Ioulia T. Papaioannou

Modeling and Field Measurements of Photovoltaic Units Connected to LV Grid. Study of Penetration Scenarios

The operation of photovoltaic (PV) units connected to the grid is characterized by several uncertainties due to the number of currently operating units, the points where these units are sited, the exported power, and the injection of harmonic currents. The objective of this paper is to investigate the impact of the penetration of PV units in the low-voltage (LV) network. Thus, a model has been developed for the computation of load flows, harmonics, and voltages in the feeders. A PV panel is modeled as an irradiance-driven current generator, with an embodied maximum power point (MPP) tracking algorithm; it is connected to the network via electronic switches that represent the PV inverter. Simulations are performed with PSIM and Harmoniques simulator packages. Results from the simulated model are validated with data acquired from field measurements and bibliography. Finally, the acceptable penetration level of PV systems is investigated for several scenarios, depending on the topology of the LV network, the number, size, and locations of loads and PV units.

Harmonic impact of small photovoltaic systems connected to the LV distribution network

Since the penetration of photovoltaic (PV) systems in the low voltage (LV) distribution network is increasing, the need to register and model the contribution of these systems to the harmonic distortion of current and voltage waveforms is becoming an up-to-date issue. As PV systems incorporate power conditioning units, which are harmonic generating devices, they will have an influence on quality of supply, reliable operation of system equipment as well as component life expectancy. This paper investigates the harmonic impact of a 20 kWp PV system connected to the LV distribution network in Greece. The harmonic behavior of the PV plant as a function of the solar radiation under several weather conditions is analyzed. Measurements results are compared to those obtained from the power simulator package PSIMcopy. The level of penetration of PV systems in the LV distribution network without harmonic limits been exceeded is investigated.

Modeling and measurement of small Photovoltaic systems and penetration scenarios

The operation of Photovoltaic (PV) units connected to the system is characterized by several uncertainties due to the number of running units, the points where these units are sited, the exported power and the injection of harmonic currents. The objective of this paper is to investigate the penetration level of PV units in the low voltage (LV) network. Starting from field measurements a model has been created for the computation of harmonics and voltages in the grid. The PV unit is modeled as a dc voltage source connected to the network via electronic switches, representing the PV inverter. Simulations were performed in the simulator packages PSIM© and Harmoniques©. Results from the simulated model agree with the results obtained by the measurement campaign. Following this the acceptable penetration level of PV systems in the LV distribution network is investigated for several scenarios, referring the number, the locations and the operation of the units.

Reliability improvement resulting from the integration of PV systems in the Interconnected Greek Transmission System

Photovoltaic Systems (PV) are becoming one of the most developing investment areas in the field of renewable energy sources (RES). Environmental pollution renders the need for covering energy demands by renewable sources more imperative than ever. The aim of the paper is to use the estimated power production of PV units in order to evaluate the potential improvement of loss of load probability (LOLP) and loss of energy probability (LOEP). This analysis is implemented for the Interconnected Greek Transmission System (IGTS). The power output of PV units in Greece is calculated and the expected reduction of the above indices is demonstrated. Furthermore, peak shaving for the IGTS by the use of PV units is also illustrated. Finally, reliability improvement is expressed in terms of profit by comparing the cost for every kWh produced by PV units to the corresponding cost for every kWh produced by expensive units, which would otherwise cover a proportion of peak load demand.

Siting and installation of PV systems in Greece and their contribution in the reliability of the distribution network

A statement of the status quo of the PV power systems in Greece, as well as their possible contribution towards the enhancement of power distribution reliability, is the scope of the present paper. Siting and installation of PV systems is performed according to a recent Greek law and by considering environmental and geographical constraints. Meteorological data about solar radiation and temperature are computed, formulated and imported to appropriate software in order to simulate the PV units and generate their power output. The above estimated power production is compared to data concerning load shedding. Assuming that a specific proportion of the eventually unsupplied power could be provided by the accessed power generation of the PV units, the reliability of the distribution system is improved. This improvement is quantified using the distribution system reliability indices SAIDI, SAIFI and CAIDI. The resulting improvement is finally expressed in financial terms through the reduction of interruption costs.