EXPLORING THE SOLAR ENERGY POTENTIAL FOR MULTISTORIED COMMERCIAL OFFICE BUILDINGS IN A DENSE CBD AREA OF A MEGA CITY Kumar Biswajit Debnath M Tahajibul Hossain
Electricity demand and solar potential (MWh)
Sheikh Md Rezwan Md Nahid Iqbal
School of Engineering, Cardiff University Bangladesh University of Engineering and Technology Daffodil International University Bangladesh University of Engineering and Technology
[email protected] [email protected] [email protected] [email protected]
35 30 25 20 15
10 5 0 Higher estimate
Average estimate
Lower estimate
Solar potential
Fig 1: Electricity demand (higher, average and lower estimation) and solar energy generation potential of the Motijheel CBD area in Dhaka city
WHICH ARE YOUR ARCHITECTURAL (R)SOLUTIONS TO THE SOCIAL, ENVIRONMENTAL AND ECONOMIC CHALLENGES OF TODAY? Research summary Motijheel Commercial Area, the main central business district (CBD) of Dhaka city, Bangladesh has already been found through many studies to cause urban heat island (UHI) effect due to its densely built multistoried commercial buildings and lack of green areas. These buildings consume significant amount of electricity to accommodate the lighting facilities, mechanical means for ensuring thermal comfort and operating electrical appliances for a huge number of occupants. This research seeks the potential of solar energy generation by using the prospective roof and elevation surface areas of these buildings, which takes significant part in causing augmentation of mean radiant temperature against the existing electricity consumption rate. Also, this research aims to establish a comparative analysis between existing electricity demand and the solar electricity generated to explore the potential of solar energy harvesting in a densely built urban area. In addition to it, the influence of choice in lighting technology (incandescent, florescent, CFL and LED) would be further examined to see their contribution in electricity demand. This study may contribute in policy development for the already densely built high electricity demanding commercial urban areas into self-sustaining low electricity demanding urban zones. Keywords: Energy demand; solar energy potential; commercial office building.
1. Introduction
3. Methodology
With approximately 6% GDP growth, Bangladesh is a least developed country with eighth largest population approximately 150 million("World Data Bank," 2014) in 2010 in the world. The capital of Bangladesh, Dhaka, is considered as a megacity (Kabir, Endlicher, & Jägermeyr, 2010) with a population of approximately 14 million people ("City Population," 2012). In this mega city the main CBD (central business district) is situated in Motijheel area. The entire area has a high electricity demand. These buildings consume significant amount of electricity to accommodate the lighting facilities, mechanical means for ensuring thermal comfort and operating electrical appliances for a significant number of occupants. The peak time of this demand is from 9 a.m. to 5 p.m. After this period this area is nearly vacant in comparison to peak working hours. The empty flat roofs, elevation surfaces and peak demand time renders the scope of integrating solar photovoltaic electricity generation for the office spaces. The solar PV could be a source of renewable energy to contribute in the supply side as well as can reduce the demand in these buildings.
The study was divided into two parts. First a field survey was undertaken to find the electricity demand, appliance ownership, land use and floor areas of buildings. The second part a 3D model was created in ECOTECT to find out the building roof and elevation surface areas as well as the shaded areas to find out the unshaded areas for solar PV installations.
2. Research objectives
Fig 2: Methodology of the study
The objectives of this paper are to establish a comparative analysis between existing electricity demand and the solar electricity generated to explore the potential of solar energy harvesting in a densely built urban area This study may contribute in policy development for the already densely built high electricity demanding commercial urban areas into self-sustaining low electricity demanding urban zones.
The selected area of study has an area of 0.17 square kilometres (Fig 3). In the selected survey area there are 147 buildings. Among them 131 buildings are commercial and 5 buildings are governmental building. The survey was conducted in April, 2015. The electricity demand was calculated by the following equations-
Problem identification
Field survey
3D model
Building surface area
Floor area Electricity demand per unit floor area
Total energy demand Solar energy potential
Conclusion
Result and discussion
DELEC ATF DEA
(1)
ATF AFi N Fi
(2)
i 1
Here, DELEC is the total electricity demand, ATF is the total floor area, DEA is the unit electricity demand per unit area, AFi is the floor area of a building and NFi is the number of floor of a building.
irradiance (GHI) of Dhaka city, PVpELEC is the unit peak electricity generation capacity per module, EI is the Inverter efficiency and EF is the battery efficiency. The shaded surface of the buildings were calculated from the simulations. From the simulation results, the shaded roofs and shaded percentage of the elevations of each building in the surveyed area were calculated. The limitation of the study was the calculation of the solar potential and energy demand were undertaken for summer peak time only. The calculated demand and the solar potential would be compared to evaluate the prospect of solar PV in supplying necessary electricity and reducing energy demand.
N
4. Electricity demand Fig 3: Studied area ( from Google map)
The solar potential was calculated by the following equations-
ASRR ARi PRSE
(3)
ASRS ASi PSSE
(4)
i 1
i 1
NPV (ASRR ASRS ) / PVSU SPELEC NPV GHIDPVpELECEI EB
(5)
(Kabir et al., 2010)
(6)
Among the surveyed buildings, seven buildings has 20 or more floors and 27 buildings are 10 or more storied. Total floor area of the buildings were calculated by using the equation (2) and the total floor area is approximately 7.65 million square feet (sft). Table 1: The electricity demand and area demand of the surveyed buildings
Name of the building
Here, ASRR is the total exposed roof area for solar radiation, ARi is the roof area, PRSE is the percentage of roof expose area for solar radiation, ASRS is the total exposed vertical surface area for solar radiation, ASi is the vertical surface area, PSSE is the percentage of vertical surface area exposed for solar radiation, NPV is the number of solar PV modules, PVSU is the unit PV panel size, SPELEC is the total electricity generation potential by PV installations, GHID is the global horizontal
Electricity demand (kWh/sft/month)
Peoples Insurance Building Eunoos Trade Center (ETC)
1.60 2.08
Agrani bank Ltd Islam Chamber Hadi Mansion Ministry of Industries Janata Bank Limited Bangladesh Krishi Bank Bhaban Social Islami Bank Limited Union Bank Limited Uttara Bank Limited
2.26 1.51 2.06 2.83 0.95 2.06 1.89 3.23 2.83
Elite House 58 Dilkusha Road C/A, Dhaka-1000 28, Dilkusha C/A, Dhaka 1000 Jiban Bima Bhaban Dhaka Translation Shadharon Bima Bhobon
2.52 2.83 2.52 3.77 1.89 2.26
The survey showed that the average electricity demand was 2.30 kWh/sft/month in buildings. The lowest demand is 0.95 kWh/sft/month in Janata Bank Limited and the highest demand is 3.77 kWh/sft/month in Jiban Bima Bhaban. The total electricity demand was calculated by using the equation (1). The higher limit and the lower limit of the demand would be calculated from the highest and lowest demand of electricity from the survey. The average demand of the CBD would be calculated form the average electricity demand value from the survey. 5. Solar energy potential The solar potential of the building depends on the roof and vertical surface areas of the buildings, which are exposed to solar radiation (Fig. 4). For the calculation of the total exposed area equation 3 and 4 were utilized. The total roof and vertical surface area exposed to solar radiation was calculated to be 543511.8 sft and 891620.2 sft respectively. The number of PV panel was calculated by the equation 5. The unit PV panel size, was considered to be 72 cell 13.74 sft stand-alone PV panels (aliexpress, 2015). The number of PV panel modules were 39556 and 64892 for respectively roof and vertical surfaces (V.S.) exposed to solar radiation. For the calculation of total electricity generation potential in Table 2, the inverter efficiency was considered to be 90% and
battery efficiency was considered 86% (A. H. Mondal & M. Denich, 2010). The suggested values for azimuth (b) and inclination (g) were considered 0 degree from the south and 23 degree from horizontal, respectively (Chowdhury et al., 2011). Table 2: Potential power generation through standalone PV applications
Roof V.S.
PV GHI of Unit peak module Dhaka electricity number city(kWh/ generation m2/mont capacity h) per module 39556 0.90 (M. 200 Wpeak 64892 A. H. (aliexpress, Mondal & 2015) M. Denich, 2010)
Total gener ation (MW) 5.50 9.02
The total solar energy potential would be 14.51 MWpeak per month (Table 2) by utilizing equation 6. 6. Result and discussion The total calculated higher estimate electricity demand was 29 MWh per month. The average and lower estimate of the electricity demand was estimated to be 18 MWh per month and 7 MWh per month respectively. On the other hand the solar energy potential for the same building stock was calculated to be 14.51 MWpeak per month (Table 2). Assuming the working hours from 9 am to 5 pm (8 hours) and the climatic location of Bangladesh the peak efficiency of available PV modules were considered to be 18%. The peak electricity generation can reach up to 24.22 MWh per month, which more than the average demand of the area.
N Fig 4: Shadow analysis for solar energy potential (simulation results were at 4 pm)
According to Dhaka Power Distribution Company Limited (DPDC), the studied area consumes 6.5 MWh per month on average. There are 9 feeders and 3 substations in the area. The data was last updated on August, 2014. Each year the consumption is increased by 10-20%. With this consideration, the electricity demand can be 7.8 MWh per month by April, 2015.
Under these circumstances solar PV can act as the main energy source for the CBD area. But when the demand crosses the generation limit, the grid electricity can aid to fulfil the demand. For this type of system development, smart grid should be implemented. Because, on the weekends, when there is no demand in the offices, the solar PV modules can supply the generated electricity to the grid.
From the survey, there were no incandescent light found. But 45% of the total used lights were fluorescent lights, 50% were CFL lights and only 5% were LED lights.
Also, the demand can be reduced by utilizing energy efficient appliances in the offices and making the occupants aware in the buildings about the conservation of energy.
Table 3: Lighting efficiency (Boyce & Raynham, 2009)
7. Conclusion
Incandescent Fluorescent CFL LED
Lumen/W 25 70 96 100
By shifting from fluorescent and CFL lights to LED lights the CBD area can reduce the power consumption up to 1.05 MW. The calculated electricity demand range from 7-29 MWh per month. The DPDC data on real demand is within the estimated electricity demand. The solar potential is also would be able to fulfil the demand up to 24.22 MWh. But for total dependency on the solar PV is not a suitable solution because, I. The calculated solar potential does not met the higher estimation of the calculated demand, and II. The solar radiation is not going to be at the peak level all the time throughout the year (M. A. H. Mondal & M. Denich, 2010).
With the target of becoming a middle income country from a low income country, CBD areas in Dhaka city, are flourishing day by day. These areas are becoming higher energy demand areas for accommodating the elevated business and commerce activities. The implementation of solar PV based energy generation system can eventually solve the demand scenario. But at the time of higher demand in summer and lower solar radiation level in cloudy conditions, the solar PV system would need the partial aid of the grid electricity. On the other hand, the electricity demand also needed to be reduced by replacing energy efficient appliances and systems. The reduced energy demand would create more stable demand range of electricity in the building, which would be fulfilled by the solar PV systems only. The future studies can focus on the time depended solar potential of the CBD area. The fluctuation of solar radiation throughout the
year would influence the solar energy generation potential. Also, the research can extend the study area to the total Dhaka city and eventually leading towards the entire country.
8. References aliexpress. (2015). Supply 200W solar panel 72 cell mono crystalline solar modules BP- JLS72M -200W. Retrieved 04/05/2015, from http://www.aliexpress.com/item/Supply200W-solar-panel-72-cell-mono-crystallinesolar-modules-BP-JLS72M-200W-positivetolerance/ Boyce, P., & Raynham, P. (2009). SLL Lighting Handbook. Chowdhury, S. A., Mourshed, M., Kabir, S. M. R., Islam, M., Morshed, T., Khan, M. R., & Patwary, M. N. (2011). Technical appraisal of solar home systems in Bangladesh: A field investigation. Renewable Energy, 36(2), 772-778. doi: http://dx.doi.org/10.1016/j.renene.2010.0 7.027 City Population. (2012). City Population. from www.citypopulatiuon.de Kabir, M. H., Endlicher, W., & Jägermeyr, J. (2010). Calculation of bright roof-tops for solar PV applications in Dhaka Megacity, Bangladesh. Renewable Energy, 35(8), 1760-1764. Mondal, A. H., & Denich, M. (2010). Hybrid systems for decentralized power generation in Bangladesh. Energy for Sustainable Development, 14(1), 48-55. doi: http://dx.doi.org/10.1016/j.esd.2010.01.00 1 Mondal, M. A. H., & Denich, M. (2010). Assessment of renewable energy resources potential for electricity generation in Bangladesh. Renewable and Sustainable Energy Reviews, 14(8), 2401-2413. doi: http://dx.doi.org/10.1016/j.rser.2010.05.0 06
World Data Bank. (2014). Retrieved 13/10/2014, from http://databank.worldbank.org/
