Investigations of a 20 year old air-based solar installation were made to quantify the degradation of system components as well as operation of the system as a whole. The current solar fraction of the system is extremely low at 13 percent. Experiments show a marked degradation in both the transmittance-absorbance product and the loss coefficient of the collector array. The pebble beds were also subject to high losses through the building foundation as well as non-uniform flows caused by an obstruction in the upper plenum. The effects of these degradations would lower the solar fraction from an optimum of 44 to 32 percent. The low value for the current performance is attributed to poor sensor placement and the control strategy.
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