Few funds are drawn to geothermal projects because of that long payback period.

The segment is capital intensive and has a long payback period.

The long payback has left many shareholders unimpressed and the stock has fallen 7 percent in the past week.

Traditional solar photovoltaics have long payback times and are even trickier for the dumb electric grid to handle than wind.

The rating also reflects the company's increasing exposure to the commercial leasing property segment, which is capital-intensive and involves long payback periods.