Concentrating photovoltaics have the greatest performance for high solar efficiency, but current designs feature large high-profile tracking platforms that are expensive and laborious to install and maintain, and are vulnerable to even moderate winds. Moreover, their air cooling can only handle relatively low concentrations, and then only at elevated temperatures that can only shorten operating life. A previously described new approach has been implemented in a prototype that has been operating since last winter. This is an array of 450X concentrator utilizing 15mm-square water-cooled triple-junction cells, in lensed troughs that utilize flotation both for structural support and azimuth tracking. The troughs tilt as low as 24° solar altitude, for elevation tracking. The troughs float in only 14" of water, in circular ponds that can be close packed to cover 70% of the land with lenses, one-two orders of magnitude more effective land coverage than conventional concentrating systems, needing only two square miles per peak GigaWatt. The sealed troughs are mass-produced off-site and quickly installed by a small crew without any cranes or heavy machinery. Current costs are already under $2/Watt, and should drop in half for large-scale city-powering applications. The lens and auxiliary optics are discussed, and the water cell-cooling system is thermally analyzed.