$7.(10$ pts$.)$ We talked about biomass and fossil fuels as ways of storing solar energy. It$$s been

estimated that the efficiency of conversion of the energy in sunlight to energy stored in the

chemical bonds of the products of photosynthesis $($in biomass$)$ is about $4\%.$ Assume that $2\%$ of

accumulated biomass eventually winds up being converted to coal. The efficiency of a reasonably

typical pulverized$-$coal$-$fired power plant, in terms of conversion of the chemical energy in the

coal to electricity leaving the plant to consumers, is $35\%.($a$)$ What is the overall efficiency for

conversion of sunlight to electricity via biomass and coal as intermediates? $($Notice that we have

not taken into account energy requirements for mining and transporting the coal.$)($b$)$ Look up the

efficiency of conversion of sunlight into electricity in a silicon photovoltaic cell. $($c$)$ Compare your

answers to a and b and comment on the comparison.