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This work presents a discrete model for the thermo-hydraulic analysis of a novel polymeric solar thermal absorber with tapered headers and lens-shaped absorber strings. The numerical model developed is based on empirical correlations for laminar and turbulent flow regimes. The principal aim of this study is to ascertain if tapered headers help improve flow distribution in parallel-flow absorbers under laminar and turbulent flow conditions. In order to verify the model, the simulation results are compared to the measurement for total pressure drop and two studies from the previous literature for flow distribution. Altogether, a good agreement is found in all comparison cases, and the proposed numerical algorithm is proven to be robust and stable for complex thermo-hydraulic analysis. The results are then elaborated by comparing the tapered case to several conventional cases with cylindrical headers but with identical riser configurations to the original model. The results indicate that using tapered headers in compact absorbers with relatively large area ratios can noticeably reduce non-uniformity, especially up to middle range flows, by maintaining higher Reynolds numbers in the headers. The developed model can be used to optimize the hydraulic design of solar collectors with complex geometries and large area ratios. © 2022 The Authors