Elsevier

Energy and Buildings

Volume 62, July 2013, Pages 459-468
Energy and Buildings

Urban solar energy potential in Greece: A statistical calculation model of suitable built roof areas for photovoltaics

https://doi.org/10.1016/j.enbuild.2013.03.033Get rights and content

Highlights

  • Solar potential statistical model is presented for multifamily buildings in Greece.

  • Analysis of a large building sample was completed to produce and validate the model.

  • Interesting outcomes are derived about the actual solar potential in Greek cities.

Abstract

Determining the actual solar potential for applications in the complex urban environment is a difficult task, particularly when there is a lack in background information, such as the texture and structure of the urban landscape, as this was until very recently the case in Greece. In this paper a simplified yet effective methodological approach for the evaluation of solar architecturally suitable areas of flat roof surfaces on typical multi-storey, multifamily buildings is presented. It is based on a statistical calculation model for solar potential that has been validated, by analysing actual measurements carried out in the city of Thessaloniki in Northern Greece. The model can be either used by private engineers or it can be alternatively incorporated in geoinformatics decision-making tools, such as GIS, to aid planners, regulators and developers to determine the solar potential. Finally, it is of great interest to notice that the PV potential of the multifamily buildings considered in the validation, proved to be rather poor. The solar utilization roof factor in the majority of the examined building cases was approximated only between 25 and 50%.

Introduction

Determining the actual solar potential for urban renewable applications can be a challenging task. The complex urban environment, with varying building block densities and even more so building elevations, combined with limited available construction data about the existing building stock, are the main reasons for the difficulties emerging in the effort to assess solar potential. In the case of Greece, no any thorough study has been conducted in this field until 2012, although solar thermal applications in the residential building sector are widespread and photovoltaics are rapidly increasing. This is associated with the lack of available data about the urban landscape, which prevents a flexible yet also valid estimation of suitable application areas. Against this background, the present paper aims at presenting a simplified, yet effective, methodological approach for the evaluation of the solar architecturally suitable areas of flat roof surfaces particularly for photovoltaics (PVs) in typical multi-storey, multifamily (MF) buildings, which represent the majority of the building stock in Greece but also in most other European cities. These areas are actually the available roof surfaces for the PV installations obtained by subtracting from the gross roof areas the sum of the occupied areas by the roof elements and the shaded roof parts. Therefore, a statistical calculation model was produced and validated by analysing actual measurements of solar potential that were carried out in a sample of representative buildings in the city of Thessaloniki in Northern Greece (40°38′ North and 22°56′ East). The present model can be used by architects, engineers and developers to assess the solar potential in specific buildings. In addition, it can be incorporated in geoinformatics decision-making tools, such as GIS, in order to support planners, developers and authorities to assess the urban solar potential over an extended geographical area.

PVs are a truly elegant means of producing electricity on site, directly from the sun, without concern for the energy supply or environmental harm. They represent a favourable case easy and fast installation, low maintenance requirements and the ability to produce electricity on site within the urban built environment. In that sense, there is a growing consensus that PVs for individual buildings, known as building integrated or applied PVs (BIPVs or BAPVs respectively), will be the top selection among the continuously widespread distributed PV applications.

In Greece the PV market in the building sector is growing rapidly after 2009, due to the great feed-in tariff incentives granted especially for residential applications. In detail, no authorization and construction regulations as well as particular incentives were specified, until a national development programme was put into force for first time in 2009 by means of Law 3734, providing potential investors with a remarkably high tax-free tariff (0.55 €/kWh) for 25 years as well as determining clarified and simplified grid-connection procedures. Since then, the development of PV installations was immediate with over 50,000 applications (450 MWp approximately) submitted in three years’ time to the Distribution System Operator (DSO), namely the Public Power Corporation (PPC), for grid-connection offer. Within these applications, over 28,700 were already put into operation in 2012, representing a cumulative capacity of 256 MWp.

Within this context, the current paper studies the potential of PV technology in the Greek residential building stock and motivated by the fact that the urban environment in Greece is complex with various building block densities and miscellaneous building elevations as well as limited available construction data, a simple calculation model was established for estimating solar suitable roof areas, after statistically analysing real measurements of a building sample. Pitched roofs were excluded from the examined sample, as they are very rare in the urban building stock in Greece, but whatsoever can be more straightforwardly classified and elaborated compared to flat roofs, as it is also argued by Hachem et al. [1].

Section snippets

Related work

The current work, apart from the calculation of the solar architecturally suitable rooftop areas on MF buildings, is also intended to compensate to a degree for the lack of methodologies developed for those purposes.

Buildings’ heterogeneity and the complexity of the urban environment generally require assumptions and input data for the solar energy use computation, which will ensure that only safe propositions and valid information will be produced about PV utilization, thus eliminating

Methodological approach

The methodological process adopted for this research consists of a three-step procedure:

  • a.

    The first step included the examination of 129 representative Greek MF buildings, which led to actual measurements of solar suitable flat roof-top area.

  • b.

    In the second step, the calculation model was generated by means of a statistical analysis of the gathered data.

  • c.

    Finally, in the third step, the developed model was validated, by comparing predicted and measured solar areas for a randomly selected,

Flat roof configurations

The examined building blocks were located in the two largest municipalities of Thessaloniki urban area, namely Thessaloniki and Kalamaria (Fig. 7). The attempt to statistically analyze the real measurements and create algorithms for solar potential, forced us to select a typical and big enough sample consisting of 129 residential MF buildings with multiple orientations and elevations. The representativeness was assured by choosing units with specific typical roof configurations, according to

Model presentation

The model was generated by means of statistical analysis, initially examining the entire roof sample, but also by separating it either into three classes based on the roofs’ orientation or alternatively into five classes based on the position of the stairwell and elevator shaft, as presented in Table 1. Overall, nine specific models were obtained and assessed. Furthermore, three additional algorithms were produced for the cases of roofs attached to higher neighbouring buildings. In Table 3 the

Conclusions

In the work presented in this paper, a model for roof-top surfaces was produced by means of a statistical analysis of real calculations for determining the solar potential of existing MF buildings in a typical Greek city. The proposed model is based on structural, typological and functional features of the buildings which have been categorized according to the orientation of the roofs. The input data required for the models’ direct application include simply the unavailable areas of roof

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