| 1. |
- Andreasen, J. G, et al.
(författare)
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Selection and optimization of pure and mixed working fluids for low grade heat utilization using organic Rankine cycles
- 2014
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Ingår i: Energy. - 0360-5442. ; 73
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Tidskriftsartikel (refereegranskat)abstract
- We present a generic methodology for organic Rankine cycle optimization, where the working fluid is included as an optimization parameter, in order to maximize the net power output of the cycle. The method is applied on two optimization cases with hot fluid inlet temperatures at 120°C and 90°C. Pure fluids and mixtures are compared to see how mixed working fluids affect performance and important design parameters. The results indicate that mixed working fluids can increase the net power output of the cycle, while reducing the pressure levels. The maximum net power output is obtained by fluids with a critical temperature close to half of the hot fluid inlet temperature. For some mixtures we find the maximum net power when the temperature glide of condensation matches the temperature increase of the cooling water, while for other mixtures there are large differences between these two parameters. Ethane is a fluid that obtains a large net power increase when used in mixtures. Compared to pure ethane, an optimized ethane/propane mixture attains a 12.9% net power increase when the hot fluid inlet temperature is 120_C and a 11.1% net power increase when the hot fluid inlet temperature is 90°C.
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| 2. |
- Bagge, Hans, et al.
(författare)
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Measurements of household electricity and domestic hot water use in dwellings and the effect of different monitoring time resolution
- 2011
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Ingår i: Energy. - : Elsevier BV. - 1873-6785 .- 0360-5442. ; 36:5, s. 2943-2951
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Tidskriftsartikel (refereegranskat)abstract
- The use of household electricity and domestic hot water has been measured for 72 apartments in an apartment building located in the south of Sweden. The measurements were carried out with samples every 6 s, a tenfold increase in resolution compared to available published data, during a measurement period of five days, in the winter season, including a weekend. The influence of the time resolution on the distribution of data was analysed by integrating the 6 s data to represent longer logging intervals. Extreme values, especially the high values, are shown to be reduced if the time interval is increased. The maximum household electric power was 50% higher at a 6 s resolution compared to 60 s and the corresponding difference for domestic hot water flow was 40%. Daily variations has to be considered for photovoltaic installations and solar thermal collectors, energy simulations of buildings need at least hourly data and all kind of power design in a building or its services benefits from much more resolved data. (C) 2011 Elsevier Ltd. All rights reserved.
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| 3. |
- Bahaj, AbuBakr S., et al.
(författare)
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Shaping array design of marine current energy converters through scaled experimental analysis
- 2013
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 59:0, s. 83-94
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Tidskriftsartikel (refereegranskat)abstract
- Marine current energy converters or tidal turbines represent an emerging renewable energy technology that can provide a predictable supply of electricity. Single devices are in operation around the world with aspirations to deploy farms or arrays of multiple devices. We present an experimental study that has characterised the downstream wake flow around a 1/15th-scale turbine in a large circulating water channel and a series of experiments involving static actuator disks at 1/120th-scale allowing simulation of multiple-device layouts. Our analysis demonstrates that the near wake is highly turbulent with structures generated by the rotor and support structure. This region of flow may prove difficult to numerically simulate with a high degree of accuracy. In the far wake the performance of static actuator disks can be matched to mechanical rotors reducing scale and cost facilitating replication of complex array geometries. Here the ambient turbulence and geometric properties of the device/channel drive the wake recovery towards free stream conditions. Devices operating downstream of others will be subject to a non-steady flow field making comparative performance difficult. We discuss the possibility of unequal device specification and rated power within an array (unlike wind farms) providing a more representative measure of array performance.
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| 4. |
- Blarke, Morten B, et al.
(författare)
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Intermittency-friendly and high-efficiency cogeneration : Operational optimisation of cogeneration with compression heat pump, flue gas heat recovery, and intermediate cold storage
- 2011
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 36:12, s. 6867-6878
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Tidskriftsartikel (refereegranskat)abstract
- This paper develops, implements, and applies a mathematical model for economic unit dispatch for a novel cogeneration concept (CHP-HP-FG-CS (CHP with compression heat pump and cold storage using flue gas heat)) that increases the plant's operational flexibility. The CHP-HP-FG-CS concept is a high-efficiency and widely applicable option in distributed cogeneration better supporting the co-existence between cogenerators and intermittent renewables in the energy system. The concept involves integrating an efficient high-temperature compression heat pump that uses only waste heat recovered from flue gases as low-temperature heat source, and an intermediate cold thermal storage allowing for non-concurrent operation of the cogeneration unit and the heat pump unit. The model is applied for a paradigmatic case study that shows how the integration of a heat pump affects the operational strategy of a cogeneration plant. It is found that CHP-HP-FG-CS offers significant reductions in fuel consumption (-8.9%) and operational production costs (-11.4%). The plant's fuel-to-energy efficiency increases from 88.9 to 95.5%, which is state-of-the-art. The plant's intermittency-friendliness coefficient Rc improves only marginally due to the constrained nature of the low-temperature heat source and the associated small capacity of the heat pump unit. Significant improvements in Rc are found when increasing the heat pump capacity assuming the availability of an unconstrained heat source
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| 5. |
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| 6. |
- Börjesson, Martin, 1980, et al.
(författare)
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Cost-effective biogas utilisation – A modelling assessment of gas infrastructural options in a regional energy system
- 2012
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Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 48:1, s. 212-226
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Tidskriftsartikel (refereegranskat)abstract
- The current utilisation of biogas from anaerobic digestion is low compared to the technical potential. This study investigates requirements for policy support to overcome techno-economic barriers of biogas utilisation and effects of different biogas distribution strategies. Two potential sectors for biogas use are covered: the transport sector and the district heating sector. A quantitative, optimising, energy system modelling approach is applied and the region of Västra Götaland, Sweden, is studied. The model has a high geographical resolution and locations of both biogas feedstock and potential markets are taken into account. The results show that a small part of the technical biogas potential can be cost-effectively utilised without biogas subsidies or larger infrastructural investments. Comparably low subsidies give significant increases in cost-effective biogas utilisation levels, but utilisation close to the full technical potential is linked to high subsidies. From a techno-economic perspective, biogas is best used as vehicle gas. Since local vehicle gas markets are limited, enhanced biogas distribution conditions not only imply larger total cost-effective biogas utilisation, but also a larger share of biogas as vehicle gas. Compared to distribution strategies based on truck transports and regional biogas grids, an expanded natural gas grid presents possibilities but also risks.
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| 7. |
- Coville, Aidan, et al.
(författare)
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The effect of missing data on wind resource estimation
- 2011
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 36:7, s. 4505-4517
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Tidskriftsartikel (refereegranskat)abstract
- Investment in renewable energy sources requires reliable data. However, meteorological datasets are often plagued by missing data, which can bias energy resource estimates if the missingness is systematic. We address this issue by considering the influence of missing data due to icing of equipment during the winter on the wind resource estimation for a potential wind turbine site in Norway. Using a mean-reverting jump-diffusion (MRJD) process to model electricity prices, we also account for the impact on the expected revenue from a wind turbine constructed at the site. While missing data due to icing significantly bias the wind resource estimate downwards, their impact on revenue estimates is dampened because of volatile electricity spot prices. By contrast, with low-volatility electricity prices, the effect of missing data on revenue estimates is highly significant. The seasonality-based method we develop removes most of the bias in wind resource and revenue estimation caused by missing data.
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| 8. |
- Dahlquist, Erik, 1951-, et al.
(författare)
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How to save energy to reach a balance between production and consumptionof heat, electricity and fuels for vehicles
- 2012
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 46:1, s. 16-20
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Tidskriftsartikel (refereegranskat)abstract
- There is a potential to utilize a significant amount of renewable energy in Sweden and European union(EU). Biomass can fulfil some 8500e12,500 TW h/y in EU, while the total utilization was 16,084 TW h/y2009. Even though there is a significant amount of wind power, hydro power and potentially also solarpower, it still is most economical to reduce the consumption of heat, electricity and fuels for vehicles. Asaved kWh is normally cheaper than to produce one extra. In this paper different opportunities for savingenergy will be discussed. This includes manufacturing industries, process industries, power plants andenergy systems including distribution of power and smart grids, food production and transportation.There is also a major potential to save energy in buildings, both in the north where it is cold, and in thesouth where it can be very hot summer time. Here the potential is to avoid cooling instead. Technicalsolutions as well as economic incentives are covered. Environmental aspects are addressed, so that thesolutions will be long term sustainable.
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| 9. |
- Difs, Kristina, et al.
(författare)
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Energy conservation measures in buildings heated by district heating - A local energy system perspective
- 2010
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Ingår i: Energy. - : Elsevier Science B.V., Amsterdam.. - 0360-5442 .- 1873-6785. ; 35:8, s. 3194-3203
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Tidskriftsartikel (refereegranskat)abstract
- The extensive energy use in the European building sector creates opportunities for implementing energy conservation measures (ECMs) in residential buildings. If ECM are implemented in buildings that are connected to a district heating (DH) system, the operation of DH plants may be affected, which in turn may change both revenue and electricity production in cogeneration plants. In this study a local energy system, containing a DH supplier and its customer, has been analysed when implementing three ECMs: heat load control, attic insulation and electricity savings. This study is unique since it analyses economic and CO2 impacts of the ECMs in both a user and a supplier perspective in combination with a deregulated European electricity market. Results show that for the local energy system electricity savings should be prioritised over a reduction in DH use, both from an economic and a global CO2 perspective. For the DH supplier attic insulation demonstrates unprofitable results, even though this measure affects the expensive peak load boilers most. Heat load control is however financially beneficial for both the DH supplier and the residences. Furthermore, the relation between the fixed and variable DH costs is highlighted as a key factor for the profitability of the ECMs.
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| 10. |
- Endalew, Abebe K., et al.
(författare)
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Heterogeneous catalysis for biodiesel production from Jatropha curcas oil (JCO)
- 2011
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 36:5, s. 2693-2700
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Tidskriftsartikel (refereegranskat)abstract
- This work focuses on the development of heterogeneous catalysts for biodiesel production from high free fatty acid (FFA) containing Jatropha curcas oil (KO). Solid base and acid catalysts were prepared and tested for transesterification in a batch reactor under mild reaction conditions. Mixtures of solid base and acid catalysts were also tested for single-step simultaneous esterification and transesterification. More soap formation was found to be the main problem for calcium oxide (CaO) and lithium doped calcium oxide (Li-CaO) catalysts during the reaction of jatropha oil and methanol than for the rapeseed oil (RSO). CaO with Li doping showed increased conversion to biodiesel than bare CaO as a catalyst. La(2)O(3)/ZnO, La(2)O(3)/Al(2)O(3) and La(0.1)Ca(0.9)MnO(3) catalysts were also tested and among them La(2)O(3)-ZnO showed higher activity. Mixture of solid base catalysts (CaO and Li-CaO)and solid acid catalyst (Fe(2)(SO(4))(3)) were found to give complete conversion to biodiesel in a single-step simultaneous esterification and transesterification process. (C) 2011 Elsevier Ltd. All rights reserved.
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