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Sterner M.,Fraunhofer Institute for Wind Energy and Energy System Technology | Fritsche U.,Oeko - Institute e.V.
Biomass and Bioenergy | Year: 2011

With Germany as the point of energy end-use, 70 current and future modern pathways plus 4 traditional biomass pathways for heat, power and transport have been compiled and examined in one single greenhouse gas (GHG) balancing assessment. This is needed to broaden the narrow focus on biofuels for transport and identify the role of bioenergy in GHG mitigation. Sensitivity analysis for land-use changes and fossil reference systems are included. Co-firing of woody biomass and fermentation of waste biomass are the most cost-efficient and effective biomass applications for GHG emission reduction in modern pathways. Replacing traditional biomass with modern biomass applications offers an underestimated economic potential of GHG emission reduction. The range of maximum CO2 equivalent GHG reduction potential of bioenergy is identified in a range of 2.5-16 Gt a-1 in 2050 (5-33% of today's global GHG emissions), and has an economic bioenergy potential of 150 EJ a-1. © 2011 Elsevier Ltd.

Venayagamoorthy G.K.,Clemson University | Rohrig K.,Fraunhofer Institute for Wind Energy and Energy System Technology | Erlich I.,University of Duisburg - Essen
IEEE Power and Energy Magazine | Year: 2012

The intelligent integration of wind power into the existing electricity supply system will be an important factor in the future energy supply in many countries. Wind power generation has characteristics that differ from those of conventional power generation. It is weather dependent in that it relies on wind availability. With the increasing amount of intermittent wind power generation, power systems encounter more and more short-term, unpredicted power variations. In the power system, supply and demand must be equal at all times. Thus, as levels of wind penetration into the electricity system increase, new methods of balancing supply and demand are necessary. © 2003-2012 IEEE.

Stetz T.,Fraunhofer Institute for Wind Energy and Energy System Technology | Marten F.,University of Stuttgart | Braun M.,Fraunhofer Institute for Wind Energy and Energy System Technology
IEEE Transactions on Sustainable Energy | Year: 2013

This work discusses the technical and economical benefits of different active and reactive power control strategies for grid-connected photovoltaic systems in Germany. The aim of these control strategies is to limit the voltage rise, caused by a high local photovoltaic power feed-in and hence allow additional photovoltaic capacity to be connected to the mains. Autonomous inverter control strategies, which do not require any kind of data communication between the inverter and its environment, as well as an on-load tap changer for distribution transformers, is investigated. The technical and economical assessment of these strategies is derived from 12-month root mean square (rms) simulations, which are based on a real low voltage grid and measured dc power generation values. The results show that the provision of reactive power is an especially effective way to increase the hosting capacity of a low voltage grid for photovoltaic systems. © 2010-2012 IEEE.

Da Costa J.P.,Federal University of Santa Maria | Pinheiro H.,Federal University of Santa Maria | Degner T.,Fraunhofer Institute for Wind Energy and Energy System Technology | Arnold G.,Fraunhofer Institute for Wind Energy and Energy System Technology
IEEE Transactions on Industrial Electronics | Year: 2011

This paper proposes a new robust controller in a stationary reference frame for doubly fed induction generators (DFIGs) of grid-connected wind turbines. Initially, a DFIG dynamic model is derived from the voltage and flux equations in αβ coordinates, where uncertainties and disturbances intrinsic to the system are accounted for as perturbation terms are added to the nominal model. Then, a controller design procedure that guarantees the DFIG stability under uncertainties and disturbances at the grid side is presented in detail. It is demonstrated that a very fast dynamic behavior can be obtained with the proposed controller, which improves the transient response of the grid-connected DFIG, particularly under conditions of unbalanced voltage dips resulting from asymmetrical network faults. In order to conform with the fault ride-through capability requirements, this paper proposes a new reference strategy, which is divided into normal and fault operation modes. Experimental results are given to support the theoretical analysis and to illustrate the performance of the grid-connected DFIG with the proposed controller. © 2010 IEEE.

Hochloff P.,Fraunhofer Institute for Wind Energy and Energy System Technology | Braun M.,Fraunhofer Institute for Wind Energy and Energy System Technology | Braun M.,University of Kassel
Biomass and Bioenergy | Year: 2014

Increasing shares of intermittent power sources such as solar and wind will require biomass fueled generation more variable to respond to the increasing volatility of supply and demand. Furthermore, renewable energy sources will need to provide ancillary services. Biogas plants with excess generator capacity and gas storages can adapt the unit commitment to the demand and the market prices, respectively. This work presents a method of day-ahead unit commitment of biogas plants with excess generator capacity and gas storage participating in short-term electricity and control reserve markets. A biogas plant with 0.6MW annual average electric output is examined in a case study under German market conditions. For this biogas plant different sizes of the power units and the gas storage are compared in consideration of costs and benefits of installing excess capacity. For optimal decisions depending on prices, a mixed-integer linear programming (MILP) approach is presented.The results show that earnings of biogas plants in electricity markets are increased by additional supplying control reserve. Furthermore, increasing the installed capacity from 0.6MW to 1MW (factor 1.7) leads to the best cost-benefit-ratio in consideration of additional costs of excess capacity and additional market revenues. However, the result of the cost-benefit-analysis of installing excess capacity is still negative. Considering the EEG flexibility premium, introduced in 2012 in the German renewable energy sources act, the result of the cost-benefit-analysis is positive. The highest profit is achieved with an increase of the installed capacity from 0.6MW to 2MW (factor 3.3). © 2013 Elsevier Ltd.

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