Photovoltaic Owners Research Articles

Probabilistic simulation framework for balanced and unbalanced low voltage networks

In Low Voltage (LV) distribution networks, the high volatility of distributed photovoltaic (PV) generation has a severe impact on the variation of operation indices, in steady state conditions. During periods with high PV injection and low demand, LV feeders are more and more subject to overvoltage events and temporary PV units’ cut-offs. As a result, the delivered power quality is affected and network operational expenses increase. Moreover, the income of the PV owner is decreased due to the loss of generated energy. For efficiently addressing such operational issues, long term observability analytics of the LV network are required. Distribution System Operators (DSOs) currently deploy such studies in a deterministic manner, focusing on “worst-case” hypothesis, without considering the uncertainty of nodal power injection and consumption. This approach can lead to over restrictive decisions and costly technical solutions. For refining DSO strategies to the variability of network states, probabilistic methods are highly recommended. In this context, this paper presents a Monte-Carlo (MC) framework that simulates the steady operation of the LV network by elaborating user-specific smart metering (SM) measurements. The presented framework integrates a complete three-phase power flow algorithm that can analyse most possible LV network configurations, balanced and unbalanced, considering nodal power injections and consumptions as random variables of each network state. Such unbalanced power flow algorithms had not up to now been linked with probabilistic analysis using network-specific SM readings. For demonstrating the interest of the proposed framework, the latter is used to simulate several configurations in an existing LV feeder with high PV integration and SM deployment.

Stochastic Reactive Power Management in Microgrids With Renewables

Distribution microgrids are being challenged by reverse power flows and voltage fluctuations due to renewable generation, demand response, and electric vehicles. Advances in photovoltaic (PV) inverters offer new opportunities for reactive power management provided PV owners have the right investment incentives. In this context, reactive power compensation is considered here as an ancillary service. Accounting for the increasing time-variability of distributed generation and demand, a stochastic reactive power compensation scheme is developed. Given uncertain active power injections, an online reactive control scheme is devised. This scheme is distribution-free and relies solely on power injection data. Reactive injections are updated using the Lagrange multipliers of a second-order cone program. Numerical tests on an industrial 47-bus microgrid and the residential IEEE 123-bus feeder corroborate the reactive power management efficiency of the novel stochastic scheme over its deterministic alternative, as well as its capability to track variations in solar generation and household demand.

Smart inverter operation in distribution networks with high penetration of photovoltaic systems

With the growing number and capacity of photovoltaic (PV) installations connected to distribution networks, power quality issues related to voltage regulation are becoming relevant problems for power distribution companies and for PV owners. In many countries, like Italy, this has required the revision of the standards concerning the connection to the public distribution network of distributed renewable generation. The new standards require a flexible operation of generation plants that have to be capable to change the active and reactive power dynamically in function of the network parameters (i.e. frequency and network local voltage) in local control or following external commands. Therefore, this paper investigates the use of smart inverter in a critical PV installation, where relevant voltage fluctuations exist. A case study, with real network parameters monitoring data and measurements, is discussed in the paper with the aim of showing how ‘smart’ features of new inverters can be implemented to increase PV plant integration in low voltage distribution networks.

The economic effect of electricity net-metering with solar PV: Consequences for network cost recovery, cross subsidies and policy objectives

Net-metering is commonly known as a practice by which owners of distributed generation (DG) units may offset their electricity consumption from the grid with local generation. The increasing number of prosumers (consumers that both produce and consume electricity) with solar photovoltaic (PV) generation combined with net-metering results in reduced incomes for many network utilities worldwide. Consequently, this pushes utilities to increase charges per kWh in order to recover costs. For non-PV owners, this could result into inequality issues due to the fact that also non-PV owners have to pay higher chargers for their electricity consumed to make up for netted costs of PV-owners. In order to provide insight in those inequality issues caused by net-metering, this study presents the effects on cross-subsidies, cost recovery and policy objectives evolving from different applied netmetering and tariff designs for a residential consumer. Eventually this paper provides recommendations regarding tariffs and metering that will result in more explicit incentives for PV, instead of the current implicit incentives which are present to PV owners due to net-metering.

Simple and low-cost method of planning for tree growth and lifetime effects on solar photovoltaic systems performance

The use of distributed solar photovoltaic (PV) systems is growing more common as solar energy conversion efficiencies increase while costs decrease. Thus, PV system installations are increasing in non-optimal locations such as those potentially shaded with trees. Tree-related shading can cause a significant power loss and an increasing collection of laws have been enacted and are under development to protect the right of PV owners to solar access. This paper provides a new method to predict the shading losses for a given tree species, orientation to a PV array, and geographic location using existing free tools in order to assist in the prevention of conflicts by creating an environment where PV systems and trees can coexist while maximizing PV performance. This methodology is applied to a case study in the Midwest US. Tree growth characteristics including height, crown width, and growth rate were investigated. Minimum planting distances were quantified based on tree species and orientation of planting with respect to the PV system and conclusions were drawn from the results. This novel open low-cost method to predict and prevent tree shading from negatively impacting the performance of roof-mounted PV systems assists in planning of technical design.

Capturing Inherent Variability in Solar PV Energy through Realistic Estimates: A Case Study for the State of Minnesota

ABSTRACT Solar photovoltaic (PV) deployment in the United States and the world is gaining accelerated momentum. It is very important for the solar PV industry standards to be realistic in its energy production estimates. The model of choice for most solar PV installers, enthusiasts and owners is the use of National Renewable Energy Laboratory (NREL) PV Watts' simulation program. Through systematic analysis of multiple installations in the State of Minnesota, real data are analyzed and compared to the PV Watt's simulated results. It has been determined through this analysis that PV Watts is aggressive, unattainable and misleads the public in its energy estimates for the State of Minnesota. It has also been discussed that to obtain more realistic solar PV energy estimates, one must use of range of production rather than just one value. Giving one value for solar PV energy estimates has the tendency to mislead because a low value estimate would make solar PV unattractive and a high value estimate will not be...

Training and certification of PV installers in Europe

The high photovoltaic (PV) market growth rates, which are further favored by the EU supporting policies and the national regulatory frameworks, may result to a threat for the PV industry due to the lack of adequately skilled workforce for PV installation and maintenance. This fact may result in poorly installed systems with negative impact on the industry’s credibility and development. The PVTRIN, an Intelligent Energy Europe project, addresses to these issues by developing a training and accreditation scheme for technicians/engineers focusing to the installation and maintenance of small scale PV systems. The training and certification will incorporate the criteria set by the 2009/28/EC Directive regarding requirements for certified training courses and training providers, providing a supporting instrument for EU Member States to meet their obligations for acknowledged certifications for RES installers till 31/12/2012. Creating a qualified PV installers workforce, the increased confidence of potential PV owners will lead to market growth.

Collaborative Reactive Power Control of Photovoltaic Power Generation Systems in a Future Distribution Network Based on Reactive Power Price

Future Japanese power grids will be supported by many photovoltaic (PV) generation systems installed in distribution networks as their essential components. However, they might make it difficult to keep the voltage profile appropriate in case that a large amount of power flows back from them. Although the voltage profile can be properly adjusted by power factor control, such a control gives economic disadvantage to the PV owners. In this paper the authors propose a new collaborative voltage control by monetary transactions among the PV owners. A new reactive pricing is proposed and studied using a simple distribution model. It is shown that the proposed incentive successfully increases the total income by coordination of reactive power output among them. The proposed system eventually increases the total income of the PV owners who contributed to the power factor control.

Transactions between electric utility and photovoltaic owner

Residential customers with surplus photovoltaic energy in excess of their load have the option of either selling that energy or storing it in batteries and consuming it later. Their choice depends on the financial transaction contract that exists between them and the electric utility. The buyback ratio can be used to characterize these financial transactions. The issue of the buy-back ratio, its implications, and how it affects the financial transactions are considered. Many factors that affect the buy-back ratio are discussed from the electric utility perspective, and a range of buy-back ratios is determined from the utility point of view. Results show that the buy-back ratio decreases with penetration of photovoltaic energy.