Integrated PV in shading systems for Mediterranean countries: Balance between energy production and visual comfort

doi:10.1016/j.enbuild.2014.03.046

Energy and Buildings

Volume 77, July 2014, Pages 445-456

https://doi.org/10.1016/j.enbuild.2014.03.046 Get rights and content

Highlights

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The Brise–Soleil is among the most effective shading systems with PV.
•
Louver PV systems can be effective when their width is minimized to 1.5 cm.
•
The overestimation of daylight levels measured in physical models can be decreased.

Abstract

Fixed shading systems are saving energy by reducing the cooling loads of the space they shade, but can be a source of energy losses due to the increased need of daylight that they create and the increased needs for heating during winter. Aim of this paper is the comparative assessment of different typologies of buildings’ shading systems with integrated photovoltaics (PV). The assessment is focused on their energy efficiency and degree of internal visual comfort conditions that they can ensure. The purpose of the comparison is to optimize the combination of shading systems and their integrated solar cells.

Shading systems are grouped and studied according to their energy savings (production and reduction of cooling loads) and to the quality of the visual interior environment. For the study, computer simulations are used for the energy loads (needs/production) and both computer simulation and experimental physical models are used for the daylighting assessment. Moreover, through this research, the effect of specific geometrical characteristic of the PV modules installed is analyzed in relation to the energy needs and to the resulting visual conditions. Systems such as Brise–Soleil are proved to be the most efficient for integration of PV modules in relation to energy saving and quality interior conditions.

Introduction

The issue of Building Integrated PV (BIPV) has been developed extensively since the 90s. It is still though under extensive research in relation to the transparency of the PV material, the position of the integration in the building [1] and to the tracking system used [2], [3].

Integration of Photovoltaic (PV) materials to shading systems was proposed in 1998 [4]. Since then, various shading types have been used mostly according to their energy balance and less according to esthetics and interior comfort conditions [5], [6], [7]. The most of the researches though, experiments with specific simple geometries of canopy horizontal or inclined systems and louvers systems [8]. There is a gap in the research bibliography on other geometrical types of shading systems. Especially for office units, due to the specific demands for visual comfort and the increased needs for quality lighting, balancing the above mentioned facts is more crucial.

Additionally, a gap exists concerning the efficiency of PV shading systems in Mediterranean countries where the amount of solar radiation is higher than the rest of Europe. The annual solar energy at horizontal plane is exceeding 1650 kWh/m² [9] and encourages the installation of such shading systems.

The main objective of this paper is to evaluate various types of fixed shading systems with integrated PV facing south in Mediterranean countries according to their ability to save energy and to provide visual comfort. Measurements and experimental work has been done for two typical cities in Mediterranean area: Athens (37.58° N, 23.42° E) and Chania in Crete (35.30° N, 24.01° E). Some useful details are already presented in another publication [10]. In this paper a more detailed analysis is presented in relation to visual comfort conditions and to specific geometrical detailing of the integrated PV. We examine the resulting visual comfort conditions that most energy efficient systems can create. We additionally examine the influence of the changeability of the PV thickness to the improvement of the interior visual comfort conditions.

Section snippets

Methodology

Basic aim of the current research is to find optimization points of the shading system with integrated PV, between energy savings for heating, cooling, lighting the space and visual comfort conditions. The results of Mandalaki et al. [10] are used in the part that concerns energy consumption for heating, cooling and lighting (Geometry A). Further on, different geometrical configurations of PV shading systems are examined, in order to evaluate the effect to visual comfort conditions and to

Geometry A – energy savings

According to Mandalaki et al. [10], all examined systems can support the electricity needs during the hours when the daylight level falls below 500 lux. If the electricity produced from the PV will be used to heat and cool the internal space, the most energy efficient system (the system consuming the least energy from non renewable sources), is the system of Surrounding Shade. The systems of Brise–Soleil Full facade, Canopy inclined double and Canopy inclined single are also considered to be

Geometry A – evaluating visual comfort conditions

In order to evaluate visual comfort conditions, both daylight levels through the value of Daylight Autonomy Levels (DA) and daylight quality through the values of Useful Daylight Illuminance (UDI) and Daylight Glare Index (DGI) are examined.

Geometry A – balancing energy savings and visual comfort

In order to evaluate the performance of the examined shading systems, a table is being created that incorporates all the examined values related with visual comfort and energy savings examined in previous paragraphs (Fig. 8). This table brings together conclusions in relation to all examined factors. The measuring scale is based on three basic categories, starting from the most efficient in terms of the factor examined: Best – Middle–Low. When values of the same examined factor are very close

Geometry B – visual comfort conditions

As a next step for evaluating the potentials of integrating PV in Shading Systems we evaluated the reduction of the thickness of the PV panels and how this is affecting the interior visual conditions.

Firstly, we evaluated the influence of this change to the experimental work that we did in order to evaluate daylight levels. We compared measurements of the daylight levels calculated by Mandalaki et al. [10] to the new simulations done for louver shading systems of 1.5 cm thickness. We showed that

Discussion and conclusions

We have attempted to combine the different and occasionally contradicting properties of the various shading systems with integrated PV examined in relation to their ability to save energy and to provide high quality of daylight. We have concluded that systems of Brise–Soleil Full and Semi facade can best achieve these two goals.

According to Mandalaki et al. [10] the most energy efficient systems are Surrounding Shading, Canopy Inclined Double, Brise Soleil Full facade and Canopy Inclined

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Integrated PV in shading systems for Mediterranean countries: Balance between energy production and visual comfort

Highlights

Abstract

Introduction

Section snippets

Methodology

Geometry A – energy savings

Geometry A – evaluating visual comfort conditions

Geometry A – balancing energy savings and visual comfort

Geometry B – visual comfort conditions

Discussion and conclusions

Energy and Buildings

Solar Energy

Solar Energy

Energy and Buildings

Solar Energy

Energy and Buildings

Applied Energy

Study on thermal performance of semi-transparent building-integrated photovoltaic glazings

Energy and Buildings

Evolutionary based maximum power point tracking technique using differential evolution algorithm

Energy and Buildings

Building – integrated photovoltaic, design for commercial and institutional structures

A Source Book for Architects

Experimental investigation of performance of a multι – purpose PV -slat window

Solar Energy Materials and Solar Cells