In the 1970s & 1980s the interest in green power was driven by the goal of replacing fossil fuels after the first oil shock in the mid 1970s
Now, the broader goal includes minimizing the emission of CO2.
WHY GREEN POWER? There are considerable external costs for electricity from fossil fuels that someday must be taken into account as concerns about global warming become real. While contributions from renewable energy is small, with the exception of hydro, their market penetration is growing at a much faster rate than from conventional sources.
As the concerns about the availability & environmental impacts of fossil fuels become more wide spread, the interest on environmentally benign renewable energy technologies will surely take center stage among engineers & policymakers.