Large Solar Heating Research Articles

Creation of a Heat and Salt Flux Dataset Associated with Sea Ice Production and Melting in the Sea of Okhotsk

Abstract Sea ice formation, its transport, and its melting cause the redistribution of heat and salt, which plays an important role in the climate and biogeochemical systems. In the Sea of Okhotsk, a heat and salt flux dataset is created in which such sea ice processes are included, with a spatial resolution of ~12.5 km. The dataset is based on a heat budget analysis using ice concentration, thickness, and drift speed from satellite observations and the ECMWF Interim Re-Analysis (ERA-Interim) data. The salt flux calculation considers both salt supplied to the ocean from sea ice production and freshwater supplied when the ice melts. This dataset will be useful for the validation and boundary conditions of modeling studies. The spatial distribution of the annual fluxes shows a distinct contrast between north and south: significant ocean cooling with salt supply is shown in the northern coastal polynya region, while ocean heating with freshwater supply is shown in the south. This contrast suggests a transport of freshwater and negative heat by ice advection. The annual fluxes also show ocean cooling with freshwater supply in the Kashevarov Bank (KB) region and the central and eastern Sea of Okhotsk, suggesting the effect of warm water advection. In the ice melt season, relatively prominent ice melting is shown in the coastal polynya region, probably due to large solar heating of the upper ocean. This indicates that the polynya works as a “meltwater factory” in spring, contrasting with its role as an “ice factory” in winter. In the coastal polynya region, the spatial distribution of phytoplankton bloom roughly corresponds with the ice melt region.

Demonstration of Three Large Scale Solar Process Heat Applications with Different Solar Thermal Collector Technologies

The recently started European FP7 Project InSun aims to demonstrate the reliability and efficiency of three different collector technologies suitable for industrial process heat supply in different climatic regions. The technologies demonstrated reach from improved flat-plate collectors for supply temperatures of up to 95°C in moderate northern Europe climate to tracked concentrating collectors (linear Fresnel collectors and parabolic trough collectors) for supply temperatures between 160 and 250°C in hot and dry Mediterranean climate in Italy and Spain. The main problem for a fast market development if this young and innovative technology is that a reliable performance of the production process has still a much higher priority for the industrial companies than energy savings reached. In consequence often only proven and standardized solutions are considered with payback times not longer than 3 to 5 years. Apart from the cost issue which changes with changing energy prices and the industrialization of the production process of the collectors, the reliability of the technology needs to be demonstrated. Here, intelligent control strategies for the integration in different industrial processes and methods for automated performance observations are required. These topics are given a high priority within the InSun project team with ZAFH-NET as coordinating research partner, EURAC as scientific research partner and Soltigua, Solid and Solera as industrial partners. This paper reports on the preliminary design of the three installations in terms of system layout, foreseen operating conditions and the industrial processes involved.

Evaluation of the Potential of Large Solar Heating Plants in Spain

An evaluation of Central Solar Heating Plants with Seasonal Storage in Spain has been performed with dynamic simulations built on TRNSYS. The model has been designed for several Spanish cities that are representative of the different climatic areas with a significant demand of thermal energy for heating. The system should cover the heating demand of 1000 apartments of 100 m2 in multifamily buildings with similar features, providing a solar fraction of about 50% without wasting solar heat in summer and without oversizing the seasonal storage tank. Climatic and specific demand data for each city have been used. The model simulates the solar collector field, pipe lines, heat exchangers, a seasonal storage tank, pumps, auxiliary boiler and auxiliary pieces of equipment needed in the model. The obtained results show that CSHPSS with a solar fraction of about 50% require in the case of Spain a relatively small Ratio Area of solar collectors versus heating Demand and a high Ratio of seasonal storage tank Volume versus solar collector Area. The estimated cost of the heat produced in CSHPSS with a solar fraction of 50% can be competitive with the heat cost of domestic heat boilers, which is a very common solution for heating in residential buildings in Spain. The obtained results show that CSHPSS represent an interesting and promising alternative for covering the heating demand in residential buildings in Spain.

IEA-SHC Task 45: Large Solar Heating/Cooling Systems, Seasonal Storage, Heat Pumps

Large solar thermal systems have proven to be cost effective in several cases - and the combination of a large solar system with long term storage and also heat pump seem to be very attractive in an efficient modern energy system due to:•flexibility when supplying combined heat and power production in a liberal market for electricity•potential for obtaining very high solar and renewable fractions of supply.The use of solar thermal in connection with district heating is far behind (relatively only one tenth of) the use of solar thermal in individual houses - even though it is in most cases much cheaper to supply solar energy centrally to a district heating network, than to supply solar energy to individual houses.In Denmark right now “an explosion” in numbers of large scale solar district heating systems is seen. Not because of special subsidy schemes - but simply because the systems in many cases are competitive with gas and biomass based district heating systems.The main overall objective of the IEA-SHCi Task 45 is to assist in a strong and sustainable market development of large solar heating and cooling systems. The task will focus on the “MW-size” systems for district heating and cooling applications.The general outcome of the Task will be increased use of cost effective, well designed and well operated large scale solar thermal systems throughout the world - and a strong network of experts and professionals in the field.Main deliverable will be a “Design Handbook for Large Solar Heating/Cooling Systems”

Sea-ice retreat in the Sea of Okhotsk and the ice–ocean albedo feedback effect on it

Sea-ice retreat processes are examined in the Sea of Okhotsk. A heat budget analysis in the sea-ice zone shows that net heat flux from the atmosphere at the water surface is about 77 W m−2 on average in the active ice melt season (April) due to large solar heating, while that at the ice surface is about 12 W m−2 because of the difference in surface albedo. The temporal variation of the heat input into the upper ocean through the open water fraction corresponds well to that of the latent heat required for ice retreat. These results suggest that heat input into the ice–upper ocean system from the atmosphere mainly occurs at the open water fraction, and this heat input into the upper ocean is an important heat source for ice melting. The decrease in ice area in the active melt season (April) and the geostrophic wind just before the melt season (March) show a correlation: the decrease is large when the offshoreward wind is strong. This relationship can be explained by the following process. Once ice concentration is decreased (increased) by the offshoreward (onshoreward) wind just before the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration. This positive feedback is regarded as the ice–ocean albedo feedback, and explains in part the large interannual variability of the ice cover in the ice melt season.

Pre-Heating Storage Design of Solar Heating System Based on SVM

The heating model of pre-heating storage in advance during the valley period of electricity is proposed to solve the intermittent heating problem brought by large solar heating systems affected by change in climate and day and night or other factors. Aiming at best energy saving and the capability of continues heating of solar heating system, the SVM is applied to predict the start time, the highest temperature, the volume of water and other key parameters of the model. The solar heating system apply the pre-heating storage control model that has been trained to meet the practical requirements of different consumers and climate in the application process. Experimental results show that the pre-heating storage model can improve the energy efficiency of large solar heating system and the capacity of real-time continuous heating. The article provides a new control model with large-scale solar heating system.

Energy and cost studies of semi-transparent photovoltaic skylight

Sustainability is the trend of the modern building designs, in which solar energy conversion systems and daylighting schemes are widely considered as the important building energy strategies to reduce the peak cooling and electrical demands, generate clean energy and save the building electricity expenditures. A semi-transparent photovoltaic (PV) is a renewable energy product producing electricity via solar cells and allowing natural light entering into the interior spaces for daylighting designs. The PV modules are effective in reducing the cooling demand, especially for the skylight atrium that often receives large solar heat gains. This paper studies the thermal and visual properties, energy performance, environmental and financial issues of such semi-transparent PV skylights. Field measurements including solar irradiance, daylight illuminance and electricity generated were carried out. Case studies based on a circulating atrium were conducted to evaluate the energy use, cooling requirements and monetary implications when the PV skylights together with the daylight-linked lighting controls were applied. The results indicated that such an integrated system could save the overall electricity expenditures and benefit to the environmental and financial aspects.

Heat losses of large tray solar collectors with exposed evaporation surface

An analytic expression for determining the heat losses from the exposed surface of large tray solar water heating collectors via evaporation is proposed, and a numerical example of its practical implementation is presented.

Optimization of solar water heating systems through water replenishment

In a typical solar water heating system, cold water is replenished into the storage tank as soon as the load is served. However, it is possible to determine the water replenishment profile (i.e., the quantity of the cold makeup water to be supplied to the storage tank over a day) that optimizes the overall system. In this paper, the effect of water replenishment on the system sizing is studied and a novel strategy for water replenishment is proposed to improve the design and performance of solar water heating systems. Based on an analytical technique, an approximate water replenishment profile is proposed to size a solar water heating system near-optimally. The problem is analyzed using a methodology called design space approach. Design space of a solar water heating system identifies all possible and feasible designs on a collector area vs. storage volume diagram. For illustration of the proposed methodology, an example problem is solved. It is observed that the annualized system cost can be reduced by 13.7%. For the cost-optimal system configuration, a reduction of 12.7% in the collector area and 10.2% reduction in the storage volume are observed. The proposed methodology is particularly important and advantageous for large commercial and industrial solar water heating systems.

An investigation of the potential for natural ventilation and building orientation to achieve thermal comfort in warm and humid climates

The aim of this study was to analyze the most important factor, the climatic conditions with respect to thermal comfort in buildings. The impact of building location and climate and orientation on thermal comfort were investigated. With the help of dynamic computer simulations the different hourly weather data were analyzed. First of all the climate determines the amount of solar radiation and mean outside temperature that a building is exposed to. The climate also influences the amount of energy that is used for heating and cooling but also the amount of energy that is used for lighting. There is solar excess which determines the amount of solar energy that is unwanted in the building. With growing amounts of glass and a glazing system that allows large solar heat gains,the impact of orientation is substantial. A detailed analysis was conducted to evaluate the potentials for improving thermal comfort. Detailed results are given in sample graphics and tables in the study. In a tropical climate the improvement in comfort by NV range between 9% and 41% (Kuala Lumpur in April). For a subtropical climate the improvements vary between 3% and 14%. In a temperate climate the improvements vary between 8% and 56%. The results showed that NV has a good potential in tropical and temperate climates but not in subtropical climates. Especially in Hong Kong it seems to be very difficult to apply NV. The results showed that in particular in the hottest period (summer) the potential for comfort improvements is rather small. The design of climate responsive building envelopes should take this into consideration.

Thermal Performance of a Large Low Flow Solar Heating System With a Highly Thermally Stratified Tank

In year 2000 a 336 m2 solar domestic hot water system was built in Sundparken, Elsinore, Denmark. The solar heating system is a low flow system with a 10000 l hot-water tank. Due to the orientation of the buildings half of the solar collectors are facing east, half of the solar collectors are facing west. The collector tilt is 15° from horizontal for all collectors. Both the east-facing and the west-facing collectors have their own solar collector loop, circulation pump, external heat exchanger and control system. The external heat exchangers are used to transfer the heat from the solar collector fluid to the domestic water. The domestic water is pumped from the bottom of the hot-water tank to the heat exchanger and back to the hot-water tank through stratification inlet pipes. The return flow from the DHW circulation pipe also enters the tank through stratification inlet pipes. The tank design ensures an excellent thermal stratification in the tank. The solar heating system was installed in May 2000. The thermal performance of the solar heating system has been measured in the first two years of operation. Compared to other large Danish solar domestic hot water systems the system is performing well in spite of the fact that the solar collectors are far from being orientated optimally. The utilization of the solar radiation on the collectors is higher, 46% in the second year of operation, than for any other system earlier investigated in Denmark, 16%–34%. The reason for the good thermal performance and for the excellent utilization of the solar radiation is the high hot-water consumption and the good system design making use of external heat exchangers and stratification inlet pipes.

Development of 12.5m2 solar collector panel for solar heating plants

Theoretical and experimental investigations have elucidated how different changes in the design of the 12.5 m 2 HT flat-plate solar collector from the Danish company ARCON Solvarme A/S influence the solar collector efficiency and the yearly thermal performance. The collector is designed for medium and large solar heating systems. Based on the theoretical findings a prototype of an improved HT solar collector was built and tested side-by-side with the original HT solar collector. The improved HT collector makes use of a changed insulation material, an absorber with improved absorptance and emittance, and a changed antireflection treated glass cover. Calculations based on the measured efficiencies showed that the yearly thermal performance is increased by 23–37% at operation temperatures between 40°C and 80°C when using the improved HT collector. The cost of the collector was however only increased with about 5%.

Thermal advantages for solar heating systems with a glass cover with antireflection surfaces

Investigations elucidate how a glass cover with antireflection surfaces can improve the efficiency of a solar collector and the thermal performance of solar heating systems. The transmittances for two glass covers for a flat-plate solar collector were measured for different incidence angles. The two glasses are identical, except for the fact that one of them is equipped with antireflection surfaces by the company SunArc A/S. The transmittance was increased by 5–9%-points due to the antireflection surfaces. The increase depends on the incidence angle. The efficiency at incidence angles of 0° and the incidence angle modifier were measured for a flat-plate solar collector with the two cover plates. The collector efficiency was increased by 4–6%-points due to the antireflection surfaces, depending on the incidence angle. The thermal advantage with using a glass cover with antireflection surfaces was determined for different solar heating systems. Three systems were investigated: solar domestic hot water systems, solar heating systems for combined space heating demand and domestic hot water supply, and large solar heating plants. The yearly thermal performance of the systems was calculated by detailed simulation models with collectors with a normal glass cover and with a glass cover with antireflection surfaces. The calculations were carried out for different solar fractions and temperature levels of the solar heating systems. These parameters influence greatly the thermal performance associated with the antireflection surfaces.

Relationship between ice decay and solar heating through open water in the Antarctic sea ice zone

We demonstrate the importance of heat entering the open water area from the atmosphere on sea ice decay in the Antarctic Ocean. The heat budget analyses, both from the European Centre for Medium‐Range Weather Forecasts and the in situ data, show that the net heat input at the water surface reaches 100–150 W m−2 in the active ice melting season due to large solar heating, while that at the ice surface is nearly zero because of the difference in surface albedo. Thus heat input to the ice‐upper ocean system can be approximated as the product of the net heat at the water surface and the fraction of open water. Climatology data show that the total heat input to the upper ocean in the active melting season is comparable to the total latent heat required for sea ice melting in the whole Antarctic sea ice zone. The temporal variation of the heat input to the upper ocean corresponds well to the melting rate of sea ice, which is calculated from the Special Sensor Microwave Imager (SSM/I) data, in large ice extent sectors where the effect of advection is relatively small. These results suggest that melting of sea ice in the Antarctic Ocean is mostly accomplished by the heat input to the upper ocean through the open water area. On seasonal timescales the amount of heat supplied to the upper ocean is determined by the seasonal cycle of net heat input at the water surface, whereas the variability on shorter timescales and interannual differences are determined by the variation of the open water fraction.

Performance of a Large Parabolic Trough Solar Water Heating System at Phoenix Federal Correctional Institution

At Phoenix Federal Correctional Institution in Arizona, the Federal Bureau of Prisons (FBP) completed a 1,584 m2 (17,040 square feet) parabolic trough solar water heating system financed, installed and operated under an Energy Savings Performance Contract (ESPC) with Industrial Solar Technology Corp (IST). The ESPC was developed under a Cooperative Research and Development Agreement with the National Renewable Energy Laboratory (NREL). The system incorporates a 87 m3 (23,000 gallon) storage tank. The system delivered 1,161,803 kWh (3,964 million Btu) of solar heat from March 1, 1999 to February 29, 2000. This energy would have cost $77,805.74 if purchased from the utility (based on the monthly average $/kWh cost). Sale of this energy to the prison provided $70,025.18 in revenue to IST (a rate negotiated at 90 percent of the monthly average $/kWh utility cost). Thus, the prison saved $7,780.56 (the remaining 10 percent). A photograph of the collector system is presented in Figure 1. Results show that the system delivers heat reliably, with only minor operational problems which are listed and discussed. The system delivered a minimum of 80,315 kWh (274 Btu) in January 2000 to a maximum of 130,979 kWh (447 Million Btu) in October 1999. The prison pays IST for energy delivered by the solar system at a rate equal to 90 percent of the monthly average utility rate (10 percent guaranteed savings), over 20 years. Details of the establishment of the payment structure and the cost savings to the prison are discussed. Annual Emissions Savings are estimated by EPA multipliers [1] for Arizona as 627,374 kg/yr of CO2, 2,324 kg/yr of SO2 and 2,297 kg/yr of NOx. Other benefits to the prison are also discussed, such as reduced operations and maintenance on the electric water heaters and a greater capacity to deliver hot water. [S0199-6231(00)00704-8]

Heat transfer analysis of low thermal conductivity solar energy absorbers

Polymers have been proven to be high potential low-cost materials for the design and mass production not only for ordinary solar water heaters but also for very simple large size, modular solar collectors, suitable for easy erection of large solar heating plants. Their major drawback for solar–thermal conversion applications is their low thermal conductivity, which prohibits their use unless an appropriate absorber design is employed. The low thermal conductivity of polymers has imposed the need of a particular absorber design, which is basically composed of a pair of dark, closely spaced parallel plates at the top of which solar radiation is absorbed, forming a thin channel for the flow of the heat transfer fluid. The aim of the present work is to investigate the particular limitations of this polymer plate absorber design, for a wide range of collector loss and convective heat transfer coefficients between heat transfer fluid and absorber plate. The aim is also to calculate the particular collector efficiency factors and conditions under which the associated collector performance parameters should be modified to account for the finite absorber plate conductance. This conductance was proven to be another decisive absorber design parameter, improper selection of which may probably lead to strong deterioration of the collector efficiency.

99/02109 A review of large-scale solar heating systems in Europe: Fisch, M. N. et al. Solar Energy, 1998, 63, (6), 355–366

In Denmark solar fractions up to about 50% are seen for large scale solar district heating systems. The feasibility of higher solar fractions has been investigated in a case study. There is no direct subsidy for solar heating in Denmark, but the taxes on the alternative (fuels) affects the feasibility of solar heating for any district heating plant. The results show that solar heat can be provided at competitive costs compared to what is seen at many Danish district heating plants. The utility in the case study has not yet decided on a solar district heating system size.

Comparison of methodologies for tmy generation using 20 years data for Athens, Greece

The need of accurate Test Reference Years (TRYs) for simulations has been well recognised over the years. Various methods for deriving TRYs have been developed, but their final results can be significantly different. In this paper, the major methodologies reported in literature were applied to 20-year hourly measurements of weather data from Athens, covering the period 1977 to 1996. Seventeen TRYs were produced in total. The basis to select the “best” performing TRY includes meteorological criteria (inherent in the selection process used by each method) and comparisons of results from various simulations for typical energy systems (i.e. a solar water heater, a building, a large scale solar heating system with interseasonal storage and a photovoltaic system). Based on the results of each simulation exercise, a scoring system was developed and applied. The best performing TRY was found to be the one produced by a modified Festa-Ratto method.

Cumulative Energy and Emission Balance of Large Solar Heating Systems

The savings of solar energy installations are often disputed with respect to money, energy and emissions. In order to give a better insight, the various processes related to the production and operation of a large solar heating system are investigated. Material masses and operation data were obtained from a big housing project which we had planned and which is in operation; energies required and emissions were taken from literature.

97/03900 Design, analysis and performance of low-cost plastic film large solar water heating systems

97/03900 Design, analysis and performance of low-cost plastic film large solar water heating systems