Optimizing design of household scale hybrid solar photovoltaic + combined heat and power systems for Ontario[edit | edit source]
Abstract: This paper investigates the feasibility of implementing a hybrid solar photovoltaic (PV) + combined heat and power (CHP) and battery bank system for a residential application to generate reliable base load power to the grid in Ontario. Deploying PV on a large-scale has a penetration level threshold due to the inherent power supply intermittency associated with the solar resource. By creating a hybrid PV+CHP system there is potential of increasing the PV penetration level. One year of one second resolution pyranometer data is analyzed for Kingston Ontario to determine the total amount of PV energy generation potential, the rate of change of PV power generation due to intermittent cloud cover, and the daily CHP run time required to supply reliable base load power to the grid using this hybrid system. This analysis found that the vast majority of solar energy fluctuations are small in magnitude and the worst case energy fluctuation can be accommodated by relatively inexpensive and simple storage with conventional lead-acid batteries. For systems where the PV power rating is identical to the CHP unit, the CHP unit must run for more than twenty hours a day for the system to meet the base load requirement during the winter months. This provides a fortunate supply of heat, which can be used for the needed home heating. This paper provides analysis for a preliminary base line system.
- When the cost of PV electricity is equivalent to conventional grid electricity the PV penetration level is set only by technical limitations.
- This tilt angle also eliminates the complication of snow shadowing which can have a significant impact on yearly system performance.
- The frequency of varying magnitudes of solar energy change on a per second basis (dE/dt) was found by extracting histogram.
- The vast majority of the change in solar energy is small in magnitude and is associated with the natural daily cycle of solar energy and noise in the measurement system.
Abstract: Over the last 30 years, a large amount of research on PV-Thermal (PVT) collectors has been carried out. An overview of this research is presented, both in terms of an historic overview of research projects and in the form of a thematic overview, addressing the different research issues for PVT.
- The idea of an air collector that can run without access to the grid, with the additional benefit of having an irradiance-controlled mass flow.However research institutes and commercial companies have extended this idea to PVT-air collectors with PV over the entire absorber. However, this method also has some drawbacks. The thermal resistance between the PV laminate and the absorber may become too large for good thermal performance especially when air enclosure in the glue layer is significant, and the additional glueing step is not optimal for commercial manufacturing. Furthermore, the white tedlar rear that is generally used for c-Si modules, has relatively large reflection losses.
- Ventilation of BIPV: Whereas the initial question was how to cool the PV, this research naturally lead to the question how much heat was produced and how it could be applied.
- In the case of a solar thermal collector, a good efficiency requires a good solar absorption and a good heat transfer. Furthermore, the higher the required temperature level, the higher the required amount of insulation.
- The reduction in thermal efficiency is due to 4 effects: 1. the absorption factor of the PV-surface is lower than the absorption factor of a conventional collector surface due to reflections at the various layers in the PVlaminate; 2. the PV-surface is not spectrally selective, resulting in large thermal radiation losses; 3. the heat resistance between the absorbing surface and the heat transfer medium is increased due to additional layers of material. This implies a relatively hot surface of the PVT-panel, leading to additional heat losses and a small decrease in electrical performance and 4. the energy that is converted to electrical output is lost for the thermal output. However, as this effect is intended, it will not be discussed further.
- Five aspects have been found in the literature on the absorbance of PVT-collectors: 1. reducing reflection at the additional top cover (in case of a glazed module); 2. reducing reflection at the PVT-absorber top surface; 3. reducing reflection at the PV top grid; 4. increasing absorption in PV and rear contact and 5. increasing absorption in the opaque surface below the PV.
Performance analysis of photovoltaic-thermal collector by explicit dynamic model[edit | edit source]
Abstract: Although the performance of hybrid photovoltaic-thermal (PV/T) collector had been studied both experimentally and numerically for some years, the thermal models developed in previous studies were mostly steady-state models for predicting the annual yields. The operation of a PV/T collector is inherently dynamic. A steady-state model is not suitable for predicting working temperatures of the PV module and the heat-removal fluid during periods of fluctuating irradiance or intermittent fluid flow. Based on the control-volume finite-difference approach, an explicit dynamic model was developed for a single-glazed flat-plate water-heating PV/T collector. A transport delay fluid flow model was incorporated. The proposed model is suitable for dynamic system simulation applications. It allows detailed analysis of the transient energy flow across various collector components and captures the instantaneous energy outputs.
- The operation of a PV/T collector is inherently dynamic. The excitations like solar irradiance and wind are transient in nature.
- There will be no heat flow across this plane at any time under proper operation. The edges and bottom surface of the panel are inserted with thermal insulation. For a compact and thin panel design, the losses of the absorbed solar energy.
- Temperature gradient is treated separately with that in the transverse direction (Y -direction). In this way, the energy exchange across various components can then be handled by considering their mean temperatures.
Abstract: Long term evaluation of an asymmetric CPC PV-thermal hybrid built for high latitudes, MaReCo (MaximumReflectorCollector), is performed in Lund, lat 55.7°, and this paper discusses output estimates and characteristics of the system. The output estimates are calculated using the MINSUN simulation program. To get the input for MINSUN, measurements were performed on two MaReCo prototypes. These measurements show that the front reflector collects most of the irradiation in the summer, and the back reflector in the spring and fall. Two different reflector materials were used, anodized aluminium and aluminium laminated steel. The steel based reflector was selected for its rigidness. The output estimates show no difference in yearly output between the two reflector materials, both back reflectors deliver 168 kW h/(m2 cell area) of electricity compared to 136 kW h/m2 cell area for cells without reflectors. The cells facing the front reflector deliver 205 kW h/(m2 cell area) of electricity. The estimated output of thermal energy was 145 kW h/(m2 glazed area) at 50 °C. The estimates show that the optimal placement of the photovoltaic cells is facing the front reflector, but having cells on both sides is in most cases the best option.
- The electricity generation is impeded by high temperatures, and cooling the cells actively with water is one efficient way to increase the yield.
- Two different MaReCo prototypes were characterized, MaReCo1 and MaReCo2.
- The cells were laminated onto an aluminium profile that was eloxidized to a dark colour to improve its heat absorbing properties
- In the mornings and evenings,the part of the absorber closest to the gables will be shaded.
- The reflectance of the steel based reflector is slightly lower in the wavelength interval where the solar cells operate.
- By visual inspection, there was a considerably larger number of imperfections in the aluminium reflector troughs, which shows the difference in rigidness between the steel reflector and the aluminium reflector.
Abstract: The utilization of solar energy can be made by photovoltaic (PV) cells to generate electric power directly and solar thermal (T) panels can be applied to generate heat power. When the utilization of the solar energy is necessary to generate electric power, the option of using T panels in combination with some heat / electric power conversion technology can be a viable solution. The power generated by utilizing the solar energy absorbed by a given area of solar panel can be increased if the two technologies, PV and T cells, are combined in such a way that the resulting unit will be capable of co-generation of heat and electric power. In the present paper combined Photovoltaic / Thermal panels are suggested to generate heat power to produce hot water, while the photovoltaic part is used to obtain electric power mainly for covering the electric power consumption of the system, to supply the electronic control units and to operate pump drives etc. Ac and dc supplies are provided by converters for covering self-consumption and possibly the need of some household appliances. The development and design of the system is made by extensive use of modeling and simulation techniques. In the paper a part of the simulation studies, carried out to determine the energy balance in the electric energy conversion section of the system and the control structure, assuming stand-alone operation is presented.
- The mechanical energy provided by the turbine is converted into electric energy and fed to the utility mains or a group of loads via an AC to AC converter.
- As both the PV cells and the batteries are expensive components. The energy balance in the long run is basically determined by the energy supplied by the PV cells and the energy consumed by the load. However, losses of the energy conversion and the charge controller have to be taken into account.
- The operation of the charge controller is based on a voltage regulation loop that keeps the battery voltage at the level determined by a battery voltage reference signal in case of surplus charge.
- The operation of the MPPT controller in this study is based on the principle of determining the derivative c = dP/dV of the solar cell.
Abstract: The present commercial photovoltaic solar cells (PV) converts solar energy into electricity with a relatively low efficiency, less than 20%. More than 80% of the absorbed solar energy is dumped to the surroundings again after photovoltaic conversion. Hybrid PV/T systems consist of PV modules coupled with the heat extraction devices. The PV/T collectors generate electric power and heat simultaneously. Stabilizing temperature of photovoltaic modules at low level is higly desirable to obtain efficiency increase. The total efficiency of 60–80% can be achieved with the whole PV/T system provided that the T system is operated near ambient temperature. The value of the low-T heat energy is typically much smaller than the value of the PV electricity. The PV/T systems can exist in many designs, but the most common models are with the use of water or air as a working fuid. Efficiency is the most valuable parameter for the economic analysis. It has substantial meaning in the case of installations with great nominal power, as air-cooled Building Integrated Photovoltaic Systems (BIPV). In this paper the performance analysis of a hybrid PV/T system is presented: an energetic analysis as well as an exergetic analysis. Exergy is always destroyed when a process involves a temperature change. This destruction is proportional to the entropy increase of the system together with its surroundings—the destroyed exergy has been called anergy. Exergy analysis identifies the location, the magnitude, and the sources of thermodynamic inefficiences in a system. This information, which cannot be provided by other means (e.g., an energy analysis), is very useful for the improvement and cost-effictiveness of the system. Calculations were carried out for the tested water-cooled ASE-100-DGL-SM Solarwatt module.
- Applications of solar energy can be broadly classified into two categories: thermal systems (T) that convert solar energy into thermal energy and photovoltaic systems (PV) that convert solar energy directly into electrical energy.
- To reduce the module temperature an air-cooling or water-cooling of a flat plate collector is used in a hybrid PV/T system
- In this configuration, the air at first enters the flow channel formed by the glass cover and the upper metallic collector, and then under it. In consequence, this flow arrangement effects greater heat removal from the top absorber plate and reduces the heat loss from the collector.
- It is impossible to obtain the maximum electric and thermal efficiency simultaneously—a kind of tradeoff is necessary. The most important parameters are the flow rate and the inlet temperature, since the cell temperature depends strongly on them
- Exergy analysis is used in the field of industrial ecology as a tool to both decrease the amount of exergy required for a process and use available exergy more efficiently.
Abstract: It is well known that efficiency of photovoltaic solar cells decreases with an increase of temperature, and cooling is necessary at high illumination conditions such as concentrated sunlight, or cosmic or tropical conditions. The purpose of present study was to investigate the opposite option: to make a cell work at relatively high temperature (around 100–200 °C) and use the excessive heat in a hybrid system of some kind to increase the total efficiency of solar energy utilization. Author(s) studied the temperature dependence of the solar cell parameters both theoretically and experimentally, for the basic cells with p–n junction and the Schottky barrier, taking account of the different carrier transport mechanisms and recombination parameters of the cell material. The possibility of usage of the concentrated sunlight was also taken into account. The experiments conducted in the temperature interval of 25–170 °C and the calculated data show a real possibility of construction of a two-stage solar-to-electric energy converter with high-temperature second stage, having the overall conversion efficiency of 30–40%.
- A PV solar cell operated at high temperature could be coupled with a heat engine which hot side temperature is determined by the PV cell, making a two-stage hybrid conversion system.
- One-dimensional theoretical models of p–n junction and Schottky barrier valid for ideal diode approximation is considered.
- Rapid short-circuit current increase with S while open-circuit voltage increases slowly under the same conditions. The efficiency η features almost linear increase; it reaches the value of 22.3% for 100-times concentrated sunlight, while the modest concentration S=10 already gives 20.3% efficiency yield.
- The efficiency of the cells with metal–semiconductor (MS) junction depends mainly on the height of potential barrier φb formed between the parts of the device.
- Current transport through MS interface was considered to fit thermal emission approximation for the case of crystalline silicon characterized with comparatively high carrier mobility values. Total device current was determined from the continuity equations under minority carrier drift current transport approximation.
- It follows from our theoretical consideration that the initial (room temperature) efficiency of both devices is practically the same; Schottky diodes are less sensitive to the deep level impurities than the p–n junction diode and have a smaller temperature dependence of the efficiency at equal conditions; the concentration of radiation leads to the decrease of the temperature dependence of cell's efficiency.
Rural electrification with photovoltaic hybrid plants—state of the art and future trends[edit | edit source]
Abstract: This paper presents an economic approach for rural electrification with photovoltaics world-wide. It concentrates on the most suitable technologies for supplying single or multiple consumers via stand-alone systems and examines the perspectives for local grid formation. After considering the promising applications in rural areas, advantageous system configurations that can cope with the various requirements of decentralized electrification stand out clearly. Apart from the already well-established photovoltaic (PV) application in supplying power to minute isolated consumers far away from the grid, such as solar homes, stand-alone PV hybrid configurations for power needs up to a few 10 kW are now presenting a promising application.
The results of a comprehensive cost analysis comparing the most applicable supply configurations are presented in this paper in order to determine cost-effective solutions. The design options and the technical performance features of the various PV systems applied are discussed, thus covering important applications and different power ranges. Conventional systems of today, as well as advanced systems offering the potential for covering all fields of application for decentralized power generation in the future are highlighted. The recent developments presented concern the system design techniques, modern energy management systems as well as suitable monitoring, supervising and controlling for decentralized PV integration on a large scale.
- The paper concludes with a reference list of institutes working on systems technology/power conditioning and control of PV hybrid plants.
- PV-only and PV±diesel hybrid systems are at the beginning of the development cycle and considerable cost reductions are to be expected in the future.
- In order to cope with the power fluctuations and the resulting dynamic plant performance, DC busses have to be applied for coupling PV generators or other renewable energy converters to batteries where AC busses are used for coupling consumer loads. In spite of the achievable reliability, this design oers specialized hybrid plant solutions and does not allow decentralized systems configurations with utility-grid-compatible components.
- By adding an auxiliary generator system this unit can be regarded as a supply guarantee, whereas the PV generator and the battery can be designed to a very much smaller scale, as was done with the previous one.
- Obviously the electricity price will increase if the electric consumption becomes smaller than the design value.The plant is also able to provide more energy annually than it is designed for, but in this case with a reduced power supply guarantee. In contrast, the PV hybrid system appears not to be sensitive to power demand variations around its designed size, which is caused by the collaboration between the PV system and the gen-set.
Abstract: Solar energy is one of renewable energy sources which have potential for future energy applications. New technology developments in solar energy utilization are expected to result in the improvement of the photovoltaic performance with lower production cost. This will increase the demand and viability for commercial applications. The current popular technology converts solar energy into electricity and heat separately. The photovoltaic-thermal (PV/T) hybrid system is designed to generate thermal and electrical energy simultaneously. It is well known that using a hybrid system can eliminate the need for external source of electrical energy. This paper presents research and development activity being carried out at Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia in order to realise the technology.
- PV modules can only provide electrical energy. By changing the preserve PV module with some specific modification, we can thus produce electrical energy and thermal energy with the new design of this PV/T.
- Based on the design, the efficiency of the electricity is reduced more than 50% when the PV plate is covered by the glass plate as in commercial module.
- The principle of water based PV/T is similar to the air based collector where cold water is used as a medium to absorb heat from the sun which is later can be used for low heat temperature processes.
- The open circuit voltage (Voc) is similar for different solar irradiance but the short circuit current (Isc) increase when solar irradiance increases. Increasing the flow rate will increase the heat transfer coefficient between the channel walls and the working fluid, resulting in a lower mean photovoltaic cells temperature. This will increase the electrical efficiencies of the collector.
Abstract: In this communication, an attempt has been made to develop a thermal model of an integrated photovoltaic and thermal solar (IPVTS) system developed by previous researchers. Based on energy balance of each component of IPVTS system, an analytical expression for the temperature of PV module and the water have been derived. Numerical computations have been carried out for climatic data and design parameters of an experimental IPVTS system. The simulations predict a daily thermal efficiency of around 58%, which is very close to the experimental value (61.3%) obtained by Huang et al.
- In this paper, a thermal model of an IPVTS system as proposed validated by their experimental results. The design parameters and climatic data of IPVTS system have been used for numerical computations.
- In the thermal section: i)heat capacity of PV/T system,solar cell material,tedlar and insulation have been neglected. ii)One-dimensional (1D) heat conduction has been considered for the present study. iii)The transmissivity of EVA is approximately 100%.iv)A mean temperature is assumed across each layer. v)Water flow between the tedlar and the insulation material is uniform for forced convection.vi)The system is in quasi-steady state.
- Similarly heat transfer between solar cell & tedlar, tedlar & insulator , and also energy balance for the storage tank were modeled.
- Result shows that there is fair agreement between experimental value of cell temperature, Tc(exp) and the theoretical value, Tc(th). The correlation coefficient and root mean square deviation are found to be 0.98% and 7.22% respectively.
- Hourly variations of theoretical and experimental water temperatures in the storage tank shows that theoretical value is higher than the experimental value, the correlation coefficient and root mean square percent deviation are 0.99% and 5.87% respectively.
- The effect of mass flow rate on the hourly variation of water temperature shows that the flow rate has only a small effect on the hourly variation of water temperature over the range of flow rates considered. Hence one can conclude that the optimum mass flow rate lies between 0.005 and 0.075 kg/s.
- The water temperature increases with increasing length as expected. It is also important to note that there is only marginal increase in water temperature for lengths greater than 4 m. Hence the optimum length of the PV module is 4 m for the present set of design and climatic parameters.
- Similarly result indicates that the optimum value of water mass is about 60 kg for present set of design and climatic parameters, depending upon requirement of water temperature.
- P. Derewonko and J. M. Pearce, "Optimizing design of household scale hybrid solar photovoltaic + combined heat and power systems for Ontario," in 2009 34th IEEE Photovoltaic Specialists Conference (PVSC), 2009, pp. 001274-001279.
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- R. K. Jardan, I. Nagy, A. Cid-Pastor, R. Leyva, A. El Aroudi, and L. Martinez-Salamero, "Combined Photovoltaic / Thermal Energy System for Stand-alone Operation," in IEEE International Symposium on Industrial Electronics, 2007. ISIE 2007, 2007, pp. 2403–2408.
- Ewa Radziemska, "Performance Analysis of a Photovoltaic-Thermal Integrated System," International Journal of Photoenergy, vol. 2009, Article ID 732093, 6 pages, 2009. doi:10.1155/2009/732093
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- H. A. Aulich, F. Raptis, and J. Schmid, "Rural electrification with photovoltaic hybrid plants—state of the art and future trends," Progress in Photovoltaics: Research and Applications, vol. 6, no. 5, pp. 325–339, Sep. 1998.
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