Short-term uncertainty in long-term energy system models — A case study of wind power in Denmark

When wind power constitutes a larger share of the electricity production mix, credible and reliable modelling of its operation in long-term investment models becomes increasingly important. In this paper the intermittent characteristics of wind power are modelled as a stochastic parameter in a long-term TIMES model of the Danish heat and electricity sector. To our knowledge, this is not a common approach in long-term investment models, and has not been done previously in TIMES, where the short-term uncertainty of wind power is normally taken into account by a deterministic constraint that ensures excess back-up capacity. In our model, the stochasticity gives lower total energy system costs, significant lower investments in wind power, less expected electricity export and higher expected biomass consumption compared to using the traditional deterministic approach. Also, the deterministic investment strategy can be insufficient in periods with poor wind conditions. Based on our findings, we recommend using a stochastic representation of intermittent renewables in long-term investment models to provide more solid results for decision makers.     

Economic assessment of virtual power plants in the German energy market — A scenario-based and model-supported analysis

The energy transition (“Energiewende”) in Germany will result in a substantial transformation of the energy supply system. Virtual power plants are expected to be important components of the new intelligent energy infrastructure. They aggregate beside different types of distributed generation units also active consumers and storage technologies in order to integrate these in a profit-maximising, system-stabilising, and sustainable way. The assessment of the economic performance of virtual power plants requires a scenario-based and model-supported analysis. In this relation, future energy market conditions are simulated using the scenario methodology. Starting from the year 2015, three scenarios have been identified that illustrate alternative energy developments in Germany by 2030. Based on these scenarios, the additional revenues potential of the modeled virtual power plant is identified when compared to an independent and non-market-oriented operation mode of distributed energy resources. According to the model results, revenues of the VPP can increase by 11% up to 30% in the analyzed scenarios in 2030 due to the market-oriented operation mode. Nevertheless, the amount and composition vary depending on technology-specific subsidies, temporary nature of power demand and price structures in the energy market. Fluctuating renewable energies are expected to benefit from the market-oriented operation mode in the virtual power plant, especially through the EEG direct marketing. The selective and regulated shutdown of renewable energies in times of negative electricity prices may lead to further cost savings. The utilization of temporary price fluctuations in the spot market and the demand-oriented provision of control power offer high additional revenue potential for flexible controllable technologies such as battery storage, biomethane as well as combined heat and power units. Finally, the determination of the long-term profitability of a virtual power plant still requires a full-scale cost–benefit analysis. For this holistic approach, the model results provide a reliable scientific basis.     

Optimal placement of PMUs for the smart grid implementation in Indian power grid—A case study

Efficient utilization of energy resources is essential for a developing country like India. The concept of smart grid (SG) can provide a highly reliable power system with optimized utilization of available resources. The present Indian power grid requires revolutionary changes to meet the growing demands and to make the grid smarter and reliable. One of the important requirements for SG is the instantaneous monitoring of the voltage, current and power flows at all buses in the grid. The traditional monitoring system cannot satisfy this requirement since they are based on nonlinear power flow equations. Synchro-phasor-measurement devices like phasor measurement units (PMUs) can measure the phasor values of voltages at installed buses. Consequently, the currents passing through all branches connected to that bus can be computed. Since the voltage phasor values at the neighboring buses of a bus containing the PMU can be estimated using Ohm’s law, it is redundant to install PMUs at all the buses in a power grid for its complete observability. This paper proposes the optimal geographical locations for the PMUs in southern region Indian power grid for the implementation of SG, using Integer Linear Programming. The proposed optimal geographical locations for PMU placement can be a stepping stone for the implementation of SG in India.     

Rationality of energy efficiency improvement targets under the PAT scheme in India – A case of thermal power plants

The market-based Perform Achieve and Trade scheme was introduced in India to enhance the energy efficiency of energy-intensive sectors, and for thermal power plants by reducing their specific energy consumption within the framework of a tradable certificate scheme. International experience suggests that effectiveness of such schemes is greatly influenced by the assigned targets of the obligated units. Setting rational targets is thus, a key aspect of successful implementation of the scheme. In the present study, we examine the rationality of the targets set for the power sector of India, based on comparing it with energy saving potential of the plants, and the targets assigned to the respective plants. Data envelopment analysis models are used to determine relative efficiency and energy saving potential. The study results indicate that in most cases, (i) The targets are much less than the actual potentials of the thermal power sector, (ii) There exist substantial inefficiencies within the system in both energy use and managerial dexterity; and (iii) If the sector realizes its full potential, then the Energy Saving Certificate market may witness a surplus of 4.7 million certificates on account of thermal power sector alone.     

Feasibility analysis of solar photovoltaic array cladding on commercial towers in Doha,Qatar – a case study

Building-integrated photovoltaic (BIPV) technology has become a major area of research due to environ-mental concerns. This article studies the feasibility of cladding high-rise towers in Doha with solar photovoltaic modules. Specifically, the case of the Qatar Financial Centre (QFC) is discussed. The major aim of the work is to evaluate the technical feasibility, economic impact and environmental effects of using photovoltaic panels on commercial towers in Qatar. Experimental data on solar irradiance and the effect of shading on the QFC Tower are presented. Numerical calculations are done using solar pathfinder software. The studies show that, although there is a significant amount of saving in CO₂ emission by using BIPV on towers in Doha, the payback period is still very long due to the cheaper cost of grid electricity in Qatar and poor conversion efficiency of PV panels. The complete system layout is presented and viable solutions are investigated.     

Economic analysis of a typical solar–coal hybrid power plant

Since the 1990s, solar energy has been hybridized with fossil power plants to improve reliability and efficiency. This study proposed an economical model for the solar–coal hybrid system. A conventional 200 MW coal-fired power plant was hybridized with solar heat at approximately 300°C and compared with a typical solar-only thermal power plant. The annual thermal performances of the proposed system were estimated and they were economically assessed using the economic model. The appropriate replacement configurations for the system can be determined for lower solar electricity cost. Therefore, this system may utilize solar energy on the utility scale cost-effectively.     

Impact of cofiring biomass with coal in power plants – A techno-economic assessment

Biomass cofiring in existing coal-fired boilers has emerged as a prospective option for voluntary reduction in CO₂ emissions to mitigate the global warming problem. However, the associated cost increase plays a crucial role for this retrofitting. A techno-economic model for the estimation of economics of cofiring is presented in this paper using the pilot plant test results for biomass cofiring and general heat and mass balance. A sensitivity analysis is carried out with this developed model to investigate the effects of different operating and logical parameters on the economics of biomass coal cofiring process. Significant results of this sensitivity analysis are also presented in this paper. The presented results may be useful for a plant owner to decide regarding the economic feasibility of retrofitting for biomass cofiring. On the other hand, it will also help to estimate the required incentives for this purpose.     

Impact of unplanned power flows in interconnected transmission systems – Case study of Central Eastern European region

The unplanned power flows at the interconnections of the Central Eastern Europe and Central Western Europe electricity markets are assessed. The assessment is accomplished using optimal power flow simulations of the linked transmission systems of Germany, Poland, the Czech Republic, Austria and Switzerland. The unplanned flows are modeled using a multivariate model that is a function of time series of wind- and solar-generated electricity, power demand and commercial power flows. It is shown that for the case of Poland there is a 25% higher loading on sections of transmission grid in Poland due to the unplanned flows. The unplanned power flows are largely a consequence of the wind-generated electricity in northern Germany that must be routed to southern Germany through the grid in Central Eastern Europe region due to an inadequate grid capacity along the north–south German corridor. It is shown without the planned 2020 developments of the grid, Poland's grid will be very susceptible to congestion and destabilization.     

Optimisation of hybrid cane-based combined heat and power-concentrating solar thermal power plants of 30 MW

The benchmarking and optimal power extraction from a cane-based combined heat and power (CHP) plant using state-of-the-art processes has been underestimated. This study indicates that the export power potential can be much more than the presently achieved values of 5.8–7.0 MW/1000 tcd (tonnes crushing per day). It can be 11–12 MW/1000 tcd. By integration of cane-based CHP with concentrating solar thermal (CST) – parabolic trough concentrators (PTC) systems of even size, the heat rate (power only) can be decreased from 2984.12 to 2088.89 kcal/kWh and the overall efficiency (power +heat) of 48.59% can be enhanced to 69.41%. The CHP potential of sugar mills will be considerable enhanced to 12 MW/1000 tcd by four elements: (a) integration with solar-concentrating collectors, (b) the use of high-efficiency, high-pressure boilers (>11.0 MPa and 560°C), (c) three-dimensional designed stage optimised steam turbines with high isentropic efficiencies of 92–94+% and (d) minimising in-house steam demand to below 225 kg/t of cane (=9.37 t/h per 1000 tcd) and in-house electric demand to below 22 kWh/t of cane (=0.91 MW/1000 tcd). Auxiliary power must be below 8% of the power export. Matching policy incentives will help in new initiatives and quick take off of new projects. The estimated potential for India for cane-based CHP is around 7 GW without solar systems and is 10 GW for hybrid CST–PTC cane-based systems. This is a zero fossil fuel-consuming technology.     

Assess the potential of solar irrigation systems for sustaining pasture lands in arid regions – A case study in Northwestern China

The combined impact of global climate change and increasing human activities has led to the severe deterioration of grasslands in China. Using the solar irrigation systems is an effective way for sustaining pasture lands in arid regions. A solar irrigation system is the device that uses the solar cell from the sun’s radiation to generate electricity for driving the pump. And photovoltaic pump consists of an array of photovoltaic cells and pumps water from a well or reservoir for irrigation. Although ecologists and organizations constantly work and find ways to conserve grasslands through irrigation systems that use solar energy, issues on water resources are not yet thoroughly discussed. This paper takes into account the main factors in the study of water resources, including precipitation and groundwater, to analyze the feasibility of using a photovoltaic (PV) pumping irrigation. The appropriate area for such a PV pumping irrigation in Qinghai Province is also presented. The results show that the grasslands appropriate for PV pumping cover about 8.145 million ha, accounting for 22.3% of the grasslands in the entire province. Finally, the problems and countermeasures of PV pumping irrigation, including the impact on regional water balance, groundwater level and highland permafrost, are also considered.     

What hinder the further development of wind power in China?—A socio-technical barrier study

Promoting wind power is a long-term strategy of China to respond to both energy shortage and environmental pollution. Stimulated by various incentive policies, wind power generation in China has achieved tremendous growth, with the cumulative installed capacity being the largest worldwide for five consecutive years since 2010. However, obstructed by various barriers, wind power provides only 2.6% of national electricity generation in China, despite the strong support from the government. From a socio-technical transition perspective, this paper aims to systematically analyze the barriers hindering the further development of China's wind power. A wind power niche model is established to illustrate the complex interactions among actors in the wind power industry and electricity supply regime. Then, qualitative content analysis is adopted to process the related evidence and data, and four categories of socio-technical barriers are identified, including technology, governance, infrastructure and culture barriers. The study shows that various interrelated barriers form a blocking mechanism which prohibits the further development of wind power in China. Policy suggestions are proposed to eliminate the barriers and further empower the wind power niche. The lesson learned from China can offer useful references for other economies to promote wind power industries of their own.     

Building energy index and end-use energy analysis in large-scale hospitals—case study in Malaysia

Hospital energy consumption is relatively high, while saving energy and reducing cost comprise one of the most important challenges considered by the majority of building designers, engineers, and decision makers. An end-use energy analysis was conducted in a large-scale hospital in Malaysia to identify energy apportioning and energy end use in the areas of air conditioning, lifts, lighting, equipment, and others. The analysis was carried out by assessing the collected desktop and field data as well as some calculations. The Building Energy Index (BEI) was calculated to compare the consumption levels in the selected hospital, which is a typical hospital building, with other hospitals in Malaysia as well as low energy buildings and Malaysian standards. The main energy source in this case study was electricity with a supply of around 75 % of total energy consumption. The current average annual electricity consumed by this hospital was 44,637,966 kWh, out of which 63 % was used by air conditioning systems and 17 % by lighting. The BEI comparison revealed that the calculated BEI of 384 kWh/m²/year is significantly higher than Malaysian rating systems and standards which recommend 200 kWh/m²/year for hospitals, 135 kWh/m²/year for commercial sectors, and is higher than previously observed hospitals with a BEI of less than 300 kWh/m²/year.     

Location of Swedish wind power—Random or not? A quantitative analysis of differences in installed wind power capacity across Swedish municipalities

The amount of installed wind power varies significantly across municipalities although the financial support for wind power production and the technology available is identical in all Swedish municipalities. This study analyses how local differences between municipalities, such as local wind prerequisites and socioeconomic conditions, might explain the establishment of wind power. The analysis is carried out for a cross section of Swedish municipalities. The time periods before and after 2006 are analyzed separately; and results reveal that the factors affecting wind power establishments are different between the two periods. In the later time period we found a statistically significant positive relationship between good wind resources and the presence of wind power as well as with the amount of wind energy installed. This result is consistent with the idea that the first wind power investments in Sweden were highly affected by individual wind energy enthusiasts, while in the more recent large-scale investments market-based judgments about future profitability may have become increasingly important. In addition, previous experience seems to be a factor that in itself facilitates additional future wind power establishments, thereby pointing to the role of accumulated institutional capacity.     

Wind farm—A power source in future power systems

The paper describes modern wind power systems, introduces the issues of large penetration of wind power into power systems, and discusses the possible methods of making wind turbines/farms act as a power source, like conventional power plants in power systems. Firstly, the paper describes modern wind turbines and wind farms, and then introduces the wind power development and wind farms. An optimization platform for designing electrical systems of offshore wind farms is briefed. The major issues related to the grid connection requirements and the operation of wind turbines/farms in power systems are illustrated.     

Transient performance of a two-dimensional salt gradient solar pond—A numerical study

Solar ponds have recently become an important source of energy that is used in many different applications. The technology of the solar pond is based on storing solar energy in salt-gradient stratified zones. Many experimental and numerical investigations concerning the optimum operational conditions and economical feasibility of solar ponds have been published in the last few decades. In the present study, a novel two-dimensional mathematical model that uses derived variables is developed and presented. This model utilizes vorticity, dilatation, density, temperature and concentration as dependent variables. The resulting governing partial differential equations are solved numerically in order to predict the transient performance of a solar pond in the two-dimensional domain. The boundary conditions are based on measured ambient and ground temperatures at Kuwait city. Based on the present formulation, a computer code has been developed to solve the problem at different operating conditions. The results are compared with the available experimental data and one-dimensional numerical results. Two-dimensionality effects are found to depend mainly on the aspect ratio of the pond. A parametric study is conducted to determine the optimum pond dimensions and operating conditions.     

Estimation of monthly solar radiation from measured temperatures using support vector machines – A case study

Solar radiation is the principal and fundamental energy for many physical, chemical and biological processes. However, it is measured at a very limited number of meteorological stations in the world. This paper presented the methods of monthly mean daily solar radiation estimation using support vector machines (SVMs), which is a relatively new machine learning algorithm based on the statistical learning theory. The main objective of this paper was to examine the feasibility of SVMs in estimating monthly solar radiation using air temperatures. Measured long-term monthly air temperatures including maximum and minimum temperatures (T_max and T_min, respectively) were gathered and analyzed at Chongqing meteorological station, China. Seven combinations of air temperatures, namely, (1) T_max, (2) T_min, (3) T_max ? T_min, (4) T_max and T_min, (5) T_max and T_max ? T_min, (6) T_min and T_max ? T_min, and (7) T_max, T_min, and T_max ? T_min, were served as input features for SVM models. Three equations including linear, polynomial, and radial basis function were used as kernel functions. The performances were evaluated using root mean square error (RMSE), relative root mean square error (RRMSE), Nash-Sutcliffe (NSE), and determination coefficient (R²). The developed SVM models were also compared with several empirical temperature-based models. Comparison analyses showed that the newly developed SVM model using T_max and T_min with polynomial kernel function performed better than other SVM models and empirical methods with highest NSE of 0.999, R² of 0.969, lowest RMSE of 0.833 MJ m^?2 and RRMSE of 9.00%. The results showed that the SVM methodology may be a promising alternative to the traditional approaches for predicting solar radiation where the records of air temperatures are available.     

The effect of residential solar photovoltaic systems on home value: A case study of Hawai‘i

An investment in solar photovoltaic (PV) is considered a home improvement, and should be reflected in home sales prices. However, uncertainty about PV policies and information asymmetries may result in an imperfect pass-through. Hawai‘i serves as an illustrative case study to assess the impact of PV on home prices because Hawai‘i has the highest number of PV installations per capita nationwide. Applying a hedonic pricing model using home resale and PV building permit data from 2000 to 2013 for Oʻahu, I find that the presence of PV adds on average 5.4% to the value of a home. The value of PV exceeds total average installed costs because many of Hawai‘i's electricity circuits have reached legal limits for PV installations and thus many neighborhoods could technically no longer install additional PV capacity. Therefore, the value of the system goes beyond its capital investment—on average, by $5000—to incorporate expected electricity savings.     

A theoretical study of molten carbonate fuel cell combined with a solar power plant and Cu–Cl thermochemical cycle based on techno-economic analysis

A novel power and hydrogen coproduction system is designed and analyzed from energetic and economic point of view. Power is simultaneously produced from parabolic trough collector power plant and molten carbonate fuel cell whereas hydrogen is generated in a three-steps Cu–Cl thermochemical cycle. The key component of the system is the molten carbonate fuel cell that provides heat to others (Cu–Cl thermochemical cycle and steam accumulator). A mathematic model is developed for energetic and economic analyses. A parametric study is performed to assess the impact of some parameters on the system performance. From calculations, it is deduced that electric energy from fuel cell, solar plant and output hydrogen mass are respectively 578 GWh, 25 GWh and 306 tons. The overall energy efficiency of the proposed plants is 46.80 % and its LCOE is 7.64 c€/kWh. The use of MCFC waste heat allows increasing the solar power plant efficiency by 2.15 % and reducing the annual hydrogen consumption by 3 %. Parametric analysis shows that the amount of heat recovery impacts the energy efficiency of fuel cell and Cu–Cl cycle. Also, current density is a key parameter that influences the system efficiency.