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Oat Errish Farm

When EvoEnergy were contacted to design and install a bespoke solar PV system for a project to be featured by Grand Designs, they jumped at the opportunity to get involved. Below is the story of how EvoEnergy worked with the client to achieve a unique PV system that was required to integrate seamlessly with a challenging curved timber roof.

Although EvoEnergy no longer install solar PV on domestic properties, in 2016 they received an unusual enquiry that their technical and design team were excited to make an exception for. Far from a typical domestic property, Stephen Tetlow and his Wife, Elizabeth, were embarking on a challenge to build their dream home in the Devon countryside, using a snake-like ‘spiral’ design inspired by a fossil they had found in their cottage garden.

Using his extensive career experience in electrical and mechanical engineering, Stephen designed a home that combined several innovations to create something truly unique. This included a curved timber roof and large windows to let light flood in to the 5-bedroom, 2-storey home in addition to utilising low-carbon technologies such as solar PV and geo-thermal for power and heat. The design was also led by their ambition to create a build that ensured the isolated house would connect firmly with the surrounding meadows.

The project plans and value of the build were so captivating that it caught the attention of Grand Designs who decided to feature the ‘Snake House’ project on their Channel 4 programme (see bottom of page for video).

Given the complexity of the design, the project commanded a bespoke solar PV solution that integrated seamlessly with the curved wooden roof panels. The installation of the PV system would also be periodic; the mounting/panels, wiring and inverters would need to be installed at different times around the various construction phases of the build.

Snake house solar panels

Given there was no ‘off-the-shelf’ solution that would work in this scenario, EvoEnergy approached a panel-manufacturer to create each module – 33 in total (5.34 kWp) – to their exact specification including size, flexibility and lamination. As some sections of the roof accommodated larger panels, a few modules were manufactured with additional unique specification to the others; larger panels, that subsequently also produced a higher output.

The modules themselves were eventually formed from a number of polymer layers, designed to encapsulate and protect the silicon modules from weathering and cracking in the often harsh conditions found on the roof. To give an idea of the types of material designed into the layers; some are used for the windscreens of commercial airliners and also on vehicle coatings for Antarctic expeditions.

A large amount of ‘trial and error’ was put into the formation of the modules to achieve the tough enduring finish required; where glass, plastic polymer and aluminium traditionally offer tried and tested solutions.

The solar panel mounting system

During the early stages, EvoEnergy were involved in the decision making process with the Architects and Mr Tetlow to develop a mounting system for the solar panels that would allow a seamless roof integrated finish. Ventilation under the modules also needed to be considered to allow modularity in the event of future failures.

After several designs were experimented with, a metal ‘hockey puck’ system with angled brackets was decided as the best solution. Over this, a lattice of green oak beams was installed acting as a stable mounting frame for the panels, solar optimisers and cladding.

To minimise wind vibration of the solar panels, additional cross-bracing was added along the panel edges to achieve a strong solution for the client.

To ensure cables were correctly routed and out of view, EvoEnergy installed the panel cabling during the early stages of the build to ensure that the aesthetics of the property wouldn’t be ruined by external cables.

Due to the unusual shape of the house, each solar panel is mounted at its own individual pitch and orientation.


Given the bespoke specification of each of the solar panels – both in size and output – a traditional inverter and string set up would be highly inefficient and unable to cope with such complexities. EvoEnergy therefore used market-leading SolarEdge technology to overcome this problem.

The panels were turned in to ‘smart’ panels by connecting SolarEdge optimisers to the rear of each panel meaning that, regardless of its size, the technology would optimise its output individually before sending the output to the inverter; traditionally, without optimisers a domestic system’s output is only as strong as its least performing panel.

By connecting the SolarEdge inverters to the internet and sending monitoring data to SolarEdge’s online portal, the system’s generation as the sun rises in the east and moves across the sky can be seen in real-time via the portal’s graphical playback.

Grid connection

The project also required a new three-phase grid connection which presented a challenge when installing and commissioning the PV system. As the solar panels were designed to be the same thickness as the final cladding, by sitting flush this exposed the risk of a lightening strike on the PV system. EvoEnergy therefore installed a type II surge protection device to protect the system in such an eventuality.

This also required careful coordination with the local Domestic Network Operator (DNO) to ensure that the system was installed and then earthed. The PV system was commissioned separately once electricity had been connected to the property.

EPC and energy savings for the snake house

The Energy Performance Certificate (EPC) of the home is rated ‘A’ and estimates that the Tetlow’s will only pay around £50 per month to heat and light their large 244 square metre, 5-bedroom home. With the average energy bill for a ‘large’ home coming in around £125 per month, this highlights how much power will be self-generated onsite by the solar and other low-carbon technologies.

Quick Stats

  • Location Devon
  • System Size 5.34 kWp
  • Panel model GB-Sol
  • Inverter model SolarEdge
  • Anuual output 5,671 kWh
  • Annual CO2 savings 1,994 kg