Development of an analytical model for the daily performance of solar thermal systems with experimental validation

Flat plate collectors are the most widespread solar thermal collectors for low-temperature level applications as domestic hot water production and space heating. The objective of this study is to present a simple and analytical model for the prediction of the daily performance of an integrated system with flat plate collector. The developed model is tested with experimental results from a laboratory integrated system. This experimental set-up is investigated with details in order to determine its thermal performance and its dynamic response. After the validation of the developed model, the model is extended to realistic weather data for the climate conditions of Athens (Greece). The integrated system is evaluated energetically and financially by examining twelve typical days, one for every month. It is found that the investigated system can produce 2171 kW h thermal energy during the year with a mean thermal efficiency equal to 54.24%. The payback period is calculated at 5.03 years, an acceptable value which indicates sustainability. The present analysis clearly indicates that the developed model can be used for quick and accurate calculations on solar thermal systems in order to evaluate and optimize them on a daily basis.