The large oak tree makes 2.2 metric tons of wood over the 50 year growth lifespan. This wood has the heating value of 20 MJ/kg. Tree has the canopy of 10 meters in diameter and canopy gathers solar energy over 6 month growing season every year at average rate of 177 W/m2; suppose no solar energy is collected during other 6 months when tree is dormant and looses it's leaves.
i) Determine tree's efficiency for converting solar energy to wood heating value.
ii) How this compares to commercial photovoltaic cells today?