| 1. |
- Alvarez, Rene, et al.
(författare)
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Semi-continuous co-digestion of solid slaughterhouse waste, manure, and fruit and vegetable waste
- 2008
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 33:4, s. 726-734
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Tidskriftsartikel (refereegranskat)abstract
- The potential of semi-continuous mesophilic anaerobic digestion (AD) for the treatment of solid slaughterhouse waste, fruit-vegetable wastes, and manure in a co-digestion process has been experimentally evaluated. A study was made at laboratory scale using four 2 L reactors working semi-continuously at 35 degrees C. The effect of the organic loading rate (OLR) was initially examined (using equal proportion of the three components on a volatile solids, VS, basis). Anaerobic co-digestion with OLRs in the range 0.3-1.3 kg VS m(-3) d(-1) resulted in methane yields of 0.3 m(3) kg(-1) VS added, with a methane content in the biogas of 54-56%. However, at a further increased loading, the biogas production decreased and there was a reduction in the methane yield indicating organic overload or insufficient buffering capacity in the digester. In the second part of the investigation, co-digestion was studied in a mixture experiment using 10 different feed compositions. The digestion of mixed substrates was in all cases better than that of the pure substrates, with the exception of the mixture of equal amounts of (VS/VS) solid cattle-swine slaughterhouse waste (SCSSW) with fruit and vegetable waste (FVW). For all other mixtures, the steady-state biogas production for the mixture was in the range 1.1-1.6 L d(-1), with a methane content of 50-57% after 60 days of operation. The methane yields were in the range 0.27-0.35 m(3) kg(-1) VS added and VS reductions of more than 50% and up to 67% were obtained.
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| 2. |
- Bernhoff, Hans, et al.
(författare)
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Wave energy resources in sheltered sea areas : A case study of the Baltic Sea
- 2006
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 31:13, s. 2164-2170
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Tidskriftsartikel (refereegranskat)abstract
- Wave energy is a renewable source, which has not yet been exploited to a large extent. So far the main focus of wave energy conversion has been on the large wave energy resources of the great oceans on northern latitudes. However, large portions of the world potential wave energy resources are found in sheltered waters and calmer seas, which often exhibit a milder, but still steady wave climate. Examples are the Baltic Sea, the Mediterranean and the North Sea in Europe, and ocean areas closer to the equator. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. In the present work we instead focus on wave power plants consisting of a number of small wave energy converters, forming large arrays. In this context, we look at advantageous arrangements of point absorbers, and discuss the potential of the Baltic Sea as a case study.
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| 3. |
- Boström, Cecilia, et al.
(författare)
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Experimental results of rectification and filtration from an offshore wave energy system
- 2009
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 34:5, s. 1381-1387
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Tidskriftsartikel (refereegranskat)abstract
- The present paper presents results from a wave energy conversion that is based on a direct drive linear generator. The linear generator is placed on the seabed and connected to a buoy via a rope. Thereby, the natural wave motion is transferred to the translator by the buoy motion. When using direct drive generators, voltage and current output will have varying frequency and varying amplitude and the power must be converted before a grid connection. The electrical system is therefore an important part to study in the complete conversion system from wave energy to grid connected power. This paper will bring up the first steps in the conversion: rectification and filtration of the power. Both simulation studies and offshore experiments have been made. The results indicate that this kind of system works in a satisfactory way and a smooth DC power can be achieved with one linear generator.
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| 4. |
- Cirne, Dores, et al.
(författare)
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Anaerobic digestion of lipid-rich waste - Effects of lipid concentration
- 2007
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 32:6, s. 965-975
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Tidskriftsartikel (refereegranskat)abstract
- The influence of lipid concentration on hydrolysis and biomethanation of a lipid-rich (triolein) model waste was evaluated in batch. The effect of increasing the concentration of lipid from 5% to 47% (w/w), based on chemical oxygen demand (COD), was investigated. The methane recovery observed was above 93% for all tests. An initial lag phase of approximately 6-10 days was observed for all tests. The methane production rate observed was similar for tests with 5%, 10% and 18% lipid (w/w, COD basis). For higher amounts of lipid (31%, 40% and 47%), a stronger inhibition was observed. However, the process was able to recover from the inhibition. When the effect of addition of lipase on enzymatic hydrolysis of lipids was studied, the results showed that the higher the enzyme concentration, the more accentuated was the inhibition of methane production. The enzyme appears to enhance the hydrolysis but the intermediates produced caused inhibition of the later steps in the,degradation process. Since the volatile fatty acid (VFA) profiles presented similar trends for the different concentrations of lipid tested, the major obstacle to methane production was the long-chain fatty acids (LCFA) formation. (c) 2006 Elsevier Ltd. All rights reserved.
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| 5. |
- Eriksson, Sandra, et al.
(författare)
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Simulations and experiments on a 12 kW direct driven PM synchronous generator for wind power
- 2008
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 33:4, s. 674-681
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Tidskriftsartikel (refereegranskat)abstract
- A direct driven permanent magnet (PM) synchronous generator has been designed and constructed and results from the first experimental tests are presented. The generator has been designed using the finite element method (FEM) and dynamic simulations have been performed to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface mounted, arched PMs. A complete experimental setup has been constructed consisting of a motor, a frequency converter, a gearbox and electrical loads. Oscilloscopes are used to measure the voltage and the current for each phase. Measurements have been performed for both full load and no load at rated speed. The harmonic content of the voltage is analyzed and compared to results from simulations. Furthermore, the generated electric power has been calculated from knowing the voltage and current and is compared to the simulated power. The agreement between experimental results and results from simulations based on finite element calculations is very high.. especially considering harmonics. Several sources of error are suggested that could cause the small differences between the simulated results and the measured data for the constructed generator.
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| 6. |
- Fiedler, Frank, et al.
(författare)
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Thermal performance of combined solar and pellet heating systems
- 2006
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 31, s. 73-88
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Tidskriftsartikel (refereegranskat)abstract
- Various pellet heating systems are marketed in Sweden, some of them in combination with a solar heating system. Several types of pellet heating units are available and can be used for a combined system. This article compares four typical combined solar and pellet heating systems. System 1 and 2 with a pellet stove, system 3 with a store integrated pellet burner and system 4 with a pellet boiler. The often lower efficiency of pellet heaters compared to oil or gas heaters increases the final energy demand. Consequently, heat losses of the various systems have been studied. The systems have been modeled in TRNSYS and simulated with parameters identified from measurements. For almost all systems the flue gas losses are the main heat losses except for system 3 where store heat losses prevail. Relevant are also the heat losses of the burner and the boiler to the ambient. Significant leakage losses are noticed for system 3 and 4. For buildings with an open internal design system I is the most efficient solution. Other buildings should preferably apply system 2 or 3. The right choice of the system depends also on whether the heater is placed inside or outside of the heated area. Unlike the expectations and results from other studies, the operation of the pellet heaters with modulating combustion power is not necessarily improving the performance. A large potential for system optimisation exists for all studied systems, which when applied could alter the relative merits of the different system types
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| 7. |
- Gebremedhin, Alemayehu, et al.
(författare)
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Sustainable energy system - A case study from Chile
- 2009
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Ingår i: RENEWABLE ENERGY. - : Elsevier BV. - 0960-1481. ; 34:5, s. 1241-1244
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents some of the results of a power system analysis for Chile. The two major Chilean electric systems are roughly modelled and optimized using a linear programming method with the option to integrate renewable energy sources like wind power, solar power, mini-hydropower and biomass-fired power and also "municipal waste". A total of four different scenarios are outlined: reference system, new production units, gas and coal price variations and a policy measure to encourage power production based on renewable energy. The objective of the scenarios was to illustrate under what conditions integration of the different energy sources in the existing production system is possible. The study shows that even under current conditions, mini-hydro and waste to energy plants are economically viable. Wind power might be interesting alternatives if policy instrument measures are applied. On the other hand, it is hard for the other energy sources to enter the system even when higher price levels of gas and coal are applied. The system is more sensitive to coal price increases than to gas price increases and this mainly encourages CO2 emission reduction.
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| 8. |
- Gustavsson, Mathias, 1969
(författare)
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With time comes increased loads - An analysis of solar home system use in Lundazi, Zambia
- 2006
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 32:5, s. 796-813
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Tidskriftsartikel (refereegranskat)abstract
- Solar energy can bring a number of electric services to the user but also puts up a number of limitations in terms of usage. The design of the system will affect the output from the system as well as the technical life. This article is based on a case-study of a photovoltaic-Energy Service Company (PV–ESCO) project company in Lundazi, Zambia. The solar technology has enabled clients to improve light quality in their houses or shops, which is the most valued benefit according to clients. Clients to the ESCO have acquired a number of electric appliances since they received the service. Radio cassette players are commonly found in households both with and without solar services, while TV sets has been acquired first after they have received this service. To the clients the solar services have resulted in an improvement of the living standards. Energy use and charge was logged during a six-month period. Average usage range from 10 to 14 Ah/day. The load is concentrated to mornings and evenings, but the possibility to access energy services, such as light during the night, is appreciated by the clients. The average energy output from the solar module is 14.5 Ah/day. Increased panel effect, change of the cutting points of the regulator and improve the users knowledge on proper operation of the system are options to tackle the situation of increased loads put on the system.
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| 9. |
- Göransson, Lisa, 1982, et al.
(författare)
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Dispatch modeling of a regional power generation system - Integrating wind power
- 2009
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 34:4, s. 1040-1049
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Tidskriftsartikel (refereegranskat)abstract
- A modeling tool has been developed which can be used to analyze interaction between intermittent wind power generation and thermal power plant generation in a regional electricity grid system. The model uses a mixed integer programming (MIP) approach to determine the power plant dispatch strategy which yields the lowest systems costs. In the model, each large thermal plant is described separately, including properties such as start-up time, start-up cost and minimum load level. The model is evaluated using western Denmark as a case study.For western Denmark, it is found that the inclusion of start-up performance (i.e. start-up time and related costs) and minimum load level of the power generating units have a significant impact on the results. It is shown that the inclusion of these aspects influences the analysis of the effect of wind power variations on the production patterns of thermal units in the system. The model demonstrates how the introduction of wind power production and associated variations change the dispatch order of the large thermal power plants in the western Denmark system so that the unit with the lowest running costs no longer has the highest capacity factor. It is shown that this effect only is detected if start-up performance and minimum load level limitations are included in the optimization. it can also be concluded that start-up performance and minimum load level must be taken into account if the total system costs and emissions are not to be underestimated. The simulations show that if these aspects are disregarded, both total costs and total emissions of the power system are underestimated, with 5% in the case of western Denmark. Models such as the one developed in this work can be efficient tools to understand the effects of large-scale wind power integration in a power generation system with base load plants.
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| 10. |
- Hatwaambo, Sylvester, et al.
(författare)
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Projected beam irradiation at low latitudes using Meteonorm database
- 2009
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 34:5, s. 1394-1398
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Tidskriftsartikel (refereegranskat)abstract
- The quantitative analysis of beam radiation received on a solar concentrator may be understood by evaluating the projected solar height angle or profile angle along the north-south vertical plane. This means that all the sunrays projected along the north-south vertical plane will be intercepted by a collector provided the projection angle lies within the acceptance angle. The Meteonorm method of calculating solar radiation on any arbitrary oriented surface uses the globally simulated meteorological databases. Meteonorm has become a valuable too for estimating solar radiation where measured solar radiation data is missing or irregular. In this paper we present the projected beam solar radiation at low latitudes based on the standard Meteonorm calculations. The conclusion is that there is potential in using solar concentrators at these latitudes since the projected beam radiation is more during winter periods than in summer months. This conclusion is in conformity with the design principle of solar collectors for worst case conditions. (C) 2008 Elsevier Ltd. All rights reserved.
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