Consider that you want to replace an electric water heating system with a thermal solar panels array. The total cost of the panels is $2,000 and the government provides a 30% cost subvention to incentivize this kind of change. Based on an energy audit, the existing water heater uses 200 kilowatt-hours (kWh) of electricity monthly, which currently costs $0.12 per kWh (price that increases 3% per year). If the solar heaters have an expected life of 10 years and can save the total cost of heating water with electricity, Find the internal rate of return. b. What is the simple payback period of this investment? a