Solar radiation contributes to surface energy balance, purpose PVGIS irradiation estimates depend on receiving planar geometry. We quantified the effect of changing flat tilt from 18° to 30° for Bikoro and Inongo during 2020 2023. Forty eight monthly peer per site were analysed using absolute and relative differences, paired t tests and Wilcoxon signed rank tests. In Bikoro, mean irradiation decreased from 152.43 to 143.85 kWh m 2 month 1, corresponding to 8.57 kWh m 2 month 1 5.91 on average across months . In Inongo, it decreased from 154.12 to 146.27 kWh m 2 month 1, corresponding to 7.84 kWh m 2 month 1 5.44 . Differences were statistically clear at both sites Wilcoxon, p 10 6 , but reversed during May–July, when the 30° plane received slightly more energy. T2m remained unchanged because it is an atmospheric variable independent of planar orientation. Tilt is therefore a modelling parameter that must be reported explicitly and should not be interpreted as a change in local climate. PVGIS SARAH3 solar irradiation flat tilt sensitivity analysis Central Congo Basin Bikoro Inongo. 441-444 Issue-5 Volume-10 Mambu Tshipasi le Fils | Ngindu Buabua David | Mumay Muluba John