This study aims to supply electricity energy via a hybrid PV(photovoltaic)-Diesel-Battery for a summer house which is located remotely from the grid connection in Kilis province of southern Turkey (Latitude: 36° 43', Longitude: 37° 07', Altitude: 664m). Summer houses are widespread in this area, and it is impossible for these buildings to benefit from grid connection. Optimal sizing of hybrid PV-Diesel-Battery systems prove to be very economical as an energy source for these houses. The optimization demonstrated that the lowest investment cost was 12,400 Turkish liras, and renewable energy part of the proposed system was calculated as 79%. In this respect, the system was optimally sized with a PV of 3kW, a diesel generator of 1kW, a converter of 2kW and 6 units of battery. PV panels and diesel generator generate 4248 and 773kWh/year, respectively, which amounts to 5021kWh/year. This is a Hybrid PV-Diesel-Battery system. It consists of renewable (PV System) and non-renewable (Diesel Generator) energy sources. Therefore, this paper focuses on optimal sizing of the proposed system. Total annual energy demand is 2353.8kWh/year, and the remaining amount is stored in the batteries. Total renewable production divided by load, total renewable production divided by generation, and renewable energy part of the proposed system are 116.38%, 84.6%, and %79, respectively. In addition to its cost effective energy supply, the system is also environment-friendly. Hybrid PV-Diesel-Battery system prevented 44.024 tCO2, 123.39kg of CO, 13.471kg of UHCs, 9.16kg of PM, 90.52kg of SO2 and 1100.33kg of NOx. This study can also be adapted for other cities and regions.