According to a report by SBI Energy, the return on investment for solar power is better than for any other source of renewable energy, thanks to big technological improvements expected to drive down costs. The report said the cost of solar energy is expected to be $1 per watt by 2020, with the typical payback period down to three to five years instead of seven to 10 years.The "Global Solar Inverters Markets" report by SBI said the cost of large solar power will decrease by half about e