How much energy that we can enjoy from sun

How much energy that sun can give us as a free gift? I stumbled across a term, solar constant (=1361 Watt/m^2), which means the maximum energy density that sun can give us is 1361 Watt/m^2.  This term is associated with the energy that our rooftop solar panels can generate and probably any engineer that learned Planck's radiation law before should know how to calculate this 1361 W/m^2.   Since sun surface temperature can reach 5800K, it will generate 2.04e7 W/m^2/sr energy flux density.   The subtended angle from earth to sun is 0.53 deg.  Therefore, maximum power density that sun can give us is 2.04e7 *3.14 *sin(0.53/2)^2 = 1370 Watt/m^2 (God never allows sun to give us more energy density than this solar constant!)  However, at average 5500K sun surface temperature and consumer-grade silicon solar panel can absorb only 0.4-0.8 um wavelength, sun only emits 7.4e6 W/m^2/sr to silicon solar panels.    This implies that solar panel can best absorb 7.4e6 *3.14 *sin(0.53/2)^2 = 500 W/m^2.   At 20% efficiency, no wonder most of the rooftop solar panel can only generate 100 Watt/m^2 (i.e., 7% of solar constant).  That means for 10m^2 rooftop solar panel, it can only generate 1 kWh electricity per hour.