Energy and cost analysis of a solar-hydrogen combined heat and power system for remote power supply using a computer simulation

A simulation program, based on Visual Pascal, for sizing and techno-economic analysis of the performance of solar-hydrogen combined heat and power systems for remote applications is described. The accuracy of the submodels is checked by comparing the real performances of the system’s components obtained from experimental measurements with model outputs. The use of the heat generated by the PEM fuel cell, and any unused excess hydrogen, is investigated for hot water production or space heating while the solar-hydrogen system is supplying electricity. A 5 kWh daily demand profile and the solar radiation profile of Melbourne have been used in a case study to investigate the typical techno-economic characteristics of the system to supply a remote household. The simulation shows that by harnessing both thermal load and excess hydrogen it is possible to increase the average yearly energy efficiency of the fuel cell in the solar-hydrogen system from just below 40% up to about 80% in both heat and power generation (based on the high heating value of hydrogen). The fuel cell in the system is conventionally sized to meet the peak of the demand profile. However, an economic optimisation analysis illustrates that installing a larger fuel cell could lead to up to a 15% reduction in the unit cost of the electricity to an average of just below 90 c/kWh over the assessment period of 30 years. Further, for an economically optimal size of the fuel cell, nearly a half the yearly energy demand for hot water of the remote household could be supplied by heat recovery from the fuel cell and utilising unused hydrogen in the exit stream. Such a system could then complement a conventional solar water heating system by providing the boosting energy (usually in the order of 40% of the total) normally obtained from gas or electricity.     

Dynamic modeling and evaluation of solid oxide fuel cell - combined heat and power system operating strategies

Operating strategies of solid oxide fuel cell (SOFC) combined heat and power (CHP) systems are developed and evaluated from a utility, and end-user perspective using a fully integrated SOFC-CHP system dynamic model that resolves the physical states, thermal integration and overall efficiency of the system. The model can be modified for any SOFC-CHP system, but the present analysis is applied to a hotel in southern California based on measured electric and heating loads. Analysis indicates that combined heat and power systems can be operated to benefit both the end-users and the utility, providing more efficient electric generation as well as grid ancillary services, namely dispatchable urban power.Design and operating strategies considered in the paper include optimal sizing of the fuel cell, thermal energy storage to dispatch heat, and operating the fuel cell to provide flexible grid power. Analysis results indicate that with a 13.1% average increase in price-of-electricity (POE), the system can provide the grid with a 50% operating range of dispatchable urban power at an overall thermal efficiency of 80%. This grid-support operating mode increases the operational flexibility of the SOFC-CHP system, which may make the technology an important utility asset for accommodating the increased penetration of intermittent renewable power.     

Energy and exergy analyses of a combined ammonia-fed solid oxide fuel cell system for vehicular applications

In this study, both energetic and exergetic performances of a combined heat and power (CHP) system for vehicular applications are evaluated. This system proposes ammonia-fed solid oxide fuel cells based on proton conducting electrolyte (SOFC-H⁺) with a heat recovery option. Fuel consumption of combined fuel cell and energy storage system is investigated for several cases. The performance of the portable SOFC system is studied in a wide range of the cell’s average current densities and fuel utilization ratios. Considering a heat recovery option, the system exergy efficiency is calculated to be 60-90% as a function of current density, whereas energy efficiency varies between 60 and 40%, respectively. The largest exergy destructions take place in the SOFC stack, micro-turbine, and first heat exchanger. The entropy generation rate in the CHP system shows a 25% decrease for every 100 °C increase in average operating temperature.     

Optimization of a 30 kW SOFC combined heat and power system with different cycles and hydrocarbon fuels

Solid oxide fuel cells (SOFCs) could generate power cleanly and efficiently by using a wide range of fuels. Through the recovery and utilization of the energy in the SOFC tail gas, SOFC combined heat and power (CHP) systems achieve efficient cascade utilization of fuels. In this article, an efficient 30 kW SOFC CHP system with multiple cycles is designed based on a commercial kw-level SOFC device. The energy and substances could be recycled at multiple levels in this system, which makes the system do not need external water supply anymore during working. Meanwhile, the performance, fuel applicability, flexibility and reliability of the system are investigated. Finally, an optimized operating condition is confirmed, in which the electrical efficiency is 54.0%, and the thermoelectric efficiency could reach 88.8% by using methanol as fuel.     

Energy efficiency analysis and impact evaluation of the application of thermoelectric power cycle to today’s CHP systems

High efficiency thermoelectric generators (TEG) can recover waste heat from both industrial and private sectors. Thus, the development and deployment of TEG may represent one of the main drives for technological change and fuel substitution. This paper will present an analysis of system efficiency related to the integration of TEG into thermal energy systems, especially Combined Heat and Power production (CHP). Representative implementations of installing TEG in CHP plants to utilize waste heat, wherein electricity can be generated in situ as a by-product, will be described to show advantageous configurations for combustion systems. The feasible deployment of TEG in various CHP plants will be examined in terms of heat source temperature range, influences on CHP power specification and thermal environment, as well as potential benefits. The overall conversion efficiency improvements and economic benefits, together with the environmental impact of this deployment, will then be estimated. By using the Danish thermal energy system as a paradigm, this paper will consider the TEG application to district heating systems and power plants through the EnergyPLAN model, which has been created to design suitable energy strategies for the integration of electricity production into the overall energy system.     

From solar to hydrogen: Preliminary experimental investigation on a small scale facility

Issues of exhaustible natural resources, fluctuating fossil fuel prices and improvements in electric power systems motivated governments to behave positively toward the development of distributed generation. In addition, progresses in small size generation technologies and storage systems give rise to a significant diffusion in microgrids, working together with conventional power grid. Indeed, in the next future, domestic microgrids are expected to play a fundamental role in electric power networks, driving both the academic and industrial research interests in developing high efficient and reliable conversion and storage technologies.In this context, this study presents a feasible configuration of a solar-hydrogen integrated microgrid and documents the procedure to characterize the overall efficiency of a laboratory scale test facility. Experimental results highlight that the most significant inefficiencies in the solar to hydrogen conversion process are mainly attributed to the solar to electrical energy conversion process, being responsible for about 89% of losses. The overall laboratory scale solar to hydrogen chain can reach conversion efficiency up to 5.3%.     

Experimental results for hybrid energy storage systems coupled to photovoltaic generation in residential applications

An experimental solar-hydrogen powered residence simulator was built and tested. The system consisted of a solar photovoltaic array connected to an electrolyzer which produced hydrogen as a means of energy storage. The hydrogen was used to produce electricity in a fuel cell that operated in parallel with a battery to meet dynamic power demand similar to that found in residential applications. The study demonstrated the technical feasibility of operating such a system under the simultaneous dynamics of solar input and load. Limitations of current fuel cell and electrolyzer designs, as they pertain to both power delivery and energy storage, were identified. The study also established the need to understand and address dynamic performance in the design and application of solar-hydrogen reversible fuel cell hybrid systems. An economic analysis found that major cost reductions would need to be achieved for such systems to compete with conventional energy storage devices.     

Performance analysis of a micro-combined heating and power system with PEM fuel cell as a prime mover for a typical household in North China

Proton exchange membrane (PEM) fuel cells produce a large amount of waste heat while generating electricity through electrochemical reactions, making them suitable for driving combined heating and power (CHP) systems. According to the hourly thermal and electric loads in a typical North China household, a 2-kW PEM fuel cell-based micro-CHP system with a lithium-ion battery energy storage system is proposed in this paper. The thermal and economic performances of the micro-CHP system with a lithium-ion battery (CHPWB) and a CHP system without a lithium-ion battery (CHPWOB) are comparatively analyzed by developing a thermal and economic performance analysis model on the MATLAB/Simulink platform. The thermal-load-following strategy is adopted during the design and simulation process. The results indicate that the storage capacity of the lithium-ion battery decreases by 6.6% after one cycle. The lithium-ion battery can be charged by the fuel cell stack during off-peak hours or using commercial electricity, and the charging cycle of the system is one week long. The average total efficiency of the CHPWB system can reach 81.24% with considering the energy loss in each conversion process, which is 11.02% higher than that of the CHPWOB system. The daily hydrogen consumption of the CHPWB system can be reduced by 14.47% compared with the CHPWOB system under the same operating conditions, and the average daily costs can be reduced by 8.4% and 9.5% when the lifespan is 10 and 15 years, respectively.     

Evaluation of a low temperature fuel cell system for residential CHP

CHP (combined heat and power) is a technology that allows to provide electrical and thermal energy. CHP is normally used in systems that produce wasted heat at high temperature to recover energy and increase overall system efficiency. The aim of this work is to investigate the possibility to recover heat produced by a 5 kW PEFC system for residential applications (hot water and building heating). As known, PEFCs work at low temperature (60-90 °C) and the experiments have been carried out in order to improve the overall system efficiency by reusing heat that is normally wasted.The work was developed during an Italian National project PNR-FISR “Polymeric and Ceramic Fuel Cell” coordinated by CNR-ITAE. A 5 kW PEFC system, developed with NUVERA Fuel Cells in the framework of the project, was tested in cogeneration configuration recovering wasted heat with a heat exchanger directly connected to cathode out.Tests on PEFC system were carried out in the range 2.5-5 kW, maintaining the working stack temperature at 71 °C. Heat, produced at different power levels, was removed from the system by using a regulated water flow in the heat exchanger. A peculiar feature of the system is the so-called “direct water injection” at the cathode, that allows simultaneous cooling and humidification of the stack. This characteristic permitted the recovery of most of the waste heat produced by the fuel cell.The performance of the PEFC unit was analyzed in terms of electrical, thermal and total efficiency. Tests showed that it is possible to obtain water at about 68 °C under different power levels. Moreover, experimental data showed that heat recovered was maximum when heat exchanger worked at nominal power and, under these conditions, the overall system efficiency increased up to 85%.     

Direct synthesis of formic acid as hydrogen carrier from CO2 for cleaner power generation through direct formic acid fuel cell

The objective of this work is to develop a process flow modeling for the synthesis of formic acid from CO₂ and H₂ for energy storage and transport purposes. The use of formic acid as an energy storage medium is promising due to difficulties in hydrogen storage, where formic acid can be stored for a longer time with less losses, and then can be utilized in a direct formic acid fuel cell for cleaner power generation. The process flow is developed using Aspen Plus and Engineering Equation Solver to obtain the energy and mass balances, efficiencies, fuel utilization, and Nernst voltage of the direct formic acid fuel cell. The model is validated against data available in the literature for operating parameters. The results show that the operation parameters such as formic acid formation rate, heat duty, and work values, fuel cell efficiency have a significant influence on the overall performance. The proposed system forms formic acid from gaseous H₂ and CO₂ with an energy efficiency of about 19%. The formed formic acid is initially stored in a tank for energy storage and then used in a direct formic acid fuel cell to produce about 168 kW power with an energy efficiency of 16% at 0.7 V, 25 °C and 1 bar.     

Comparative analyses of seven technologies to facilitate the integration of fluctuating renewable energy sources

An analysis of seven different technologies is presented. The technologies integrate fluctuating renewable energy sources (RES) such as wind power production into the electricity supply, and the Danish energy system is used as a case. Comprehensive hour-by-hour energy system analyses are conducted of a complete system meeting electricity, heat and transport demands, and including RES, power plants, and combined heat and power production (CHP) for district heating and transport technologies. In conclusion, the most fuel-efficient and least-cost technologies are identified through energy system and feasibility analyses. Large-scale heat pumps prove to be especially promising as they efficiently reduce the production of excess electricity. Flexible electricity demand and electric boilers are low-cost solutions, but their improvement of fuel efficiency is rather limited. Battery electric vehicles constitute the most promising transport integration technology compared with hydrogen fuel cell vehicles (HFCVs). The costs of integrating RES with electrolysers for HFCVs, CHP and micro fuel cell CHP are reduced significantly with more than 50% of RES.     

Hydrogen as a vector for central receiver solar utilities

An assessment is presented to use hydrogen or hydrogen-rich fuels as a vector in the Central Receiver Solar Utility (CRSU) concept.

The CRSU is conceived to meet primarily the domestic energy requirements for space heating and hot water production of a community. It normally operates to provide low grade heat with sensible seasonal heat storage and district heating systems. However, there are institutional problems connected with using sensible heat storage and low grade energy distribution systems into dwellings.

An alternative to this would be to produce hydrogen and hydrogen-rich fuels by using an advanced conversion technology and eliminate low grade heat storage and distribution systems. Two developing technologies, namely high temperature electrolysis and thermochemical processes, are considered for production of the vector. Then, an assessment is carried out at the conceptual level for fully dedicated Central Receiver Solar Utility Plants which integrate a central receiver system, thermochemical plant or electrical power generating system and synthetic fuel production plant with necessary auxiliary sub-systems.

It is shown that for a 10% capital recovery factor, the cost of hydrogen at the plant will be about $18 per GJ using thermochemical processes and about $20 per GJ using high temperature electrolysis processes.

The solar-hydrogen can also be converted to a more easily stored fuel for domestic use such as methanol, ethanol, ammonia or fuel oil. In this case, there is a distinct possibility that by using waste heavy fuels, tar sands and biomass, the cost of synthetic fuel can be considerably reduced.     

Techno-economic analysis of using corn stover to supply heat and power to a corn ethanol plant – Part 2: Cost of heat and power generation systems

This paper presents a techno-economic analysis of corn stover fired process heating (PH) and the combined heat and power (CHP) generation systems for a typical corn ethanol plant (ethanol production capacity of 170 dam³). Discounted cash flow method was used to estimate both the capital and operating costs of each system and compared with the existing natural gas fired heating system. Environmental impact assessment of using corn stover, coal and natural gas in the heat and/or power generation systems was also evaluated. Coal fired process heating (PH) system had the lowest annual operating cost due to the low fuel cost, but had the highest environmental and human toxicity impacts. The proposed combined heat and power (CHP) generation system required about 137 Gg of corn stover to generate 9.5 MW of electricity and 52.3 MW of process heat with an overall CHP efficiency of 83.3%. Stover fired CHP system would generate an annual savings of 3.6 M$ with an payback period of 6 y. Economics of the coal fired CHP system was very attractive compared to the stover fired CHP system due to lower fuel cost. But the greenhouse gas emissions per Mg of fuel for the coal fired CHP system was 32 times higher than that of stover fired CHP system. Corn stover fired heat and power generation system for a corn ethanol plant can improve the net energy balance and add environmental benefits to the corn to ethanol biorefinery.     

Design and energy evaluation of a stand‐alone copper‐chlorine (Cu‐Cl) thermochemical cycle system for trigeneration of electricity,hydrogen, and oxygen

In this article, a new stand‐alone Cu‐Cl cycle system (SACuCl) for trigeneration of electricity, hydrogen, and oxygen using a combination of a specific combined heat and power (CHP) unit and a 2‐step Cu‐Cl cycle using a CuCl/HCl electrolyzer is presented. Based on the self‐heat recuperation technology for the CHP unit and the heat integration of the Cu‐Cl cycle unit, the power efficiency of the SACuCl for 5 prescribed scenarios (case studies) is predicted to achieve about 48% at least. The SACuCl uses the technologies of the dry reforming of methane and the oxy‐fuel combustion to achieve a relatively high CO₂ concentration in the flue gas, and CO₂ emissions for power generation could be almost restricted by 0.418 kg/kWh. From the aspect of the electricity required for hydrogen production, it is verified that the 2‐step Cu‐Cl cycle system is superior to the conventional water electrolyzer because the CHP process supplies the heat/electricity for Cu‐Cl thermochemical reactions and a thermoelectric generator is connected to the exhaust gas for recovering the power consumption from the compressor and the CuCl/HCl electrolyzer. Finally, the heat exchanger network and the pinch technology are employed to determine the optimum heat recovery of the Cu‐Cl cycle. In case 5 analyzed for the SACuCl, the electricity required for the heat‐integrated 2‐step Cu‐Cl cycle is predicted to dramatically decrease from 4.39 to 0.452 kWh/m³ H₂ and the cycle energy efficiency could be obviously increased from 23.77 to 31.97%.     

Hybrid power generation system of solar energy and fuel cells

This paper introduces the methods of integration of solar energy and low‐temperature solid oxide fuel cells. On the one hand, we design the system that integrates the solar photovoltaic cells and fuel cells. On the other hand, solar energy is concentrated to heat up the fuel cell and supply the working temperature at hundreds Celsius degrees by Fresnel lens. Then the fuel conversion efficiency is increased because of gain from the solar energy. Moreover, integration of solar thermal energy power system with the fuel is a good method for resolving the instability of solar energy. CHP (combined heat and power) is another aspect to enhance the design hybrid system overall efficiency. Finally, we present a novel device but built on different scientific principle. It can convert solar energy and chemical energy of fuel to electric energy simultaneously within the same device to integrated solar cell and fuel cell from the device level. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance assessment of a direct steam solar power plant with hydrogen energy storage: An exergoeconomic study

Power generation and its storage using solar energy and hydrogen energy systems is a promising approach to overcome serious challenges associated with fossil fuel-based power plants. In this study, an exergoeconomic model is developed to analyze a direct steam solar tower-hydrogen gas turbine power plant under different operating conditions. An on-grid solar power plant integrated with a hydrogen storage system composed of an electrolyser, hydrogen gas turbine and fuel cell is considered. When solar energy is not available, electrical power is generated by the gas turbine and the fuel cell utilizing the hydrogen produced by the electrolyser. The effects of different working parameters on the cycle performance during charging and discharging processes are investigated using thermodynamic analysis. The results indicate that increasing the solar irradiation by 36%, leads to 13% increase in the exergy efficiency of the cycle. Moreover, the mass flow rate of the heat transfer fluid in solar system has a considerable effect on the exergy cost of output power. Solar tower has the highest exergy destruction and capital investment cost. The highest exergoeconomic factor for the integrated cycle is 60.94%. The steam turbine and PEM electrolyser have the highest share of exergoeconomic factor i.e., 80.4% and 50%, respectively.     

TRNSYS simulation models for solar-hydrogen systems

A solar-hydrogen system is a kind of stand-alone power system (SAPS), which can supply low energy dwellings with energy. With TRNSYS (a transient system simulation program) it is possible to perform parametric studies to find possible system configurations for different climates and loads. The systems simulated in this study consist of a photovoltaic (PV) cell array, an electrolyzer, a hydrogen (H₂) storage, a fuel cell, a catalytic burner, a lead-acid battery, DC/DC converters, DC/AC inverters, diodes, a solar collector, and a water storage tank. The main equations for the PV cell, electrolyzer and fuel cell are provided, while the other models are only briefly described. Simulations are performed for conventional low energy dwellings located in northern latitudes and results for different system configurations and operation schemes are given. The results show that the size of the solar-hydrogen system for a conventional low energy house located in Trondheim, Norway (63°N), needs to be quite large. This is mainly due to the somewhat high energy requirements assumed, but also due to the low insolation available. Simulations of the same dwelling located in lower latitudes, in more favorable climates, and/or with lower energy needs (e.g., future dwellings), show how the size of the solar-hydrogen system can be significantly reduced. The study also illustrates the importance of minimizing the thermal and electrical loads before designing a solar-hydrogen system for energy self-sufficient buildings.     

Design of experiment study of the parameters that affect performance of three flow plate configurations of a proton exchange membrane fuel cell

Low temperature hydrogen fuel cells are electrochemical devices which offer a promising alternative to traditional power sources. Fuel cells produce electricity with a reaction of the fuel (hydrogen) and air. Fuel cells have the advantage of being clean; only producing water and heat as by products. The efficiency of a fuel cell varies depending on the type; SOFC with CHP for example, can have a system efficiency of up to 65%.     

Harvesting of PEM fuel cell heat energy for a thermal engine in an underwater glider

The heat generated by a proton exchange membrane fuel cell (PEMFC) is generally removed from the cell by a cooling system. Combining heat energy and electricity in a PEMFC is highly desirable to achieve higher fuel efficiency. This paper describes the design of a new power system that combines the heat energy and electricity in a miniature PEMFC to improve the overall power efficiency in an underwater glider. The system makes use of the available heat energy for navigational power of the underwater glider while the electricity generated by the miniature PEMFC is used for the glider's sensors and control system. Experimental results show that the performance of the thermal engine can be obviously improved due to the high quality heat from the PEMFC compared with the ocean environmental thermal energy. Moreover, the overall fuel efficiency can be increased from 17 to 25% at different electric power levels by harvesting the PEMFC heat energy for an integrated fuel cell and thermal engine system in the underwater glider.     

Role of hydrogen in future North European power system in 2060

The Balmorel model has been used to calculate the economic optimal energy system configuration for the Scandinavian countries and Germany in 2060 assuming a nearly 100% coverage of the energy demands in the power, heat and transport sector with renewable energy sources. Different assumptions about the future success of fuel cell technologies have been investigated as well as different electricity and heat demand assumptions. The variability of wind power production was handled by varying the hydropower production and the production on CHP plants using biomass, by power transmission, by varying the heat production in heat pumps and electric heat boilers, and by varying the production of hydrogen in electrolysis plants in combination with hydrogen storage. Investment in hydrogen storage capacity corresponded to 1.2% of annual wind power production in the scenarios without a hydrogen demand from the transport sector, and approximately 4% in the scenarios with a hydrogen demand from the transport sector. Even the scenarios without a demand for hydrogen from the transport sector saw investments in hydrogen storage due to the need for flexibility provided by the ability to store hydrogen. The storage capacities of the electricity storages provided by plug-in hybrid electric vehicles were too small to make hydrogen storage superfluous.