International Energy Agency Task Research Articles

Solar Energy in the Nordic Built Environment: Challenges, Opportunities and Barriers

Within the framework Solar Heating and Cooling Programme of the International Energy Agency Task 51 “Solar Energy in Urban Planning”, case studies from Norway, Sweden, and Denmark were collected and analyzed through a comparative approach. The cases were first classified based on their urban characterization (existing and new urban areas) and then compared within the same country or in a cross-country perspective according to three areas of interest (i.e., Scale and planning process, Legislation and planning process, Targets and goals). The comparisons follow a common template of five sections describing the role of the involved stakeholders and highlighting challenges, barriers, and opportunities for the deployment of active solar systems and passive solar strategies. Both technical and non-technical aspects are considered. Among the technical aspects, the focus is on the adoption of solar energy strategies (e.g., solar accessibility, daylighting), the estimation of solar potential and energy generation. Regarding the non-technical aspects, the focus is on identifying barriers and challenges for the adoption of solar systems in relation to national and local legislation. The findings show that municipalities can have a crucial role in facilitating the adoption of solar energy solutions in cities by embracing ambitious visions and storytelling, as well as being directly financially involved as owners or subsidizing bodies. The findings also demonstrate the value of the use of indicators to evaluate the performance of masterplans, the combination of analogue and digital tools in the design process, and the performance of solar simulations from early stages to foster awareness among the involved stakeholders. Despite these positives, the Scandinavian legislation on solar energy utilization in the urban context still displays fragilities, making the creation of guidelines a pressing need.

Analysis of the DANAERO wind turbine field database to assess the importance of different state‐of‐the‐art blade element momentum (BEM) correction models

AbstractAerodynamic loads of wind turbine blades are often predicted by manufacturers using the blade element momentum (BEM) theory, for which many corrections have been proposed in the literature. The physical impacts of such corrections on field measurements have seldom been assessed because of the relative unavailability of dedicated measurements. Based on the unique full‐scale database of the DANAERO project, available through the IEA (International Energy Agency) Task 29, this work incrementally applies on aerodynamic field measurement improvements of the BEM theory: atmospheric boundary layer vertical velocity gradient, neighboring wake, yaw misalignment, wind inflow location, tower shadow effect, cone angles modeling, blade aeroelastic deformation, and dynamic wake. This is performed using the iBEM method (inverse Blade Element Momentum), which back‐calculates the aerodynamic coefficients (lift—CL and drag—CD) using aerodynamic loads from field tests.

Reversible ammonia-based and liquid organic hydrogen carriers for high-density hydrogen storage: Recent progress

Liquid hydrogen carriers are considered to be attractive hydrogen storage options because of their ease of integration into existing chemical transportation infrastructures when compared with liquid or compressed hydrogen. The development of such carriers forms part of the work of the International Energy Agency Task 32: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia-based and liquid organic hydrogen carriers, with a particular focus on the challenge of ensuring easily regenerable, high-density hydrogen storage.

Aerodynamic measurements on wind turbines

This article reviews the aerodynamic measurement programs on wind turbines that have been performed in the last decades. It is largely based on results from four projects carried out under auspices of the International Energy Agency (IEA), which are denoted as IEA Tasks 14, 18, 20, and 29. The aim of these projects was to collect and analyze aerodynamic measurements on five field facilities (IEA Tasks 14 and 18), the National Renewable Energy Laboratory Phase VI turbine placed in the large NASA Ames wind tunnel (IEA Task 20), and the Mexico turbine placed in the Large Low Speed Facility of the German Dutch Wind tunnel DNW (IEA Task 29). Other experimental programs with an important aerodynamic content are touched upon as well. Research areas for which these measurements have led to important progress are identified. The progress is illustrated with analyses on these experiments. It is shown that detailed aerodynamic measurements are an absolute necessity for the validation and improvement of wind turbine design codes, where it is also concluded that the amount of measurement data which has been produced until now is still far too limited.This article is categorized under: Wind Power > Science and Materials

Power curve measurement uncertainty – follow up comparative exercise for IEA Task 32

A comparative exercise for estimating the uncertainty associated with new methods for power performance measurements was coordinated by the International Energy Agency (IEA) Wind Task 32. Both IEA Task 32 and the Power Curve Working Group (PCWG) have identified the application of the new uncertainty guidelines as a problem area. One time series dataset from a wind turbine, hub height mast and vertical profiling lidar was provided to calculate the power curve using three different wind speed definitions. For each wind speed definition, participants had to estimate the wind speed measurement uncertainty based on the guidance provided by the June 2016 Final Draft International Standard (FDIS) of IEC 6140012-1 Edition 2. The comparative exercise included three iterations over the course of one year to incrementally harmonize the calculations and assumptions. The exercise showed significant variability among participants reflecting difficulty with the interpretation and application of the informative guidance. It also demonstrated that when using current technology and the available calibration techniques the use of a standalone lidar with a short met mast resulted in a significantly higher uncertainty compared to only using a hub height mast (with some measurements of wind shear and wind veer in the lower rotor).

Wind power forecasting: IEA Wind Task 36 & future research issues

This paper presents the new International Energy Agency Wind Task 36 on Forecasting, and invites to collaborate within the group. Wind power forecasts have been used operatively for over 20 years. Despite this fact, there are still several possibilities to improve the forecasts, both from the weather prediction side and from the usage of the forecasts. The new International Energy Agency (IEA) Task on Forecasting for Wind Energy tries to organise international collaboration, among national meteorological centres with an interest and/or large projects on wind forecast improvements (NOAA, DWD, MetOffice, met.no, DMI,...), operational forecaster and forecast users.The Task is divided in three work packages: Firstly, a collaboration on the improvement of the scientific basis for the wind predictions themselves. This includes numerical weather prediction model physics, but also widely distributed information on accessible datasets. Secondly, we will be aiming at an international pre-standard (an IEA Recommended Practice) on benchmarking and comparing wind power forecasts, including probabilistic forecasts. This WP will also organise benchmarks, in cooperation with the IEA Task WakeBench. Thirdly, we will be engaging end users aiming at dissemination of the best practice in the usage of wind power predictions. As first results, an overview of current issues for research in short-term forecasting of wind power is presented.

Performance Evaluation of Lighting and Daylighting Retrofits: Results from IEA SHC Task 50

This article presents some results from a large monitoring campaign performed in 22 buildings around the world as part of International Energy Agency (IEA) Task 50 “Advanced lighting solutions for retrofitting buildings”. This article mainly addresses the work of Subtask D, which aims to demonstrate sound lighting retrofit solutions in a selection of representative, typical Case Studies. In order to evaluate the Case Studies, a monitoring protocol was developed to assess the overall lighting performance taking into consideration: 1) Energy use, 2) Retrofit costs, 3) Photometric assessment, and 4) User assessment. The monitoring was carried out from June 2014 to December 2015 in 22 non-residential buildings in ten countries. This article presents results from selected Case Studies, drawing conclusions regarding retrofit solutions as well as reflecting on methodological procedures for the measurements and data collection. Measured data as well as key conclusions from Subtask D will be summarized in an electronic web and portable sourcebook at the end of the IEA Task 50 (December 2015), which will be freely available through the Internet.

Build-up and performance test of a novel solar thermal roof for heat pump operation

ABSTRACTGlobal increase in energy demand and fossil fuel prices loaded ever-increasing pressure on identifying and implementing new means to utilise clean and efficient energy resources. Due to the environmental benefits, technical and economic possibilities of Solar-Assisted Heat Pump Systems, there has been a growing interest for such hybrid systems with a variety of system configurations for various climates. International Energy Agency Task 44 of the Solar Heating and Cooling Programme has recently started working on finding methods to most effectively use solar heat pump systems for residential use. In the present study, a novel solar thermal roof collector was developed by primarily exploiting components and techniques widely available on the market and coupled with a commercial heat pump unit. The proposed indirect series Solar-assisted Heat Pump system was experimentally tested and system performance was investigated. Yet, the analysis based on indoor and outdoor testing predominantly focuses on the solar thermal roof collector. A detailed thermal model was developed to describe the system operation. Also, a computer model was set up by using Engineering Equation Solver to carry out the numerical computations of the governing equations. Analyses show that the difference in water temperature could reach up to 18°C while maximum thermal efficiency found to be 26%. Data processing of the series covering the test period represents that Coefficient Performance of the heat pump (COPHP) and overall system (COPSYS) averages were attained as COPHP = 3.01 and COPSYS = 2.29, respectively. An economic analysis points a minimum payback period of about three years for the system.

Rooftop wind monitoring campaigns for small wind turbine applications: Effect of sampling rate and averaging period

Small wind turbines are often sited in more complex environments than the open terrain sites assumed in relevant installation guidelines or in the international small wind turbine design standard IEC61400-2. The built environment is an example of such a complex environment and installation of small wind turbines on the rooftops of high buildings has been suggested by architects and project developers as a potential means of incorporating sustainable energy generation into building design. In the absence of guidelines for installing wind turbines in the built environment, two key wind measurement parameters are the rate at which a data acquisition system (DAQ) samples the sensor, and the period over which the sampled data is averaged.This paper presents the results of the effect of sampling rate and averaging period on turbulence measurements from a monitoring system on a building rooftop, in order to inform the process of developing guidelines. The results will inform the development of a Recommended Practice of wind resource assessment in the built environment, via the International Energy Agency Task 27. The key finding of the paper is that, in general, 10 Hz sampling and 10 min averaging period give upper estimates for turbulence intensity and maximum values of the turbulence power spectra. Using these conservative values in the design of the turbine may be the best approach to ensure that the turbine can handle both the fatigue loads and resonance due to gusts.

Review of International Solar Cooling Incentive Schemes

Each country has a range of government incentive and industry development programmes, which have been designed with the intention of assisting the renewable energy and building energy efficiency industries. These programmes call up procedures for inter alia quantifying benefits, rating effectiveness and achieving robust measurement and verification.Under Subtask C “Market Support Measures” of International Energy Agency Task 48 Quality Assurance & Support Measures for Solar Cooling, a country by country database of relevant standards, processes and incentives was created and links to the needs of the solar heating and cooling industry were identified.Analysis of this database is intended to provide insight into the needs of alternative policy interventions, and support the development of a scientific evidence base and tools to inform policy makers. In this way this exercise is intended to encourage the development and adoption of successful solar air conditioning support measures.This paper presents the insights from the incentive review and presents possible approaches to guide the future development of effective standards, guides and rating frameworks.

Performance and safety of rooftop wind turbines: Use of CFD to gain insight into inflow conditions

The installation of small and medium-size wind turbines on the rooftops of high buildings has been often suggested by architects and project developers as a potential solution for achieving sustainable energy in building design. In such locations, however, because of the presence of buildings and other adjacent obstructions, wind is normally turbulent, unstable and weak, in terms of direction and speed. The use of wind turbines in the built environment poses challenges to overcome, including energy yield reduction due to lower mean wind speeds in urban areas, and environmental impacts because of their close vicinity to people and property.There is a need to understand the inflow wind conditions for a small wind turbine in the built-environment. A resource assessment of the potential wind turbine site in the built environment can determine the wind characteristics including zones of wind acceleration, recirculation, blocking and channelling. This knowledge is crucial for input into the design process of a small wind turbine to accurately predict blade fatigue loads and ensure that it operates safely, and performs optimally in the environment.Computational Fluid Dynamics (CFD) is a useful method to model wind flows in order to perform a resource assessment for the application of small wind turbines in a manner that requires less time and investment than a measurement campaign. This paper presents the results of research using a CFD code to model wind flows over the roof of a building and assesses the possibility of combining a CFD package with wind atlas software to form a wind energy resource assessment tool for the application of small wind turbines on the roof of a building. Experimentation with the model shows that the results are particularly sensitive to building height and shape, roof shape, wind direction, and turbine installation height and location. The results will be used to help develop a recommended practice of wind resource assessment in the built environment, in an international collaborative effort via the International Energy Agency Task 27.

Evaluation of integrated hydrogen systems: IEA Task 18

The International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) established in 2004 a task (Annex 18) on the topic of “Integrated Systems: Evaluation of Hydrogen Demonstration Projects”. During 6 years, divided in two phases, this annex has been working in order to search and provide information on progress in the hydrogen economy around the world. Spain is one of the 15 member countries since the phase 1. The task has followed three main targets: ▪ To develop a database that includes national documents, national capabilities and a compilation of demonstration projects of each member country. ▪ To evaluate several hydrogen demonstration systems deployed within the participating countries. These projects have in common that modeling tools are used to help guide, assess, and evaluate the overall design and performance. ▪ To find best practices, trends and lessons learned with respect to realization and operation of integrated hydrogen systems. The participation of INTA in this Annex, as a national member and the coordination of a capability analysis work group inside the Spanish Hydrogen and Fuel cell Platform (PEHFC), has helped to complete and update a database on the State of the art of hydrogen activities in Spain.

An Empirical Validation of Modeling Solar Gains Through a Glazing Unit Using Building Energy Simulation Programs

Empirical validation of building energy simulation tools is an important component in assessing the reliability of the simulation software. An experiment performed in conjunction with the International Energy Agency's Task 34/Annex 43 was used to assess the performance of four building energy simulation codes used to model an outdoor test cell with a glazing unit. The experiment was run for a 20-day period during October 2004, and experimental cooling powers were compared with predictions from (1) EnergyPlus, (2) DOE-2.1E, (3) TRNSYS-TUD, and (4) ESP-r. Detailed code inputs for optical and thermophysical properties as well as the impact of thermal bridges were quantified through experiments and simulations; numerous statistical parameters and sensitivity analyses were implemented to facilitate a thorough comparison of predicted and experimental cooling powers. The mean percentage differences for all four codes were: 1.9% for EnergyPlus, −3.6% for DOE-2.1E, −6.2% for TRNSYS-TUD, and 3.1% for ESP-r. The implications of various modeling procedures as well as a detailed discussion of the results are provided, specifically concerning the sensitivity of the code cooling power predictions to the selection of convective heat transfer coefficients and algorithms.

Measured performance of 12 demonstration projects—IEA Task 13 “advanced solar low energy buildings”

This paper presents the results obtained from measurements and experiences gained from interviews on 12 advanced solar low energy houses designed and built as part of the International Energy Agency (IEA) Solar Heating and Cooling Programme—Task 13. Three years after the IEA Task 13 formally ended, the results were collected by means of questionnaires sent to the former participants in Task 13. A small IEA working group was responsible for collecting and processing the results. The paper gives a brief presentation of the houses and the applied energy saving measures. Measured and expected energy consumptions and indoor climate conditions are compared and differences explained. Special innovative installations and systems are described and evaluated. In general the measured energy consumption was higher than the expected values due to user influence and unforeseen technical problems but still an energy saving of 60% compared with typical houses was achieved. Prevention of overheating requires special attention also at northern latitudes. Interviews with occupants revealed the need to explain the building’s behaviour thoroughly to its users and elaboration of user manuals.

IEA bioenergy agreement task XI: Municipal solid waste conversion to energy end of task review

This paper overviews the main work and achievements of the International Energy Agency's Task on Municipal Solid Waste (MSW) conversion to energy. The objectives of the Task were to encourage information exchange between research and development programmes and other new initiatives relating to energy recovery from MSW, and to use this information to benefit research, development and deployment programmes on energy recovery from MSW in participating countries. Governments are now encouraging the sustainable use of MSW resources, both domestically and as part of their international obligations. These encourage development of a waste management hierarchy which places greater emphasis on waste prevention and minimisation through materials and energy recovery. The IEA Task provided participating countries with an international perspective in the areas of thermal technologies (incineration of MSW and refuse derived fuel and ash residues), biological technologies (landfill gas and anaerobic digestion of MSW) and generic issues relating to MSW conversion technologies (source separation, recycling, mechanical processing, sampling and analytical protocols). Work was carried out through meetings, study tours and networks. The main benefits from this international collaboration were that participants obtained up-to-date information on technical and non-technical issues affecting energy from waste technologies, including legislation, methodologies, and plant experience, that they could then use to encourage the development of energy from waste in their own countries. The work of the Task will continue for a further three years during 1995–1997.

Analysis methodology, experimental investigation, and computer optimization of a passive solar commercial building in the Belgian climate

The Fondation Universitaire Luxembourgeoise (FUL) building (completed in 1986) has been selected as a Belgian candidate for participation in the IEA (International Energy Agency) Task XI project devoted to passive solar commercial buildings. Therefore, an evaluation methodology has been set up and a monitoring plan has been defined and performed. Together with this experimental investigation, intensive computer simulation work has defined an optimized design of the building. The main results show that the recorded performance can be improved to an extent of 15% energy savings, which yields a correct performance for a passive solar building in the temperate maritime Belgian climate.