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PVT collectors are an emerging technology which combines the generation of solar electricity and heat within a single component. Low heat losses and a high thermal efficiency are essential for the application in conventional solar thermal systems with fluid temperatures up to 90 °C. Glazed PVT collectors with low emissivity coatings offer highest energy yields. However, excessive stagnation temperatures require an adapted collector design to avoid material aging and collector failure. Two innovative PVT collectors with overheating protection are built and tested, and the effect on temperatures and performance is studied. Venting the PVT collector with ambient air reduces the maximum absorber temperatures from 148 °C to 102 °C. An innovative switchable film insulation renders an unprecedented switching range of thermal losses resulting in an uncritical maximum absorber temperature of 87 °C. Thus, conventional PV modules and inexpensive materials can be employed in collector and system, which might offset the additional costs for the overheating protection. Next to the improved reliability, also the electrical efficiency benefits from a lower temperature load.

A design of a box-type solar cooker was modeled and tested in the region of Sfax-Tunisia. This solar cooker was designed to allow reaching relatively high temperatures during days with low solar radiation owing to four outer reflectors. A mathematical model, which is based on thermal balances, was developed and implemented in a Matlab program to predict the thermal performances of the solar cooker. Several tests were effectuated in order to validate the robustness of the mathematical model and to determine the thermal performance of the solar cooker. The obtained results showed an acceptable matching between the experimental temperature values and the computed temperature values with a maximum error inferior to 4%. It was also proven that the use of four outer reflectors improved the optical efficiency of the solar cooker. Indeed, the first figure of merit passed from 0.07 to 0.14 and the maximum temperature of the absorber plate passed from 81.3 °C to 133.6 °C. The sensible loading test revealed that the calculated second figures of merit for different water loads were in the range of 0.34–0.39. Finally, two real cooking process were carried out where 72 min and 107 min were required to fully cook rice and beans respectively.

Solar building envelopes are attracting increasing interest. Building-integrated solar thermal (BIST) systems are one of the subgroups of solar building envelopes. This paper summarizes the most important contributions of recent years and extends them. First, BIST elements are defined and available BIST elements are presented. Then, the general functions which BIST systems can provide are presented and the conflict between the constant U and g values of simple planning software and the variable g and U values of BIST elements is discussed. Measurements to characterize BIST elements are presented as well as a design parameter space in which the current BIST elements are located and which can be used when developing innovative new components. Methods to evaluate and compare BIST technologies are presented. The substantial cost savings which were achieved in three building projects between 2002 and 2009 are discussed. Roles within the building process are presented, as well as the general methods and challenges for economic BIST calculations and one economic calculation as an example. Based on existing building processes, a vision for future BIST building process integration is presented. Simple BIST models, which need no programming, are provided with easy-to-use equations. The challenges of standards and regulations are outlined and future research topics are presented. This paper summarizes important recent contributions to BIST research as a basis for future progress in building-integrated solar thermal systems. Instead of aiming to cover all recent BIST developments, the focus is on BIST research findings which are relevant for cost reduction of BIST components and therefore necessary for the economic success of BIST technology. These are discussed, together with proposals for future research.

Optical assessment of Central Receiver Solar Tower systems should be based on annual simulations due to the high variability of solar radiation throughout the year. The most basic approach is using a discretization of the temporal domain which requires a large number of computationally costly optical simulations. This study proposes an alternative approach based on a discretization of the sky which reduces the required number of simulations and therefore the computational effort significantly. For the subsequent annual performance assessment data three different interpolation methods are presented, compared and their respective advantages and drawbacks are discussed. The methodology is demonstrated by means of three representative heliostat field setups: the PS10 field, the Gemasolar field and a small, generic field. In this context, the dependency of the interpolation accuracy with respect to the resolution of the sky grid is investigated. For this purpose, annual optical efficiency weighted with direct normal irradiation is used as an integral figure of merit, while the Root-mean-square deviation is calculated as a benchmark value for single time step assessment. Eventually, it is shown that the proposed method decreases the required time for the annual optical assessment by several orders of magnitude while maintaining the original accuracy.

The Linear Fresnel Collector (LFC) technology is currently being commercialised by several companies for the application in solar thermal power plants. This study compares the electricity generation costs for LFC and Parabolic Trough Collector (PTC). PTC is the most commercial CSP technology to date and is therefore regarded as the benchmark. For reasons of comparability, direct steam generation is assumed for both LFC and PTC. For the LFC, cost data comparable to typical CSP plant sizes are hardly available. Therefore, the break even cost – referring to aperture-specific collector investment – is determined, where cost-parity of the electricity generation with a PTC reference plant is reached. This study varies the assumptions on collector performance and operation and maintenance costs to reflect different designs of LFC technologies. The calculations were carried out using cost and hourly simulation performance models. Depending on the assumptions, the costs for a linear Fresnel collector solar field should range between 78 and 216 €/m 2 to reach cost-parity at assumed reference solar field costs of 275 €/m 2 for the PTC. The LFC principle of arranging the mirrors horizontally leads to lower aperture-related optical efficiency which must be compensated by lower cost per m 2 of aperture compared to PTC. The LFC is a collector with significant cost reduction potential, mainly due to cheaper mirrors and structural advantages.The presented cost and performance targets shown in this study must be met by LFC technology developers to reach the PTC benchmark.