Life cycle cost assessment of building integrated photovoltaic thermal (BIPVT) systems

doi:10.1016/j.enbuild.2010.03.017

Energy and Buildings

Volume 42, Issue 9, September 2010, Pages 1472-1481

https://doi.org/10.1016/j.enbuild.2010.03.017 Get rights and content

Abstract

The present paper deals with an analysis of the building integrated photovoltaic thermal (BIPVT) system fitted as rooftop of a building to generate electrical energy higher than that generated by a similar building integrated photovoltaic (BIPV) system and also to produce thermal energy for space heating. A thermodynamic model has been developed to determine energy, exergy and life cycle cost of the BIPVT system. The results indicate that although the mono-crystalline BIPVT system is more suitable for residential consumers from the viewpoint of the energy and exergy efficiencies, the amorphous silicon BIPVT system is found to be more economical. The energy and exergy efficiencies of the amorphous silicon BIPVT system are found to be 33.54% and 7.13% respectively under the composite climatic conditions prevailing at New Delhi. The cost of power generation is found to be US $ 0.1009 per kWh which is much closer to that of the conventional grid power.

Introduction

The energy consumption can be examined under four main sectors namely; industrial, residential, transportation and agriculture. According to Cengel [1], the energy required for space heating in buildings has the highest share of about 40% of the total energy consumed in the residential sector (Table 1). The electricity production based on fossil or nuclear fuels induces substantial social and environmental costs, whereas in case of renewable energy sources these are lower. The renewable global status report [2] indicates that the power production by way of solar photovoltaic (PV) has grown more than any other renewable energy source. It has a great prospect of cost break-even, with respect to the conventional grid power for residential consumers. The production capacity has grown at an average of 48% each year and the cumulative global production is now at 12.5 × 10³ MW.

The main technology routes as seen today can be characterized into silicon based PV, non-silicon based thin film PV and new concept devices (Fig. 1). In 2008, worldwide production of PV modules used in consumer products includes 42.2% mono-crystalline silicon (c-Si), 45.2% poly-crystalline silicon (p-Si), 2.2% ribbon silicon (r-Si), 5.2% amorphous silicon (a-Si), 4.7% cadmium telluride (CdTe) and 0.5% copper indium gallium selenide (CIGS) [3]. The reliability and lifetime of the PV systems are growing steadily. Depending upon the production technology used, nowadays the PV manufacturers offer a 5–30 years service life guarantee.

The performance of a PV can be described in terms of its energy conversion efficiency, the percentage of incident solar energy (input) that the cell converts into electricity under standard rating conditions. The overall electrical efficiency of the PV module can be increased by increasing the packing factor (PF) and decreasing the temperature of the PV module [4], [5]. Table 2 presents the conversion efficiency, efficiency correction coefficient and expected life of the cell and modules with different production technologies [6], [7].

Historically, the stand alone photovoltaic (SAPV) has not been a cost-effective source of power generation. Benemann et al. [8] realised the installation of BIPV system at Aachen, Germany where the PV arrays were integrated into a curtain wall façade with isolating glass. Such systems have improved the economics by allowing some cost of the PV system to be shared by the building. Yet the purchase, design, installation and maintenance of the BIPV systems cost more than those in the standard contemporary building skins.

In typical BIPV applications the increase of solar cell temperature results in the decrease of energy conversion efficiency. Air-cooled hybrid photovoltaic–thermal (PVT) systems consist of PV modules with an air channel at their rear surface and usually ambient air is circulated in the channel to achieve both PV cooling and thermal energy output. The thermal energy obtained can be used to fulfil the thermal requirements of the building. A large number of theoretical as well as experimental works has been reported on hybrid PVT systems [9], [10], [11], [12], [13], [14], [15], for extraction of heat from the PV modules.

BIPVT is a relatively new technology which merges hybrid PVT with BIPV systems, simultaneously providing both the electrical and the thermal energy onsite. Due to sharing of resources like materials and functions in the integration, the BIPVT system becomes cheaper than that having four separate products [6]. Moreover, the complete system installed by a single team results in further cost reduction. Agrawal and Tiwari [16] used an opaque type BIPVT system fitted as the rooftop of a laboratory over an area of 65 m². It was concluded that for a mass flow rate of 0.2 kg/s the system at Bangalore produces annual 15766 kWh and 16708 kWh electrical energy and exergy respectively which is 629 kWh and 1571 kWh higher than that of a similar Building Integrated Photovoltaic (BIPV) system. Optimization of the system configurations under cold climatic conditions has also been presented [17]. The life cycle assessment has been applied to SAPV systems, hybrid PVT systems and BIPV systems by several researchers [18], [19], [20], [21]. The present paper presents the life cycle cost (LCC) assessment methodology for the BIPVT systems. It also aims to compare the performance and economic feasibility of different BIPVT systems.

Section snippets

Problem identification

BIPVT systems similar to those installed on the roof of an experimental laboratory at the Centre for Sustainable Technology, Indian Institute of Science, Bangalore has been considered for the roof of the buildings at New Delhi. Fig. 2 shows an orthographic view of the experimental laboratory with BIPVT systems as the rooftop at New Delhi. As New Delhi is situated at 28°35′N, the optimum angle for fitting the BIPVT systems is due south inclined at an angle of 30° to the horizontal. The system

Thermal modelling

Experimental validated methodology of Tiwari and Sodha [22], [23], [24] were used for thermal modelling of the components of the BIPVT system. The assumptions made are as follows:

(a)
The system is in quasi-steady-state condition.
(b)
The specific heat of air does not change with a rise in its temperature, i.e. it remains constant.
(c)
The transmissivity of ethylene vinyl acetate (EVA) is approximately 100 percent.
(d)
The heat loss from the side of the system is negligible, and
(e)
The airflow through duct is uniform

Energy analysis

The actual electrical efficiency of the BIPVT systems is given by [25], $η_{c a} = η_{r e f} [1 - ϕ_{r e f} (T_{c} - T_{r e f})]$

Quantities $η_{r e f}$ , $T_{r e f}$ and $ϕ_{r e f}$ are usually given by the photovoltaic module manufacturers but they can be also obtained from flash tests. Thus, the hourly electrical output of the BIPVT systems is given by

${\dot{E}}_{e l}$ = actual cell efficiency × solar insolation $= η_{c a} \times I (t) \times b L \times n_{s} \cdot n_{p}$

The rate of useful thermal energy obtained from BIPVT systems is given by ${\dot{E}}_{t h} = n_{p} \times {\dot{m}}_{a i r} C_{a i r} (T_{a i r o u t} - T_{r}) = n_{p} \times {\dot{m}}_{a i r} C_{a i r} (1 - e^{- \frac{n_{s} \cdot b L \times U_{L}}{{\dot{m}}_{a i r} C_{a i r}}}) [U_{t a i r} (T)]$

Exergy analysis

According to Coventry [26], exergy (sometimes called availability) is defined as the maximum theoretical useful work obtainable from a system as it returns to equilibrium with the environment. With the exergy approach, it becomes possible to assign coherent values to the different energy forms (work, heat, electrical energy, etc.) that take into account the two key energy parameters namely quantity and quality. According to Patela [27], total exergy inflow to the system is given by $\dot{E} x_{i n} = I (t) \times [1 - \frac{4}{3} \times]$

Life cycle cost assessment

There are numerous costs associated with acquiring, operating, maintaining and disposing of a system. In Life Cycle Cost (LCC) assessment, all relevant present and future costs associated with the system are summed in present value during a given life period. The purpose is to estimate the overall cost of project alternatives and to select the design that ensures the facility will provide the lowest overall cost of ownership consistent with its quality and function. Fig. 4 shows the line

Methodology

The approach uses individual BIPVT system to compute the energy, exergy and the outlet air temperatures using basic thermal modelling and heat transfer relations. The outlet air from one BIPVT system in a column is used as the inlet air in the next BIPVT system. For the first BIPVT system, the inlet air is the mixture of circulated air of the room and the fresh ambient air. Since the net mass flow rate of air inside the duct is 1 kg/s, the velocity of air inside the duct is 3.2 m/s. The following

Results and discussions

Fig. 5 shows that the annual electrical output from the mono-crystalline silicon (c-Si) BIPVT is maximum (15131 kWh) while that of the amorphous silicon (a-Si) BIPVT is minimum (6066 kWh). This is owing to the higher electrical conversion efficiency of the c-Si BIPVT than the other systems. The system with higher electrical energy uses higher amount of solar isolation and thereby remains with smaller portion to get converted into thermal energy. Therefore, the annual thermal output of the

Conclusions

Performance analysis and life cycle cost are evaluated for the BIPVT systems with different solar cells under the composite climatic condition of New Delhi and compared with the similar BIPV system. The results show that the use of BIPVT systems is always advantageous both from the efficiency and the economic point of view than similar BIPV systems. The mono-crystalline silicon BIPVT systems have higher energy and exergy efficiencies and are suitable where energy and exergy demands are higher

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Life cycle cost assessment of building integrated photovoltaic thermal (BIPVT) systems

Abstract

Introduction

Section snippets

Problem identification

Thermal modelling

Energy analysis

Exergy analysis

Life cycle cost assessment

Methodology

Results and discussions

Conclusions

Solar Energy

Solar Energy

Renewable and Sustainable Energy Reviews

Solar Energy Materials & Solar Cells

Solar Energy

Energy Conversion and Management

Renewable Energy

Energy

International Journal of Thermal Sciences

Applied Energy

Applied Energy

Renewable and Sustainable Energy Reviews

Energy Policy

Applied Energy

Renewable Energy