Thermal Energy Output Research Articles

Thermal Load based Adaptive Tracking for Flat Plate Solar Collectors

The energy output of solar-thermal systems using flat plate collectors can be improved by tracking. Tracking is well known as a path for increasing the amount of solar radiation received by the collector; additionally the paper proposes a new concept that considers the inverse tracking as a viable option for protecting the collectors against overheating. An analysis of the thermal energy output and conversion efficiency is done considering forward tracking in three different days with different radiation profile (cloudy, sunny and mixed days), followed by an analysis of the inverse tracking concept. The in-field data show that there is a limiting angle below which inverse tracking is not effective and this value is estimated at 40° as compared with the optimal orientation. A logical scheme is proposed based on four different programs for forward tracking, inverse tracking, maximum inverse tracking or fixing the collector; this decisional scheme covers a broad range of functional situations having as central concept the production of thermal energy only when needed, for satisfying the demand, decreasing the energy consumption for forced circulation and supporting the systems reliability and safety.

Performance Study of Thermoelectric Solar-Assisted Heat Pump with Reflectors

The simultaneous conversion of solar radiation into thermal and electrical energy in a thermoelectric (TE) solar-assisted heat pump is, for the purposes of this study, referred to as hybrid conversion. To capture more thermal and electrical energy, flat-plate reflectors have been mounted on a TE solar collector. To obtain higher solar radiation intensity on the TE solar collector, the position of the reflectors has been changed and the optimal position of the reflectors determined by both experimental measurements and numerical calculation so as to obtain maximal concentration of solar radiation intensity. The calculated values have been found to be in good agreement with measured ones. Improvements to the thermal energy and electrical power outputs of the system can be achieved by the use of the TE solar-assisted heat pump with reflectors. For the optimum position of the reflectors, the coefficient of performance (COP) of the system formed from a TE solar collector integrated with a heat pump (TESC-HP) was 5.60. The power output and conversion efficiency of the TE modules can reach 10.09 W and 2.40%, respectively, being improved by 34.5% and 18.2%, respectively, compared with the TESC-HP without reflectors.

Energy matrices analyses of hybrid photovoltaic thermal (HPVT) water collector with different PV technology

In this paper, an attempt has been made to evaluate and compare the energy matrices of a hybrid photovoltaic thermal (HPVT) water collector under constant collection temperature mode with five different types of PV modules namely c-Si, p-Si, a-Si (thin film), CdTe and CIGS. The analysis is based on overall thermal energy and exergy outputs from HPVT water collector. The temperature dependent electrical efficiency has also been calculated under composite climate of New Delhi, India.It is observed that c-Si PV module is best alternative for production of electrical power. Maximum annual overall thermal energy and exergy is obtained for c-Si PV module. The maximum and minimum EPBT of 1.01 and 0.66years on energy basis is obtained for c-Si and CIGS respectively, whereas on exergy basis maximum EPBT of 5.72years is obtained for a-Si and minimum of 3.44 in obtained for CIGS PV module. EPF and LCCE increase with increasing the life time of the system.

Geothermal Energy for Northern Canada: Is it Economical?

We examined the potential of geothermal energy development in northern Canadian communities to support local energy demand, along with providing an initial assessment of the economic viability of geothermal energy resources for (a) low enthalpy heating systems and (b) electrical power generation from high temperature resources. We estimate yearly energy production and cost per kWh for geothermal systems using scenarios for thermal and electrical production sustained over 15 years from temperatures reached in the 2–6-km depth range. All the calculations are based on a borehole fluid productivity of 30 kg/s. We assume this to be feasible in sedimentary aquifers and through fractured granites. Under such an assumption and assumptions made on the efficiency of heat exchangers, our modeling shows that thermal energy output for 120°C from 3- to 5-km wells can be as low as 5–8 cents/kWh thermal. For a 6 km depth, the cost of thermal energy can be as low as 1–2 cents/kW thermal for thermal energy production of 100–200 MWh annually.

Validated dynamic energy model for a Stirling engine μ-CHP unit using field trial data from a domestic dwelling

This paper presents the development and validation of a dynamic energy performance model for a WhisperGen Stirling engine micro-CHP (μ-CHP) Mk 4 unit. The model is based on empirical equations for different system characteristics (start-up, continuous operation and shutdown) developed using measured performance data. The model was implemented using MatLab program and its validation was undertaken against measured performance data from a unit installed in a dwelling under field trial in Northern Ireland. Given a heat demand profile for a domestic dwelling, the model can be used to predict the heat and electricity output. Using heat and electricity data for a dwelling over a period of 1 month, the model over-predicted the total electrical and thermal energy output from the μ-CHP unit by 1.4% and 4.2% respectively. The model predicted the electrical power output with a mean absolute error of 7.4% and a cumulative over-prediction of 4.7%. The thermal power output was predicted with a mean absolute error of 7.2% and a cumulative under-prediction of 3.7%.

Environmental impact assessment of nuclear assisted hydrogen production via Cu–Cl thermochemical cycles

Abstract The variation of environmental impacts with the efficiency of a hydrogen plant and the thermal output of a nuclear plant are studied for nuclear-based hydrogen production using three-, four- and five-step Cu–Cl cycles for thermochemical water splitting (TWS). Results are presented, on the basis of 1 kg hydrogen production, for two impact categories: global warming potential (GWP) and acidification potential (AP). Environmental impacts are evaluated with several approaches. First, environmental effects are calculated by varying the thermal output ratio, which represents the thermal energy used in Cu–Cl cycle divided by the total thermal energy output of nuclear plant, from 0.1 to 1. The results show that GWP can be decreased from 3.32 to 0.346 kg CO2-eq for the five-step cycle. Second, the hydrogen plant efficiency is altered from 0.34 to 0.65 to examine the corresponding change in environmental impacts. Increasing the hydrogen plant efficiency to 0.65 decreases the GWP to 0.4 kg CO2-eq and the AP to 2.1 × 10−3 kg SO2-eq.

Complementary configuration and operation of a CCHP-ORC system

The electricity to thermal energy output ratio is an important impact factor for the operating modes and performances of combined cooling, heating and power (CCHP) systems. If the energy requirements of users are managed to just match this ration, the system efficiency would reach the maximum. However, due to the randomness of load demands, this situation is rare to be achieved in practice. To solve this problem, a complementary CCHP-ORC system is configured in this paper. The salient feature of this system is that its electricity to thermal energy output ratio can be adjusted by changing the loads of electric chiller and organic Rankine cycle (ORC) dynamically. For this system, an optimal operation strategy and a corresponding implemented decision making process are presented within a wide load range. Case studies based on a hypothetical CCHP-ORC system for a hotel in Beijing are implemented. The results show that the primary energy consumption, the carbon dioxide emissions and the operation cost of the proposed CCHP-ORC system are all better than those of the conventional CCHP system.

UP SCALING AND TEST RESULTS OF AN ADVANCED FRESNEL GREENHOUSE

A greenhouse with Fresnel lenses in the south facing roof and a receiver for concentrated Photovoltaics with water cooling (CPVT system) will result in electrical and thermal energy output from the solar energy excess entering a greenhouse. The PV system converts about half of the direct radiation into heat and electricity. During periods with direct radiation this will significantly reduce the heat load on the greenhouse. For an optimal performance the roof elements must be asymmetric with a steep inclination at the north side (the exact angle of course depends on the latitude of the building site). The Fresnel lens structure is best oriented in upwards direction. In the current design, two lenses are placed in the inner space of a double glass. This prevents pollution and condensation on the lenses. By the upward facing of the lens structure, the focus quality is preserved over a much broader range of angles of incidence compared to a lens with downward facing structures. Each PMMA lens with a size of 1.20×1.52 m is composed of 12 ‘tiles’ for easy production. The focal distance of the lens is 1,875 m and the geometrical concentration factor is 50×. This means that in most cases the focus line is thinner than 3 cm. The performance of the lens with respect to the shape of the focal area and the position of the focal line has been analyzed with ray tracing techniques. From this analyses and by the development of a smart tracking system only two motors can bring the receivers in the required positions. One motor controls the distance between lens and receiver and the other controls the translocation of the receivers parallel to the lens. The second conclusion was that the positions of the focal line are within the bounds of the greenhouse construction for almost the whole year. Only in winter, in the early morning and at the end of the day, the focal line will be unreachable. The 480 m2 greenhouse, with the LCPVT system based on Static Fresnel lenses and a 40 m CPVT-module and a 200 m CT-module, is designed by Bode Project Engineering and constructed by Technokas in Bleiswijk the Netherlands.

Maximising the energy output of a PVT air system

Simultaneously generating both electricity and low grade heat, photovoltaic thermal (PVT) systems maximise the solar energy extracted per unit of collector area and have the added benefit of increasing the photovoltaic (PV) electrical output by reducing the PV operating temperature. A graphical representation of the temperature rise and rate of heat output as a function of the number of transfer units NTUs illustrates the influence of fundamental parameter values on the thermal performance of the PVT collector. With the aim of maximising the electrical and thermal energy outputs, a whole of system approach was used to design an experimental, unglazed, single pass, open loop PVT air system in Sydney. The PVT collector is oriented towards the north with a tilt angle of 34°, and used six 110Wp frameless PV modules. A unique result was achieved whereby the additional electrical PV output was in excess of the fan energy requirement for air mass flow rates in the range of 0.03–0.05kg/sm2. This was made possible through energy efficient hydraulic design using large ducts to minimise the pressure loss and selection of a fan that produces high air mass flow rates (0.02–0.1kg/sm2) at a low input power (4–85W). The experimental PVT air system demonstrated increasing thermal and electrical PV efficiencies with increasing air mass flow rate, with thermal efficiencies in the range of 28–55% and electrical PV efficiencies between 10.6% and 12.2% at midday.

Carbon Credits Earned by Hybrid Photovoltaic Thermal Array

In this paper, a study has been carried out to evaluate carbon credit earned by hybrid photovoltaic thermal (PVT) array. The study has been based on overall thermal energy and exergy output of PVT array. The hybrid PVT array is a proposed system consisting of 36 hybrid PVT modules connected in a series and parallel combinations. The annual energy and exergy gain has been evaluated by considering four types of weather conditions (a, b, c, and d types) of Bangalore. This paper gives the total carbon credit earned by as per norms of Kyoto Protocol Bangalore climatic conditions. We have found that the total carbon credit earned by hybrid PVT array annually in terms of thermal energy is Rs. 1.34 lakhs and in terms of exergy is Rs. 0.61 lakhs, respectively. The total annual monetary gain in terms of overall thermal energy gain and overall exergy gain comes out to be Rs. 3.83 lakhs and Rs. 1.75 lakhs, respectively.

Performance Study of a Double-Pass Thermoelectric Solar Air Collector with Flat-Plate Reflectors

In this paper the results of the influence of flat-plate reflectors made of aluminum foil on the performance of a double-pass thermoelectric (TE) solar air collector are presented. The proposed TE solar collector with reflectors was composed of transparent glass, an air gap, an absorber plate, TE modules, a rectangular fin heat sink, and two flat-plate reflectors. The flat-plate reflectors were placed on two sides of the TE solar collector (east and west directions). The TE solar collector was installed on a one-axis sun-tracking system to obtain high solar radiation. Direct and reflected incident solar radiation heats up the absorber plate so that a temperature difference is created across the TE modules to generate a direct current. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the absorber plate. Ambient air flows through the heat sink located in the lower channel to gain heat. The heated air then flows to the upper channel, where it receives additional heating from the absorber plate. Improvements to the thermal energy and electrical power outputs of the system can be achieved by the use of the double-pass collector system with reflectors and TE technology. It was found that the optimum position of the reflectors is 60°, which gave significantly higher thermal energy and electrical power outputs compared with the TE solar collector without reflectors.

Instantaneous performance of solar collectors for domestic hot water, heating and cooling applications

This study has been carried out with a building experimental solar facility based on a 9-year-old field of 50 m 2 flat plate solar collectors located south of Madrid, Spain. Building domestic hot water production and heating and cooling applications were implemented in the facility. Experimental data corresponding to 100 operating variables (mainly temperatures and flow rates) were recorded during an entire year at intervals of 10 min, and from this data, all of the relevant performance parameters were derived. Three thermocouples measured the centre point instantaneous temperatures of the glass cover, the box back surface and the absorber plate of one of the collectors. A 1D collector transient model, based on thermal resistances and capacitances, has been developed and validated with the experimental database. Both experimental and modelled collector thermal energy output and outlet temperatures were obtained under instantaneous real operating conditions. The individual effect on the drop of the thermal energy output can be summarised in the following yearly averaged values: 15.0% due to collector surface aging, 15.7% due to thermal loss produced by wind velocity magnitude and direction, ±3.2% variations due to thermal capacitance and 7.6% due to incident angle of irradiance. Finally, the repercussions on the performance of the real applications are discussed.

Design and Experimental Study for Using PV/T Collectors in the Faculty of Mechanical Engineering University of Aleppo

Abstract In recent years building integration of solar thermal with PV modules has become more and more popular in different countries, where national support programs have accelerated the dissemination of grid connected PV systems. The installation of a (BIPV) systems have certain advantages compared to a traditional PV or thermal system mounted in a separate structure on the roofs. The main purpose of this project to evaluate the feasibility of using combined PV/T collectors in typical Syrian building installations, and to test this system as a optional solution for a public, governmental or service sector buildings, there are two main advantages for such systems, large area of the roofs are suitable for mounting such systems, and specially for periodic uses or where short term thermal and electrical energy outputs are needed. PV/T collectors being considered in this paper are collectors which can provide both electrical and thermal energy. An experimental model of PV/T air collector was designed and constructed on the roof of Faculty of Mechanical Engineering in University of Aleppo, then it was inspected. This model consisted of a conventional air solar thermal collector with PV cells. One of the main conclusions of this study is that the thermal linking between PV cells and absorber plate is very important for the thermal efficiency. The electrical efficiency is depend on the flow rate of the air which passes through the collector, because the PV cells are on the inlet, then the cool air will pick the heat generated from the PV cells, so it will become relatively warm after passing under the PV cells, and thus PV cells will have a higher electrical output. This results of the measurement show that the project will provide yearly saving for the building about: thermal energy 6133 S.P/year (2496 kW/year) and electrical energy saving 1579 S.P/year (520 kW/year).

Aspects and improvements of hybrid photovoltaic/thermal solar energy systems

Hybrid photovoltaic/thermal (PV/T or PVT) solar systems consist of PV modules coupled to water or air heat extraction devices, which convert the absorbed solar radiation into electricity and heat. At the University of Patras, an extended research on PV/T systems has been performed aiming at the study of several modifications for system performance improvement. In this paper a new type of PV/T collector with dual heat extraction operation, either with water or with air circulation is presented. This system is simple and suitable for building integration, providing hot water or air depending on the season and the thermal needs of the building. Experiments with dual type PV/T models of alternative arrangement of the water and the air heat exchanging elements were performed. The most effective design was further studied, applying to it low cost modifications for the air heat extraction improvement. These modifications include a thin metallic sheet placed in the middle of the air channel, the mounting of fins on the opposite wall to PV rear surface of the air channel and the placement of the sheet combined with small ribs on the opposite air channel wall. The modified dual PV/T collectors were combined with booster diffuse reflectors, achieving a significant increase in system thermal and electrical energy output. The improved PV/T systems have aesthetic and energy advantages and could be used instead of separate installation of plain PV modules and thermal collectors, mainly if the available building surface is limited and the thermal needs are associated with low temperature water or air heating.

Double-Pass Photovoltaic-Thermal Solar Air Collector with Compound Parabolic Concentrator and Fins

A solar energy heat collector was combined with photovoltaic cells to form one single hybrid energy generating unit. This system produces both thermal and electrical energies simultaneously. An experimental setup of a double-pass photovoltaic-thermal solar air collector with a compound parabolic concentrator (CPC) and fins was designed and fabricated to study the performance over a range of operating conditions. The collector is designed in such a way that the absorber surface is partially covered by solar cells. A CPC is used to enhance more electrical and thermal energy output from the collector. However, solar cells perform poorly at high operating temperatures. Therefore, fins are attached at the back side of the absorber surface to improve this situation. A circulating air stream passes through an upper channel and then under the absorber plate or lower channel of the collector carrying away the excess heat and thus maintaining the cells at the optimum operating conditions. The performance of the system has been measured. The thermal, electrical, and combined electrical thermal efficiencies of the collector are presented and discussed.

05/01136 DynaMotive seeks to change fuels equation

Prior to commercial operation, large solar systems in utility-size power plants need to pass performance acceptance tests conducted by the engineering, procurement, and construction (EPC) contractor or owners. In lieu of the present absence of ASME or other international test codes developed for this purpose, the NREL undertook the development of interim Guidelines to provide recommendations for test procedures that can yield results of a high level of accuracy consistent with good engineering knowledge and practice. The Guidelines contained here follow the general approach of the earlier NREL report on parabolic trough collector fields, but in this case are specifically written for power tower solar systems composed of a heliostat (reflector) field directing the sun's rays to a receiver (heat exchanger) on a high central tower. The working fluid in the tower receiver can be molten salt, water/steam, air, CO2, or other suitable fluids, each with its own particular attributes.The fundamental differences between acceptance of a solar power plant and a conventional fossil-fired plant are the inherently transient nature of the energy source and the necessity to use a performance projection model in the acceptance process. Two primary types of test runs are to be conducted. The first – the Short-Duration Steady-State Thermal Power Test (Power Test) – measures the thermal power output of the solar system under clear-sky conditions over a short period, during which thermal equilibrium and stable steady-state conditions exist, and compares the measured results to performance model projections for those conditions. The second test type – the Long-Duration Production (or Reliability) Test (Production Test)– is a continuous multi-day energy test that gathers multiple detailed daily thermal energy outputs and compares the results to projections from a performance model. Both clear-sky and partly cloudy conditions are acceptable. Additionally, the functionality of the solar system should be observed with regard to such items as daily startup, normal operation, standby and shutdown.

시설원예용 제습기 개발

Relative humidity of air In the greenhouse has to be maintained at 70 to 80 percents to provide a better growth condition of crops. To control relative humidity of air in the greenhouse, a dehumidifier functioning by refrigeration cycle was designed and manufactured in this study. And, results of its performance test in the greenhouse site were reported. The developed dehumidifier has separated condenser and evaporator in the heat exchanger part in order to increase dehumidifying capacity at a low temperature condition. When the conditions of incoming air into the dehumidifier were temperature of <TEX>$15\~25^{\circ}C$</TEX> and relative humidity of <TEX>$0\~95\%$</TEX>, quantity of condensed water per hour, ie, dehumidification rate was <TEX>$4.7\~7.0\;kg/hr$</TEX>. Relative humidity difference was not greater than 5 percents at various locations in the greenhouse due to proper distributing of dehumidified air through vinyl duct. Thermal energy output from the developed dehumidifier was about 8,5000 kcal/hr that was 7 percents of maximum greenhouse heating load of 10 a.

Performance, cost and life-cycle assessment study of hybrid PVT/AIR solar systems

An alternative and cost-effective solution to building integrated PV systems is to use hybrid photovoltaic/thermal (PV/T) solar systems. These systems consist of PV modules with an air channel at their rear surface, where ambient air is circulating in the channel for PV cooling and the extracted heat can be used for building thermal needs. To increase the system thermal efficiency, additional glazing is necessary, but this results in the decrease of the PV module electrical output from the additional optical losses of the solar radiation. PV/T solar systems with air heat extraction have been extensively studied at the University of Patras. Prototypes in their standard form and also with low-cost modifications have been tested, aiming to achieve improved PV/T systems. An energetic and environmental assessment for the PV and PV/T systems tested has been performed by the University of Rome ‘La Sapienza’, implementing the specific software SimaPro 5·1 regarding the life-cycle assessment (LCA) methodology applied. In this paper electrical and thermal energy output results for PV and PV/T systems are given, focusing on their performance improvements and environmental impact, considering their construction and operation requirements. The new outcome of the study was that the glazed type PV/T systems present optimum performance regarding energy, cost and LCA results. Copyright © 2005 John Wiley & Sons, Ltd.

Evolutionary programming-based methodology for economical output power from PEM fuel cell for micro-grid application

This paper presents a methodology for finding the optimal output power from a PEM fuel cell power plant (FCPP). The FCPP is used to supply power to a small micro-grid community. The technique used is based on evolutionary programming (EP) to find a near-optimal solution of the problem. The method incorporates the Hill–Climbing technique (HCT) to maintain feasibility during the solution process. An economic model of the FCPP is used. The model considers the production cost of energy and the possibility of selling and buying electrical energy from the local grid. In addition, the model takes into account the thermal energy output from the FCPP and the thermal energy requirement for the micro-grid community. The results obtained are compared against a solution based on genetic algorithms. Results are encouraging and indicate viability of the proposed technique.

Derivation of efficiency factors for uneven irradiation on a fin absorber

In the equation for thermal energy output from a flat-plate solar collector (written as a function of the collector mean heat carrier temperature), both the gain and the loss terms are multiplied by the collector efficiency factor, F ′. For a concentrating collector with an uneven (non-uniform) irradiation on the absorber, the efficiency factor for the gain term, here called the optical efficiency factor, F ′ c, is different from F ′ and is a function of the irradiation distribution on the absorber. If the heat loss coefficient is assumed to be constant across the fin, the optical efficiency factor for absorbed irradiation at a certain distance from the edge of the absorber is independent of absorbed irradiation at other locations and can therefore be expressed F ′ c( x), where x is the distance from the edge of the absorber. Close to the edge, F ′ c( x)< F ′ and close to the pipe, F ′ c( x)> F ′. In this paper formulas are derived for calculating F ′ c( x) for a fin absorber with constant fin thickness. By weighting F ′ c( x) with the absorbed irradiance, S c( x), and integrating across the absorber, an absorber average optical efficiency factor, F ′ c,a, is obtained. This value replaces F ′ in the gain term of the equation for thermal energy output. If, instead, the energy output equation is expressed as a function of the inlet temperature, F ′ c,a can be used for calculating a corresponding heat removal factor for uneven irradiation, F R, c . Formulas for calculating the temperature distribution across the absorber for the case of uneven irradiation are also derived.