Can an absorber made of aluminium fins clamped to copper tubes outperform a conventional absorber plate? That question drove a TÜBİTAK 1707 R&D project (no. 3225044) we ran with Innorma R&D, Solimpeks' R&D start-up, from December 2022 to May 2024. The goal: an absorber design that lifts the performance of both thermal and hybrid PVT collectors while making production feasible locally in Turkey.
What did we build?
Ten prototypes in total:
| Prototype group | Units | Configuration | | --- | --- | --- | | Standard thermal collector | 1 | Wunder ANSG 2108 (reference) | | Standard PV/T collector | 1 | Solimpeks PV-T (reference) | | Finned thermal collectors | 4 | 7 or 9 absorber pipes; 150 or 315 fins | | Finned PV/T collectors | 4 | 7 or 9 absorber pipes; 112 or 229 fins |
The finned plates replace traditional absorbers with aluminium fins clamped to copper tubes — a construction that can cut costs and reduce shading at off-angles. It promises better heat capture in thermal mode and solid electrical output in PV/T, with peaks around 220–250 W under good sun, while staying lighter or more compact where needed.
How did the design take shape?
Work Package 1 covered design and simulation: SolidWorks 3D models, Flow Simulation CFD, and an EES mathematical model to predict heat flows. We tested configurations with 7, 9, even 11 pipes initially, and dialled in parameters such as 6 mm fin spacing, with boundary conditions — irradiation of 1000 W/m², ambient of 30°C — chosen to mimic Solar Keymark test conditions. Early runs showed promise, but also hinted that fewer fins might avoid shadows at 45° sun angles.
In Work Package 2, the prototypes took shape: aluminium sourced for fins, copper tubes assembled, and PV cells laminated over the finned structure for the hybrid versions. Work Package 3 refined the designs — simulations at oblique angles confirmed that high fin counts cast shadows and drop efficiency, so we halved the counts in places, to 150 fins for thermal and 112 for PV/T. In the models, that lifted outlet temperature differences from about 2.5°C in the standard units to 3.6°C in our 9-pipe PV/T. We scoped production lines, too.
What did outdoor testing show?
In Work Package 4 we rigged five thermal and five PV/T collectors in parallel, pumping water at 0.03–0.07 kg/s and logging irradiation, wind, temperatures at multiple points, and electrical output for PV/T — data every 5 seconds via dataloggers. The standard collectors edged ahead in direct sun, but the finned versions pulled ahead at angles, grabbing more heat when light slants. Electrical output held steady, with PV peaks at 250 W under 1000 W/m², aligning with Eurofins benchmarks, though clouds dipped outputs mid-test.
What were the hard lessons?
Simulations nailed trends but sometimes overstated gains — real tests showed smaller temperature boosts, possibly due to wind or uneven fins. Cutting fins solved shading but added weight in spots, nudging us to rethink materials. Sourcing took trials as well: aluminium rolls and precise crimping needed iterations, with early leaks fixed by adjusting tools. For industrialisation, a phased rollout (manual assembly first, then a dedicated line as volumes grow) looks like the most efficient route.
The gains were real, though. The finned design hit a 3–4°C temperature difference in oblique scenarios, which could mean real savings under variable sunshine. PV/T outputs matched the standards but with potential for cheaper local manufacture — our estimates peg amortization at three years with steady sales. One team huddle stands out: debating fin density late into a session, we landed on 112 for PV/T after scrapping a denser batch — the right balance of cost and performance. Localising absorber production also cuts import reliance and supports sustainability goals, and supportive local-production policy can speed the scale-up.
Who benefits from finned collectors?
Homes, hospitals, hotels, factories, and farms — anywhere reliable heat supports operations such as crop drying or greenhouse heating without heavy upkeep. Contractors and energy firms installing solar systems are key users too, especially those keen to swap imported absorbers for local ones to trim costs and boost self-reliance.
Where were the results published?
The PV/T results are published in a peer-reviewed paper: Büker M.S., Onay A.E. (Innorma R&D) and Dağ H.I. (Solimpeks), "Comparative Thermal and Electrical Performance Analysis of PV/T Collectors with Different Finned Absorber Configurations", Journal of Climate Change (2025), doi:10.70917/jcc-2025-028. The TÜBİTAK-funded study reports that the 229-fin PV/T variant has a 24.48 % higher CO2-reduction potential than the standard design.
What comes next?
Wrapped in May 2024, the project underscores our knack for turning ideas into practical solar hardware: finned absorbers can enhance collectors in non-ideal, real-world setups. Building from past efforts — hybrid systems and EU projects — we are mulling integrations such as smarter controls for variable weather. Reach out if you are keen on details or team-ups.
