Residential or small scale commercial solar installations require site surveys in the planning stage to evaluate obstacles that may block light access to a planned array or collector. This can be done by remote sensing techniques and later refined by on-site evaluations. A variety of tools exist to perform these evaluations. Techniques are available in literature for calculating the effect of this known horizon profile on the expected irradiation available to the collector. In this paper, we evaluated the sensitivity of the irradiation to uncertainty in the horizon profile measurement using software written in Python. Uncertainty in both the azimuth and altitude of the horizon can originate from several sources depending on the tool being employed. The uncertainties in measurement couple with the various approximations made in the use of conventional tools such as System Advisor Model (SAM), to produce a cumulative uncertainty. In order to estimate the sensitivity, a set of hypothetical horizon profiles were generated and annual and monthly irradiation were estimated based on TMY3 solar resource data. Estimates of the impact of the horizon profile on the solar resource were made using shading calculation techniques from literature. Variations in the altitude and azimuth of the horizon profile were introduced and the resulting impact on the estimated irradiation is reported. This data may guide interpretation of site survey measurements and future tool development.