Using GIS to estimate the replacement potential of solar energy for urban dwellings[edit | edit source]
This paper focuses on a system design using GIS for urban planners.advisers. The system design combines commercial database and GIS packages to provide a flexible means of predicting the solar energy potential and energy consumption of dwellings. By incorporating customized tools designed to derive useful data directly from digital maps and aerial photographs, it addresses the significant problem of data collection for urban-scale energy modelling The Solar Energy Planning (SEP) system software is used , which combines widely used commercial database and GIS (geographical information system) packages. These are dynamically linked to provide a flexible and efficient way of deriving and exploiting useful data from digital maps and aerial photographs by means of a novel set of customized GIS tools. A city area of interest to the user could be selected by using the area select custom tool in the GIS. The map data derivation tools could then extract the data from footprints linked to Address Point data found within the search area.
Multicriteria GIS modeling of wind and solar farms in Colorado[edit | edit source]
The objectives of this research are to: 1) determine which landcover classes are affiliated with high wind and solar potential; and 2) identify areas that are suitable for wind and solar farms using multicriteria GIS modelling techniques.
The following variables were obtained from digital databases:Solar Potential,Distance to Transmission Lines,Distance to Cities,Population Density,Distance to Roads,Land cover,Federal Lands. Ideal conditions were defined for these and also, each was assigned weights based on their relative importance to one another. Annual direct normal solar radiation GIS data for concentrating systems, which track the sun throughout the day and transmission lines vector files were also obtained from NREL. The GIS model indicated that ideal areas for solar development are located in northwestern Colorado and east of Denver. Only 191 km2 of the state had model scores that were in the 90e100% range. These results suggest that the variables used in this analysis have more of an effect at eliminating non-suitable areas for large-scale solar farms
Solar electricity prospects in Oman using GIS-based solar radiation maps[edit | edit source]
Without an accurate database and knowledge of most appropriate locations of renewable energy applications in the country, investment in renewable energy will not be efficient and profitable. This can be achieved by producing solar radiation maps.Precise solar maps will be increasingly important as investors seek assurance that deals will be really profitable. Better information means quicker decisions saving money and bringing renewable energy resources into production more quickly. This paper discusses solar power prospects in Oman.The methodology of producing solar radiation maps using GIS tools is then discussed. A solar radiation map can be generated by using solar radiation data obtained from measurement stations. However, such a method is not applicable to many parts of the globe due to insufficiency of measurement stations.
Topography is a key factor that determines the spatial variability of radiation. Variation in elevation, orientation (slope and aspect), and shadows cast by topographic features all affect the amount of radiation received at different locations. This spatial variability also changes with time of day and time of year. The solar radiation analysis tools, in the ArcGIS Spatial Analyst extension, enables to map and analyze the effects of the sun over a geographic area for specific time periods. It accounts for atmospheric effects, site latitude and elevation, steepness (slope) and compass direction (aspect), daily and seasonal shifts of the sun angle, and effects of shadows cast by surrounding topography
It is found that if only 10% of the land of Oman with a slope less than 1% is considered an exploitable land for the parabolic trough CSP technology, then the total calculated potential of yearly electricity generation would be about 7.6 million GWh, which is many multiples of (680 times) the current generation supply in Oman.
PV site suitability analysis using GIS-based spatial fuzzy multi-criteria evaluation[edit | edit source]
This paper presents some preliminary results from a research study conducted on solar energy resource assessment in Oman. Different PV technologies were considered for implementation.
Comparing the CSP and PV technologies, the CSP necessitates larger amounts of water for cooling and mirror washing than the PV. Therefore, for arid countries with scarce fresh water resources, the PV technology is more suitable, environment friendly, and economical. Besides, the implementation of PV plants is much faster than the CSP ones, which gives it more flexibility to cope easily with the development of the grid system.
Using GIS and Multi- Criteria Analysis (MCA) together provide a fine lens for the optimal site selection for plants. The principal of the MCA is to condense complex problems with multiple criteria into finest ranking of the best scenarios from which an option is selected. The analytical hierarch process (AHP) is another approach used in decision-making strategies. It is a robust structured approach dealing with complex decisions. The AHP is based on the additive weighting model
Solar energy resource assessment and site suitability for large PV farms implementations is affected by different factors which can be classified in three main categories: Technical, Economical and Environmental. Some factors such as-dust and sand risk factors are only specific to the region and may not apply for other countries with temperate climate. The tool used in this analysis is the Fuzzy Logic Ordered Weight Averaging (FLOWA) module developed by Boroushaki and Malczewski Electric power generation potential of the country or a region is estimated based on the calculated yearly solar radiation per unit surface, the total exploitable area, and the efficiency of the technology used to convert solar radiation into electricity.
Mapping of solar energy potential in Indonesia using artificial neural network and geographical information system[edit | edit source]
The objective of this study is to determine the theoretical potential of solar irradiation in Indonesia by using artificial neural networks (ANNs) method.As developing country and wide islands area, Indonesia has the limitation on the number of meteorological station to record the solar irradiation availability; this study shows the ANN method can be an alternative option to estimate solar irradiation data. Since ANN is highly nonlinear and requires no prior assumption concerning the data relationship, it has become a useful tool for predicting solar irradiation. Particularly, in the meteorological and solar energy resources fields, ANN based models have been successfully developed to model different solar radiation variable in many locations.Inputs for the networks are latitude, altitude, and mean sunshine duration. In order to train the neural network, satellite data from 30 cities spread over Indonesia were used as training (25 cities) and testing (5 cities) data. ArcGIS was used as effective tool to visualize the map of solar resources by provincial boundaries in monthly basis.
Geographical Information Systems(GIS)and Multi-Criteria Decision Making(MCDM) methods for the evaluation of solar farms locations: Case study in south-easternSpain[edit | edit source]
This paper is based on the combination of a Geographic Information System (GIS)and tools or multi-criteria decision making(MCDM)methods in order to obtain the evaluation of the optimal placement of photovoltaic solar power plants in the area of Cartagena in southeast Spain. The combination GIS–MCDM generates an excellent analysis tool that allows for the creation of an extensive cartographic and alphanumeric database that will later be used by multi-criteria methodologies to simplify problems to solve and promote the use of multiple criteria. n GIS two types of criteria will be reflected: constraints or restrictive criteria, and weighting criteria or factors. Constraints or restrictive criteria make it possible to reduce the area of study by discarding those areas that prevent the implementation of renewable energy plants. These criteria is obtained from the legislation. Through the use of MCDM the criteria or factors mentioned are weighted in order to evaluate potential sites to locate a solar plant. Analysis and calculation of the weights of these factors is conducted using Analytic Hierarchy Process (AHP). The assessment of the alternatives according to their degree of adequacy is carried out through the TOPSIS method TOPSIS is based on the concept that the chosen alternative should have the shortest distance from the Positive Ideal Solution (PIS) and the farthest from the Negative Ideal Solution (NIS). The final ranking is obtained by means of the closeness index. This paper has demonstrated how it is possible to combine a Geographic Information System with Multi-criteria Decision Making Methods (GIS–MCDM) for use or application in the field of renewable energies, for example when a developer wants to implant a photovoltaic solar farm with specific characteristics (surface to occupy, installed power, etc.), the starting point is to select the best location based on such characteristics. Using GIS–MCDM tools, the difficult task of searching for sites is facilitated so the developer can choose those areas which, from an energy point of view, are optimal and they are also adapted to his or her needs.
However, the analysis conducted has weaknesses that could be strengthened by including linguistic labels in the methodology which could be applied in the definition of certain factors whose nature is qualitative.
GIS-based approach for potential analysis of solar PV generation at the regional scale: A case study of Fujian Province[edit | edit source]
This paper presents a case study of using high resolution grid map of solar radiation combined with the other restriction factors to evaluate the comprehensive potential analysis of solar PV generation at the regional scale, in order to present a framework of decision support tool for solar energy management in a regional area. The cost of PV generation is calculated based on the geographical distribution of technical potential. Moreover, geospatial supply curve (GSC) is employed to portray the evolution of available potential of photovoltaics (PV) generation with the increase of the generation cost. By integrating the economic evaluation variables of net present value and simple payback period, grid-based economic feasibility of PV generation project is then carried out
the first step is to evaluate the potential for exploiting solar energy sources, including geographical and technical potential in suitable areas with the aid of GIS spatial analysis functions. The second step is to assess economic feasibility for PV generation. To exactly estimate the solar radiation for the study area, a high resolution solar radiation map for Fujian Province was calculated by using the solar radiation analyst module of ArcGIS 9.3. The module accounts for atmospheric effects, site latitude and elevation, steepness (slope) and compass direction (aspect), daily and seasonal shifts of the sun angle, and effects of shadows cast by surrounding topography. For assessing the amount of electricity potential from solar PV,three categories of potential are defined :Geographical potential, Technical potential & Economic potential. The cost-benefit analysis is critical for appraising the feasibility of PV projects Basically This paper presented a computational procedure to derive a regional model of solar PV generation potential and its economic feasibility with the aid of the solar radiation analysis tool and map algebra functionality in the ArcGIS software.
GIS-based solar farms site selection using analytic hierarchy process (AHP) in Karapinar region, Konya/Turkey[edit | edit source]
Site selection for solar farms is a critical issue for large investments because of quality of terrain, local weathering factors, proximity to high transmission capacity lines, agricultural facilities and environmental conservation issues. Multi criteria evaluation methods are often used for different site selection studies. The purpose of this study was to determine suitable site selection for solar farms by using GIS and AHP in the study area. The final index model was grouped into four categories as "low suitable", "moderate", "suitable" and "best suitable" with an equal interval classification method.
n the first step, GIS data sets of study area (residential areas, land use, roads, slope and transmission lines) were collected for study area from different sources.In the next step, the weights for each of identified environmental and economic objectives were calculated with AHP which is one of the MCDM methods using Microsoft Excel and performed overlay analysis using a GIS for site selection of solar farms. In this study, land suitability map was prepared as five map layers including distance from residential, land use, distance from roads and distance from transmission lines. ArcGIS software was used in this process for overlay analyses. Determined numerical values from LSI divided into four grades (low suitable, moderate, suitable and best suitable) according to criteria and buffer zones were built. The higher score is more suitable area for solar farm areas.
Final suitability map was created for combined all criteria.
GIS-based photovoltaic solar farms site selection using ELECTRE-TRI: Evaluating the case for Torre Pacheco, Murcia, Southeast of Spain[edit | edit source]
This paper proposes the use of a Geographic Information System (GIS) in order to identify the best plots suitable for installing photovoltaic solar farms in the Municipality of Torre Pacheco, in the southeast of Spain. The plots are classified according to multiple evaluation aspects, by developing a multi criteria model and applying the ELECTRE-TRI method using the Decision Support System IRIS.The GIS provides a cartographic and alphanumeric database, including two factors of distinct nature: restrictions and criteria. The restrictions are entered into the GIS using layers defined from the current legislation which reduce the study area by eliminating those areas in which photovoltaic solar farms cannot be implemented. ELECTRE methods are based on the construction and exploitation of an outranking relation. Once all the parameters have been introduced, the IRIS program is run providing a graph. The main contribution of this paper is the combination of this geographic information system with a multicriteria decision analysis Method (ELECTRE-TRI, which is based on the exploitation of an outranking relation devoted to the sorting problem)
Solar power potential mapping in India using remote sensing inputs and environmental parameters[edit | edit source]
The paper maps the district-wise potential for concentrating solar power (CSP) and centralized solar photovoltaic (SPV) technology based power plants in India. The evaluation is based on remotely-sensed annual average global horizontal irradiance (GHI) and direct normal irradiance (DNI) provided by National Aeronautics and Space Administration (NASA) surface meteorology and solar energy program. The solar irradiation data (GHI and DNI), land-use data and Digital Elevation Model (DEM) were used in GIS environment while employing land-use criteria and topography to exclude unsuitable sites for harnessing solar energy. Furthermore, land-cover factor, number of sunshine hours and conversion efficiencies were taken into account to calculate technical potential in suitable land areas for solar power development. Remote sensing and GIS could be utilized to assess the potential for various renewable energy alternatives while including aspects such as, geographical location , technology used for harnessing renewable energy,economic viability and others. The main objective of this study is to calculate district-wise technical potential for solar energy in India using remotely sensed solar irradiation data while considering land-use and topography exclusion criteria. The technical potential is calculated both for CSP and centralized SPV technology independently to identify geographical locations best suited for respective technology and the hybrid ones. For SPV potential calculation, all the areas with a solar resource equal to or greater than 4.0 kWh/m2/day were included. The solar potential results presented in this study for Indian districts would certainly benefit planners and policy makers to make sound decisions for site selection, planning of solar parks, and installation of suitable solar power technologies at the best suitable sites.
GIS-based method to evaluate the photovoltaic potential in the urban environments: The particular case of Miraflores de la Sierra[edit | edit source]
The purposes of this study were to develop a multi-criteria approach based on Geographic Information Systems (GIS), Light Detection and Ranging (LIDAR) and hourly horizontal radiation data to explore the possibility of installing photovoltaic (PV) systems in urban environments, and to evaluate the resulting annual production of electricity. LIDAR data provide an accurate description of urban environments by creating a Digital Surface Model (DSM), which is used to calculate the local inclination and orientation of roofs by means of the shadow effect of the various components (including other buildings and trees). The radiation incident on the panels is calculated with a geometric method based on the hourly horizontal radiation broken down into its diffuse and direct components. the efficiency of the panels and different sources of losses, especially temperature, are incorporated into the assessment of the effective production. The five most common panel technologies are considered: Si Mono, Si Multi, CIS, TeCd, Ai amorfo
This article presents an efficient model developed in ARCGIS using LIDAR data.Depending on the primary purpose, the choice of the most suitable technology may be different. For example, in the case study, Si amorphous panels are the most efficient, but their total production is less than a third of what could be obtained with Si mono crystalline panels. Therefore, the minimum energy produced is an important constraint on the choice of technology.
Solar resources and power potential mapping in Vietnam using satellite-derived and GIS-based information[edit | edit source]
The present paper presents maps of the solar resources in Vietnam and of the solar potential for concentrating solar power (CSP) and for grid-connected photovoltaic (PV) technology. The mapping of solar radiation components has been calculated from satellite-derived data combined with solar radiation derived from sunshine duration and other additional sources of information based on reanalysis for several atmospheric and meteorological parameters involved. Geographic Information Systems (GIS) have been used for combining the solar potential with the land availability according each scenario to deliver the technical solar potential maps of Vietnam. Vietnam has a dense and long database of sunshine duration measurements consisting of 171 stations distributed along the country which have been recording daily values of sunshine duration since 1984. Meteosat IODC (Indian Ocean Data Coverage) images for the period 2003–2012 were used to compute daily values of GHI and DNI (Direct Normal Irradiation) in Vietnam. Solar global irradiation and additional meteorological variables have been computed with SKIRON model. SKIRON is a mesoscale numerical model based on the Eta prediction model, and uses input data from the Global Forecast System (GFS)On the other hand, the knowledge of solar radiation components for clear sky conditions, mainly GHI and direct normal irradiance (DNI), is frequently useful since it determines the upper bound of the solar resource expected for a specific site. The solar potential for Vietnam has been estimated and mapped from several hypothesis and scenarios concerning the solar resource availability and the solar technology systems to be taken into account. Solar resource availability has been obtained from the solar resource mapping for Vietnam estimated from satellite imagery, ground measurements and reanalysis of several atmospheric and meteorological variables.
Using GIS analytics and social preference data to evaluate utility-scale solar power site suitability[edit | edit source]
Determining socially acceptable and economically viable locations for utility-scale solar projects is a costly process that depends on many technical, economic, environmental and social factors. This paper presents a GIS-based multi-criteria solar project siting study conducted in the southwestern United States with a unique social preference component. Proximity raster layers were derived from features including roads, power lines, and rivers then overlain with 10 × 10 m raster terrain datasets including slope and potential irradiance to produce a high resolution map showing solar energy potential from "poor" to "excellent" for high potential counties across the southwestern United States. Similar maps were produced by adding social acceptance data collected from a series of surveys showing the potential public resistance to development that can be expected in areas of high solar energy suitability. Applying social preferences to the model significantly reduced the amount of suitable area in each of the selected study areas. The methods demonstrated are expected to help reduce time, money, and resources currently allocated toward finding and assessing areas of high solar power suitability. In addition to physical constraints, social attitudes can also affect where and solar development occurs. While research demonstrates that majority of Americans support renewable energy generally and solar energy in particular and development of utility-scale solar has been impeded due obstacles such as cost, efficiency, and regulations. A typical explanation of slow development tended to place blame on local residents' opposition to proposed development.
Indeed, even environmentalists have opposed proposed projects due to the impacts of solar facilities on rare desert plants and animals In the San Luis Valley of Colorado, local residents sided with environmental groups to oppose a concentrated solar power (CSP) facility due to the impact the project would have on the local ecosystem, especially with regards to transmission line siting. This example is not an isolated case.
Each selected site was processed by PVMapper [38] to analyze the maximum slope, minimum irradiance value, and distance to nearest river, road, and major grid power line. The PVMapper scorecard tool uses GIS layers to give an overview of the site terrain slope, soil, solar irradiance potential and land cover as well the distance to such features as the nearest transmission lines, rivers, and roads. Avoiding unforeseen public resistance will overall reduce the soft costs associated with solar development.
Modelling solar potential in the urban environment: State-of-the-art review[edit | edit source]
doi:10.1016/j.rser.2014.08.060 S. Freitas, C. Catita, P. Redweik, and M. C. Brito, "Modelling solar potential in the urban environment: State-of-the-art review," Renewable and Sustainable Energy Reviews, vol. 41, pp. 915–931, Jan. 2015. Cityscapes provide a complex environment, where solar radiation is unevenly distributed, especially since urban features started to propagate more and more vertically. Due to the dynamic overshadowing effects present on building surfaces, quantifying these phenomena is essential for predicting reductions in solar radiation availability that can significantly affect potential for solar energy use. Numerical radiation algorithms coupled with GIS tools are a pathway to evaluate those complex effects. Accurate representation of the terrain, vegetation canopy and building structures allows better estimation of shadow patterns. Higher spatial and temporal resolutions deliver more detailed results, but models must compromise between accuracy and computation time. In this paper, models ranging from simple 2D visualization and solar constant methods, to more sophisticated 3D representation and analysis, are reviewed. Web-based solar maps, which rely on the previous features to successfully communicate the benefits of the solar resource to the public and support in the policy-making process, are also addressed. Meteorological stations generally measure global and diffuse irradiation received on the horizontal plane and the direct component can be obtained from: Ghoriz=Dirhoriz+Difhoriz=DirnormcosZ+Difhoriz where Ghoriz is the global horizontal irradiance, Dirnorm is the direct normal irradiance, Difhoriz is the diffuse horizontal irradiance and Z is the sun׳s zenith angle. The paper showed that the improving ability to describe the physical behaviour of solar radiation has been incorporated into the methods, with model after model trying to overcome previous limitations. Thanks to the fast development of information technology, solar mapping models are today far more powerful, allowing user-friendly detailed analysis and representation of the radiation phenomena, thus reaching out outside the traditional architecture and engineering niches. An emerging trend is the employment of these GIS tools for energy analysis in the urban environment.
U.S. Renewable Energy Technical Potentials: A GIS-Based Analysis[edit | edit source]
- Utility-Scale Photovoltaics (Urban)
The process for generating technical estimates for urban utility-scale PV begins with excluding areas not suitable for this technology. First the areas are limited to those within urbanized area boundaries as defined by the U.S. Census Bureau (ESRI 2004) and further to those with slopes less than or equal to 3%. Parking lots, roads, and urbanized areas are excluded.The remaining land is grouped into contiguous areas and areas less than 18,000 square meters (m2) are removed to ensure that total system size is large enough to be considered a utility-scale project. The PV system assumed in this analysis was a 1-axis tracking collector with the axis of rotation aligned north-south at 0 degrees tilt from the horizontal, which has a power density of 48 MW per square kilometer (MW/km2)
- Utility-Scale Photovoltaics (Rural)
Technical potential estimates for rural utility- scale PV begin by first excluding urban areas as defined by the U.S. Census Bureau's urbanized area boundaries data set. percent slope for areas outside the urban boundaries is calculated and all areas with slopes greater than or equal to 3% are eliminated. Federally protected lands, inventoried roadless areas, and areas of critical environmental concern are also excluded, as they are considered unlikely areas for development.
- Concentrating Solar Power
Concentrating solar power (CSP) is defined as power from a utility-scale solar power facility in which the solar heat energy is collected in a central location. The technical potential estimates for CSP were calculated using satellite-modeled data from the National Solar Radiation Database (Wilcox, 2007), which represent annual average direct normal irradiance (DNI). Only areas with DNI greater than or equal to 5 kWh/m2/day are considered viable.
Luminescent Solar Concentrator[edit | edit source]
Luminescent solar concentrators operate on the principle of collecting radiation over a large area, converting it by luminescence and directing the generated radiation into a relatively small output target. They can be produced in many different colors, can be cut to essentially any desired shape, and are relatively robust. Alongside the A2 highway near Den Bosch, The Netherlands, two test noise barriers are installed that generate solar energy. Playing a key role in the test are the LSC panels. Owing to their many colors the LSC are visually very attractive, which makes them ideal for use in many different situations in the built environment
Read more at: http://phys.org/news/2015-06-solar-energy-noise-barriers-highway.html#jCp
Direct versus indirect illumination of a prototype luminescent solar concentrator[edit | edit source]
The luminescent solar concentrator could find application as an alternative way of generating electricity from sunlight in urban settings by virtue of its aesthetic and performance qualities. An LSC is a plastic plate filled or topped by luminescent molecules. The luminophores absorb incident sunlight and re-emit this light at longer wavelengths. A significant fraction of the re-emitted light remains trapped within the plastic light guide by total internal reflection. The main exit for this trapped light is from the edges of the device, where one can mount thin, long photo voltaic (PV) cells for converting the emission light into electricity. A positive feature is the capability of absorbing sunlight from both front and rear sides and the potential to function in diffuse light conditions.
- In particular, it has long been stated that the device functions equally well in direct and diffuse light, especially useful in the built environment but with little verification of this statement. In this work,the validity of this claim has been tested by comparing the performance of the luminescent solar concentrator in outdoor conditions ranging from clear to cloudy.
- A prototype LSC was assembled by Airbus Defence and Space Netherlands from a 60 * 40 * 2 cm3 cast Plexiglas plate (Evonik) doped with Lumogen F 305 dye. The plate is held vertically be means of a handling frame made of aluminum. A pyranometer was used to collect solar irradiation data at the test site which was then fed to a data logger. The power efficiency is thus calculated based on the ratio between the power generated (by the cells) from the entire edge surfaces of the light guide to the solar irradiation incident on the primary surface of the light guide.
Direct vs. indirect incident illumination: The most striking trend in the results is the dramatic jump in normalized edge efficiency measured simultaneous with the drop in solar irradiance. Normalized electrical output efficiency increases by up to 100% in these conditions.
- Explanation for increased efficiency: It has been shown by ray-tracing modelling techniques that the photon collection efficiency of a Red 305 based LSC is 21% with diffuse light while only 9% with the direct component. This is because short wavelength light is scattered more effectively in the atmosphere so the diffuse spectrum is blue rich and can be better harvested by the LSC. Under sunny conditions, the fraction of light coming in from behind the LSC is small compared to the front side illumination. However, under cloudy conditions and late evenings when the solar disk disappears, the difference between front and back becomes smaller. As a result, this unrecorded rear-side irradiance under cloudy conditions could contribute a larger fraction to the electrical output, affecting the efficiency values.
- In an urban setting there is a great variety of lighting conditions, both in intensity and spectral distribution. Solar energy generators must contend with clouds, shading, a moving solar disk, and seasonal changes. One of the advantages of employing luminescent solar concentrator devices in the built environment is their relative insensitivity to changes in these lighting conditions.
- The constant energy output demonstrates less tendency to 'spike' under different lighting conditions, and thus makes the device easier to integrate in a global energy network, providing a reliable source of power. The absolute output of the LSC is considerably less than a PV panel of the same size. However, the aesthetic difficulty in integrating the PV panel coupled with its sometimes problematic behavior in low light, cloudy, or warm conditions could leave room for the LSC to be used in areas where PV panels are not considered viable.
Optimizing luminescent solar concentrator design[edit | edit source]
- In this paper an optimization analysis is presented based on the implementation of a genetic algorithm, the theoretical
limits of efficiency are provided for one, two and three layer configurations and give guidance for the properties required for luminescent materials, such as quantum nano crystals, to operate efficiently in planar LSC configurations.
- All luminescent matter must obey a thermodynamic relationship between emission and absorption called the Kennard-Stepanov (K-S) relationship.It establishes a relationship between absorption, emission and temperature. The K-S relation requires that there will be some emission at any energy where there is absorption (and vice versa).
- The objective of the global optimization was to find the optimal emissive energy and the respective energy absorption edge that provide the maximum optical efficiency for a given LSC configuration while maintaining the K-S condition.
- Model of perfect luminescent matter: Because the K-S theory relates emission and absorption, there must be absorption in the perfect emission band and emission in the perfect absorption band.
- The perfect K-S model has four parameters: the band gap energy, the width of the perfect emission peak, the absorption threshold, and the crossover energy.
- Global optimization with genetic algorithm: A heuristic evolutionary technique known as a genetic algorithm (GA), which uses a coding variable instead of the variables themselves, was chosen to determine the optimized parameters that define the limits on efficiency of a specific LSC configuration.
- The results show that a single layer configuration is far from optimal and adding a second layer in the LSC with wavelength shifted material in the near infrared region significantly increases the power output, while the gain in power by adding a third layer is relatively small.For perfect luminescent materials the efficiency goes from 21.3% for one layer to 29.5% for two layers and 33.6% for three layers. Hence,under ideal conditions, a third layer does not add very significantly to the overall efficiency.
Better luminescent solar panels in prospect[edit | edit source]
- LSC panels have not yet come onto the market because of their modest light-to-electricity conversion efficiencies — a result of several light-loss mechanisms in the devices.
- These include restricted absorption ranges, losses from dye-emitted light directed outside the angles required for total internal reflection and absorption of light by the polymer that makes up the light guide. But the crucial loss mechanism that must be addressed is re-absorption of the dye-emitted light.
- Most LSCs use organic fluorescent dyes as the absorbing and emitting species. There are many advantages to organic dyes: they are efficient light absorbers; they can have fluorescence yields approaching 100%; and they are generally soluble in the polymeric light-guide host. However, the Stokes shift of these dyes — that is, the separation of their absorption and emission peak wavelengths — is often small, yielding a significant overlap of the absorption and emission profiles. This causes re-absorption of dye-emitted light when it encounters subsequent dye molecules in the light guide
- The reabsorption results in light loss from the device, either because the reabsorbing dye has a fluorescence yield of less than 100% because the re-emitted light cannot be totally internally reflected and so is lost through the top or bottom surfaces of the light guide.
- Inorganic quantum dots have long been studied as possible alternatives to organic dyes. For example, inorganic particles made up of a Cadmium Selenide (CdSe) core and a cadmium sulfide (CdS) outer shell have been developed for LSCs that have large Stokes shifts and so low re-absorption losses. A promising route to further minimizing losses by using zinc selenide/zinc sulfide (ZnSe/ZnS) core/shell nanocrystals 'doped' with ions of manganese (Mn2+) and cadmium (Cd2+) as the luminescent is also being researched species.
- Minimal absorption and emission spectral overlaps would reduce losses of light-guided emission to scattering and absorption by the polymer host itself, dramatically extending the possible operational size of the LSC.
- Once polymer sheets are available that contain such luminophores with good absorption in the peak of the solar pectrum, it will be possible to tackle the second major loss mechanism of LSCs, which is emission through the top and bottom surfaces of the light guide. This can be overcome by applying selective reflectors to the LSC surface5. Successful outcomes on all these fronts could increase the efficiency of LSCs to levels that would enable their use in large-area urban settings.
Patterned dye structures limit re-absorption in luminescent solar concentrators[edit | edit source]
- A main factor limiting LSC efficiency is internal losses due to re absorption of light emitted by the dye molecules. The reabsorbed photon is potentially lost in one of two main ways: 1) re-emission at angles outside the LSC waveguiding modes, or 2) transferral into heat due to < 100% quantum yield of the fluorophore. For an LSC with a refractive index of 1.5 (typical of many polymers) it has been reported that re absorption may account for ∼ 25% of light loss.
- This work describes a method for limiting internal losses of a luminescent solar concentrator (LSC) due to re absorption through patterning the fluorescent dye doped coating of the LSC. By engineering the dye coating into regular line patterns with fill factors ranging from 20 - 80%, the surface coverage of the dye molecules were reduced, thereby decreasing the probability of the re-emitted light encountering another dye molecule and the probability of re absorption.
- B270 Glass (50 x 50 x 3 mm3) and PMMA (50 x 50 x 5 mm3) substrates were used as waveguides. A polyimide (Nissan 130 or JSR AL-1051) adhesion layer was spun onto the glass substrates at 3000 rpm for 60 s.
- Absorption spectra of most samples were measured using a Shimadzu UV-3102 PC spectrometer. Edge emission of the wave-guides was measured by a SLMS 1050 integrating sphere (Labsphere) equipped with a diode array detector. The LSCs were exposed to a collimated light source from a 300 W solar simulator with filters to approximate the 1.5 AM (global) solar spectrum (Lot-Oriel) located at a distance of 15 cm from the top surface of the wave-guide.
- The edge emissions from all four edges of each waveguide were measured to determine the effect of dye coverage on the edge output and efficiency of the LSCs.
- The relative efficiency of the patterned LSC system, defined as the ratio of total integrated edge emission (350-750 nm) to the total energy absorbed by the sample, increased with decreasing area of dye coverage. At 30% dye coverage, the relative light emission efficiency of the patterned LSC on glass was more than double the efficiency of the
100% covered sample.
- It was thus demonstrated that the relative efficiency of light emission from the edges of an LSC can be significantly improved by reducing the dye surface coverage of the waveguide via patterning.
Using Lenses to Improve the Output of a Patterned Luminescent Solar Concentrator[edit | edit source]
- Previous work demonstrated that re-absorption, a major loss mechanism in luminescent solar concentrators (LSCs), could be reduced by patterning luminescent dyes on the device surface; emission efficiency improved considerably. However, total light output decreased due to reduced absorption of the incident light. The results of adding a (poly)carbonate lens system to a patterned wave-guide to focus more of the incident light on the line patterns has been presented in this work.
- The drawback of patterning is incident photons encountering the clear regions pass through the substrate without being
absorbed, resulting in lower edge emissions.
- In this work, a lens system on top of the waveguide to focus incident light on the dye patterns,is described,this simultaneously increases the absorption of the LSC while maintaining enhanced emission efficiency.The objective of the lens array design is to maintain a high dye concentration to maximize absorption of the dye structures and use the lenses to collect from larger areas, effectively bringing the light to the dye, while maintaining the high emission efficiency of the patterned LSCs.
- A lens capable ofcollecting light from at least ± 20 ° and focusing it on a dye pattern was demonstrated.
- Designing the lens was performed using a commercial software package. The modeled lens array was fabricated by compression molding (poly)carbonate (PC) using a milled copper plate as mold. Photographs of the resulting lens arrays edge profile were digitized and modeled using MATLAB programming to compare with the intended lens shape.
- The recorded edge emission of the lenses combined with the patterned LSC with a black absorbing background were compared to the edge emission of the same line pattern LSC without the lenses on top and to a 100% covered LSC
- The lens design was based on the position of the sun relative to the city of Eindhoven in the Netherlands.
Using a sun position calculator (Forster Engineering Services, Australia) for Eindhoven , changes in the azimuthal and elevation angle of the sun were > 200 °and ∼ 60 ° , respectively, from sunrise to sunset in the month of June, when the changes in the sun's position are the largest.
- The lens array made of (poly)carbonate was designed to focus solar radiation on dye structures and was integrated with patterned LSCs. The acceptance angle of the lens array was investigated by examining the performance of the integrated LSC
system in a range of ± 30 ° incident angles.
- The lens array was able to focus light incident within the range of ± 20 ° directly on the lines of dye structure as confirmed by a near constant edge output of the integrated system
- The addition of the PC lens array increased the line patterned LSC edge output by ∼ 60%. This was the first instance of a less than fully covered LSC wave-guide outperforming a fully-covered wave-guide.
Increased efficiency of luminescent solar concentrators after application of organic wavelength selective mirrors[edit | edit source]
- Organic wavelength-selective mirrors are used to reduce the loss of emitted photons through the surface of a luminescent solar concentrator (LSC). A theoretical calculation suggests that application of a 400 nm broad reflector on top of an LSC containing BASF Lumogen Red 305 as a luminophore can reflect 91% of all surface emitted photons back into the device.
- Used in this way, such broad reflectors could increase the edge-emission efficiency of the LSC by up to 66%. Similarly, 175 nm broad reflectors could increase efficiency up to 45%.
Theoretical
- The maximum total increase in LSC efficiency (𝜂𝐿𝑆𝐶,max) is a combination of both incident and emitted light reflection and can be calculated from the efficiency of the reflector and the absorbable incident light that passes through the reflector. This increase can be described by the number of photons leaving the edge of the LSC when a cholesteric filter is added (𝑛𝑒𝑑𝑔𝑒,𝑐ℎ𝑜𝑙) and the number of photons leaving the edge of the LSC without a cholesteric filter (𝑛𝑒𝑑𝑔𝑒,𝑏𝑎𝑟𝑒).
- Although a complete calculation ofηLSC,maxrequires a detailed knowledge of the processes in the waveguide, a rough estimate can be obtained:
𝜂𝐿𝑆𝐶,max=f(1+𝑛𝑒𝑑𝑔𝑒,𝑐ℎ𝑜𝑙)
- It was found that By adding a 400 nm broad reflector at the top of an LSC, the efficiency could be increased
by up to 66%. If a reflector with a more narrow reflection band is added to the top of the LSC, increases of 45% or 35% could be achieved for 175 nm broad reflectors and 75 nm broad reflectors, respectively. Experimental
- The broadband reflectors were made from two stacked right-handed narrowband reflectors applied to a manually rubbed half wave plate centered at 560 nm (Edmund Optics). A mixture of reactive LC mesogen LC242 (BASF), varying concentrations chiral dopant LC756 (BASF), 1% of photoinitiator Irgacure 184 (Ciba) and 1% of surfactant to induce planar alignment at
the liquid crystal-air interface in xylene (1:1 by weight, Aldrich) were spin coated at 800 rpm for 30 seconds. After spincoating, the samples were immediately heated on a hot stage at 90 °C for 30 seconds and then photo-polymerised by UV-exposure in a nitrogen atmosphere. Before applying the second reflecting layer with a higher concentration of chiral dopant, the first layer was treated with an oxygen-plasma for 1 minute at 60W, to improve the wetting of the LC layer. A similar process was applied to the rear side of the same halfwave plate following an identical procedure.
- Application of cholesteric reflectors to an LSC with a peak absorbance of approximately 1.0 increased edge output by a maximum of 4.5% when the reflector with the onset wavelength of 700 nm is added: similar increases are seen in samples with higher absorbance (2.36). At lower peak absorption (<0.1) the increase in efficiency is much higher, with a peak increase in efficiency of 30% at 740 nm. However, this is lower than was calculated.
- There are several differences between the theoretical approach and the experimental measurements. First, the reflectivity of the experimental reflectors is not as good as calculated in theory. Second, the theoretical approach assumed that all light reflected back into the LSC by the reflectors reaches the edge of the LSC. In the experiments this is not the case. Photons reflected back into the LSC can be re-absorbed by the luminophores in the LSC due to the overlap in absorption and emission spectra. Reflected photons not immediately absorbed will not be in waveguide mode, so they will encounter the white scatterer underneath the sample, potentially multiple times.
- If the reflectors have non-unity reflectivity it can result in additional losses. Finally, the emission profile is assumed to be spherical for the calculations. In actual practice, the emission profile will not be spherical due to dichroic absorption and emission of the luminophore in combination with the collimated incident light.
- These results demonstrate that re-absorption has a large influence on the effectiveness of the reflectors.
