Antonios G. Marinopoulos

Grid integration aspects of large solar PV installations: LVRT capability and reactive power/voltage support requirements

The current work focuses on two specific issues concerning grid-connected solar PV units, i.e. the fault ride-through capability, also called low voltage ride-through capability, and the voltage support function through reactive power injection during faults. With the first one the PV unit can actually provide some limited grid support, whereas with a defined reactive power characteristic it can give a complete dynamic grid support. These two requirements, already known for wind power generation but new for the PV, have been recently introduced in the German technical guidelines for connection to the MV grid. Scope of the paper is to implement these requirements in a large solar PV plant, modeled in DIgSILENT PowerFactory, in order to understand its operation, and to evaluate its behavior and impact on the grid, in terms of stability and voltage support during grid fault.

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.

Investigating the impact of wake effect on wind farm aggregation

Aggregation methodologies for creating equivalent wind farm models are needed for power system transient stability studies involving large wind farms. One strong argument in the literature suggests single machine equivalent representation of wind farm with the assumption that all wind turbines receive the same incoming wind speed and thus operate at the same loading condition. In this paper, we examine how the validity of such single machine equivalent is affected under different wind speeds across a feeder in a wind farm with many WTGs. In particular, we compare the total active power output from the WTGs which indicates significant difference between single machine equivalent and full wind farm model under certain wind speed ranges and distances between the WTGs. We then conclude the need to use multi-machine equivalent representation for large wind farm in order to achieve adequate accuracy under the full range of wind conditions.

PV systems penetration and allocation to an urban distribution network: A power loss reduction approach

This paper examines the impact of Distributed Generation to loss reduction in power distribution networks. In specific, the way that penetration level and allocation of PV units in a distribution Medium Voltage feeder affects power losses is investigated. Different approaches, regarding PV units placement across the feeder and their capacity, are analyzed and useful conclusions regarding the penetration level of PV units and their optimal placement across distribution feeders for loss reduction are derived.

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.

A Correlation Index to Evaluate Impact of PV Installation on Joule Losses

This paper proposes a new correlation index, in order to connect the sizing and the siting of a PV unit with the respective impact on Joule losses of a radial distribution feeder. Randomly generated scenarios for PV units siting are investigated and based on the results the proposed index is formulated, corrected, and validated. The index incorporates factors such as: 1) the correlation coefficient between the installed PV capacity per node and the respective power rating of the distribution transformer, and 2) the size of a PV unit in relation to its distance from the feeding end. The importance of this index lies in the fact that it may be used from the DSO to evaluate the contribution of a new PV unit interconnection to the annual Joule losses of a line beforehand, and thus perform a better cost allocation.

Dynamic modelling of a grid-connected PEM fuel cell in a distributed generation network

This paper presents a dynamic Proton Exchange Membrane Fuel Cell Model (PEMFC) model based on mass balance and semi-empirical equations. A complete PEMFC System containing a Power Conditioning Unit (PCU) is also investigated and various scenarios are simulated to assess the behaviour of a grid-connected FC in a Distributed Generation (DG) network.

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.

Evaluation of a very large scale PV power system with energy storage for capacity firming

Current technology developments in energy storage and PV systems raise new possibilities for combining them, in order to deal with grid integration of PV systems. This paper studies the operation of a very large scale PV power plant, which includes an energy storage system for capacity firming. The energy storage is distributed in the PV plant, i.e. many energy storage units are connected in parallel with each PV array before the central solar inverter. The benefits of this configuration are explained in the paper, whose scope is to evaluate the complete system. A tool has been created in order to perform the sizing of the energy storage, according to a desired operation and evaluate the system using the LCOE.