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Abstract--In this paper, the electrical response of a partially shaded photovoltaic (PV) array, comprising several strings connected in parallel, is investigated. The PV array is simulated by employing an enhanced version of the widely used single-diode model, reformulated in an explicit manner employing the Lambert W function. The multiple maximum power points (MPPs) that appear on the P-V characteristic of the array in partial shading conditions are analyzed, in terms of their number and properties. Simplified empirical expressions are then derived to calculate the voltage, current and power for each local MPP, at any irradiance level and temperature, using only datasheet information, in a most simple and straightforward manner, without resorting to detailed modeling and simulations. The derived formulae are validated using both simulation and experimental results.

The generation management concept for non-interconnected island (NII) systems is traditionally based on simple, semi-empirical operating rules dating back to the era before the massive deployment of renewable energy sources (RES), which do not achieve maximum RES penetration, optimal dispatch of thermal units and satisfaction of system security criteria. Nowadays, more advanced unit commitment (UC) and economic-dispatch (ED) approaches based on optimization techniques are gradually introduced to safeguard system operation against severe disturbances, to prioritize RES participation and to optimize dispatch of the thermal generation fleet. The main objective of this paper is to comparatively assess the traditionally applied priority listing (PL) UC method and a more sophisticated mixed integer linear programming (MILP) UC optimization approach, dedicated to NII power systems. Additionally, to facilitate the comparison of the UC approaches and quantify their impact on systems security, a first attempt is made to relate the primary reserves capability of each unit to the maximum acceptable frequency deviation at steady state conditions after a severe disturbance and the droop characteristic of the unit’s speed governor. The fundamental differences between the two approaches are presented and discussed, while daily and annual simulations are performed and the results obtained are further analyzed.

Hybrid power stations (HPSs) are virtual power plants comprising storage and renewable energy source facilities operated in a coordinated manner as dispatchable stations. The HPS concept has been introduced as a means to increase renewable penetration in saturated island systems. The main objective of this study is to shed light on the operation of batterybased HPSs in small-island systems and their investment feasibility. Anticipated benefits for the island system are quantified in terms of system production cost and renewable penetration, while the exploitation of available renewable energy by the HPS is analyzed and the internal operation of its components is evaluated. A mixed integer linear programming generation scheduling approach is used to conduct daily and annual simulations of the entire island generation system, while at the same time optimising the internal management of the HPS as well. Based on the operating results thus obtained, the economic feasibility of battery-based HPS investments using wind, photovoltaics or their combination as the renewable generation component is assessed, by utilising the levelised cost of energy as the primary evaluation index and accounting for the life expectancy of the HPS battery storage system.