| 1. |
- Gong, Mei, 1967-, et al.
(author)
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Exergy Analysis of the Supply of Energy and Material Resources in the Swedish Society
- 2016
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In: Energies. - Basel : M D P I AG. - 1996-1073. ; 9:9
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Journal article (peer-reviewed)abstract
- Exergy is applied to the Swedish energy supply system for the period 1970–2013. Exergy flow diagrams for the systems of electricity and district heating as well as for the total supply system of energy and material resources for 2012 are presented. The share of renewable use has increased in both electricity and district heat production. The resource use is discussed in four sectors: residential and service, transportation, industry and agriculture. The resource use is also analyzed with respect to exergy efficiency and renewable share. The total exergy input of energy and material resources amounts to about 2700 PJ of which about 530 PJ was used for final consumption in 2012. The results are also compared with similar studies. Even though the share of renewable resource use has increased from 42% in 1980 to 47% in 2012, poor efficiency is still occurring in transportation, space heating, and food production. A strong dependence on fossil and nuclear fuels also implies a serious lack of sustainability. A more exergy efficient technology and a higher renewable energy share are needed in order to become a more sustainable society.
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| 2. |
- Mashad Nemati, Hassan, 1982-, et al.
(author)
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Stream Data Cleaning for Dynamic Line Rating Application
- 2018
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In: Energies. - Basel : MDPI. - 1996-1073. ; 11:8
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Journal article (peer-reviewed)abstract
- The maximum current that an overhead transmission line can continuously carry depends on external weather conditions, most commonly obtained from real-time streaming weather sensors. The accuracy of the sensor data is very important in order to avoid problems such as overheating. Furthermore, faulty sensor readings may cause operators to limit or even stop the energy production from renewable sources in radial networks. This paper presents a method for detecting and replacing sequences of consecutive faulty data originating from streaming weather sensors. The method is based on a combination of (a) a set of constraints obtained from derivatives in consecutive data, and (b) association rules that are automatically generated from historical data. In smart grids, a large amount of historical data from different weather stations are available but rarely used. In this work, we show that mining and analyzing this historical data provides valuable information that can be used for detecting and replacing faulty sensor readings. We compare the result of the proposed method against the exponentially weighted moving average and vector autoregression models. Experiments on data sets with real and synthetic errors demonstrate the good performance of the proposed method for monitoring weather sensors.
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| 3. |
- Averfalk, Helge, 1988-, et al.
(author)
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Pipe Sizing for Novel Heat Distribution Technology
- 2019
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In: Energies. - Basel : MDPI. - 1996-1073. ; 12:7
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Journal article (peer-reviewed)abstract
- This paper assesses pipe sizing aspects for previously proposed, novel, low heat distribution technology with three pipes. Assessment issues include heat loss, pressure loss, and pipe sizing for different typical pipe configurations. This assessment has been provided by the analysis of a case area with single-family houses. Concerning heat loss, the proposed three-pipe solutions have the same magnitude of heat loss as conventional twin pipes, since lower return temperatures compensate for the larger heat loss area from the third pipe. Regarding pressure loss, the main restriction on the size of the third pipe is limited to the pressure loss in the third pipe. Thermostatic valves to manage the flow rate of the third pipe are advocated, since alternative small pumps have not been found to be commercially available. The pipe sizing recommendation is that the third pipe for recirculation purposes can be two to three standard pipe sizes smaller than the corresponding supply and return pipe, if no prosumer is connected in the heat distribution network.
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| 4. |
- David, Andrei, et al.
(author)
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Heat Roadmap Europe : Large-Scale Electric Heat Pumps in District Heating Systems
- 2017
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In: Energies. - Basel : MDPI. - 1996-1073. ; 10:4
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Journal article (peer-reviewed)abstract
- The Heat Roadmap Europe (HRE) studies estimated a potential increase of the district heating (DH) share to 50% of the entire heat demand by 2050, with approximately 25–30% of it being supplied using large-scale electric heat pumps. This study builds on this potential and aims to document that such developments can begin now with technologies currently available. We present a database and the status of the technology and its ability of expansion to other European locations by reviewing experiences aimed at further research or application in the heating industry. This is based on a survey of the existing capacity of electric large-scale heat pumps with more than 1 MW thermal output, operating in European DH systems. The survey is the first database of its kind containing the technical characteristics of these heat pumps, and provides the basis for the analysis of this paper. By quantifying the heat sources, refrigerants, efficiency and types of operation of 149 units with 1580 MW of thermal output, the study further uses this data to analyze if the deployment of this technology on a large-scale is possible in other locations in Europe. It finally demonstrates that the technical level of the existing heat pumps is mature enough to make them suitable for replication in other locations in Europe.
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| 5. |
- Lygnerud, Kristina, 1976-
(author)
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Business Model Changes in District Heating : The Impact of the Technology Shift from the Third to the Fourth Generation
- 2019
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In: Energies. - : MDPI. - 1996-1073. ; 12:9
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Journal article (peer-reviewed)abstract
- This paper addresses the implications on the business model of district heating companies of the technology shift targeting lower temperatures in the distribution network. Lower temperatures are valuable, since heat supply to low-energy buildings with low grid losses is facilitated. In addition, low-temperature heat sources can be integrated into an efficient energy system, improving the environmental performance of the industry. This technology shift opens a window of opportunity to update the business logic in the sector, since the lower temperatures allow a diversification of the value proposed to customers and a closer, long-term customer relationship. The extent to which the business model is impacted by the shift is not known. Thus, six cases of low temperature implementation from five European countries have been identified. Interviews with the project managers of the implementations show that the six cases made limited change to the primary business model when making the technological shift. Consequently, there is an unexplored potential for updating the value proposition and the customer relationship.
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| 6. |
- Möllerström, Erik, 1984-, et al.
(author)
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Improvement of AEP Predictions with Time for Swedish Wind Farms
- 2021
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In: Energies. - Basel : MDPI. - 1996-1073. ; 14:12
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Journal article (peer-reviewed)abstract
- Based on data from 2083 wind turbines installed in Sweden from 1988 onwards, the accuracy of the predictions of the annual energy production (AEP) from the project planning phases has been compared to the actual wind-index-corrected production. Both the electricity production and the predicted AEP come from Vindstat, a database that collects information directly from wind turbine owners. The mean error for all analyzed wind turbines was 13.0%, which means that, overall, the predicted AEP has been overestimated. There has been an improvement of accuracy with time with an overestimation of 8.2% for wind turbines installed in the 2010s, however, the continuous improvement seems to have stagnated around 2005 despite better data availability and continuous refinement of methods. Dividing the results by terrain, the error is larger for wind turbines in open and flat terrain than in forest areas, indicating that the reason behind the error is not the higher complexity of the forest terrain. Also, there is no apparent increase of error with wind farm size which could have been expected if wind farm blockage effect was a main reason for the overestimations. Besides inaccurate AEP predictions, a higher-than-expected performance decline due to inadequate maintenance of the wind turbines may be a reason behind the AEP overestimations. The main sources of error are insecurity regarding the source of AEP predictions and the omission of mid-life alterations of rated power. © 2021 by the authors.
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| 7. |
- Möllerström, Erik, 1984-, et al.
(author)
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Noise Emission of a 200 kW Vertical Axis Wind Turbine
- 2016
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In: Energies. - Basel : MDPI. - 1996-1073. ; 9:1
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Journal article (peer-reviewed)abstract
- The noise emission from a vertical axis wind turbine (VAWT) has been investigated. A noisemeasurement campaign on a 200 kW straight-bladed VAWT has been conducted, and the result hasbeen compared to a semi-empirical model for turbulent-boundary-layer trailing edge (TBL-TE) noise.The noise emission from the wind turbine was measured, at wind speed 8 m/s, 10 m above ground, to96.2 dBA. At this wind speed, the turbine was stalling as it was run at a tip speed lower than optimaldue to constructional constraints. The noise emission at a wind speed of 6 m/s, 10 m above groundwas measured while operating at optimum tip speed and was found to be 94.1 dBA. A comparisonwith similar size horizontal axis wind turbines (HAWTs) indicates a noise emission at the absolutebottom of the range. Furthermore, it is clear from the analysis that the turbulent-boundary-layertrailing-edge noise, as modeled here, is much lower than the measured levels, which suggests thatother mechanisms are likely to be important, such as inflow turbulence.
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| 8. |
- Möllerström, Erik, 1984-
(author)
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Wind Turbines from the Swedish Wind Energy Program and the Subsequent Commercialization Attempts – A Historical Review
- 2019
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In: Energies. - Basel : MDPI. - 1996-1073. ; 12:4
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Research review (peer-reviewed)abstract
- This paper summarizes wind turbines of Swedish origin, 50 kW and above. Both the large governmental-funded prototypes from the early 1980s and following attempts to build commercial turbines are covered. After the 1973 oil crisis, a development program for wind turbine technology was initiated in Sweden, culminating in the early 1980s with the 2 and 3-MW machines at Maglarp and Näsudden. However, government interest declined, and Sweden soon lost its position as one of the leading countries regarding wind turbine development. Nevertheless, several attempts to build commercial wind turbines in Sweden were made in the following decades. Most attempts have, like the earlier prototypes, used a two-bladed rotor, which has become synonymous with the Swedish wind turbine development line. The current ongoing Swedish endeavors primarily focus on the niche-concept of vertical axis wind turbines (VAWTs), which is a demonstration of how far from the broad commercial market of Sweden has moved. Thus far, none of the Swedish attempts have been commercially successful, and unlike countries like Denmark or Germany, Sweden currently has no large wind turbine producer. Suggested reasons include early government interventions focusing on two-bladed prototypes and political disinterest, with wind power grants cut in half by 1985, and the domestic industry not being favored in government policies for deploying wind power.
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| 9. |
- Negash, Teklebrhan, et al.
(author)
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An Assessment of Wind Energy Potential for the Three Topographic Regions of Eritrea
- 2020
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In: Energies. - Basel : MDPI. - 1996-1073. ; 13:7
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Journal article (peer-reviewed)abstract
- This paper presents the wind energy potential and wind characteristics for 25 wind sites in Eritrea, based on wind data from the years 2000–2005. The studied sites are distributed all over Eritrea, but can roughly be divided into three regions: coastal region, western lowlands, and central highlands. The coastal region sites have the highest potential for wind power. An uncertainty, due to extrapolating the wind speed from the 10-m measurements, should be noted. The year to year variations are typically small and, for the sites deemed as suitable for wind power, the seasonal variations are most prominent in the coastal region with a peak during the period November–March. Moreover, Weibull parameters, prevailing wind direction, and wind power density recalculated for 100 m above ground are presented for all 25 sites. Comparing the results to values from the web-based, large-scale dataset, the Global Wind Atlas (GWA), both mean wind speed and wind power density are typically higher for the measurements. The difference is especially large for the more complex-terrain central highland sites where GWA results are also likely to be more uncertain. The result of this study can be used to make preliminary assessments on possible power production potential at the given sites. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
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| 10. |
- Spirito, Giulia, et al.
(author)
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Potential Diffusion of Renewables-Based DH Assessment through Clustering and Mapping : A Case Study in Milano
- 2021
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In: Energies. - Basel, Switzerland : MDPI. - 1996-1073. ; 14:9
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Journal article (peer-reviewed)abstract
- This work aims at developing a methodology for the assessment of district heating (DH) potential through the mapping of energy demand and waste heat sources. The presented method is then applied to the Metropolitan City of Milano as a case study in order to investigate the current and, especially, the future sustainability of DH with the foreseen building refurbishment and consequent heat demand reduction. The first step is the identification of the areas the most interesting from a heat density and an economic point of view through a clustering algorithm, in which lies the main novelty of the work. The potential is then assessed by investigating their synergy with the available heat sources, which are mapped and analyzed in terms of recoverable thermal energy and costs. In future scenarios with foreseen heat demand reduction, low-temperature networks and excess heat sources are considered, such as metro stations and datacenters, together with the conventional sources, such as thermoelectric plants. The outcomes prove that lower heat demand corresponds to higher network costs with consequently reduced district heating potential but also prove that the properties of low-temperature district heating can potentially compensate for the drop in its cost-effectiveness. Another interesting finding is that the renovation of buildings in an area should be not performed evenly but with criteria; for instance, in synergy with DH diffusion. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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