The effect of measurement time resolution on the peak time power demand reduction potential of domestic solar hot water systems

The electrical resistance showerhead is the water heating technology used in over 70% of the Brazilian dwellings. These high power (5–8 kW are typical) instant heating devices contribute significantly to the demand peak in the early evening, and are a major burden to distribution utilities in Brazil. The objective of this paper is to define consumer showering patterns, and analyze the influence of the power demand measurement time resolution on the potential of peak time power demand reduction provided by Domestic Solar Hot Water (DSHW) systems. Results show that the measurement of electrical power demand in a 15-min interval is not adequate to evaluate and verify the benefits provided by the use of DSHW systems, because it heavily underestimates the active power demand reduction at peak hours. This work suggests that a 1-min time resolution can be considered appropriate to assess the potential impacts caused by the use of DSHW systems on the peak hours demand reduction.     

Demand side resource operation on the Irish power system with high wind power penetration

The utilisation of demand side resources is set to increase over the coming years with the advent of advanced metering infrastructure, home area networks and the promotion of increased energy efficiency. Demand side resources are proposed as an energy resource that, through aggregation, can form part of the power system plant mix and contribute to the flexible operation of a power system. A model for demand side resources is proposed here that captures its key characteristics for commitment and dispatch calculations. The model is tested on the all island Irish power system, and the operation of the model is simulated over one year in both a stochastic and deterministic mode, to illustrate the impact of wind and load uncertainty. The results illustrate that demand side resources can contribute to the efficient, flexible operation of systems with high penetrations of wind by replacing some of the functions of conventional peaking plant. Demand side resources are also shown to be capable of improving the reliability of the system, with reserve capability identified as a key requirement in this respect.     

Prediction of global solar irradiance based on time series analysis: Application to solar thermal power plants energy production planning

Due to strong increase of solar power generation, the predictions of incoming solar energy are acquiring more importance. Photovoltaic and solar thermal are the main sources of electricity generation from solar energy. In the case of solar thermal energy plants with storage energy system, its management and operation need reliable predictions of solar irradiance with the same temporal resolution as the temporal capacity of the back-up system. These plants can work like a conventional power plant and compete in the energy stock market avoiding intermittence in electricity production.This work presents a comparisons of statistical models based on time series applied to predict half daily values of global solar irradiance with a temporal horizon of 3 days. Half daily values consist of accumulated hourly global solar irradiance from solar raise to solar noon and from noon until dawn for each day. The dataset of ground solar radiation used belongs to stations of Spanish National Weather Service (AEMet). The models tested are autoregressive, neural networks and fuzzy logic models. Due to the fact that half daily solar irradiance time series is non-stationary, it has been necessary to transform it to two new stationary variables (clearness index and lost component) which are used as input of the predictive models. Improvement in terms of RMSD of the models essayed is compared against the model based on persistence. The validation process shows that all models essayed improve persistence. The best approach to forecast half daily values of solar irradiance is neural network models with lost component as input, except Lerida station where models based on clearness index have less uncertainty because this magnitude has a linear behaviour and it is easier to simulate by models.     

Demand side management—A simulation of household behavior under variable prices

Within the next years, consumer households will be increasingly equipped with smart metering and intelligent appliances. These technologies are the basis for households to better monitor electricity consumption and to actively control loads in private homes. Demand side management (DSM) can be adopted to private households. We present a simulation model that generates household load profiles under flat tariffs and simulates changes in these profiles when households are equipped with smart appliances and face time-based electricity prices.     

Demand side management for water heating installations in South African commercial buildings

The largest percentage of the sanitary hot water used in South African buildings is heated by means of direct electrical resistance heaters. This is one of the major contributing factors of the undesirable high morning and afternoon peaks imposed on the national electricity supply grid. Water heating therefore continues to be of concern to ESKOM, the country's only electrical utility company. The so‐called in‐line water heating system design methodology was developed to address this problem. This paper investigates the potential impact of in‐line systems on the national peak electrical demand. A computer simulation model was developed that combines a deterministic mathematical model with a statistical approach in order to predict the diversity factors associated with both the existing and in‐line design methodologies. A study was also conducted to estimate the total installed water heating capacity in the national commercial building sector. This figure can be combined with the simulated diversity factor to determine the peak electrical demand. The deterministic model includes the detailed simulation of the hot water storage vessel, the electrical heater and the system control algorithm. The mathematical model for the storage vessel is based on an electrical analogue approach that includes the effects of conduction as well as forced and natural convection. This model was verified extensively with the aid of laboratory measurements and compared with existing storage vessel models. It was found that the new storage vessel model could predict the supply temperature within 2 per cent for a system configuration with the heater in parallel outside the reservoir and within 12 per cent for a configuration with the heater situated inside the reservoir. This compares favourably with existing models found in the literature. The complete simulation based on the statistical approach showed that extensive application of the new design methodology could result in a reduction of approximately 75 MW in the total maximum peak demand imposed on the electricity supply grid in wintertime. This is 58 per cent of the current peak demand due to commercial water heating and 12.5 per cent of the peak load reduction target set by ESKOM until the year 2015. Copyright © 2001 John Wiley & Sons, Ltd.     

The sun’s total and spectral irradiance for solar energy applications and solar radiation models

Using the most recent composite time series of total solar irradiance spaceborne measurements, a solar constant value of 1366.1 W m⁻² is confirmed, and simple quadratic expressions are proposed to predict its daily value from the Zurich sunspot number, the MgII index, or the 10.7 cm radio flux index. Whenever these three indices are available on a daily basis (since 1978), it is possible to predict the sun’s irradiance within 0.1% on average, as accurately as current measurements.Based on this value of the solar constant, an improved approximation of the extraterrestrial solar spectrum from 0 to 1000 μm is proposed. It is obtained by dividing the spectrum into nine bands and selecting representative (and recent) spectra, as well as appropriate scaling coefficients for each band. Comparisons with frequently used spectra are discussed, confirming previous findings of the literature.This synthetic and composite spectrum is proposed at 0.5-nm intervals in the UV (280–400 nm), 1-nm intervals between 0–280 and 400–1705 nm, 5-nm intervals between 1705 and 4000 nm, and progressively larger intervals beyond 4 μm, for a total of 2460 wavelengths.     

Desalination by solar-powered reverse osmosis in a remote area of the Sultanate of Oman

The Ministry of Water Resources successfully conducted an experimental study on the use of solar power to desalinate brackish ground water at their Heelat ar Rakah camp, a remote location some 900 km south of Muscat, the capital of Oman. The system comprises components for pre-treatment of pumped well water to separate hydrogen sulphide, acid dosing to correct the pH, cartridge filtration, a solar powered reverse osmosis unit, and a reject-water evaporation pond. The solar powered system comprises a 23.2 m² solar photovoltaic generator with a peak capacity of 3250 W_p, a boost charge battery of 200 Ah at 48 VDC, a charge controller, a sine-wave inverter of 3000 VA with an output of 230 V, 50 Hz, and necessary controls and instrumentation. The design water output of 5 m³/day during 5 h (of each day) was achieved, with the output sometimes exceeding 7.5 m³/day. The average cost of production is estimated at US$6.52/m³ over the 20-year lifetime of the equipment. The study has demonstrated that solar-powered reverse osmosis systems are particularly appropriate to remote locations that have limited or no access to supply services such as fuel, power or potable water.     

A new approach for predicting vertical global solar irradiance

Solar irradiance, particularly on vertical surfaces, plays a major role in determining the thermal and energy performance of a building. It is important to the design and analysis of both active solar systems and passive solar buildings. Many mathematical models are mainly developed to predict the sky-diffuse irradiance on inclined surfaces from the measured horizontal diffuse component. This paper presents an approach to estimate the vertical global irradiance based on direct beam and ground-reflected components which can be accurately determined. Hourly data recorded from January 1996 to December 1998 in Hong Kong were used for the model development. The performance of the proposed model and two well-known anisotropic inclined surface models (Muneer and Perez) was evaluated against data measured in 1999. Statistical analysis indicated that the proposed model gives reasonably good agreement with measured data for all vertical planes. Although the new model has been found less effective than the Perez model, its simplicity nature provides buildings designers a convenient and reliable alternative in the estimation of vertical solar irradiance.     

The stochastic two-state solar irradiance model (STSIM)

A novel irradiance model is presented that simulates solar irradiance as a stochastic process with two states. The model contains, as a sub-model, the stochastic insolation model, which divides time into sunny periods and periods when the sun is hidden behind clouds, based on a homogeneous recurrent Markov process with two states. The irradiance model by itself calculates the irradiance depending on the state indicated by the sub-model. Methods are shown of how to adjust the model based on data easily available from meteorological stations.     

Performance of off-grid residential solar photovoltaic power systems using five solar tracking modes in Kunming,China

This paper compares the performance of a 2.02 kW_p off-grid residential solar photovoltaic (PV) power system using PVSYST simulation software for a household in Kunming, Yunnan province, China. The monthly available solar energy; missing energy; array, final, and reference yields, performance ratio; and array capture and system losses were analyzed for five solar tracking modes: fixed tilted plane, seasonal tilt adjustment, horizontal axis tracking, vertical axis tracking, and dual axis tracking. Although there were some similar aspects across the five systems, minimum available solar energy (2461 kWh/y) and maximum missing energy (134.68 kWh/y) were obtained using the fixed tilted plane system (tilt angle = 25°, azimuth angle = 0°), whereas maximum available solar energy (3081 kWh/y) and minimum missing energy (48.53 kWh/y) in October were obtained using the dual axis tracking system. Average monthly performance ratio was maximal for the fixed tilted plane system (0.689), and minimal for the dual axis tracking system (0.596).     

Economic and environmental impacts from the implementation of an intelligent demand side management system at the European level

This paper presents the results of an analysis on the economic and environmental impacts of the application of an intelligent demand side management system, called the Energy Consumption Management System (ECMS), in the European countries. The ECMS can be applied for the control of individual, widely distributed electric loads, using the power distribution network as the command communication channel. The system can be applied in public lighting, in the tertiary and residential sectors, as well as in the industry. A top-down analysis investigates the possible penetration levels in each application area. The long-term impacts following the application of system are evaluated using the LEAP2006 platform. The WASP IV model is also used for the optimization of the power generation expansion and the corresponding calibration of LEAP2006. Several operational strategies combining variable market penetration of the ECMS and expected energy savings are examined. Results show that, under a logical market penetration, a reduction of 1–4% in primary energy, of 1.5–5% in CO₂ emissions and a 2–8% saving in investment costs for power generation expansion is to be expected for the EU-15. The results also justify that innovative devices may be attractive to end users and also help in the implementation of global energy-saving policies.     

Energy management in solar thermal power plants with double thermal storage system and subdivided solar field

In the paper, two systems for solar thermal power plants (STPPs) are devised for improving the overall performance of the plant. Each one attempts to reduce losses coming from two respective sources. The systems are simulated and compared to a reference STPP.     

Direct and indirect uncertainties in the prediction of tilted irradiance for solar engineering applications

Global radiation measured on fixed-tilt, south-facing planes (40° and vertical) and a 2-axis tracker at NREL’s Solar Radiation Research Lab. in Golden, CO is compared to predictions from ten transposition models, in combination with either optimal or suboptimal input data of horizontal irradiance. Suboptimal inputs are typically used in everyday engineering calculations, for which the necessary data are usually unavailable for the site under scrutiny, and must be estimated in some way. The performance of the transposition models is first evaluated for ideal conditions when optimal data are used. In this specific case, it is found that the Gueymard and Perez models provide the best estimates of global tilted irradiance under clear skies in particular.The performance of four direct/diffuse separation models is also evaluated. Their predictions of direct and diffuse radiation appear biased in most cases, with a model-dependent magnitude. Finally, the performance of the resulting combinations of separation and transposition models is analyzed in a variety of situations. When only global irradiance is known, the accuracy of the tilted irradiance predictions degrades significantly, and is mainly conditioned by the local performance of the direct/diffuse separation method. For the south-facing vertical surface, inaccuracies in the ground reflection calculations becomes another key factor and significantly increase the prediction error. The Reindl transposition algorithm appears to perform best in this case. When using suboptimal input data for the prediction of plane-of-array irradiance on a moderately tilted plane (40°S) or a 2-axis tracking plane, the Hay, Reindl and Skartveit models are less penalized than others and tend to perform better. It is concluded that further research should be conducted to improve the overall process of predicting irradiance on tilted planes in realistic situations where no local high-quality irradiance or albedo measurements are available.     

Efficacy of solar power units for small-scale businesses in a remote rural area, South Africa

Much work has considered the practicalities and affordability of solar systems for domestic energy supplies in remote rural areas. There is less understanding of its utility for small-scale business enterprises in such areas. We examined the patterns of use of two 12 V and one 24 V systems for small-scale enterprises housed in transportable containers. Monitoring of load shed and top of charge indicated that the 12 V systems were inadequate to meet the requirements of the enterprises. The 24 V operation performed a lot better. Despite some technical limitations the system offered a number of social, economic and environmental positives; primarily the offering of business products not otherwise available in the area, incomes to the entrepreneurs and greater connectivity with regional centres through office services such as cell-phone charging and faxing. Customers of the small-scale enterprises felt that their presence in the area saved them some money because they no longer had to travel as frequently to regional urban centres.     

New equations for the calculation of the horizon brightness irradiance in the model of Perez

In this technical note authors propose new expressions to calculate the diffuse irradiance coming from the horizon brightness band on a tilted plane. As in the model of Perez, it is assumed that the radiance from this band is a constant. New expressions are more exact than previous ones as they eliminate some of the simplifications considered in the model of Perez. For small slope angles new expressions give irradiance values up to 32.98% higher than with the cited model. Notwithstanding, when slope angle increases obtained differences sharply decrease at the beginning and this decrease becomes practically linear from about 40° on.     

The impacts of solar water heating in low-income households on the distribution utility’s active, reactive and apparent power demands

In Brazilian low-income households, water-heating requirements are typically met by electrical showerheads. On average, 73.1% of all residential units in the country are equipped with these resistance-heating devices, with nominal powers ranging from 3 to 8 kW. This situation imposes a considerable burden on the electricity utility companies, since electrical showerheads typically represent the highest load but the lowest utilization (load factor) in a residential consumer unit. Furthermore, typical utilization times coincide with, and contribute to, the electrical power demand peaks in Brazil, rendering these low-cost, high-power electrical devices a high-cost consumer for the electrical system to cater for. For low-income residential consumers, electricity tariffs are subsidized, and utilities must therefore make a considerable investment in infrastructure for a limited return. In this paper we analyze the impacts of solar water heating in low-income households on the distribution utility active, reactive and apparent power demands. We have monitored a statistically representative group of low-income residences equipped with a compact domestic solar water heater in Florianopolis - Brazil for 1 year. We show that in comparison with identical residential units using electrical showerheads, with the adoption of solar water heating the reductions in the active, reactive and apparent power demands on the distribution utility were 49%, 29% and 49% respectively.     

Testing of a new solar coating for solar water heating applications

A novel and affordable solar selective coating exhibiting higher solar absorption efficiency compared to the commercial black paint coating used in most ordinary solar water heating systems (SWHSs) has been developed. The coating is fabricated by embedding a metallic particle composed of a nickel-aluminium (NiAl) alloy into the black paint. The optical behaviour of several percentages of the NiAl alloy in the coating is studied using UV-Vis and IR spectroscopies. The chemical composition of the coating was characterized using XRD and thermo-gravimetric analysis (TGA) for both the black and alloy-containing paint. The results allowed deducing that the optimum composition to consider for further testing was 6% NiAl alloy by mass. The applicability of the coating in a real thermosyphonic SWHS was evaluated throughout the year, spanning both hot and cold seasons. It is found that the new coating shows better performance compared to the untreated black paint by an average of 5 °C over a period of 1 year. The corrosion resistance of the coating was investigated using electrochemical polarization and weight-loss measurements in the corrosive medium of 3% NaCl in 0.50 M HCl. Higher inhibition efficiency of corrosion was found for the alloy-containing paint compared to the untreated paint by more than 12%. Finally, Scanning Electron Microscopy (SEM) was used to explore the morphology of the modified coating surface, and compared to the untreated surface.     

Thermal management of solar photovoltaics modules for enhanced power generation

Industry and government interest in solar energy has increased in recent years in the Middle East. However, despite high levels of solar irradiance in the Arabian Gulf, harsh climatic conditions adversely affect the electrical performance of solar photovoltaics (PV). The objective of this study is to compare the annual performance characteristics of solar PV modules that utilize either sun-tracking or water cooling to increase electrical power generation relative to that of stationary, passively cooled modules in the Middle East climatic conditions. This is achieved using an electro-thermal model developed and validated against experimental data acquired in this study. The model is used to predict the annual electrical power output of a 140 W PV module in Abu Dhabi (24.43°N, 54.45°E) under four operating conditions: (i) stationary geographical south facing orientation with passive air cooling, (ii) sun-tracked orientation with passive air cooling, (iii) stationary geographical south facing orientation with water cooling at ambient air temperature, and (iv) stationary geographical south facing orientation with water refrigerated at either 10 °C or 20 °C below ambient air temperature. For water cooled modules, annual electrical power output increases by 22% for water at ambient air temperature, and by 28% and 31% for water refrigerated at 10 °C and 20 °C below ambient air temperature, respectively. 80% of the annual output enhancement obtained using water cooling occurs between the months of May and October. Finally, whereas the annual yield enhancement obtained with water cooling at ambient air temperature from May to October is of 18% relative to stationary passive cooling conditions, sun-tracking over the complete year produces an enhancement of only 15% relative to stationary passive cooling conditions.     

Energy,exergy, and exergoeconomics (3E) analysis and multi-objective optimization of a multi-generation energy system for day and night time power generation - Case study: Dezful city

The present study aimed to investigate a multi-generation energy system for the production of hydrogen, freshwater, electricity, cooling, heating, and hot water. Steam Rankine cycle (SRC), organic Rankine cycle (ORC), absorption chiller, Parabolic trough collectors (PTCs), geothermal well, proton exchange membrane (PEM) electrolyzer, and reverse osmosis (RO) desalination are the main subsystems of the cycle. The amount of exergy destruction is calculated for each component after modeling and thermodynamic analysis. The PTCs, absorption chiller, and PEM electrolyzer had the highest exergy destruction, respectively. According to meteorological data, the system was annually and hourly tested for Dezful City. For instance, it had a production capacity of 13.25 kg/day of hydrogen and 147.42 m³/day of freshwater on 17th September. Five design parameters are considered for multi-objective optimization after investigating objective functions, including cost rate and exergy efficiency. Using a Group method of data handling (GMDH), a mathematical relation is obtained between the input and output of the system. Next, a multi-objective optimization algorithm, a non-dominated sorting genetic algorithm (NSGA-II), was used to optimize the relations. A Pareto frontier with a set of optimal points is obtained after the optimization. In the Pareto frontier, the best point is selected by the decision criterion of TOPSIS. At the TOPSIS point, the exergy efficiency is 31.66%, and the total unit cost rate is 21.9 $/GJ.     

Recent improvements of the Meteorological Radiation Model for solar irradiance estimates under all-sky conditions

This study presents the recent improvements of the Meteorological Radiation Model (MRM v6) against previous model versions for more accurate estimates of the solar radiation components, i.e. global, diffuse and direct. The MRM v6 follows a different approach for the simulation of the atmospheric conditions by selecting the most appropriate aerosol model (desert, urban, maritime or continental), and usage of look-up tables for the spectral variation of the aerosol optical depth (AOD) and single scattering albedo (SSA). Furthermore, the MRM v6 uses hourly data of sunshine duration in order to achieve better simulations under cloudy skies. The results show that the MRM v6 improves the estimates of the measured global, diffuse and direct solar irradiances at Athens, Greece since the Root Mean Square Error (RMSE) becomes 13.7%, 40.8% and 24.2%, respectively, against 18.0%, 44.5% and 34.1% for the MRM v5. A decrease is also found in Mean Bias Error (MBE), especially for the diffuse (from 26.2% to 19.5%) and direct (from −9.0% to −2.4%) irradiances, indicating that the inclusion of the aerosol properties in MRM v6 significantly improves the estimations. The MRM simulations are very satisfactory on monthly basis indicating that the model is suitable for solar energy applications.