existing Enphase based solar system.

The main reasons for choosing an 'in roof' solution are aesthetics, the ability to integrate seamlessly with the four Velux windows (two on each side) and the ability to avoid fitting a new roof and then covering it up with solar panels.

We know that in roof solar panels can be less efficient as they get hotter but, ours 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 would also not require any bird protection mesh.

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 Veridian in-roof mounting system seems to be very well regarded in the solar Facebook groups but, more expensive as it uses aluminium mounting trays.

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 2800W 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, the sun does not get high enough to hit the East & West facing roof aspects during the day.

The PVGIS figures show that the East facing roof would add about 1800kWh per year and the West facing roof another 2600kWh. Our existing South aspect roof generated 7400kWh in 2023.

The combined figure is 11,800kWh and about 60% more than we currently produce over a whole year.

These numbers are probably low. I think we can get more than 3200W of solar panels on both new roof aspects.

The additional solar panels will not just provide more peak power. They will 'fatten out' 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 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.

We are also looking at adding a second Tesla Powerwall to our system, to ensure some of the planned HVAC components can run on cheap rate electricity throughput the whole day. This will mean we can run our home using only cheap rate electricity and solar energy. It will also mean we can run our home through longer power outages and the two Powerwalls will be able to handle house loads up to 10kW. Both will charge at 5kW too and take less than 3 hours to fully charge on cheap rate electricity.