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Solar-Energy Surface Potentials 2005

Introduction

Full knowledge of the long-term potential of solar-energy utilization in a metropolitan area increases the possibility for taking energy-efficient construction and the use of renewable energies into account in urban planning, both in new project planning and in urban rehabilitation. To support this important climate-protection goal, an assessment in the context of an examination of the Berlin building stock was carried out with regard to the fundamental suitability of buildings for the installation of solar-technology systems (Solarer Rahmenplan Berlin) (“Berlin Solar Framework Plan,” available only in German).

The results of research project “Leitbilder und Potenziale eines solaren Städtebaus” (“Models and Potential of Solar Urban Development,” avail. only in Ger), presented by the contractor Ecofys in 2004 were the basis for this work. This project categorized the entire building stock of the Federal Republic of Germany by so-called urban-space types.

This typology is based on three aspects:

  • the break-down of the municipal building stock into urban spaces, depending on the history of their development
  • the demarcation of the urban spaces according to particularly favorable or unfavorable technical and structural prerequisites for passive and active solar-energy use
  • the recognizable changes in use and modernization requirement within the next approx. two decades, from which the possibilities of influencing urban planning and urban renewal on structural and technical changes will become apparent.

Urban spaces with similar structural and technical conditions, and similar urban-development histories, can be assigned a comparable solar potential.

In this context, the “potential urban solar-energy surfaces” are defined as the “solar potential.” The urban solar-energy surface potential takes as its point of departure such a technical aspect as the identification of suitable areas in the building shell, and includes additional urban-development aspects, such as architectural heritage/ preservation of historical monuments, and technical/economic aspects, for the ascertainment of the potential.

The following criteria yield the urban solar-energy surface potential (listed in order of significance):

  • All areas – façades and roofs – facing south ± 45 degrees can potentially be used. Moreover, a shade-analysis procedure is used to select those surfaces which are exposed to sunlight at 12:00 noon on December 21st.
  • All areas are examined according to urban-development criteria and possibilities for realization. The result is that façades in particular prove to be less suitable for active solar energy systems.
  • Sufficient window area should be available for passive solar-energy use. Gains in passive solar use are not only the most favorable form solar-energy use, but also increase residential quality by providing good sunlight exposure.
  • Sufficient and suitable areas should be available for solar-thermal heat production, both for warm-water supply and as a support for home heating.
  • Suitable areas for photovoltaic power generation should be available.
  • Basically, in cases of competition for space, solar-thermal energy should receive priority over PV. Notwithstanding, photovoltaic facilities should get the “better” surfaces, because solar-thermal production reacts less sensitively to shading than does photovoltaics.

Solar-quality figures are established for each urban-space type on the basis of the surface potential ascertained. They show the relationship between the gross roof or façade surfaces ascertained on the one hand, and their proportions utilizable for solar systems on the other. For example, a solar-quality figure of 1.0 means that the entire area of a roof can be used for solar technology; a quality value of 0.0 on the other hand means that there is no room at all on the roof or façade for solar systems. The façades of inner-city apartment blocks often have such values, due to the strong shading effects. The highest quality figures are assigned to roof areas on planned trade and service locations. A listing of all quality figures is shown in Table 2.

In sum, the present “solar-energy surface potential” examination ascertained a long-term potential contribution from solar-thermal energy of about 12 % to the heat supply of Berlin. This is a perspective for 2050, which also takes into account the reduction in heating requirements for buildings due to renewal cycles. As the long-term practicable contribution of photovoltaics to the Berlin power supply, a share of about 9 % was ascertained.