The lifetime of the project is taken to be 25 years. According to the avail­able information, the current interest rate and inflation rate in Nigeria are 12% and 8% respectively [15] and from this these, the annual real interest rate is determined as 3.7% using Fisher expression. This value represents current real interest rate. The initial fixed capital cost which can be used to prepare the site for the system and other initial installation costs is taken as $25000 and the overall system operation and maintenance cost of $1500 per year is assumed.