Criteria and policies to master the visual impact of solar systems in urban environments: The LESO-QSV method

Increased use of solar collectors in buildings is necessary but poses major challenges in existing built environ ments, especially where architectural quality is an issue. The large size of solar systems at the building scale requires careful planning, as they may easily end up compromising the aesthetics of buildings, threatening the identity of entire contexts. A new method named LESO-QSV(for Laboratoire d'Energie SOlaire - Qualite Sensibilite-Visibilite) has been developed to help authorities promote solar energy use while preserving the quality of pre-existing urban areas. The vision underlining the approach is that solar integration is possible also in delicate contexts, if appropriate design efforts and adequate cost investments are made. The issue is then no longer to be in favour or against the use of solar systems in cities, but rather to define appropriate local levels of integration quality, and to identify the factors needed to initiate smart solar energy policies able to preserve the quality of pre-existing urban contexts while promoting solar energy use. The LESO-QSV method helps tackle these issues with clear and objective proposals: First it clarifies the notion of architectural integration quality and proposes a simple evaluation method, based on a set of criteria derived from pre-existing literature. Then it helps authorities set and implement local acceptability requirements, introducing the notion of architectural "criticity" of city surfaces (LESO-QSV acceptability). The concept of "criticity", at the basis of the whole approach, is defined by the Sensitivity of the urban context where the solar system is planned, combined with its Visibility (close and remote) from the public domain. The more sensitive the urban area and the more visible the system (high "criticity"), the higher the need for integration quality. In practice, authorities will be in charge to set the desired integration quality levels for each of the defined "criticity" situations, considering local specificities (energy context, available energy sources, political and social considerations, city identity and topography, among others). To help authorities set these quality expectations, the software LESO-QSV Grid has been developed. It illustrates the acceptance impact of pre-defined sets of quality requirements, using a large number of integration examples (150 emblematic cases). These detailed examples are provided to show authorities how to objectively evaluate integration quality, but they also constitute a large set of learning examples, good and bad, for architects, installers and building owners. Finally the method proposes a way to tailor solar energy policies to local urban specificities by mapping the architectural "criticity" of city buildings surfaces, and crossing this information with a city solar irradiation map (LESO-QSV crossmapping), hence completing the characterization of the building surfaces with the potentially required effort of integration.

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

Architectural integration of solar thermal systems

Maria Cristina Munari Probst, Christian Roecker

The amount of solar energy reaching the Earth in one hour equals the total amount of primary energy used in the world during one year. Thanks to the different solar technologies presently available, most energy needs of buildings can today be covered by solar energy in its various forms. Among mature solar technologies, Among mature solar technologies, active solar thermal (ST) systems for domestic hot water production (DHW) and space heating merit to play a key role. Their proven high efficiency, low cost and short payback time naturally make them a prime choice for energy efficient buildings. Then why is this technology still largely underexploited when compared to photovoltaics (PV)? One reason seems to be that solar thermal systems are perceived as an architecturally unattractive option, while PV is seen as an appealing choice, with products well adapted to building integration, thanks to the thinness and dimensional flexibility of its modules, the choice of colour/texture, the small cables, and its light weight. Moreover, dimensioning and positioning a PV installation is easy, as electricity production can be independent of building needs or storage capacity, while this is less the case for solar thermal. Fortunately, progresses are being made in both these domains. Collector manufacturers are becoming aware of the shortcomings of their present products and work on new ones, and new simplified tools promise to assist architects in the complex dialog between architectural integration and system dimensioning.

2010

Eco-Sim: A Parametric Tool to Evaluate the Environmental and Economic Feasibility of Decentralized Energy Systems

Dasaraden Mauree, Amarasinghage Tharindu Dasun Perera, Jean-Louis Scartezzini, Karni Siraganyan

Due to climate change and the need to decrease the carbon footprint of urban areas, there is an increasing pressure to integrate renewable energy and other components in urban energy systems. Most of the models or available tools do not provide both an economic and environmental assessment of the energy systems and thus lead to the design of systems that are sub-optimal. A flexible and modular simulation tool, Eco-Sim, is thus developed in the current study to conduct a comprehensive techno-economic and environmental assessment of a distributed energy system considering different configuration scenarios. Subsequently, an intermodel comparison is conducted with the Hybrid Optimization Model for Electric Renewable (HOMER) Pro as well as with a state-of-the-art industrial tool. Eco-Sim is then extended by including the heating demand, thermal conversion (by using heat pumps and solar thermal) methods and thermal storage. A parametric analysis is conducted by considering different capacities of solar photovoltaics (PV), solar thermal panels and energy storage technologies. The levelized cost of electricity, the autonomy level and the CO2 emissions are used as the key performance indicators. Based on the analysis of a study case conducted in a neighbourhood in Geneva, Switzerland, the study reveals that, with the present market prices for batteries and seasonal changes in solar energy potential, the combination of solar PV with battery storage doesn’t bring a significant autonomy to the system and increases the CO2 emissions of the system. However, the integration of thermal storage and solar thermal generation is shown to considerably increase the autonomy of the neighbourhood. Finally, multiple scenarios are also run in order to evaluate the sensitivity of economic parameters on the performance indicators of the system. Under the assumptions of the model, to foster investments in solar PV and battery installations, falling installation costs or stronger policies in favor of renewable energy seem necessary for the future.