Solar Aided Power Generation Plant Research Articles

Improving the Thermal Power Plant Efficiency through the Use of Solar Technologies

The demand for energy is growing rapidly with the development and improvement of the standard of living in the world. The interaction between energy generation facilities and the environment is a topic that requires close attention, since these two components have a significant influence on the human existence and progressive growth of productive forces. Over the past few decades, the main attention has been paid to research aimed at improving conventional power plants, reducing harmful emissions into the environment, and introducing renewable energy sources. One of the ways to develop thermal power plants and reduce the impact on the environment is hybridization of solar technologies with thermal power plants. An overview of solar technologies used in the energy sector is given. A hybrid thermal power plant (TPP) aided by solar technology, known as Solar Aided Power Generation (SAPG), is briefly described. A hybrid model of an SAPG plant is considered, and the efficiency of such power plants is analyzed. The conditions of the People Republic of Bangladesh were chosen for the calculations. Information on the current state of the Bangladesh energy sector, on the climatic features of the country, and on the potential for introducing hybrid solar technologies in it is given. The power plant model was simulated using the Thermoflex software produced by the Thermoflow company. The calculation results have shown that the SAPG plant annually generates by about 25% more power than the standalone concentrated solar power plant.

Impact of thermal energy storage system on the Solar Aided Power Generation plant with diverse structure and extraction steam operation strategy

Solar Aided Power Generation (SAPG) plant is a type of solar thermal hybrid system. In such a system, the coupling of solar field and regenerative Rankine cycle plant is achieved through a heat exchanger system used to facilitate heat exchange process between solar fluid and feedwater to boiler. The extraction steam, which is used to preheat feedwater, is replaced/adjusted and expended further in the steam turbine to generate power. The performance of such a hybrid power system is dependent on the combinations of heat exchanger configuration and extraction steam operation strategy. The present work optimises the combinations for the SAPG plant with diverse thermal energy storage (TES) capacity, and evaluates the impact of thermal energy storage (TES) system on the SAPG plant with different combinations. A 300 MW SAPG plant is used as case study. The results indicate that the optimal combinations are heat exchanger being arranged in rear series of or in parallel of the replaced feedwater heater and replacement order of extraction steam being from high to low grade stages. The technical performance of optimal combinations are about 1.15 % to 8.85 % higher than the most commonly evaluated combinations for the SAPG plant without TES system. TES system would reduce the advantages of the optimal combinations over other combinations. However, this negative effect is very small and can be ignored. The integration of the TES system would increase the LCOE for all combinations. This impact of the TES system on the LCOE decreases with the increase in SM value.

A strategy to flexibly operate a solar aided power generation plant for wide irradiation conditions

Solar Aided Power Generation is a solar thermal hybrid power system, in which solar heat is used to replace the heat of extraction steam for a Rankine cycle power plant by preheating the power plant feedwater to boiler. In this power system, low to high temperature solar heat can flexibly replace extraction steam at different stages, the most common replacement strategy is medium to high temperature solar heat used to replace extraction steam to all high-pressure stages. However, this solar replacement strategy faces a problem of inefficient utilisation of non-ideal solar irradiation, which limits the annual solar contribution of the hybrid power system. In the present study, a novel solar replacement strategy, which can efficiently use wide range solar irradiation, is proposed. In this strategy, the extraction steam replacement stages can be flexibly selected depending on the solar radiation condition. In this study, the performance of a power system for the novel strategy and most common replacement strategy (i.e., solar heat used to replace extraction steam to all high-pressure stages) have been compared based on a hybrid power system modified from 300 MW power plant. The results indicate that the solar contribution of the power system operated with novel strategy can be improved by 6.6% and 11.9% for typical winter and summer days, respectively. Also, by using the novel strategy, the annual solar contribution and annual solar operation hours can be improved by 6.7% and 1488 h.

On the use of thermal energy storage in solar-aided power generation systems

The solar-aided power generation (SAPG) technology has been proven to be one of the most efficient ways to integrate solar thermal energy into coal-fired power plants. An open question is whether to integrate the SAPG plant with a thermal energy storage system (TES). Conventionally, most SAPG plants are not designed to include TESs due to high costs and challenges related to the intermittent nature of solar energy. To address this question, a realistic case study utilizing a 330MWe SAPG plant is investigated in this paper. The simulation shows that when the SAPG plant uses a TES with a proper regulation strategy, the energy efficiency of the SAPG can be increased by 2.5% and the levelized cost of electric energy (LCOE) can be reduced by 0.27 cents/kWh. A well-regulated TES does not deteriorate the economic performance of the SAPG plant here and has a positive impact on its operational safety (especially under sudden irradiance change). To the best of authors’ knowledge, this is the first time to study the operational strategies of TES (based on the operating characteristics of the SAPG systems) and to combine them with the TES’s size optimization to maximize the techno-economic performance of the SAPG plant.

Optimisation of Solar Aided Power Generation plant with storage system adopting two non-displaced extraction steam operation strategies

Solar Aided Power Generation (SAPG) is one of cost-effective methodologies of integrating solar heat into fossil fuel fired power plant. For such system, solar heat used to displace extraction steam to high grade extraction steam is the best choice. However, strategies to adjust low grade extraction steam would also influence the plant performance. Two strategies exist: steady temperature (ST) and steady mass flow (SMF) strategies. In present study, the impact of storage integration on the SAPG plant adopting two strategies has been investigated. For the SAPG plant with storage system, the plant using ST strategy would have higher technical and economic performance than that using SMF strategy. With the increase of the solar multiply, the advantage of the ST strategy over the SMF strategy would be decreased. However, the increase of storage capacity can alleviate this trend, especially in high radiation regions. The Levelized cost of electricity (LCOE) of the SAPG plant with storage system would be greatly promoted in low solar multiple cases. When the solar multiple increases to about 2, the LCOE of the SAPG system with and without storage capacity becomes convergence. The results give a useful guide for operation of the SAPG plant with storage system.

An improved model to evaluate the performance of solar-aided power generation plants

ABSTRACT Solar aided power generation (SAPG) is an efficient method to utilize solar thermal energy to generate power in association with traditional fossil-fueled power plants. In an SAPG plant, solar energy is used to replace extracted steam to preheat feedwater into the boiler in a regenerative Rankine power cycle. In previous SAPG plants’ performance evaluation models, a key assumption made is that the parameters at the outlets of the boiler, such as temperature and pressure, remain unchanged even if the steam mass flow rates through the boiler have changed due to the introduction of solar heat. This assumption actually makes the boiler to be modeled as a black box to simplify the model, but inevitably compromised the accuracy of the evaluation results. The error is sometimes so significant that some research conclusions are affected especially when the solar heat is used to replace the extraction steam before the reheating process. An improved SAPG evaluation model with the assumption that the boiler is modeled as a heat exchanger instead of a black box is proposed in this paper. The improved model accuracy has been demonstrated focusing on three SAPG power plants, namely 210 MW, 300 MW and 600 MW power plant. The errors are respectively reduced by 0.48%, 2.86% and 0.76% at 50% load. Moreover, three cases studies have been discussed focusing on the three SAPG power plants. The solar-power efficiency of replacing the second extraction steam is lower than that of replacing the third extraction steam after the error of boiler “black box” model is considered. The results indicate that using solar energy to replace higher stage of extraction steam is not necessarily better than replacing lower stage extraction steam as previously understood. The research provides a new insight into the role of solar replacement for different extracted steam levels in an SAPG power plant.

Measures to reduce solar energy dumped in a solar aided power generation plant

Solar aided power generation technology has been proved to be one of the most efficient ways to integrate solar energy into a coal-fired power plant. In a typical plant, the solar field size is normally designed with a solar multiple greater than one. Therefore, sometimes collected solar heat becomes surplus when the collected solar heat exceeds the heat demand. Other than being dumped, the surplus solar heat could be either charged into a thermal energy storage system if there is one; or used to preheat (feedwater) continuously. In this paper, the impacts of these two measures (being charged and preheating continuously) on the technical and economic performances of the integrated plant are analyzed in detail by undertaking a desktop case study. The results show that both measures could reduce the surplus solar heat dumped, but the economic performances vary. For the measure of preheating continuously, the maximum solar input is determined by a safety assessment to ensure a stable and safe operation. Surplus heat over this maximum amount has to be dumped. The results also show that for the plant located in Tibet China, both measures could reduce the levelized cost of energy and enhance the effective solar-to-electricity efficiency, compared to dumping case; while continuing preheating measure is superior to being charged technically and economically.

Solar aided power generation: A review

Abstract Solar Aided Power Generation (SAPG) is the most efficient and economic ways to hybridise solar thermal energy and a fossil fuel fired regenerative Rankine cycle (RRC) power plant for power generation purpose. In such an SAPG plant, the solar thermal energy is used to displace the extraction steam by preheating the feedwater to the boiler. The displaced/saved extraction steam can, therefore, expand further in the steam turbine to generate power. The research and development of the SAPG technology started in the 1990s. This paper is trying to reviews and summarises the progress of research and development of the SAPG plant technology in last almost 30 or so years, including the technical and economic advantages of SAPG over other solar thermal power generation technologies (e.g. solar alone power generation), various modelling techniques used to simulate SAPG perforamnce, impacts of SAPG plant's configuration, size of solar field and strategies to adjust mass flow rate of extraction steam on the plant perforamnce, exergy analysis of SAPG plant and operation strategies to maximise plant's economic returns etc. In addition, the directions for future R& D about SAPG technology have been pointed/proposed in this paper.

Performance maximization of a solar aided power generation (SAPG) plant with a direct air-cooled condenser in power-boosting mode

Solar aided (coal-fired) power generation (SAPG) technology has been approved to be an efficient way to use solar energy for power generation. However, most solar-rich areas are often short of cooling water supply, especially in China. The air-cooled condenser could alleviate this issue effectively for power plants in these areas. In this paper, a solar aided power generation with direct air-cool condenser (SAPG + ACC) plant is studied and optimized to maximize its performance. Due to the addition of solar heat in an SAPG plant, the exhaust steam flow rate leaving the turbine changes, especially in power-boost mode, which affects the turbine exit pressure and deviates the condenser from its designed operating condition. To achieve maximum net power output, the correlation among the optimum (turbine) exit pressure (OEP), the solar heat input and the ambient temperature, is obtained in this study. The annual plant's performances with four proposed operating strategies of the air-cooled condenser are compared and analyzed. The results show that for an SAPG + ACC plant, the operating Strategy.3, i.e. operated with the hourly OEP is the optimal one, resulting the plant has annual solar-to-electricity efficiency (SEE) of 17.82% and its levelized cost of electricity (LCOE) is of 0.09 $/kWh.

Stabilizing operation of a solar aided power generation (SAPG) plant by adjusting the burners’ tilt and attemperation flows in the boiler

Solar Aided Power Generation (SAPG) technology has been proved to be one of the most efficient ways to integrate solar energy into a coal-fired power plant. However, previous studies on SAPG systems have mainly focused on their design and design optimization. There are few studies on their operation. In an SAPG plant, solar heat is used to replace the extracted steam to preheat feedwater. However, the introduction of solar energy inevitably affects the steam flow rate through the boiler, especially when the SAPG plant is in fuel-saving operation mode, thus affecting the boiler's operation. Namely, the steam parameters at the boiler outlets would change with various solar inputs if no control mechanism were applied. A mechanism for adjusting the burners' tilt and attemperation flows in the boiler is therefore proposed in this study, in order to stabilize the temperature of the steam at the outlet of the boiler. To simulate the effectiveness of the mechanism, a transient model of the SAPG plant, including a series of modules for key components in the plant, has been developed in this study. The simulation results in a case study of a 300 MWe SAPG plant, showing the proportion of heat that was absorbed in the boiler was redistributed due to the solar input, without adjusting the burners' tilt and attemperation flows, resulting in temperature drops of superheated/reheated steam when in a fuel-saving mode. However, the simulation in the case study also shows that by swinging the burner tilt angle up to 22.7° and adjusting the attemperation flows in the super-heaters and re-heaters in the boiler, the superheated/reheated steam temperature can be restored from 523 °C and 510 °C respectively back to 543.0 °C, the desired temperature.

Simulated performance analysis of a solar aided power generation plant in fuel saving operation mode

Solar aided (coal-fired) power generation (SAPG) system has been proved to be an efficient way to utilize the solar energy for power generation. Due to the instability of the solar radiation, a SAPG system generally operates under transient working conditions. In this paper, performance simulation sub-models of main components in a SAPG plant are established based on the lumped parameter assumption. A 330 MW SAPG power plant as a case study is simulated. The variations of the performances, main parameters of the plant with the solar field heat output and the dynamic responses under a typical day are analyzed. The results show that when the heat output of the solar field changes from 0 kJ/h to 2.13 × 108 kJ/h, the coal saving rate will increase to 6.4%, and the solar power generation share (the proportion of the power from the solar energy to the total power from the SAPG plant) will increase to 7.74%. During the analysis process, in order to optimize the solar field, the concept of the solar field equivalent efficiency (SFEE) is proposed and the optimal velocity of heat transfer fluid (HTF) in absorber tube is obtained.

A technique to avoid two-phase flow in solar collector tubes of the direct steam generation system for a solar aided power generation plant

In a traditional solar aided power generation (SAPG) plant, problematic two-phase flow may be present in the solar collector tubes which can lead to burst pipes. Within the SAPG plant, it is proposed that a flash tank be applied. By using a flash tank and mandating its inlet pressure by controlling the booster pump, the preheating and overheating collectors can each be ensured to have single-phase flow. To assess the economic and performance criteria of adding a flash tank, a simulation model using is developed and using a unified matrix equation technique. This method is used to assess the effect of the flash tank on a case study 300 MW SAPG plant. Two modes of SAPG operation are considered. In the ‘single-generation mode’ only steam is introduced to the fossil-fuelled plant. In the ‘co-generation mode’ both steam, from the overheating collector, and water, from the flash tank, are introduced to the fossil-fuelled plant. The ‘co-generation mode’ is found by the authors to be the marginally better performing mode. By applying a flash tank in the SAPG system, the problem of unstable two-phase flow in solar collector tubes can be effectively overcome thereby improving the viability of implementation of retrofitted solar aided power generation to fossil-fuelled plants.

Numerical Analysis of a Solar Air Preheating Coal Combustion System for Power Generation

AbstractA new type of solar-aided power generation plant has been proposed and numerically analyzed in this work. It is composed of a parabolic trough collector field, based on gas-phase nanofluid,...

Mixed mode operation for the Solar Aided Power Generation

Integrating solar heat into a regenerative Rankine cycle power plant to displace the heat of the extraction steam is a highly efficient method to use solar thermal energy for power generation purpose. This technology is termed Solar Aided Power Generation. Such a power system can be operated for power boosting or fuel saving mode of operation. Here, we proposed a mixed mode of operation. In such a mixed mode of operation, the Solar Aided Power Generation is operated at a series of time intervals. In each time interval, such a power system is operated in one selected mode (i.e. either power boosting or fuel saving mode) with higher profitability. In this paper, the superiority of the mixed mode of operation over the single mode of operation (i.e. power boosting or fuel saving) has been demonstrated through two case studies. In these case studies, a Solar Aided Power Generation plant located in Australia and China where the market (and weather) conditions are significantly different, is assumed to operate in power boosting, fuel saving and mixed mode of operation. The results indicate that the mixed mode of operation could guarantee the best economics for such a power system over the single mode of operation in different markets. In Australia where the on-grid tariff fluctuate significantly, the annual profitability of the mixed mode of operation could be up to 12.1% higher than that of a single mode of operation. However, in China where is electricity market is controlled by the government and relatively flat, the mixed mode of operation still shows economic advantage over the single mode of operation although not much (i.e. about 2.0%).

Performance improvement of coal-fired power generation system integrating solar to preheat feedwater and reheated steam

Solar aided power generation (SAPG) technology has been proven as an efficient way to use solar energy for power generation purpose. In a SAPG plant, a solar field consisting of parabolic solar collectors is normally used to supply the solar heat to preheat feedwater and replace the high-pressure extraction steam. However, the outlet temperature of reheated steam decreased with the integration of solar thermal which sacrificed the system performance. As an improvement, the second solar field was proposed to preheat the reheated steam to maintain its outlet temperature and the average temperature of regenerative Rankine cycle before or after solar integration. Through a case study using A 600 MW supercritical SAPG plant operating in fuel-saving Using solar to preheat feedwater and reheated steam could improve overall cycle efficiency and solar-to-electricity efficiency by 1.91% and 6.01%, respectively. The solar share was expanded from 9.53% to 17.26%. The electricity generated per solar aperture area under the design condition was 187.96 W/m2, which was 26.91% higher than that of the system without the second solar field.

The Impact of Solar Radiation on the Annual Net Solar to Power Efficiency of a Solar Aided Power Generation Plant with Twelve Possible “Configuration-operation” Combinations

Abstract Solar Aided Power Generation (SAPG) has been approved to be an efficient method of using solar thermal energy. In an SAPG plant, the solar thermal energy carried by the heat transfer fluid is integrated into a regenerative Rankine cycle power plant to preheat the feedwater to the boiler. A heat exchanger which is termed as solar preheater facilitate this heat transfer process. The extraction steam which is bled from the turbine to preheat the feedwater is displaced and expended further in steam turbine to generate power. Depending on the arrangement of the solar preheater, an SAPG plant has different configurations, which is termed as solar preheater configurations. When the solar input changes, the flow rates of extraction steam is needed to be adjusted, which is termed as solar preheater operation strategies. The combinations of solar preheater configuration and operation strategies are called “configuration-operation combinations”. Previous studies proposed twelve possible “configuration-operation” combinations [1] . It was found that twelve combinations fall into six different groups in terms of annual net solar thermal to power efficiencies [1] . In present paper, the influence of solar collector area and solar radiation on the annual net solar to power efficiencies of twelve combinations has been evaluated. The SAPG plant is modified from a 300 MW power plant, and only the extraction steam to high pressure/temperature feedwater heaters is assumed to be displaced by the solar thermal energy. In addition, the annual solar radiation in three locations have been used for evaluation. The results indicate that the annual net solar to power efficiencies of twelve combinations are more sensitive to the variation of solar collector area in the location with higher annual solar radiation.

The performance of a Solar Aided Power Generation plant with diverse “configuration-operation” combinations

Solar Aided Power Generation is an efficient way to integrate solar thermal energy into a fossil fuel fired power plant for solar power generation purposes. In this particular power plant, the solar heat is used to displace the extraction steam to preheat the feedwater to the boiler. The heat exchanger, which facilitates the heat exchange between the solar heat carried by the heat transfer fluid and the feedwater, is termed a solar preheater. Four possible configurations of the solar preheater, namely Parallel 1, Parallel 2, Series 1 and Series 2, are proposed in this paper. In this type of plant, the extraction steam flow rates must be adjusted according to the solar input. The ways to control the extraction steam flow rates are termed solar preheater operation strategies. Three typical strategies: the Constant Temperature control, Variable Temperature control with high to low temperature feedwater heater displacement and Variable Temperature control with low to high temperature feedwater heater displacement have been identified. Each configuration can be operated with one of the three strategies, resulting in twelve “configuration-operation” combinations/scenarios (shown in Table 1). Previous assessments and modelling of such a plant have only been based on a single combination. In this paper, a Solar Aided Power Generation plant, modified from a typical 300MW power plant, is used to understand the plant’s performance for all twelve of the available combinations. The results show that the instantaneous and annual technical performances of such a plant are dependent on the combinations used. The scenario 10 (Table 1) is superior to the other combinations in terms of the plant’s instantaneous technical performance, while the scenarios 2, 5, 8 (Table 1) has the best plant’s annual technical performance.

Performance analysis of a solar-aided power generation (SAPG) plant using specific consumption theory

In contrast to a traditional coal-fired power generation plant where steam extracted from a turbine is used to preheat the feedwater in all preheating stages, a solar-aided power generation (SAPG) plant uses solar heat to replace a part or all of the extracted steam in one or more preheating stages. The performance of an SAPG plant with different replacements is investigated in this study by using specific consumption theory (SCT). Fuel-specific and cost-specific consumption models for SAPG plants are built based on the SCT. A typical 330 MW coal-fired power plant is used as the study case. The performance of the SAPG plant in terms of specific consumption, with steam obtained from the first through the eighth (except for the fourth) stages of extraction replaced by solar heat, is compared with that of the reference coal-fired power plant. The fuel-specific consumption of the SAPG plant is determined to be lower than that of the reference coal-fired power plant. The fuel-specific consumption accrual distribution in SAPG plants is used to assess the effect of each individual replacement. Effective strategies to reduce the specific costs of the SAPG and coal-fired power plants are proposed based on the results of this study.

A comparison of solar aided power generation (SAPG) and stand-alone concentrating solar power (CSP): A South African case study

Solar aided power generation (SAPG) is the synergy of solar and fossil plant technology, namely combining the environmental benefits of the former and the scale, efficiency and reliability of the latter. Power plant simulations were performed using weather data for Lephalale, South Africa; home to the Matimba and, currently under construction, Medupi coal-fired power stations. A SAPG plant at Lephalale was compared to a stand-alone concentrating solar power (CSP) in a good solar resource area, namely Upington, South Africa. Parabolic trough collector solar fields of equal size were considered for both configurations. The annual electricity generated from solar thermal at the SAPG plant is more than 25% greater than the stand-alone CSP plant. If the cost of SAPG is taken as 72% of the cost of a stand-alone CSP, SAPG is 1.8 times more cost effective than the stand-alone CSP option.

Exergetic and Parametric Study of a Solar Aided Coal-Fired Power Plant

A solar-aided coal-fired power plant realizes the integration of a fossil fuel (coal or gas) and clean energy (solar). In this paper, a conventional 600 MW coal-fired power plant and a 600 MW solar-aided coal-fired power plant have been taken as the study case to understand the merits of solar-aided power generation (SAPG) technology. The plants in the case study have been analyzed by using the First and Second Laws of Thermodynamics principles. The solar irradiation and load ratio have been considered in the analysis. We conclude that if the solar irradiation was 925 W/m2 and load ratio of the SAPG plant was 100%, the exergy efficiency would be 44.54% and the energy efficiency of the plant (46.35%). It was found that in the SAPG plant the largest exergy loss was from the boiler, which accounted for about 76.74% of the total loss. When the load ratio of the unit remains at 100%, and the solar irradiation varies from 500 W/m2 to 1,100 W/m2, the coal savings would be in the range of 8.6 g/kWh to 15.8 g/kWh. If the solar irradiation were kept at 925 W/m2 while the load ratio of the plant changed from 30% to 100%, the coal savings could be in the range of 11.99 g/kWh to 13.75 g/kWh.