Abstract:The Azores Regional Government, through the Sustainable Energy Action Plan for the Azorean Islands, assumed that by the year 2018, 60% of electricity would be generated from renewable energy sources. Nevertheless, by increasing renewable energy sources share in the electricity mix, peak energy that exceeds grid capacity cannot be used unless when considering energy storage systems. Therefore, this article aims at determining, among batteries and Pumped Hydro Systems, the most cost-effective energy storage system to deploy in Terceira Island, along with geothermal, wind, thermal and bio waste energy, while considering demand and supply constraints. It is concluded that a pumped hydro system sited in Serra do Morião-Nasce Água is the best option for storage of the excess generated energy when compared with batteries. However, further studies should analyze environmental constraints. It is demonstrated that by increasing the storage power capacity, a pumped hydro system improves its cost efficiency when compared with batteries. It is also demonstrated that, to ensure quality, economic feasibility, reliability and a reduction of external costs, it is preferable to replace fuel-oil by wind to generate electricity up to a conceivable technical limit, while building a pumped hydro system, or dumping the excess peak energy generated.
The aim of this paper is to evaluate the possibility of implementation of alternative renewable energy microgeneration installations in dairy farm milk collection posts, from the technical, economical and environmental perspectives.This work was performed through a dairy farm milk collection post energy audit, to perform energy profile characterization and demand requirements. Following that, a study of the weather conditions was done and the obtained data (through CLIMAAT and MacSIMAR projects) [11] was introduced in a renewable energy solutions calculator (HOMER). Moreover, a system design from the available portfolio of micro-generation devices was defined and a cost benefit analysis of the selected alternatives was done. In the end a comparison of the current implemented solution with alternative designs was performed.Results show that from the analyzed solutions for this case, the set of PV (20Kw) and Wind (3KW) with no batteries is the best one, since it presents the least cost of energy, the smallest initial capital and the highest Net Present Cost. The sensitivity analysis derive that wind micro-turbines should be installed except if the solar radiation is on its maximum value and that in no case the use of batteries is an advantage for the system operation.For systems requiring a certain degree of energy (in this case with an average of 350 kW/day), the implementation of micro generation systems, like the ones evaluated, will never be economically viable in terms of Total Economic Value, even with generous feed-in tariff schemes. It is preferable that the grid operator makes investments in renewable energy production. To improve the system energy performance, the options should be focused on energy efficiency measures.
The paradigm of smart grids has encouraged new developments of power electronics converters, for instance, in the perspective of renewables and electric mobility applications. Aligned with this perspective, this paper proposes a novel topology of a multilevel bidirectional and symmetrical (MBS) split-pi dc-dc converter. As a central distinguishing feature, it operates with three voltage levels in both dc sides (0, vdc/2, vdc), meaning that the voltage stress in each semiconductor is reduced when compared with the conventional split-pi converters, and it operates with controlled variables (voltage and current) based on the interleaved principle of operation, although it is not an interleaved split-pi converter. As demonstrated along the paper, the MBS split-pi converter can be controlled with current or voltage feedback in any of the dc interfaces, while the common dc-link voltage is controlled by the dc interface where the source is connected. The adopted current and voltage control schemes, as well as the pulse-width modulation, are presented and comprehensively explained. The validation is presented for the main operation modes, where it is possible to verify the claimed distinguishing features of the proposed MBS split-pi converter.
Abstract. The famous 3x + 1 problem involves applying two maps: T 0 (x) = x/2 and T 1 (x) = (3x + 1)/2 to positive integers. If x is even, one applies T 0 , if it is odd, one applies T 1 . The conjecture states that each trajectory of the system arrives to the periodic orbit {1, 2}. In this paper, instead of choosing each time which map to apply, we allow ourselves more freedom and apply both T 0 and T 1 independently of x. That is, we consider the action of the free semigroup with generators T 0 and T 1 on the space of positive real numbers. We prove that this action is minimal (each trajectory is dense) and that the periodic points are dense. Moreover, we give a full characterization of the group of transformations of the real line generated by T 0 and T 1 .
Wind power reduces our exposure to fuel price volatility and abrupt supply disruptions; it has no CO2 emissions and increases energy security through the diversification of the energy portfolio. If well sited and dimensioned, wind farms may contribute to decreased electricity generation costs. This article presents a combined GISs (Geographical Information Systems) and CBA (Cost Benefit Analysis) approach, in determining the most feasible sites that would be suitable for the generation of wind energy in Terceira Island, which is aimed towards efficient policy designs. Data corrected with Wind Atlas Analysis and Application Program, from local effects of the territory, are used to determine potential energy. Furthermore, a CBA is performed, without taking into consideration subsidies and economic indicators are displayed in maps using GIS. Results indicated that Terceira Island has large available areas capable of generating wind energy at low prices. On Terceira Island, while considering a 1500 kW wind farm under the best siting conditions, it is estimated to achieve a Net Present Value of nearly 3 330 000.00 €, an Internal Rate of Return of nearly 26%, and a Levelized Cost of Energy of nearly 0.04 €/KW h, without incentives. The sensitivity analysis results indicated that reductions in the energy sold may drastically impair the feasibility of a wind energy generation project, and that increases in the lifetime of a project from 15 to 25 years may improve its feasibility. The minimum wind speed required to grant feasibility of investments on Terceira Island, for 1500 kW installed power, is 6 m/s, ceteris paribus. This analysis pointed out that Serra do Cume and Serra da Ribeirinha are the most suited for wind energy projects on Terceira Island.
This paper presents the experimental validation of a unified three-port topology, integrating a renewable energy source (RES) and an energy storage system (ESS) (or an electric vehicle) with the grid-interface operating as active power filter (APF). The proposed topology is based on a three-phase grid-interface (whose role is to operate as a APF grid-tied inverter capable of compensating current harmonics, imbalanced currents and low power factor), on a RES-interface for solar photovoltaic (PV) panels (whose role is to extract the maximum power from the PV panels), and on an ESS-interface for batteries (whose role is to store/inject energy according to the power management of the electrical installation). The paper presents the control algorithms for each interface within the scope of the different operation modes allowed by the unified three-port topology. Simulation and experimental results are presented in order to validate the distinguishing aspects of the proposed unified three-port topology.
This paper presents a load-shift system with advanced functionalities to interface the power grid (PG). When compared with the conventional approach, an advanced load-shift system (aLSS) permits the compensation of power quality (PQ) problems for the grid-side, namely problems related to current harmonics, current imbalance, and power factor. The proposed aLSS is composed by a bidirectional ac-dc converter to interface the PG and by a bidirectional dc-dc converter to interface an energy storage system (ESS). Since the main innovation is related with the PG interface, the focus of this work is on the analysis of the ac-dc converter, which is based on a three-phase four-leg converter. A theoretical study and the details concerning the control algorithm are presented and discussed along the paper. A laboratory prototype of the proposed aLSS was developed and the details of implementation are described in the paper. Experimental results obtained with the developed prototype prove that the aLSS contributes for the technology progress in this area, validating a new concept of operation concerning the PQ on the PG side.
This paper presents an enhanced three-phase shunt active power filter (SAPF) that, besides its inherent functionalities of power quality problems compensation, also allows the interface of a renewable energy source (RES, namely solar photovoltaic -PV panels) and an energy storage system (ESS, namely batteries) through its dc-link. On the power grid-side, a three-phase four-wire voltage-source ac-dc converter is connected with the power grid, operating as an SAPF, whereas the RES-interface and the ESS-interface are made through a three-port multilevel dc-dc converter connected to the dc-link of the SAPF. Besides, to compensate power quality problems related to currents, the SAPF also permits the controllability of the bidirectional power exchanged between the power grid and the dc interfaces, i.e., the RES and the ESS. The operation principle of the whole system, as well as the detailed control algorithms, are described in the paper. A validation was performed through computer simulations, where it is possible to analyze the different operation modes of the enhanced SAPF interfacing a RES and an ESS through the dc-link.
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