There are many different models for justifying solar systems. One needs to take into account that the rewards of Solar are not measured over a few weeks or months, but rather a period spanning a few years. Battery based systems will always take a few years more than Grid-tied systems for the ROI to pay off. The most important factor is that it has a definite value, which is added to the value of the house. We recommend taking 75% of the pre VAT price of any system, and ‘capitalising’ that onto the value of your home or building. You can depreciate this ‘investment’ over say 25 years and work back your ROI. Most serious investors acknowledge that solar gives a better return than the Stock and Bond markets. Of course, as Eskom prices climb (and they will, increasingly, after they privatise!) so the value increases.