Colored solar façades for buildings

Solar energy is a prime way to reach net zero energy buildings. Addressing buildings’ energy needs is a priority because buildings are the largest demander of energy (followed by industry then transport). However, harvesting energy from solar farms, implies covering large areas with standard black or blue solar modules, which is generally not well accepted by the stakeholders. If architectural coherence is to be preserved, building envelopes cannot simply be covered with black panels with visible cells and contact bars. Today, panels of different colors are available to integrate solar energy smoothly into the built environment. However, while a choice of colors is good news for architecture, it should not cause excessive energy losses. The Kromatix panels presented in this paper are covered by glass that combines effects of diffuse surfaces and interference filters. With a minimal loss of efficiency, these panels pave the way to new considerations in solar architecture.

Optimisation of Urban Form by the Evaluation of the Solar Potential

Marylène Montavon

What will the cities of tomorrow look like? This is a crucial question because in the four and a half billion years of its existence, the Earth has never been so threatened, as it is today. Since 2008 half of the world's population has lived in towns – more than 70% in rich nations. Three quarters of CO2 emissions are produced in towns, 75% of the world's energy is consumed in towns. The battle for our climate, for the continuation of our species and all other life, will be largely waged in cities. Will it be possible to create the ideal ecological town? The objective of this study is to compare actual and theoretical urban forms in order to explore the diverse effects of daylighting and solar potential on densely built-up sites. Indeed, the search for ideal solar orientations has been a persistent problem from the 19th century until the beginning of the 20th. Even today, for all our scientific knowledge and empirical experience of solar energy, making the correct choice has still not crossed the boundary from an enigmatic, tricky art into the field of an exact science. As a first step, six existing urban sites in Switzerland and Brazil, as well as two projects in the United Kingdom, a few generic models and a utopian city, were modelled and analyzed. The goal was not merely the construction of new, exemplary districts but also the transformation of existing towns. The findings have been used to assess the potential of façades and roofs located in urban areas for active and passive solar heating, photovoltaic electricity generation and daylighting. The results obtained from these different case studies revealed large variations of the potential for solar energy collection on the buildings' façades and roofs. Ideally, these investigations are expected to help architects and town planners understand how to optimise solar collection on buildings design. In addition, a study was made of the Contemporary City of Three Million Inhabitants created by Le Corbusier. According to the latter, the Contemporary City could increase the urban capacity and at the same time improve the urban environment and the efficiency of the city. Therefore the present study extracted the solar potential of this utopian city in order to assess Le Corbusier's propositions. Since 1922, Le Corbusier's studies have influenced architects and town-planners in their choice of orientations and urban forms: it was therefore crucial to discover if this reliance on Le Corbusier was justified. Solar irradiation and illuminance values obtained through numerical simulations form the core part of the method. The method adopted for the entire set of computer simulations consisted in modelling — via a computer-aided drawing piece of software, namely AutoCAD — the digital model of each building or group of buildings prior to exporting them to an urban performance analysis software (PPF/RADIANCE software package). Spatial distributions of solar irradiation and daylight fluxes over the overall building façades and roofs were calculated using ray-tracing simulation techniques to determine the appropriate placement of different solar technologies (passive and active solar, photovoltaic and daylighting). Performance indicators were used to assess the solar utilisation potential of the urban sites (e.g. statistics of sky view factors and daylight factors) in order to determine the optimal solar strategies for a given urban context. In addition, various works and sun-related recommendations that have appeared mainly since the end of the nineteenth century, together with the various scientific models and software tools pertaining to this topic, are presented in this study.

EPFL2010

Assessment of Solar Thermal Power Technologies

James Spelling

In the present climate of growing awareness about the dangers of global climate change, the development of new renewable energy technologies is primordial in the efforts to reduce emissions of carbon dioxide and other greenhouse gases. Rapid increases in the price of oil and worries about the stability and security of the extraction of fossil fuels have lead to renewed interest in the development of local energy sources, thereby reducing dependence on foreign fuel sources. Amid the plethora of option available, one of the more promising solutions is the increased use of solar power. Two main contrasting technologies exist for the conversion of the Sun’s energy into useful work, namely photovoltaic cells and solar thermal systems. The development of photovoltaic power has shown massive growth in recent years despite high costs, due mainly to the modular nature of the cells which allow their installation by private citizens, coupled with a number of government incentives. Development of solar thermal power generation has however been reasonably limited until recently, with the only continually operated commercial plants being the Luz SEGS I-IX plants at Kramer Junction in the United Sates. Solar thermal power generation shows great potential for supplying the base electricity needs of numerous countries in the sun-belt regions, stretching from the tropics to the Mediterranean. This has lead to a recent renewal in the development of such systems, notably with the construction of the PS10 central receiver plant in Spain. The Spanish government plans to bring the total solar generation capacity to a total of 300 MW by 2013. In other countries around the world, interest is growing in solar thermal power, with increased government and private spending fuelling research and innovation. Most solar thermal conversion technologies are still at the experimental stage, and no single technology has yet to impose its dominance. Different countries and research groups hold different solutions dear, but if solar thermal power is to become a fully mature electricity generating technology, the best of these diverse solutions must be combined in order to achieve optimal performance of the power plants.

2008

Impact of urban morphology on building energy needs: a review on knowledge gained from modeling and monitoring activities

Olivier August Pol, Darren Robinson

Urban morphology is one of the main parameters influencing directly and indirectly buildings’ energy needs. Despite an increasing number of urban energy and environmental modelling tools addressing these issues, the complexity of physical relationships at this level often constrain urban energy modelers to simplify the problems by considering only parts of the phenomena, thus leading to diverging findings and recommendations related to the relevance of urban morphology. A systematic review of published research works in the field of urban energy and environmental modelling is performed. This involves characterising the research approach, evaluating the physical effects taken into consideration in the models applied, the types of models applied, identifying whether the effect of urban morphology is isolated from other effects, whether the urban scene considered is real or theoretical and parametrised and recognising the performance indicators used for assessment. Last but not least, the type of result and the robustness of the ensuing recommendations in terms of sustainable urban design are critically evaluated according to clearly defined assessment criteria. The main findings related to the impact of urban morphology on energy needs in the built environment are summarised and put in relation to the physical effects taken into consideration, showing that there is no common basis allowing for a generalisation of the knowledge available. Beyond an attempt to cluster the different approaches, the authors conclude that there is a clear need to further develop more comprehensive tools, but also to propose a minimal set of requirements for computational modelling activities in the urban energy field.