# Optimal Design of a Residential Photovoltaic Renewable System in South Korea
## 1 Introduction  
South Korea is in the world's top 10 energy-consuming countries, and it heavily depends on imports of fossil fuels (natural gas, coal, and oil) [1; 2; 3]. Due to recent public awareness regarding the issue of polluted air, pressure to reduce its dependency on fossil fuels has increased. In addition, the Fukushima disaster that occurred in Japan has caused the present government to support the nuclear phase-out policy.  
Therefore, various renewable energies (photovoltaics (PV), wind, geothermal, hydro, biomass, fuel cells, etc.) have been currently developed, which also helps in the country's pledge at the 2015 Paris Climate Conference to cut its carbon emissions by 37% below the business-as-usual (BAU) level by 2030.  
In addition, the Korean government has recently declared a national project aiming for power generation by renewable energies to account for 20% of the total generation output by 2030 (85,905 GWh (13.6%) by 2025 and 134,136 GWh (20%) by 2030) [4]. This project especially focuses on PV and wind energies (more than 75% with respect to the generation capacity, and more than 50% with respect to the generation amount). The Korean government plans to provide urban-type self-sufficient PV systems to 760,000 residential houses by 2022, and 1,560,000 houses by 2030 [5].  
To this end, as one of practical efforts, Korean government already ruled that 5% of total construction cost should be invested in renewable energy system for large public buildings (total floor area is greater than or equal to 3000 m\({}^{2}\)), and it also subsidizes 60% of the construction cost if private residential buildings install PV renewable systems [6].  
Korean government also plans to promote rural-area PV systems using low-interest loans and higher-weighted RECs (Renewable Energy Certificate). The REC is a market-tradable and non-tangible instrument that certifies that the owner possesses one megawatt-hour (MWh) of electricity generated from any renewable energy resource [7]. RPS (Renewable Portfolio Standard) required for large power producers (\(\geq\)500 MW) also works well after FIT (Feed-In Tariff) system ends. In order to enhance the social receptivity to PV systems, the Korean government has approved private enterprisers, to gather individual private investors, to join in PV development projects.  
The objective of this study is to propose an optimal model for residential PV system design. In this model, the construction and management costs will be minimized, while considering various practical design factors such as PV generation amounts with different tilt angles, the Korean progressive electric rate, the unit cost of a PV panel, the interest rate, the project period, the electrical usage of general electric appliances, and seasonal appliances, lighting appliances, and stand-by power.  
The rest of this paper is organized as follows. The optimal design model for the residential PV system is proposed in Section 2. Residential electricity demand is broken down in detail, and the monthly electrical generation amounts with varying tilt angles are proposed in the form of polynomial functions in Section 3. The optimal design solution is obtained by using an evolutionary algorithm, and compared with that from previous gradient-based methods in Section 4. Finally, in Section 5, we conclude our paper with some future directions.