| 1. |
- Abera, Bethlehem, et al.
(författare)
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An Overview of Biogas Plants in Ethiopia and Sweden: What Ethiopia Can Learn from Sweden
- 2023
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Ingår i: 2023 IEEE PES/IAS PowerAfrica, PowerAfrica 2023.
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Konferensbidrag (refereegranskat)abstract
- To promote the development of Ethiopia's biogas sector, this paper gives an overview and status of biogas in Ethiopia and Sweden, highlights the challenges impeding the expansion of biogas technology in Ethiopia, and tries to suggest lessons Ethiopia can learn from Sweden. Currently, Ethiopia has over 36,000 digesters installed, while Sweden has 281. The challenges to the expansion of biogas in Ethiopia stated in this paper include a lack of stated policy to include biogas as part of the energy system, a lack of research and development facilities dedicated to biogas, higher investment costs, the inefficiency of digesters, a lack of cooperation among stakeholders, and a lack of a comprehensive database on the subject. We recommend that Ethiopia learn from Sweden about developing a dedicated policy and roadmap, developing a national competence center like Sweden's Biogas Research Center, improving production and efficiency, considering multiple feedstocks, and appropriate waste collection, segregation, and allocation.
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| 2. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Automatically adjusting light spectrum for optimal short term photosynthetic rate
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of light emitting diods (LEDs) as greenhouse illumination is increasingly common. When each LED color is individually dimmable both light spectrum and light intensity can be tuned, which opens up for optimisation of photosynthesis through automatic control of light quality and quantity. However, this requires a non-destructive biological growth signal that can be measured fast, remotely and preferably without interacting with the plants. A potential candidate signal is steady-state chlorophyll a fluorescence gain at 740 nm, defined as dF740/dq, i.e. the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by a (small) change in intensity of each individual LED color in the lamp (Ahlman et al., 2017). By automatically adjusting the spectrum, to aim for equal fluorescence gains for all LED colors (Wik et al., 2014), the instant photosynthetic rate can be optimised given a preset electric power input to the lamp. When implementing such a controller though, constraints on the spectral distribution are needed to minimise a negative impact on plant morphology.
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| 3. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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LED spectrum optimisation using steady-state fluorescence gains
- 2016
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Ingår i: Acta Horticulturae. - 0567-7572. - 9789462611092 ; 1134, s. 367-374
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Tidskriftsartikel (refereegranskat)abstract
- The use of light emitting diodes (LEDs) in greenhouses entails the possibility to control the light in a better way, since both spectrum and light intensity can be adjusted. We aim at developing a method to automatically find the optimal spectrum in terms of energy consumption and plant growth. Previous work shows that chlorophyll fluorescence (ChlF) at 740 nm strongly correlates with the photosynthetic rate (carbon dioxide uptake rate) and that the net efficiency of a LED group therefore is coupled to the fluorescence gain w.r.t. energy consumption, i.e., the slope of a curve depicting steady-state ChlF versus applied power to the LED group. In the present work we compare the fluorescence gains for six different LED types (wavelength peaks from 400 to 660 nm) and six different species: tomato, cucumber, basil, lettuce (two species) and dill. We also compare two different kinds of experiments: steadystate experiments, waiting for the fluorescence to reach a steady state at a few incident light intensities, and ramp experiments, where the light intensity is increased slowly. The ramp experiment gives essentially the same information as the steady-state experiment, but was found to slightly overestimate the gains of the blue LEDs. Being aware of this, it should be possible to initially use the faster (ramp) method in order to find the right light composition, possibly using steady-state experiments for a few LED colours to fine tune the lamp. The relative order of the fluorescence gains among the tested LED groups is similar, but not identical, for all species tested. LED660 has the highest fluorescence gain w.r.t. incident photon flux density, and LED400 and/or LED530 have the lowest. However, the important quantity is in fact the fluorescence gain w.r.t. applied electrical power. If the individual electrical efficiencies of the LEDs change the most efficient power split on the different LEDs might change.
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| 4. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Light spectrum optimization for plant growth using biological feedback
- 2018
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Ingår i: EasyChair Preprints. - : EasyChair. - 2516-2314.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of light emitting diods (LEDs) as greenhouse illumination is increasingly common. When each LED color is individually dimmable both light spectrum and light intensity can be tuned, which opens up for optimisation of photosynthesis through automatic control of light quality and quantity. However, this requires a non-destructive biological growth signal that can be measured fast, remotely and preferably without interacting with the plants. A potential candidate signal is steady-state chlorophyll a fluorescence gain at 740 nm, defined as dF740/dq, i.e. the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by a (small) change in intensity of each individual LED color in the lamp (Ahlman et al., 2017). By automatically adjusting the spectrum, to aim for equal fluorescence gains for all LED colors (Wik et al., 2014), the instant photosynthetic rate can be optimised given a preset electric power input to the lamp. When implementing such a controller though, constraints on the spectral distribution are needed to minimise a negative impact on plant morphology. In this study measurements were conducted (on cucumber and lettuce) under different background light, and at each setting excitation signals were sequentially added by each of six different LED colors (peak wavelength at 400, 420, 450, 530, 630 and 660 nm). The corresponding changes in steady-state fluorescence were measured with a spectrometer and the fluorescence gain (dF740/dq) was calculated for each LED color and at each background light setting. These fluorescence gains were compared in order to evaluate the different LEDs' relative effect on photosynthesis under each of the different background light settings.
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| 5. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Relation between Changes in Photosynthetic Rate and Changes in Canopy Level Chlorophyll Fluorescence Generated by Light Excitation of Different Led Colours in Various Background Light
- 2019
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- Using light emitting diodes (LEDs) for greenhouse illumination enables the use of automatic control, since both light quality and quantity can be tuned. Potential candidate signals when using biological feedback for light optimisation are steady-state chlorophyll a fluorescence gains at 740 nm, defined as the difference in steady-state fluorescence at 740 nm divided by the difference in incident light quanta caused by (a small) excitation of different LED colours. In this study, experiments were conducted under various background light (quality and quantity) to evaluate if these fluorescence gains change relative to each other. The light regimes investigated were intensities in the range 160-1000 molm-2s-1, and a spectral distribution ranging from 50% to 100% red light. No significant changes in the mutual relation of the fluorescence gains for the investigated LED colours (400, 420, 450, 530, 630 and 660 nm), could be observed when the background light quality was changed. However, changes were noticed as function of light quantity. When passing the photosynthesis saturate intensity level, no further changes in the mutual fluorescence gains could be observed.
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| 6. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Stress Detection Using Proximal Sensing of Chlorophyll Fluorescence on the Canopy Level
- 2021
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Ingår i: AgriEngineering. - : MDPI AG. - 2624-7402. ; 3:3, s. 648-668
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Tidskriftsartikel (refereegranskat)abstract
- Chlorophyll fluorescence is interesting for phenotyping applications as it is rich in biological information and can be measured remotely and non-destructively. There are several techniques for measuring and analysing this signal. However, the standard methods use rather extreme conditions, e.g., saturating light and dark adaption, which are difficult to accommodate in the field or in a greenhouse and, hence, limit their use for high-throughput phenotyping. In this article, we use a different approach, extracting plant health information from the dynamics of the chlorophyll fluorescence induced by a weak light excitation and no dark adaption, to classify plants as healthy or unhealthy. To evaluate the method, we scanned over a number of species (lettuce, lemon balm, tomato, basil, and strawberries) exposed to either abiotic stress (drought and salt) or biotic stress factors (root infection using Pythium ultimum and leaf infection using Powdery mildew Podosphaera aphanis ). Our conclusions are that, for abiotic stress, the proposed method was very successful, while, for powdery mildew, a method with spatial resolution would be desirable due to the nature of the infection, i.e., point-wise spread. Pythium infection on the roots is not visually detectable in the same way as powdery mildew; however, it affects the whole plant, making the method an interesting option for Pythium detection. However, further research is necessary to determine the limit of infection needed to detect the stress with the proposed method.
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| 7. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Using chlorophyll a fluorescence gains to optimize LED light spectrum for short term photosynthesis
- 2017
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Ingår i: Computers and Electronics in Agriculture. - : Elsevier BV. - 0168-1699. ; 142, s. 224-234
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Tidskriftsartikel (refereegranskat)abstract
- When changing from the traditional high pressure sodium (HPS) lamps to light emitting diode (LED) lamps there is a quite unexplored energy saving potential in the fact that they are far better suited for control, since both spectrum and light intensity can be adjusted. This work aims at finding a way to automatically adjust the spectrum of a LED lamp, equipped with several different types of LEDs, to maximize plant growth by feedback of a remote online measure correlated with growth.A series of experiments were conducted on basil plants in order to examine whether remotely sensed steady-state chlorophyll fluorescence (F740) can be used for this purpose, and if its derivatives (fluorescence gains) w.r.t. applied powers change relative to each other for different light intensities and spectraA strong correlation between F740 and photosynthetic rate was indeed found. However, the order (w.r.t. LED type) of the fluorescence gains was only moderately affected by the light intensities and spectra investigated. The gain was highest w.r.t. red light (630 nm), though, when taking the electrical efficiencies of individual LED types into consideration, blue LEDs (450 nm) were equally, or even more efficient than the red onesAn online controller to regulate optimal spectrum for basil appears to be unnecessary. However, the fluorescence gains could be used to adapt to changes in the efficiencies when crops and operating conditions change, or when the diodes degrade. The method also shows promise as a tool to find optimal light intensity levels as well as identifying plant stress.
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| 8. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Using Fluorescence as Control Parameter to Decide Optimal Light Spectrum for Plant Growth
- 2015
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Ingår i: Proceedings 19th Nordic Process Control Workshop, Hurtigruta, Norway, Jan 2015. ; , s. 9:1-4.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modern greenhouses having lighting systems are large consumers of electricity. In Europe alone, the lighting consumption is estimated to 150 TWh per year. High pressure sodium (HPS) lamps are still dominating and the illumination is in general controlled manually by on/off control. Changing to light emitting diodes (LED) gives the possibility of adapting the spectrum (i.e. changing the power split to diodes of different colours) and to gradually changing the intensity, which implies an energy saving potential. The optimal spectrum might depend on a number of factors, for example plant species, required characteristics and energy use effciency on the diodes.Using LEDs with different blue to red (B:R) ratios, as a supplement to sunlight, have been investigated for growing of cucumber seedling [Hernández and Kubota, 2014] and tomato seedling [Hernández and Kubota, 2012]. Their conclusion was that 100% red LED is preferred, indicating that the blue light in the sunlight is sufficient (B:R in sunlight is about 4:3 on photons=m2=s basis [ASTM, 2012].
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| 9. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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A multiple input, multiple output model generator
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- When new methods of design and analysis are introduced in the control engineering field, it is scientificallyimportant to compare the new results with existing methods. Often this requires application of the methodson examples, and for this purpose benchmark processes are introduced. However, in many areas of controlengineering research the number of examples is limited to a relatively few examples, and in particular so whenmulti-input multi-output (MIMO) systems are considered. For a thorough assessment of a method, however, aslarge number of relevant models as possible should be used. As a remedy we propose a framework for generatinglinear multiple input, multiple output models based on predefined system properties, such as model type, size,stability, time constants, delays etc.
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| 10. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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A new method of scaling the gramian based input-output pairing methods for improved results
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A key problem in the application of process control systems is to decide which inputs should control which outputs. There are multiple ways to solve this problem, among them using gramian based measures, which include the Hankel interaction index array, the participation matrix and the Σ2 method. These methods take into account system dynamics as opposed to many other methods which only consider the steady-state system. However, the gramian based methods have issues with input and output scaling. Generally, this is resolved by scaling all inputs and outputs to have equal range. We will, however, demonstrate how this can result in an incorrect pairing. Further, we examine scaling of the gramian based measures, using either row or column sums, or by utilizing the Sinkhorn-Knopp algorithm instead. Then, to more systematically analyze the benefits of the scaling schemes, a multiple input multiple output model generator is used to test the different schemes on a large number of systems. This, along with implementation of automatic controller tuning, allows for a statistical comparison of the scaling methods. This assessment shows considerable benefits to be gained from the alternative scaling of the gramian based measures, especially when using the Sinkhorn-Knopp algorithm. The use of this method also has the advantage that the results are completely independent of the original scaling of the inputs and outputs.
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