Answer:
a) should install the solar cells
alternative 1, solar cells
initial investment $18,000
annual expenses $2,400 (5 years)
NPV = $27,097.89
AW = (10% x $27,097.89) / [1 - (1 + 10%)⁻⁵] = $7,148.36
alternative 2, power line
initial investment $27,500
annual expenses $1,000 (5 years)
NPV = $31,290.79
AW = (10% x $31,290.79) / [1 - (1 + 10%)⁻⁵] = $8,254.43
b) $23,307.10