PVOPTI-Ray, Optimization of reflecting materials and photovoltaics in urban environment with respect to energy balance and bioclimate.

The aim of this project is to develop urban energy balance models, optimized solutions for urban planning regarding the design of an urban canyon and the choice of materials as well as methods and techniques for optimizing building integrated PV, taking at the same time bioclimatic aspects into consideration.

Starting point / motivation

Cities are the biggest energy consumers and they are going to be the major victims of climate change. Against this background, the ‚Solar Cities' issue is discussed nationally and internationally: cities that are gaining most of their energy need from the sun directly with their own rooftops and facades.

Active houses and Solar Cities are thus planned in a way that they may retrieve a maximum of ‚solar harvest', directing their roofs and facades towards the sun, thus avoiding shadowing to achieve a maximum solar yield. At best, black solar modules are used with low reflection and thus a high electricity yield with up to 20%. The biggest part of the absorbed solar radiation is however transformed into heat.

So far there have not been developed any evaluation and simulation tools for the urban area which can estimate the effects of a broad roll-out of PV and insolation of facade surfaces in urban districts, especially on the micro-climate in street canyons.

In order to adapt to climate change the US are following a contrary strategy: a city with white roofs, which provide maximized reflective surfaces and minimized absorption of the solar irradiation on the city.

Reflection from the ground and surrounding buildings causes an increase of the solar radiation directed to the PV module, and entails an increase of the PV yield. At the same time the increase of reflection can cause more thermal stress and blinding for human beings. Solar modules are reducing the reflection in urban districts and may contribute to warming the environment.

Contents and goals

The final target of the study is to simulate the complex radiation and energy flows within typical street canyons and to develop concepts for simulation and planning tools which are required for an energetically and bio climatically optimized solar planning of the city.

Methods

By means of PV-tools, models for urban comfort and climate, optimal solutions for town planning in consideration of a maximum PV-yield and bioclimatic aspects such as the human well-being and the avoidance of blinding are developed. Different climatic situations are considered as well as the potential of positive effects of green facades and public green space.

Expected results

Improved coupled simulation tools

Urban energy balance models will be coupled with PV yield simulation tools and improved.

Quantification of the influencing factors

• Season, climate zone, and weather conditions (air conditions, global radiation, wind, relative humidity),
• materials (albedo, directional albedo, specific heat capacity, etc...),
• dimensions (height, width orientation) of the urban canyon,
• PV type, and aeration behind the PV modules on yield of PV modules
• local climate
• thermal stress of humans
• optical comfort (prevention of blinding)

Further analysis and deductions

Conclusions and recommendations for optimized solar city planning as well as a meaningful technological development of PV modules, requirements for traffic areas and building envelope in combination with green space planning.

Project management

Institut of meteorology, University of natural ressources and life sciences (BOKU)

Project or cooperation partners

• Austrian Institute of Technology
• Smart minerals / research institute

Prof. Dr. Philipp Weihs
Peter Jordan Strasse 82
A-1190 Wien
Tel.: +43 (1) 47654 81424 / 01 47654 81410
E-mail: philipp.weihs@boku.ac.at
Web: http://www.wau.boku.ac.at/met/