This paper presents a method for finding an optimal photovoltaic (PV) system according to Croatian legislation. The PV sizing model, in which a decision on investment is made according to economic indicators, is made using MATLAB Software. Based on the input data, the monthly PV system production is calculated, and electricity price formed. According to the PV system production and electricity price, economic indicators are calculated and obtained as output data. The model input data are solar irradiation, load diagram, PV system costs and market price of electricity while the model output data are PV system production, savings, profit, incomes, Net Present Value (NPV) and Levelized Cost of Electricity (LCOE). The obtained economic indicators are presented graphically and used for decision making on an optimal PV system size. The presented model is applied and presented in a case study.

In this paper, a method for finding the optimal size of an off-grid photovoltaic (PV) system regarding the Loss of Load Probability (LOLP) value is proposed. The proposed method is applied to an off-grid PV system in a scenario where an electricity supply needs to be provided during three summer months. According to the simulation results, 11 PV modules and 11 batteries are required with 0% LOLP. An increase in LOLP to 1% results in 10 PV modules and 7 batteries, and a 24.9% cost reduction. With 5% LOLP, the cost reduction is 39.3%, and with 10% LOLP, it is 49.5%. The use of less expensive batteries also contributes to cost reduction. With the modification of electricity consumption, one combination can be suitable for 4% lower LOLP, and the cost can be reduced to up to 7%. It can be concluded that the required increase in LOLP value leads to a decrease in the number of required PV modules and batteries and to the use of less expensive battery technologies, which then leads to cost reduction. Additionally, with the modification of electricity consumption, the amount of power deficit can be reduced, which makes one combination suitable for lower LOLP and also leads to a further system cost decrease. Lower system costs can encourage more people to invest in an off-grid PV system in locations with occasional consumption or consumption over only a few months. The cost reduction strongly depends on how willing users are to not have all their electricity demands met.