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Bringing sunshine to the city

The PV City Guide project is looking at the potential for providing pollution-free energy within dense city centres A new initiative is examining the potential benefits of integrating solar power generation into urban builtup areas.

The urban built environment provides a unique opportunity for the application and exploitation of photovoltaic (PV) systems. Cities represent a focused and significant energy demand, but also a physical infrastructure that can support localised electricity generation.

Walls and particularly roofs are exposed to solar radiation that can be converted into electricity silently and without producing pollution, by means of photovoltaic technology.

Calculations of potential estimate that installing PV units on the most favourable surfaces in urban areas can contribute up to 25 per cent of the total electricity demand of these areas.

The application of PV systems in 'stand-alone' buildings and other installations to generate electricity from solar energy is a wellestablished strategy to reduce the energy demand from non-renewable sources.

PV is often the preferred option, either when a conventional electricity supply is unavailable or when the cost of cabling and connection is high.

However, connecting PV systems to the existing grid and infrastructure readily available in cities means surplus energy can be redistributed and is thus not wasted.

Furthermore, the integration of PV as an inherent building element - referred to as Building Integrated PV (BIPV) - for example, in the form of a shading device or wall/roof cladding system, brings economic advantages in that the PV system fulfils numerous functions.

Throughout Europe there are examples of buildings and projects which demonstrate such potential.

However, the urban context is typically overlooked. This is being rectified by an EU- and Swiss-funded project which targets cities, authorities and related professionals, via municipalities, planners and architects.

The PV City Guide project is developing guidelines that address implementation, design, financial and legal aspects in the context of cities, in order to highlight and encourage the exploitation of the significant potential in these areas.

These guidelines are to be presented at international events and meetings to provide initial information to interested parties and gain further feedback from a range of experts before final production of the guide.

It is clear that a key player in this field is the municipality, both in terms of enabling and stimulating the use of PV in cities. Demystifying the technology and outlining all the interrelated issues associated with PV is a first step. This is followed by clear guidance on setting up conditions that encourage the use of PV from a practical perspective.

It is critical to identify and be able to assess the specific conditions of a particular city, rather than give generalised rules. The character of a city will influence the potential of PV and highlight strategies to maximise this potential. It is interesting to note that the climatic variations from northern to southern Europe play a less significant role than one might expect. For example, the annual availability of solar irradiation in Malmo, Sweden is only about 20 per cent less than in Florence, Italy - despite the significant difference in latitude.

The PV City Guide provides rules of thumb to determine the potential for electricity production for your city, as a function of climate, demographics and energy demand. It goes on to provide specific recommendations in relation to the urban form of a city - whether, for example, building heights are homogeneous or not, or whether the street pattern is strongly repetitive (modern) or informal (medieval).

The PV City Guide will be available by the end of the year. Log on to pvcityguide. energyprojects. net for further information. A workshop discussion to shape the final document takes place on 21 September in Basel.

The project PV City Guide is supported by the European Commission and the Swiss Federal Office for Education and Science.

Koen Steemers is director at the Martin Centre for Architectural and Urban Studies, University of Cambridge. E-mail kas11@cam. ac. uk or tel 01223 331700

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