Sensitivity of shading calculations to horizon uncertainty

Planning for solar power installations requires assessment of potential shading by nearby obstacles on the horizon. A degree of uncertainty exists in measurements of the horizon from the point-of-view of the proposed solar collector. This uncertainty takes the form of errors in the measurement of the azimuth and altitude of obstacles that may cause shading. We modeled irradiance reductions due to shading simulated horizon position measurement uncertainty. Results indicate that the sensitivity of solar simulations to horizon measurements is relatively low (around 2% per degree error for the most sensitive case observed). Beam and diffuse irradiance showed similar sensitivity to horizon measurement errors, and experienced similar trends in sensitivity relative to azimuth and altitude errors. For all cases, sensitivity to altitude errors was observed to be greater than sensitivity to azimuth errors. Conservative estimates of uncertainty in predicted irradiance based upon an existing measurement technique were around 3%.