FSO (Floating Storage and Offloading) Vessel is type of vessel used in upstream oil and gas industry to store and deliver crude oil or condensate from subsea well to trading tanker or pipeline. FSO Kakap Natuna owned by Government of Indonesia used in Natuna Sea, operates diesel engine for supplying its electrical demand. The vessel has constant operation as well as its electrical load with daily average is 11.18 MWh/day. The consideration of installing photovoltaic in this vessel are: solar radiation in that area ranging from 4.21 - 5.00 kWh/m2/day, wide surface deck with less facilities, and the cost efficiency especially related to Cost Recovery of upstream oil and gas industries. The calculation gained the usage of 6,903 m2 area in vessel's deck and 3,551 unit of solar panel that generates up to 5.6 MWh/day. Feasibility study of this installation come up with yearly cost reduction of US$ 829,687 and 4 year return period of investment. This beneficiary may lead into further policies of having such installation on FSO owned by Government that operates in prolonged period or lease FSO with charter period more than 4 years.