High Direct Normal Irradiance Research Articles

Hybrid intra-hour DNI forecasts with sky image processing enhanced by stochastic learning

We propose novel smart forecasting models for Direct Normal Irradiance (DNI) that combine sky image processing with Artificial Neural Network (ANN) optimization schemes. The forecasting models, which were developed for over 6months of intra-minute imaging and irradiance measurements, are used to predict 1min average DNI for specific time horizons of 5 and 10min. We discuss optimal models for low and high DNI variability seasons. The different methods used to develop these season-specific models consist of sky image processing, deterministic and ANN forecasting models, a genetic algorithm (GA) overseeing model optimization and two alternative methods for training and validation. The validation process is carried over by the Cross Validation Method (CVM) and by a randomized training and validation set method (RTM). The forecast performance for each solar variability season is evaluated, and the models with the best forecasting skill for each season are selected to build a hybrid model that exhibits optimal performance for all seasons. An independent testing set is used to assess the performance of all forecasting models. Performance is assessed in terms of common error statistics (mean bias and root mean square error), but also in terms of forecasting skill over persistence. The hybrid forecast models proposed in this work achieve statistically robust forecasting skills in excess of 20% over persistence for both 5 and 10min ahead forecasts, respectively.

Optimization studies for hybrid and storage designs for parabolic solar trough systems with the system advisor model

India is fast realizing its need to reduce its dependence on carbon intensive, nonrenewable energy sources and shift its focus to making greater use of renewable energy sources such as solar power. Jawaharlal Nehru National Solar Mission (JNNSM) is one of the several programs launched by Government of India to capitalize on country's enormous solar potential. One of the aims of JNNSM includes construction of concentrated solar power (CSP) demonstration projects, particularly in the north‐western region which is blessed with high direct normal irradiation (DNI). In this study, system advisor model (SAM) has been used to develop technical performance and energy generation cost estimates for different parabolic trough designs. The different plant designs include two solar‐only plants (differing in solar multiples) without storage or hybridization, one solar‐only plant with storage capacity of 4 h, and one solar trough plant integrated with natural gas hybridization. Trough plant steam cycle performance is modeled in SAM using Jodhpur, Rajasthan as the reference site. This analysis aims to provide vital technical criteria and levelized energy cost estimates that can prove instrumental for the design of CSP demonstration plants in Rajasthan. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 1247–1254, 2013

04/02896 Operational method for deriving high resolution direct normal irradiance from satellite data: Schillings, C. et al. Solar Energy, 2004, 76, (4), 475–484

04/02896 Operational method for deriving high resolution direct normal irradiance from satellite data: Schillings, C. et al. Solar Energy, 2004, 76, (4), 475–484

Validation of a method for deriving high resolution direct normal irradiance from satellite data and application for the Arabian Peninsula

Meteosat-derived hourly solar direct normal irradiances are compared to high quality ground measurements. For validation purposes the region of the Arabian Peninsula is selected due to its high solar energy potential and due to the availability of accurate ground measurements of the beam irradiance. Hourly ground data for the complete year 2000 are evaluated by automated and visual quality checks. Eight of 12 measurement sites fulfil the quality requirements and can be used for the validation purposes. The relative mean bias error, averaged over all 8 sites, is 4.3% for all-sky conditions. The relative root mean square error, averaged over all sites, decreases from 36.1% for hourly values down to 8.1% for the yearly sum. With this accuracy the method may well be applied for solar energy resource assessments in comparable regions and for detailed solar power plant simulations. Analysing one year of data of the Arabian Peninsula results in a maximum direct normal insolation of about 2650 kW h/m 2 in the north-east near Tabouk, while the minima can be found in the Al Soodah mountains with approximately 1650 kW h/m 2.

Operational method for deriving high resolution direct normal irradiance from satellite data

Ground-based measurements of solar beam irradiance are expensive and rarely available especially in the sunbelt countries, the favourable regions for concentrating solar energy techniques. A method based on satellite data is presented that calculates hourly solar direct normal irradiance for large regions and for many years with high spatial resolution independently from ground measurements. The attenuation of solar irradiance due to scattering and absorption in the cloud-free atmosphere is calculated by a clear-sky broadband parameterisation model. It uses ozone optical depth from the Total Ozone Mapping Spectrometer, aerosol optical depth from the Global Aerosol Climatology Project and water vapour from the reanalysis of the National Centers for Environmental Prediction. Attenuation due to clouds is taken into account by a cloud index that is derived from the infrared and the visible channel of the geostationary Meteosat weather satellites. As clouds have the strongest impact on beam irradiance at ground, the resolution of the cloud parameterisation dominates the overall spatial and temporal resolution. The presented algorithm provides hourly data of direct normal irradiance related to the nominal 5 × 5 km 2 resolution of Meteosat.

Computer simulation of the performance of a solar desalination plant

Extensive pilot plant experimental studies for a period of one year were carried out to study the impact of climatic conditions on the operational performance of an innovative Fresnel solar collecting system. The solar measurements revealed that the total yearly Direct Normal Irradiance (DNI) on the tested site amounts to 1132 kWh/m2. The thermal collector efficiency, which depends on climatic conditions such as solar insolation, ambient temperature, receiver temperature as well as heat losses, ranges from 60% to 80%. The cost effectiveness when the tested Fresnel solar collection system with solar multiple of 1.0 (limited to day time operation) is combined with a commercial thermal desalination plant is compared with one completely run by fossil fuel. The breakeven fuel cost whereby the levelized cost of water of the two cases will be equal is yielded at a fuel cost of $92/bbl. When the tested Fresnel solar collection system is run at a location with a relatively high annual DNI level (1937 kWh/m2), the fuel breakeven cost falls to $52/bbl. This study also revealed that combining a Fresnel solar collection system with an MED thermal desalination plant under specific climatic conditions is considered more cost effective when operated without thermal energy storage.