Airplus Renewables — XEVA — from prototype to certification, an engineering partnership with a rooftop vertical-axis wind platform
An ongoing commercial engineering partnership running the XEVA programme from prototype through certification. Generator selection, baseline CFD, iterative aerodynamic optimisation across rooftop typologies, wind-tunnel validation, and a mounting-system engineering conclusion that has shaped the product architecture itself.
The starting position
Small-scale rooftop wind has a reputation problem. The market has been shaped by a first generation of products that over-promised on siting flexibility, underperformed against marketing-case annual energy yields, and in many cases failed to reach certification at all. The underlying physics is the explanation. Wind flow over a building is not the wind flow over open terrain. Structures force the incoming wind to accelerate at the windward wall, separate at the roof edge, form a recirculation bubble over the central roof area, and re-attach downstream with elevated turbulence intensity.
A turbine placed a few metres away from its designed-for position can move from an acceleration zone into a dead zone. Turbulence increases vibration and fatigue loading and shortens service life. Power in the airstream scales with the cube of wind speed, so modest siting errors translate into large energy shortfalls. The underlying building aerodynamics are unpredictable from first principles — parapets, HVAC plant, neighbouring buildings, and roof edge geometry all alter the flow field in ways that empirical siting rules cannot fully capture.
Airplus’s product thesis is that the answer is an engineered system, not an off-the-shelf turbine bolted to a roof. XEVA’s design intent integrates the turbine aerodynamics, a tolerant multi-directional intake geometry, a mounting that permits post-install repositioning as actual on-site wind patterns become clear, and onboard storage and smoothing so the deliverable power profile is shaped to the host site’s demand rather than the raw instantaneous generation. Delivering that thesis requires an engineering programme with depth — not just a turbine design, but a siting, mounting, and power-conditioning system engineered against verified building-flow physics.
What we did
Hatch Oxford was engaged in May 2024 as the engineering partner for the XEVA programme, under a multi-year consultancy framework with work packages agreed sequentially against the product roadmap.
Phase 1 — Prototype and generator selection
We began with the generator. The Airplus base-model prototype specification needed a generator matched to the turbine’s rotor characteristics, expected operating envelope, and the power-conditioning architecture downstream. We ran the selection against the technical specification and delivered a generator choice that conformed to the prototype requirements — the first commitment in the engineering programme and the foundation on which the later aerodynamic and power-profile work would be built.
Phase 2 — Baseline CFD
Immediately after generator selection we commissioned the baseline CFD model for the base-model turbine, working through an agreed specialist sub-contractor. Baseline CFD is the entry condition for any serious rooftop wind programme — without a defensible CFD view of how the turbine interacts with characteristic building-flow regimes, there is no basis for rotor refinement, intake geometry development, or siting guidance. The baseline model established the flow fields in which the turbine would be expected to operate and the aerodynamic boundary conditions the rotor would need to perform against.
Phase 3 — CFD iteration and wind-tunnel validation
From the baseline we moved into iterative aerodynamic development. Building-flow scenarios were characterised across the representative host-site typologies — long flat-roof warehouse and industrial buildings, multi-level hospital and commercial roofs with HVAC plant and parapet disturbance, and dense urban settings with street-canyon vortex behaviour. For each typology, CFD was used to identify where on a given roof the turbine would see productive flow versus where it would sit in a recirculation bubble or a high-turbulence wake.
We then took the prototype into wind-tunnel testing to validate the CFD predictions against physical measurement. The combined CFD-plus-tunnel dataset has driven design iterations on the rotor, the intake geometry, and — importantly — the mounting system, where the emergent engineering conclusion was that post-install repositioning capability is a product requirement rather than a nice-to-have. Empirical siting rules are not sufficiently predictive for every real-world rooftop. The product needs to accommodate adjustment once the installed behaviour is observed — and that is a mechanical and mounting-system decision, not a software one.
Phase 4 — Certification (current)
The programme is now in the certification phase. Small-wind certification is where the market’s credibility problem historically originated, and it is the gate XEVA needs to pass cleanly to differentiate the product from the rooftop wind category’s legacy reputation. The certification work is ongoing and specific details remain commercially confidential to Airplus.
The commercial move
The engineering conclusion that reshaped the product architecture is that on a building, siting — not the turbine itself — is the binding constraint on rooftop wind generation.
That reframes the product. XEVA is not “a rooftop wind turbine” but a rooftop wind system — turbine, tolerant intake geometry, repositionable mounting, onboard storage and smoothing — engineered against characterised building-flow physics rather than idealised free-stream conditions. The product positioning on the deliverable power profile (clean, buffered, retrofit-compatible, additive to existing solar and storage assets) follows from the engineering conclusion, not the other way round.
For a small-wind product heading into certification, that positioning matters commercially. It is the honest answer to the market’s legitimate scepticism about rooftop wind — not a marketing claim that the turbine works anywhere, but an engineered system designed for the specific flow regimes real buildings actually generate, with the mounting flexibility to tune siting empirically post-install.
What the engagement has produced to date
- A generator selection conforming to the base-model prototype specification.
- A baseline CFD model of the base-model turbine in characteristic building-flow conditions.
- Iterative CFD development across warehouse, multi-level commercial, and dense-urban rooftop typologies.
- Wind-tunnel validation of the prototype against the CFD predictions.
- A mounting-system engineering conclusion — post-install repositioning as a product requirement — that has shaped the product architecture.
- Current-phase engineering support on the certification pathway.
Why it matters
Rooftop wind has been a sceptical category for a decade — and for good reasons. Most products that reached market did so without the building-aerodynamics engineering depth the physics requires, and the category’s credibility has paid for that. The way back into the category’s credibility runs through CFD-anchored siting work, physical-test validation, certification, and product architectures that accept the unpredictability of real buildings rather than pretending it away. That is a longer, slower engineering programme than the first-generation entrants ran — and it is the programme the market needed them to run.
The broader point is that decentralised energy for high-dependency sites — hospitals, data centres, industrial facilities, coastal infrastructure — is a market in which the winning products will be those that deliver a reliable, buffered power profile, not raw generation; and that can be sited into the messy real-world environments their host sites actually present, not the idealised conditions a spec sheet describes. Getting to that product shape requires engineering partnership across the full arc from prototype to certification, and the willingness to let the engineering evidence shape the product architecture.
A note on status
The engagement is ongoing. Certification work is live. Specific technical performance data, siting methodology detail, and certification-pathway specifics remain commercially confidential to Airplus Renewables.
