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International Journal of Low-Carbon Technologies Advance Access published December 22, 2014

Numerical assessment of energy contribution by building integrated photovoltaics in a commercial/office building refurbishment in UK

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C.U. Ikedi1,2 *, M.I. Okoroh1 and A.M. Dean1 1 School of Engineering and Technology, University of Derby, Markeaton Street, Derby, UK; 2 National Centre for Energy Research and Development, Energy Commission of Nigeria, University of Nigeria, Nsukka, Nigeria

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Abstract

Keywords: energy contribution; building-integrated photovoltaics; commercial/office building *Corresponding author. [email protected]

Received 27 February 2014; revised 13 September 2014; accepted 17 September 2014

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1 INTRODUCTION Several attempts had been made in previous similar studies to develop some form of framework or method to measure or showcase the energy contribution of various BIPV technologies and systems on applied buildings. Extensive literature review [1– 4] has shown that most previous studies base their assessments on either the intrinsic output capacity of applied BIPV systems or simulations. For instance, Braun and Ruther [1] carried out a study on the contribution of grid-connected BIPV in reducing the electrical load demands of a large and urban commercial building. The case study which was located in a warm climate in Brazil was estimated to accommodate a 1-MWp BIPV generator, which closely matches the building’s typical maximum power demands. Based on solar radiation data and simultaneous building electricity demands for the year 2007, simulation of the annual solar

generation profile of the case study shows that the 1-MWp BIPV system could account for around 30% of the total building’s energy consumption. Meanwhile, prospective investors for BIPV in the building sectors are becoming increasingly concerned on lack of numeric data/information on the actual contribution of such systems to applied buildings as a percentage impact to the total power profile rather than unparalleled showcase of predicted or simulated power performances which often do not tally with actual post commission performances. This gap has formed the basis for the numeric evaluations in this present work which are based on basic photovoltaic and numerical methods to deduce the power contribution of BIPV to applied building. Statistics have also shown that commercial/office buildings alone, account for 20% of the carbon dioxide emissions in the UK [5] and research [6], has also shown that 70% of 200 large firms surveyed in the UK would be attracted to sustainable

International Journal of Low-Carbon Technologies 2014, 0, 1– 11 # The Author 2014. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. doi:10.1093/ijlct/ctu031 1 of 11

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The generation and supply of electricity to residential and commercial/office buildings has been well established in different parts of the world for some decades now. However, sources like coal, nuclear and gas turbine electric generators which constitute most of the technologies applied in grid power stations usually involve fossil fuels and carbon dioxide emissions which are not environmentally friendly. As a solution to reduce the global carbon footprint and provide sustainable source of electricity, buildingintegrated photovoltaics (BIPV) or solar electricity has been identified as one of the most attractive sustainable energy technologies in the building sectors. This research work aims at assessing the energy impact of a grid connected solar electric system integrated in a commercial/office high-rise building in UK for a period of 1 year, by carrying out a numerical evaluation based on measured daily BIPV system energy outputs and the overall electrical energy demand of the applied building before and after the installation of the BIPV system. The results of the assessment showed that BIPV has the capacity to provide 0.4% of the total electrical energy required in applied building.

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commercial/office buildings. In addition to providing sustainable zero-carbon electrical power to an office building, innovations in PV modules can now provide natural day lighting effects in office settings as sky lighting devices [7], adding extra illumination and beauty to modern office architecture. One key benefit in the application of BIPV technology on commercial and office buildings is sustainability and according to [8]; ‘sustainable commercial buildings perform better than conventional commercial buildings in terms of wellbeing of the occupants, building value and return on investment’. In this dispensation, this study has therefore chosen a commercial/office building located in UK as a case study and derives the seasonal and annual power contribution of BIPV to the overall electrical power demand of applied building. Figure 1. Side view of the main research project site (University of Derby).

The first step in the methodology of the study was to identify a case study which involves two segments namely: the project site and the applied BIPV system.

2.1 Project site (University of Derby, UK) University of Derby, Kedleston campus is located in the Derby city which is at the south east part of Derbyshire in the East Midlands of UK. The meteorological conditions include a latitude of 528560 2000 N and longitude of 018290 4700 W, obtainable at the site of the University of Derby with a typical average temperature of about 48C in winter and about 188C in summer. The Kedleston campus high-rise building has a total area of 7733 m2 at the east wing, 5988 m2 at the north wing and 4645 m2 at the south wing suitable for solar installations. These all receive direct beam solar radiation, though some for only limited periods of the day. Part of these roof spaces by the main entrance wing of the building has been reserved and used for nine electric wind turbine generators, while the roof area on the old administration block at the north wing of the building was used for the PV integration. The BIPV system is used to offset part of the building’s electrical demand. Figure 1 shows a pictorial view of the University of Derby, Kedleston Road campus. From the preliminary site survey conducted prior to the installation of the BIPV project, the aerial view or perspective showed that there is a good solar line of site at the campus site. This means that although there are quite a number of trees within the premises, these trees are distantly located away from the building structures and in particular the area meant for the BIPV installation. Some of the trees which would have coincided with the solar line of site are found to be shorter in height than parts of the building containing the BIPV array devices. Furthermore, being located at a latitude of 528560 2000 N and longitude of 018290 4700 W, the average total daily solar radiation which can be received by a solar panel tilted at an inclination approximate to the latitude is 1.1 kWh/m2/day. 2 of 11

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Figure 2. Modular shading patterns for the research BIPV.

Figure 2 shows a 3D modular shading pattern for the project site (University of Derby) which was developed with the aid of PVsyst BIPV software with respect to the building and site coordinates. From the modular shading result (Figure 2), it can clearly be seen that the South facing coordinates from the array, represented by the blue rectangular area or strip in Figure 2, show a clear solar line of site whereas the East and North coordinates coincide with the building structure such that the North and east towers of the building constitute the tallest obstruction to the solar lines of sight. To overcome the possible shading barriers posed by the North tower of the project site for instance, BIPV installations which should be done behind the tower to the North must be either carried out on the topmost part of the North tower or outside the project building. Such options will no doubt imply huge cost or not practically feasible. The modular shading result (Figure 2) therefore formed the basis for the choice of the roof area at the old administrative building between the North

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2 CASE STUDY

Numerical assessment of energy contribution

Figure 3. The BIPV array layout (University of Derby). Figure 4. Inverter controls in the control room (University of Derby).

2.2 BIPV System The BIPV system in this case study comprises a roof array with an area of 204 m2, consisting of 72 units of ND-170E1F (170W), Si-poly sharp PV modules. The design and installation process involved in the BIPV system include: roof survey, rail markings, PV installations and inverter/equipment installations at the control room. Firstly, all the designs were checked for compliance with wiring regulations. Meanwhile, pertinent risk assessments were carried out as well as the Health and Safety method statements developed to ensure that the work is completed safely and timely. The PV modules were electrically connected in series to form ‘strings’ and then in parallel combinations compatible with the chosen inverters. Double insulated cables feed the electrical power from the array strings to DC isolators where individual strings were paralleled as required. Cable interconnections were made via double insulated connectors with an IP rating of IP67 (as defined in BS EN 60529:1992). As a strategy to minimise power loss, the DC cables between the modules and the inverters were generally kept as short as possible (Figure 3).

3 INVERTER AND CONTROL EQUIPMENT Sunny Boy synchronous inverters SB3300/3800 from SMA were used to convert the DC power derived from the PV array into AC power suitable for parallel connection to the mains utility (230 Vac/50 Hz). The inverter installations were G83/1 compliant for use in the UK and installed alongside DC and AC isolators in a ventilated control room (Figure 4). The ventilation became inevitably required as 8% of the electrical energy generated by the PV array is dissipated by the

inverters as heat and it is important therefore that the equipment room is ventilated to allow excess heat to escape. In compliance with Engineering Recommendation G59/1, the inverter units include additional control enclosure for the protection relay which provides protection against over/under voltage, over/under frequency and loss of mains. Once re-established with mains, the PV system auto-resets and synchronises without manual intervention.

4 METHODOLOGY Following the preliminary system designs and installation, post installation electrical data were retrieved from the system with the aid of high-performance data logger systems networked to different input and output terminals of the entire BIPV system. This exercise was conducted daily for 1 year. The entire set of monitored parameters include mean values for Grid Current (A), DC Current (A), Grid Voltage (V), DC Voltage (V), Operating Time Metre Change (h), Feeding Time Metre Change (h) and Total Energy Yield (kWh), where A is ampere, V is volts, W is watts and h is hours, respectively. The key parameter applied for this study is the total output energy (kWh). The monitoring was done with the aid of Kyoto platform software integrated into a state of the art SMA1 data technology. (Kyoto platform is an open text computer format which has the capability to extract large volumes of texts and data in various computer languages and this formed the basis for using the software.) The energy delivered to the building by the BIPV (kWh) was monitored on a daily basis and this was carried out for a period of 1 year in order to account for the different seasons of the year 1

SMA is a German solar energy equipment supplier founded in 1981 and based in Niestetal, Hesse, Germany. It is the world’s largest manufacturer of inverters for solar photovoltaic modules.

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tower of the building and the south coordinates in the project site which is also at a considerable safe installation height.

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namely: winter and summer. The monitoring was commenced from July 2010 to July 2011. For simplicity and evaluation purpose, the data was subsequently compressed to monthly average values for the different months of the year. Finally, graphical representations of the data were developed and applied to deduce and assess the energy impact of the BIPV on the applied building.

Figure 6. Total BIPV energy contribution—August 2010.

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The energy contribution is a measure of the electricity generated into the building by the BIPV system. The results which are calculated daily mean values in kilowatts. Hours (kWh) are presented for each month of the one year monitoring (Figures 5–17).

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Figure 5. Total BIPV energy contribution—July 2010.

5 RESULTS OF THE BIPV ENERGY CONTRIBUTION

Numerical assessment of energy contribution

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Figure 7. Total BIPV energy contribution—September 2010.

Figure 8. Total BIPV energy contribution—October 2010.

6 DISCUSSION OF THE RESULTS FOR SYSTEM’S ENERGY CONTRIBUTION The graphical results (Figures 5– 17) of the energy contributed by the BIPV system to the applied building become interesting when analysed from the perspective of solar conditions and seasons of the year. The total energy contribution in principle is a product of the power contribution and time and can be expressed as:

Total energy yield ðYÞ ¼ Power ðPÞ kW  Time ðtÞ h

ð1Þ

Substituting P for IV, where I is the current in amps (A) and V is the voltage in volts (V), then Total yield ðYÞ ¼ IVt ðkWhÞ From the graphical results (Figures 5– 17), it can be seen that the energy yield from the BIPV system is higher in the summer months than winter months. International Journal of Low-Carbon Technologies 2014, 0, 1– 11 5 of 11

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Figure 9. Total BIPV energy contribution—November 2010.

Figure 10. Total BIPV energy contribution—December 2010.

This is explained based on the fact that the summer months are characterised by clear climatic solar conditions which enhanced direct incident solar radiation on the BIPV panels, consequently maximising the system power and hence total energy yield. The winter months on the other hand were characterised by cloudy climatic conditions resulting in diffuse solar radiations which retard or impede the yielding capacity of the BIPV system. From Figures 15 to 17, the days in summer months namely May (5 and 6), June (3), July (24) 2011 recorded maximum daily 6 of 11

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energy yields of about 169.0, 180 and 175 KWh, respectively, from the BIPV while the days in the winter months namely November (6) 2010, December (25) 2010 and January (20) 2011 (Figures 9– 11) recorded about 51.0, 29.0 and 41.0 KWh, respectively, as the corresponding maximum in winter. The energy yield from the BIPV system therefore shows a significant difference or margin between winter and summer months. This difference in the system yield at different seasons in effect has an implication on the economic or financial impact of

Numerical assessment of energy contribution

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Figure 11. Total BIPV energy contribution—January 2011.

Figure 12. Total BIPV energy contribution—February 2011.

the BIPV on the applied building at the respective periods. For instance, because the graphical results show significant increment in summer months, the energy imported into the building grid by the BIPV system was correspondingly high, thereby providing more feed-in to the grid, providing financial savings at such times. The least recorded energy imported by the BIPV into the building grid within the 1-year monitoring period is 0.01 KWh which was recorded from 1 to 9 of the winter month of December

2010 (Figure 10). A similar value of 0.01 KWh was also recorded on 7 January 2011. In contrast however, the highest value of energy imported by the BIPV into the building grid within the 1-year monitoring period is 180.0 KWh which was recorded from the system in the summer month of June (Figure 16). Figures 5– 17 were based on daily values. These values were further computed into total monthly values for the purpose of International Journal of Low-Carbon Technologies 2014, 0, 1– 11 7 of 11

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Figure 13. Total BIPV energy contribution—March 2011.

Figure 14. Total BIPV energy contribution—April 2011.

computing the total percentage energy contributed by the BIPV to the grid energy demand or usage in the building. Figure 18 and Table 1 show the monthly graphical results and deduced electrical energy, respectively, contributed by the BIPV system to the high-rise commercial/office building refurbishment (University of Derby), from July 2010 to July 2011. Furthermore, Table 2 shows the electrical energy consumption of the building over a period of 2 consecutive years, before and after the BIPV, with total annual energy in each of the years, respectively. 8 of 11

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A very interesting feature in the table is the drop in the total energy consumption within the intervals following the installation and implementation of the BIPV project. This is a clear demonstration of the energy impact of the BIPV on the overall energy profile of the applied building. Finally, adding together the total monthly energy contributions in Table 1 (column 2: kWh), the total electrical energy generated and contributed by the BIPV system to the building (Kedleston campus, University of Derby) is obtained as follows: [2871.04 þ 2690.99 þ . . . þ 4905.12] kWh ¼ 22 691.31 kWh.

Numerical assessment of energy contribution

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Figure 15. Total BIPV energy contribution—May 2011.

Figure 16. Total BIPV energy contribution—June 2011.

The total recorded annual energy contributed by the BIPV system to the building within the period therefore ¼ 22 691.31 kWh. Also from Table 2, column 2, the total annual energy (from the grid) demanded or consumed by the occupants in the building between 2010 and 2011 which is the operational period of the BIPV ¼ 5628.60 kWh. Dividing the input from the BIPV by the total intake in the building gives the actual fraction of the energy contribution

from the BIPV system. The percentage energy impact or contribution made by the BIPV therefore is [22 691.31/5628, 598  100]% ¼ 0.4% of the total energy use. This means that, for every electrical energy consumed or used by the building occupants, the BIPV system has the capacity or capability to cater for 0.4% of the consumption. It is important to note that although this figure looks like a drop of water in an ocean, the contribution becomes appreciated when the size of the building (eight-storey high-rise building International Journal of Low-Carbon Technologies 2014, 0, 1– 11 9 of 11

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Figure 17. Total BIPV energy contribution—July 2011.

Figure 18. Monthly BIPV energy contribution (Kedleston, University of Derby).

with high-wattage commercial appliances including lifts) is put into consideration.

7 CONCLUSION Manufacturer’s power specifications for BIPV modules are usually based on the assumption of ideal conditions of system operation namely: the standard test condition (STC) which is the condition under which PV modules are tested and calibrated 10 of 11 International Journal of Low-Carbon Technologies 2014, 0, 1– 11

at insolation level of 1000 W/m2, air mass of 1.5AM and cell temperature of 258C. However, when these PV modules are integrated to form parts of building envelopes such as roofs, facades or windows, barriers resulting from the thermodynamic characteristics of the building space and mass as well as installation discrepancies constitute a barrier or resistance to the expected or predictable energy performance or contribution. The need therefore for actual monitoring, measurements and evaluations with respect to the obtainable grid data of the applied building cannot be overemphasised. This need forms the

Numerical assessment of energy contribution

Table 1. Monthly BIPV electricity contribution (Kedleston campus, University of Derby). Month

Energy (kWh)

July August September October November December January February March April May June July

2871.04 2690.99 1997.92 1331.04 626.80 219.59 534.51 623.99 1971.33 3035.41 3333.16 3455.53 4905.12

size of the applied building, eight-storey high-rise building, involving high-wattage appliances, the system’s contribution can be concluded to be relatively reasonable. It can also be seen from the discussion of results that the energy capacity of an applied solar electric generator in a given project is determined or influenced by particular seasons of the year with respect to characteristic conditions of solar radiation obtainable at the project site. Preliminary or pilot project designs should therefore be best conducted based on the unfavourable months of the seasons of the year particularly cloudy periods. The essence of this is to ensure that the post installations power or energy performance of applied BIPV projects does not operate below proposed expectations.

Table 2. Electricity consumption before and after BIPV (University of Derby, Kedleston). Month

2010– 11 (kWh)

2009– 10 (kWh)

Change (kWh)

%

May June July August September October November December January February March April Total

455 202 385 898 389 152 391 904 433 884 466 527 548 613 461 944 503 079 675 083 533 300 384 010 5 628 598

406 520 421 200 417 388 414 125 450 774 499 011 548 124 523 104 509 501 475 752 531 420 450 551 5 647 470

48 682 235 302 228 236 222 221 216 890 232 484 0489 261 159 26422 199 331 1880 266 541 218 872

12 28 27 25 24 27 0 212 21 42 0 215 0

rationale behind this study. In general, the integrated solar electric generator has shown maximum annual energy contribution capacity of up to 0.4% of the total energy use. Considering the

[1] Braun P, Ruther R. The role of grid-connected, building-integrated photovoltaic generation in commercial building energy and power loads in a warm and sunny climate. Energ Convers Manage 2010;51:2457– 66. [2] Eke R, Senturk A. Monitoring the performance of single and triple junction amorphous silicon modules in two building integrated photovoltaic (BIPV) installations. Appl Energ 2013;109:154– 62. [3] Fanney AH, Dougherty BP, Davis MW. Measured performance of building integrated photovoltaic panels. Sol Energ 2001;123:187– 93. [4] Lee JB, Park JW, Yoon JH, et al. An empirical study of performance characteristics of BIPV (building integrated photovoltaic) system for the realization of zero energy building. Energy 2014;66:25– 34. [5] Barlow S, Fiala D. Occupant comfort in UK offices—how adaptive comfort theories might influence future low energy office refurbishment strategies. Energ Buildings 2007;39:837– 46. [6] Miles K, David S. The “green” refurbishment of commercial property. Facilities 1996;14:15 – 9. [7] Wonga PW, Shimodab Y, Inouea M, et al. Semi-transparent PV: thermal performance, power generation, daylight modelling and energy saving potential in a residential application. Renew Energ 2008;33:1024– 36. [8] Davies R. Green Value—Green Buildings, Growing Assests. Royal Institute of Chartered Surveyors, 2005.

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REFERENCES