Depending on the solutions, you will find potential savings according to one or several of below: 

[Liters of kerosene saved per lamp x Price of 1 Liter of kerosene (USD)] - Solar lamps replace kerosene consumption and help households to save on fuel expenditure

[Mobile phone charging costs x Number of charges per year (USD)] - If solar lamps allow charging of mobile phones at home, they will reduce expenditures for charging mobile phones at a small business.

[Fuel savings in kg x Fuel price per kg (USD)] - Efficient cook stoves reduce fuel (charcoal) expenditure by 50%