Uncertainty in estimating the performance of solar thermal systems

The scope of this article is to present a methodology for the estimation of the uncertainty characterizing the energy performance of solar domestic hot water systems. The work concentrates on the uncertainty characterizing the expected annual energy output, as calculated through tests implemented according to the valid international standards. In order to cope with difficulties related to the algorithmic character of the measurement model, which cannot be explicitly formulated, Monte-Carlo simulation techniques are implemented. The component of uncertainty associated with measurement errors is estimated, on the basis of the metrological quality anticipated by the relevant testing standards. Errors due to imperfections of the energy model used through the test are also counted in, as well as uncertainties attributed to the variability of meteorological conditions. The proposed uncertainty analysis allows the realistic assessment of the actual energy provided to the user by a solar domestic hot water system. Implementation of the proposed methodology for a typical system leads to an expanded uncertainty in the order of 9% for the expected annual energy output.