There is an opportunity to improve the efficiency of flat plate solar air collectors by replacing their conventional glass covers with lightweight polycarbonate panels filled with high performance aerogel insulation. The in situ performance of a 5.4m(2) solar air collector containing granular aerogel is simulated and tested. The collector is incorporated into the external insulation of a mechanically ventilated end terrace house, recently refurbished in London, UK. During the 7 day test period, peak outlet temperatures up to 45 degrees C are observed. Resultant supply and internal air temperatures peak at 25-30 and 21-22 degrees C respectively. Peak efficiencies of 22-36% are calculated based on the proposed design across a range of cover types. Measured outlet temperatures are validated to within 5% of their predicted values. Estimated outputs range from 118 to 166 kWh/m(2)/year for collectors with different thickness granular aerogel covers, compared to 110 kWh/m(2)/year for a single glazed collector, 140k h/m(2)/year for a double glazed collector and 202 kWh/m(2)/year for a collector incorporating high performance monolithic aerogel. Payback periods of 9-16 years are calculated across all cover types. An efficiency up to 60% and a payback period as low as 4.5 years is possible with an optimised collector incorporating a 10 mm thick granular aerogel cover. (C) 2012 Elsevier B.V. All rights reserved.