Even if that number is correct for photosynthesis, there are lots of inefficiencies when it comes to converting the products of photosynthesis (biomass) into usable energy (electricity). Wood pellets burn well, but people forget that wood pellets use energy in their creation (drying) and transport (trucks). There are also a host of evils in terms of habitat destruction and emission of pollutants other than CO2. Solar panels can live quietly and locally, producing electricity directly rather than trying to convert it too and from biomass.