CI-81-10-3 -- The AII-Day Efficiency of Collector Arrays in National Solar Data Network ✓ Most Recent

A critical aspect of the design of solar energy systems is the assessment of the performance of the solar collectors to be used. System designers usually use the single panel efficiency test results derived from the criteria of ASHRAE standard 93-77 as an input to their analysis of collector performance. The ASHRAE 93-77 test results are only indicative of collector performance under a narrow range of operating conditions. 'Therefore the ASHRAE test results need to be modified in order to predict performance since arrays of collector panels in a solar energy system are exposed to a wide range of system and environmental conditions which affect their efficiency.

In this paper, field data for collector arrays from operating solar energy systems in the National Solar Data Network are analyzed to determine array performance. Data are collected every 5 min. and 20 sec. for collector array inlet and outlet temperatures, array flow rate, and outdoor ambient temperature. In addition, total insolation in the plane of the collector array is sampled every 32 sec. and 10 values are averaged to provide one value for the 5 min. and 20 sec. period. Hourly, daily, and monthly collector array efficiencies are then calculated from these data.