Performance Of Solar Thermal Systems Research Articles

A new look at the long-term performance of general solar thermal systems

This work addresses the problem of evaluating the long-term performance of solar thermal systems, which is quantified through the monthly or seasonal/annual solar fraction. It is shown that for a general solar system it may be expressed as a function of monthly utilizabilities, calculated for two different temperature (radiation) levels, which correspond to minimum and maximum operating temperatures. Both systems without storage and with storage are considered. Examples for solar cooling and solar cogeneration systems are shown.

An analytic model for the long-term performance of solar thermal systems with well-mixed storage

A simple analytic method is presented for predicting the long-term performance of solar thermal systems with well-mixed storage and loads that do not vary significantly from day to day. Recognizing that most conventionally designed systems have effective relaxation times that are long relative to the time scale of variations in insolation, but short compared to the time scale for day-to-day variations in insolation, we invoke a constant radiation model and solve the problem within that framework. The results of the analytic method are simple closed-form expressions which enable the user to understand clearly the dependence of system performance on the physically important variables. Good agreement is found between the predictions of the analytic method and the corresponding results of the F -f-chart method and computer simulations. The analytic method is furthermore applicable to all collector types and storage fluids and is not restricted to flat plates and hot water storage. The limitations of the analytic method are discussed and found not to introduce a serious restriction for commonly designed conventional systems.