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The challenges of modern power systems will inevitably impose increased ancillary service requirements to photovoltaic (PV) plants in the future, including operating reserves. Recent studies have investigated methods to maintain active power reserves without energy storage in the standard case of uniform illumination. In this paper, this functionality is extended to partial shading conditions, often encountered in PV systems. A new control scheme is proposed that permits operation at a reduced power level, estimating at the same time the shading conditions and maximum available power. This is achieved by applying a least-squares curve fitting algorithm on voltage and current measurements, without relying on any irradiance or temperature sensors. To the best of our knowledge, this is the first power reserves control scheme for PV systems under partial shading presented in the literature. The robustness and effectiveness of the proposed method are validated under rapidly changing shading conditions through simulations and experimental tests on a 2-kW PV system prototype. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) system performance is influenced by several factors, including irradiance, temperature, shading, degradation, mismatch losses, soiling, etc. Shading of a PV array, in particular, either complete or partial, can have a significant impact on its power output and energy yield, depending on array configuration, shading pattern, and the bypass diodes incorporated in the PV modules. In this paper, the effect of partial shading on multicrystalline silicon (mc-Si) PV modules is investigated. A PV module simulation model implemented in P-Spice is first employed to quantify the effect of partial shading on the I–V curve and the maximum power point (MPP) voltage and power. Then, generalized formulae are derived, which permit accurate enough evaluation of MPP voltage and power of mc-Si PV modules, without the need to resort to detailed modeling and simulation. The equations derived are validated via experimental results. [ABSTRACT FROM PUBLISHER]

Load demand in small autonomous island systems is typically covered by Diesel Units (DU). Although a favourable renewable energy source (RES) potential might exist, the technical constraints introduced by the conventional generators result in relatively low RES penetration levels, typically up to 15%–20% of the annual energy demand. To overcome such limitations, introduction of energy storage is necessary. In the case of very small islands (less than 1 MW peak load), lead-acid battery energy storage systems (BESS) constitute a technically mature solution with considerable application potential. In this paper, the potential for achieving very high RES penetration levels with the introduction of BESS in an existing small island system is investigated. An operating policy is first introduced for the overall system, including conventional generators, RES (wind and photovoltaic) stations and storage system. Simulation results are then presented to quantify the expected energy benefits in terms of RES energy penetration and the impact on the economics of the island system. The sizing of the hybrid system components is then investigated by conducting a parametric analysis and then optimized by applying genetic algorithms. [ABSTRACT FROM PUBLISHER]

In this paper, new expressions are introduced for the determination of the maximum power point (MPP) of photovoltaic (PV) systems as explicit functions of the five parameters of the single-diode model employing the Lambert W function. These equations provide the voltage and current at MPP in a direct and straightforward manner, thus dispensing with any need for iterative solution. They are initially derived for a PV system operating under uniform conditions, and subsequently extended for mismatched conditions at the PV string level. The novelty of these formulae lies in their solid theoretical foundation, which supports their validity in the general case and offers a well-founded symbolic formulation for the MPP evaluation problem. Extended simulations and experimental validation are performed to verify the accuracy and computational efficiency of the proposed equations compared with other methods available in the literature. [ABSTRACT FROM AUTHOR]