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As the temperature worldwide increases so too will the demand for air conditioning solutions. While it may seem contradictory, the heat of the sun can be effectively used to cool large areas of space in commercial and industrial complexes. As of today, the overall useful conversion of solar thermal energy to cooling is limited to 35%, as the thermal energy collection and the cooling conversion subsystems have capabilities of 50% and 70% respectively. As late as the 1960s though, house comfort conditions were only for the few. From then onwards central air conditioning systems became common in many countries due to the development of mechanical refrigeration and the rise of the standard of living. The oil crises of the 1970s stimulated intensive research aimed at reducing energy costs. Also, global warming and ozone depletion and the escalating costs of fossil fuels over the last few years, have forced governments and engineering bodies in order to re-examine the whole approach to building design and control. Energy conservation, in the sense of fuel saving, is also of great importance. Solar cooling can reduce electricity shortages by reducing peak electrical demand often driven by air conditioning and it is an active solution for reducing pollution and dependence on fossil fuel imports. There are many suitable applications for solar cooling, which include resorts, hospitals, shopping malls, schools, industrial, commercial and residential complexes as well as military bases where utility rates are high and grid connections are unavailable.

During November and December 1992 I visited several groups involved with renewable energy, most of them dealing with education. These groups and their work are described briefly in this report. The groups in Melbourne, Australia have come a long way with education in this field and we have a lot to learn from them. Government funding is needed for large scale work, but useful work can still be done at the community level with much smaller budgets.

The Thermo-Chemical Accumulator, a three-phase chemical heat pump with integral thermal storage, has been tested and modelled in the TRNSYS simulation environment. Base case system models for solar cooling applications were created for the Madrid and Stockholm climates and a number of parametric studies were carried out. The results show that the temperature lift, partially dependent on state of charge, is a limiting factor. For a purely sensible cooling load, wet cooling is required for the Madrid climate, whereas in Stockholm a dry cooler can be used for the simulated office and hotel. Dehumidification is not possible. It was shown that the machine itself has sufficient thermal storage for the office load but that it limited the solar fraction for the more uniform hotel load.

This paper presents the current status of the work in Task 32 (Advance Storage Concepts for Solar and Low Energy Buildings) of the International Energy Agency’s Solar Heating and Cooling Programme (IEA-SHC). A methodology for inter-comparison has been established and boundary conditions and reference systems for this have been defined. The current status of the projects range from recently concluded feasibility studies for chemical heat storage, to prototyping, lab testing, modelling and system simulation for advanced water stores, with and without PCM content, as well as for stores based on the sorption principle. Promising new components and solutions for more classical water tanks are also described in order to define market references.

The European Solar Engineering School ESES is a one-year masters program that started in 1999 at the Solar Energy Research Center SERC, Dalarna University College. It has been growing in popularity over the years, with over 20 students in the current year. Approximately half the students come from Europe, the rest coming from all over the globe. This paper described the contents and experiences from seven years of running the programme and the plans for adapting the programme to the Bologna process. The majority of the students from ESES have found work in the solar industry, energy industry or taken up PhD positions. An alumni group has been started that actively gives support to past, present and potential future students.

The study reported here is part of a large project for evaluation of the Thermo-Chemical Accumulator (TCA), a technology under development by the Swedish company ClimateWell AB. The studies concentrate on the use of the technology for comfort cooling. This report concentrates on measurements in the laboratory, modelling and system simulation. The TCA is a three-phase absorption heat pump that stores energy in the form of crystallised salt, in this case Lithium Chloride (LiCl) with water being the other substance. The process requires vacuum conditions as with standard absorption chillers using LiBr/water. Measurements were carried out in the laboratories at the Solar Energy Research Center SERC, at Högskolan Dalarna as well as at ClimateWell AB. The measurements at SERC were performed on a prototype version 7:1 and showed that this prototype had several problems resulting in poor and unreliable performance. The main results were that: there was significant corrosion leading to non-condensable gases that in turn caused very poor performance; unwanted crystallisation caused blockages as well as inconsistent behaviour; poor wetting of the heat exchangers resulted in relatively high temperature drops there. A measured thermal COP for cooling of 0.46 was found, which is significantly lower than the theoretical value. These findings resulted in a thorough redesign for the new prototype, called ClimateWell 10 (CW10), which was tested briefly by the authors at ClimateWell. The data collected here was not large, but enough to show that the machine worked consistently with no noticeable vacuum problems. It was also sufficient for identifying the main parameters in a simulation model developed for the TRNSYS simulation environment, but not enough to verify the model properly. This model was shown to be able to simulate the dynamic as well as static performance of the CW10, and was then used in a series of system simulations. A single system model was developed as the basis of the system simulations, consisting of a CW10 machine, 30 m2 flat plate solar collectors with backup boiler and an office with a design cooling load in Stockholm of 50 W/m2, resulting in a 7.5 kW design load for the 150 m2 floor area. Two base cases were defined based on this: one for Stockholm using a dry cooler with design cooling rate of 30 kW; one for Madrid with a cooling tower with design cooling rate of 34 kW. A number of parametric studies were performed based on these two base cases. These showed that the temperature lift is a limiting factor for cooling for higher ambient temperatures and for charging with fixed temperature source such as district heating. The simulated evacuated tube collector performs only marginally better than a good flat plate collector if considering the gross area, the margin being greater for larger solar fractions. For 30 m2 collector a solar faction of 49% and 67% were achieved for the Stockholm and Madrid base cases respectively. The average annual efficiency of the collector in Stockholm (12%) was much lower than that in Madrid (19%). The thermal COP was simulated to be approximately 0.70, but has not been possible to verify with measured data. The annual electrical COP was shown to be very dependent on the cooling load as a large proportion of electrical use is for components that are permanently on. For the cooling loads studied, the annual electrical COP ranged from 2.2 for a 2000 kWh cooling load to 18.0 for a 21000 kWh cooling load. There is however a potential to reduce the electricity consumption in the machine, which would improve these figures significantly. It was shown that a cooling tower is necessary for the Madrid climate, whereas a dry cooler is sufficient for Stockholm although a cooling tower does improve performance. The simulation study was very shallow and has shown a number of areas that are important to study in more depth. One such area is advanced control strategy, which is necessary to mitigate the weakness of the technology (low temperature lift for cooling) and to optimally use its strength (storage).

This article compares seven different external DHW units, comprising flat plate heat exchanger and flow control, with a reference method for preparing hot water. These DHW units use different control methods. The objective of the study was to determine which methods are most effective in solar combisystems and to identify other factors that strongly influence the energy savings of the system. Five of the DHW units were judged to be of interest for the study because of their measured performance or the simplicity of their design. Of these, measurement data showed that two had the same control function although of different physical construction. Thus four DHW units were modelled in the simulation environment PRESIM/ TRNSYS, parameters were identified from measured data, and annual simulations were performed with a number of parametric variations. Three of the DHW units performed significantly better than the reference system provided that they were sized correctly: microprocessor control with variable-speed pump; proportional controller with regulating valve; and a turbine pump. The most important design factors identified by the study were: the maximum possible primary flow, which needs to be suitable for the design hot water load profile; and ensuring a low temperature is returned to the store. The hot water load profile was also shown to strongly influence the energy savings, assuming that auxiliary heater’s thermostat is set so that the system just meets the worst-case discharge.

The Thermo Chemical Accumulator (TCA) is a chemical heat pump driven by low temperature heat that has integral heat storage with high energy density. This makes the device very suitable for solar cooling. The working pair consists of Lithium Chloride and water, and energy is stored and released by desorption and absorption of water under near vacuum conditions. In contrast to most absorption processes and chemical heat pumps, the TCA works with three phases: solid, solution and vapour. This results in near constant operating conditions during charge and discharge, independent of state of charge. This paper describes the fundamental working principles of the TCA as well as a simple steady state model for the TCA. A temperature difference between theoretical and effective temperature in the reactor during absorption and desorption was required in order to get reasonable agreement with measurement data of a prototype TCA machine. For absorption, this value for subcooling was 15°C, which is significantly higher than has been found for low-temperature absorption chillers, indicating potential for improvement. For desorption the value was 7.5°C. The TCA has desorption temperatures of below 100°C for ambient temperatures below 40°C, which is relatively low. The temperature lift depends on the cooling rate supplied and varies from 15°C for the design cooling rate of 5 kW per TCA unit and 30°C inlet temperature to the reactor, to 20°C for a cooling rate of 2.5 kW. The energy density for storage was 180 kWh/m3 for the tested prototype.

The aim of this investigation is to show, whether totally different calibration methods (absolute spectral response at Fraunhofer ISE, blackbody at various temperatures at SERC) give similar results for the performance of TPV cells under infrared spectra. Two cell types (InGaAs and GaSb) have been tested, applying two different methods to each cell type. Spectral responses and I-V-curves of the cells have been measured. To compare the two methods the spectra of a halogen light bulb were measured up to 1.6 µm at different lamp currents and then fitted to the Planck formula and in this way extended into the infrared. The two methods are compared to each other and results are discussed. It is shown that the I-V-curves of both cell types are independent of the used spectrum. The currents of the cells measured at SERC and calculated at Fraunhofer ISE differ only in the range of measurement errors.

The five computer programs TRNSYS, PRESIM, TRNSED, ONLINE, and PREBID have been put together into a program package which is the most complete solar energy system modeling and simulation software that is available today.

The purpose of the work, through this thesis called “Electricity Supply with PV-Wind Systems For Houses Without Grid Connection” is to analyse the economical and technical feasibility of implementing a PV-Hybrid system in a certain region of Sweden. Within all the possible combinations of hybrid systems existent all around the world, a PV-Wind system has been chosen as the one to be analysed because of two reasons. The first is that nowadays, both photovoltaic and wind turbines technologies are suffering a big growth and second, this type of system is preferred because it is environmentally friendly in its totality. The system has been placed in Borlänge, a certain region of Sweden, in order to represent a most realistic environment as possible. For that, the two principal weather data, global irradiation and wind speed, have been taken from the Swedish Meteorology Institute. After that, an electrical load is needed to simulate all the energy supplying process during one year, so, a Swedish single family house has been chosen as the load. The electrical consumption of it has been studied, and three different load scenarios have been created. These three scenarios are a standard load case, an efficient load case and the last, a saving mode load case. Each one of load cases is divided through all the 8760 hours of the year. For the simulations of each one of the scenarios, a computer program called HOMER (Hybrid Optimization Model for Electric Renewables) has been utilized. With it, once you define the system and established the constraints of the system, it calculates all the possible configurations that can be implemented and arrange them by the Total Net Present Cost. One can visualize and check the energetic and economical characteristics of each one of the configurations in order to decide which one is the most appropriate. After all the scenarios have been simulated and evaluated, some of the final conclusions that can be done is that with such a system, only the saving load case could fulfil all the constraints and be economically feasible at the same time. For the established constraints, at least 70% of load covered, almost all of the configurations in the three different scenarios are feasible but since a minimum of comfort is needed in the house, the minimum level of covered load has been decided to be 90%. With this new restriction, only some of the configurations in the saving load case are technically and economically feasible, because with the other load cases the total net present cost is too high for this kind of investment and the material to install is probably too much for a single house. As an example, one of the best systems could be the one with 1kW PV and 2 wind turbines with a 20m hub height, producing a total electrical energy of 2444kWh/year. Nevertheless, and taking into account the low average of wind speed in this region, other hybrid systems should be studied for the future or also the same type of system but placed in a region with a higher average of wind speed.

Solar-hydrogen energy system is one of the promising energy alternatives for the future which enhances solar energy utilisation. In this study different solar–hydrogen energy systems were studied: photochemical, photoelectrochemical, photobiological, electrolysis (photovoltaic and electrolyser) thermolysis and thermochemical methods. A survey of the state-of-the-art of these methods has been presented. An integrated photovoltaic/electrolysis system and a photoelectrochemical (PEC) system have been selected as showing more potential and promise for further study. On the basis of theoretical studies and assumptions a mathematical model has been developed for an integrated photovoltaic /electrolysis system. The model includes electrochemical and thermal aspects of the system. The model has been analysed and simulated for a silicon solar cell integrated with a hypothetical electrolytic cell, and shows similar results compared with that of water electrolysis in a photovoltaic driven electrolyser.

Lots of countries are now running projects in order to increase their electrification rate. One of the means used to achieve this goal is the Solar Home System, SHS. It is with this intention that a project was born in Peru. The concept was to sell a SHS which includes roughly a PV panel, a battery, one regulator and lamps with the help of a loan. This project has been carried out from 1996 to 1999 with the installation of 421 SHS. An evaluation is now necessary for the authorities to realize on the finality of those kinds of PV projects and more merely to prevent the same errors in the following SHS. This evaluation has taken into account the standard technical and economical points of view but also the social and environmental effects of those installations. It has been achieved by observations and by a survey performed in 49 families. Moreover the investigation has also lead me to meet different actors like school teacher, mayor etc. Although the social results is ambivalent (there are good and bad aspects of the electrification of a community), economically and environmentally it is success.

A space based solar power plant could be placed in a geostationary orbit 36000 km above the earth's equator. A receiving station must be north of 81.3 degrees latitude south for the satellite to be above horizon. Large areas of the Antarctic are substantially above this latitude. Since such a solution would be much more environmentally benign than land-based fossil or nuclear fuel power plants, it is proposed that the first space power plant is built for this specific purpose.

A joint project between SERC, SLU and National Renewable Energy Laboratory NREL in Golden, Colorado, USA aims at building a wood powder fuelled TPV generator. An emitter temperature around 1500 K is required. There are some different biomass fuels capable of producing this temperature in the flame, including wood powder, the only sufficiently uniform solid wood fuel. A stable flame temperature of 1500 K has been achieved in a prototype pilot-scale burner that includes feeder and combustion chamber. Furthermore, a setup for measuring TPV cell efficiency for a wide region of black body emitter temperatures and cell irradiation has been constructed and several 0.6 eV GaInAs TPV cells have been investigated. A setup for testing the chain IR emitter - selectively reflecting filter - TPV cell has been designed. In order to limit the region of filter incident angles - which will make the filter act more efficiently - a special geometry of the internally reflecting tube that transmits the radiation is considered.

A bibliography containing 200 entries on thermophotovoltaic conversion of energy between 1960 and 1995 has been compiled. The entries are categorized with respect to type and contents.

Two different concentrating mirrors have been constructed that resemble parabolic dish reflectors. Both mirrors are made of slightly curved strips of flat, bendable material. The strips of the most simplified mirror have only large-radius circles and straight lines as boundaries. The necessary equations for making the mirrors are given. Also a simple way to make a stiff, lightweight frame and support for the mirror strips has been developed. Models of the mirrors have been built and successfully used for cooking and baking.

Insolation onto and energy output from solar collectors have been estimated for some typical high latitude locations using the F-Chart computer program and weather data from the Swedish Meteorological and Hydrological Institute. Optimum tilt for south-facing collectors at Swedish latitudes is approximately latitude minus 20 degrees for maximum yearly performance, and about latitude minus 30 degrees for maximum summer performance. If tracking is considered, vertical axis tracking seems favorable with energy gain larger than normal 1-axis tracking with latitude tilted axis.

The ISES Solar World Congress Clean and Safe Energy Forever was held in Kobe, Japan, September 4-8, 1989. Short impressions from the conference and the simultaneous exhibition are given. On our (separate) ways to Kobe, Eriksson visited institutions in the Bombay, India area, and Broman one institution in Islamabad, Pakistan. Accounts of these visits are given. Three papers presented in Kobe are included in an Appendix.

The efficiency of a TPV generator is very dependent on selective optical properties of the chain emitter-filter-TPV cell-reflective backing. If a selective reflective edge filter using multiple reflections in dielectric layers is employed, the slope of the edge depends on the incidence angle interval. A special geometry, consisting of a double square cone between the (square) emitter and the (square) cell array, which narrows this angle interval significantly, has been constructed and investigated experimentally as well as with ray tracing analysis.

A joint project between NREL, SLU and UCFB aims at building a wood powder fueled TPV generator. The progress of the project is presented.

The optical efficiency is a week link in all TPV systems. Many different approaches have been studied earlier, but not much on the possibility to use interference filters. Such filters can be designed to get alsmost any desired optical performance, as long as it is allowed to use a large number of layers in the multilayer stack. In practical applications this is very often not acceptable. Nevertheless such filters can still be quite good, at least for a very narrow range of incident angles. Therefore a double-cone geometry is proposed to be used in combination with such filters. This geometry will limit the range of incident angles onto the filter, which will then act more efficiently. The influence of the geometry is evaluated by means of model experiments, and a computer program has been constructed to be able to simulate this type of geometry using ray-tracing technique.

An apparatus for measuring TPV cell efficiencies at different radiation intensities and for different graybody emitter temperatures has been constructed. The apparatus has been used for measuring V-I characteristics, efficiencies and fill factors for several InGaAs TPV cells. Measured results are used to determine how cells may function together with edge filters, and those results are compared with theory.