Suppose you are deciding whether to install rooftop solar panels on your house. The immediate installation cost is $1100. A year from now, you will start collecting annual benefits equal to $300 per year. After collecting these benefits for 4 years, you plan to sell your house. Your stream of income for this project is therefore {-1100, 300, 300, 300, 300}. You only decide to invest if the present value of this stream of income is positive.