Designing and assessing solar energy neighborhoods from visual impact

The optimal diffusion of Building Integrated PhotoVoltaics (BIPV) in cities requires diligent planning to arrange temporal and spatial distribution of energy, while preserving the aesthetics of city landscapes. Benefitting from an increasing quality of 3D models of cities, a comprehensive methodology to estimate potential energy generation from visually-acceptable PV, energy use from buildings, and economically viable micro-grid operation is proposed, by combining validated dynamic energy simulation tools into an open-source computational platform. The platform intends to be useful for urban planners and officials in charge of planning a large-scale BIPV installation into an existing neighborhood: simulations are carried out at the city scale, inclusive of façade potential, shading from vegetation and detailed roof shapes with super-structures. Social acceptability is investigated through a novel visual impact assessment methodology and grid integration solutions are analyzed with reference to their associated costs. Under a conservative scenario, a median of 10 kW hAC-electricity / m2 heated floor area per year is available from BIPV production in Geneva (Switzerland), covering 32 % electricity demand for space heating from heat pumps, or, alternatively, almost 10 times the one for space cooling. Visual impact has demonstrated not to be concurrent to grid integration constraints at the current stage, but rather to contribute to filtering building envelope surface and avoid grid curtailment of excess electricity. In the near future, with an increased grid efficiency, visual impact is expected to become a crucial criterion to limit the integration extent.

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

Establishing links for the planning of sustainable districts

Sébastien Cajot, François Maréchal, Jessen Page, Nils Christian Schüler

Cities can play a key role in mitigating climate change impacts, as they represent two thirds of the world’s energy consumption and greenhouse gas emissions. This paper presents a model-based approach to support cities in the challenge of including energy issues in early stage urban planning. Recognizing that successful planning must rely on highly integrated solutions, this paper aims, through its approach, to better understand and reinforce links between generally fragmented sectors, scales, stages and disciplines. Considering the planning framework of the Swiss canton of Geneva, the main planning instruments are presented and an in-depth analysis of the urban and energetic goals and constraints is carried out. Linking the disciplines of planning and optimization, a Mixed Integer Linear Programing (MILP) model is formulated to identify optimal energy strategies, as well as to provide insights into the urban layout, distribution and size of buildings. Additionally, this approach aims to overcome one of the difficulties of early stage planning, where information regarding energy is scarce. In this regard the proposed methodology generates building information based on available data and constraints. The simultaneous consideration of multiple scales allows to assess the interactions of building scale decisions with overall district energy supply alternatives. The resulting depiction and quantification of trade-offs should allow planners to anticipate optimal energy system configurations and adapt their plans accordingly.

vdf Hochschulverlag AG2016

Towards a digital workflow to assess visual impact of solar modules and their operation within energy-hubs

Silvia Coccolo, Pietro Florio, Amarasinghage Tharindu Dasun Perera, Jean-Louis Scartezzini

This study proposes an integrated methodology to assess the BIPV potential of existing urban neighborhoods, including social acceptance and grid infrastructure management issues; as a demonstration, a case study in Geneva, Switzerland is considered. In particular, the annual solar radiation on the outdoor exposed areas is calculated on an hourly basis and converted into electricity by considering standard monocrystalline PV modules. Social acceptability is evaluated on a discrete qualitative scale, based on the average visibility of the building envelope from the public space and assessed through a psychophysically reliable indicator. Three different envelope surface coverage ratios are assumed for BIPV, i.e. for low, medium and high visibility respectively. Renewable electricity generation is used to match the hourly electricity demand for lighting, appliances as well as an air-to-air heat pump that covers heating and cooling needs. Excess electricity is used within multi energy hubs featuring PV panels, a battery bank and an internal combustion generator; as a last resort, electricity is injected to the grid. As such, the levelized cost of energy and the grid integration level can be calculated at each time step. The financial outcome of the analysis may be used to explore novel business models for solar energy renovations in urban contexts.

IOP Science2019

Optimisation of Urban Form by the Evaluation of the Solar Potential

Marylène Montavon

EPFL2010