Adapting Integrated High Concentrated PV Modules and Evacuated Tube Collectors to Minimize Building Energy Consumption in Hot Climate

Energy consumption in buildings is considered a significant portion of gross power dissipation, so a great effort is required to design efficient construc-tion. In severe hot weather conditions as Kuwait, energy required for building cooling and heating results in a huge energy loads and consumption and ac-cordingly high emission rates of carbon dioxide. So, the main purpose of the current work is to convert the existing institutional building to near net-zero energy building (nNZEB) or into a net-zero energy building (NZEB). A com-bination of integrated high concentrated photovoltaic (HCPV) solar modules and evacuated tube collectors (ETC) are proposed to provide domestic water heating, electricity load as well as cooling consumption of an institutional facility. An equivalent circuit model for single diode is implemented to evaluate triple junction HCPV modules efficiency considering concentration level and temperature effects. A code compatible with TRNSYS subroutines is introduced to optimize evacuated tube collector efficiency. The developed models are validated through comparison with experimental data available from literature. The efficiency of integrated HCPV-ETC unit is optimized by varying the different system parameters. Transient simulation program (TRNSYS) is adapted to determine the performance of various parts of HCPV-ETC system. Furthermore, a theoretical code is introduced to evaluate the environmental effects of the proposed building when integrated with renewable energy systems. The solar absorption chiller provides about 64% of the annual air conditioning consumption needed for the studied building. The energy payback period (EPT) or solar cooling system is about 18 years which is significantly larger than that corresponding to HCPV due to the extra expenses of solar absorption system. The life cycle savings (LCS) of solar cooling absorption system is approximately $2400/year. Furthermore, levelized cost of energy of solar absorption cooling is $0.21/kWh. Hence, the net cost of the solar system after subtracting the CO 2 emission cost will be close to the present price of conventional generation in Kuwait (about $0.17/kWh). Finally, the yearly CO 2 emission avoided is approximately 543 ton verifying the environmental benefits of integrated HCPV-ETC arrangements in Kuwait.


Introduction
Buildings normally consume a significant portion of the total power utilization. If yearly energy generated from renewable systems is equivalent to the energy needed, the building is called Net-Zero Energy Building (NZEB). On the other hand, when energy generated from renewable systems is a little smaller than energy dissipated, it is identified as nearly Net-Zero Energy Building (nNZEB).
Voss et al. [1] introduced a primary solar integrated building. Many research works have implemented audit standards for the buildings and their results showed substantial energy reductions [2] [3] [4]. NZEB attainment is typically determined utilizing different factors such as energy production, net energy costs, and carbon emissions [5]. There are several net-zero energy buildings that designed and assessed all over the world [6] [7].
Rüther et al. [8] investigated the decrease in energy consumption at an international airport in Brazil utilizing integrated photovoltaic modules. Outcomes indicated that integrating these modules would provide the total energy demand for the studied airport. Zhai et al. [9] stated that about 150 m 2 of evacuated tube collector in Shanghai, may be utilized to provide the demand of a facility of 460 m 2 for cooling and heating. A solar integrated roof is installed by Yin et al. [10] utilizing PV system to minimize energy consumption. The proposed renewable roofing design is proofed to have obvious benefits compared to conventional roofing design. An economic study is carried out [11] to examine environmental impacts of BIPV.
Tsalikis and Martinopoulos [12] examined the integration of solar thermal system and PV modules in a common residential home to investigate the possibility of achieving (NZEB). They indicated that, photovoltaics can provide the required energy consumption of the studied building and the payback period is smaller than seven years. Passive office facility situated Portugal is examined by Aeleni et al. [13]. Actual consumption data are employed together with numerical simulations of integrated battery storage system. They concluded that that grid interaction and load matching is enhanced by utilizing the energy supplied by battery storage system. Also, the implementation of this system is economically feasible.
Lopes et al. [14] discussed the effect of load matching in improving net zero energy buildings performance. They made comparison between building and community levels utilizing different options. For a one-year analysis, the community facility is proven to be able to increase energy load by about 21% and the consumption of the building by about 15%. A dynamic method for accurate comparison of conventional and renewable integrated systems is introduced by Ayadi and Al-Dahidi [15]. Levelized cost of energy technique is employed to compare between renewable energy systems and traditional ones. Results indicated that combined PV and solar thermal systems can attain a significant conventional energy and levelized cost of energy discounts in comparison to traditional energy resources. Rafique et al. [16] investigated the possibility to attain zero energy communities in Pakistan. They adapted simulation software to perform the feasibility study of the suggested PV system. The system feasibility is calculated, and outcomes reveals that suggested photovoltaic integration in rural areas can supply relatively cheaper load demand in comparison to electricity prices.
Karunathilake et al. [17] stated that it is essential to know the most promising energy technology to select community optimal solution for NZEB. In that respect, renewable energy system assessment should incorporate effects of environment. Regarding environmental impacts, it is stated that small hydro and biomass combustion techniques operates better. While, small hydro, gas and biomass combustion operates better considering economic choice. Four buildings for four various weather regions in Arizona is analysed by Heine et al. [18] to evaluate the effect of battery storage on PV system. They showed that because of the discrepancy among peak hours and incident radiation, integrated PV systems can reduce only about 37% -44% of maximum energy load. On the other hand, a maximum net present value can be accomplished by utilizing extra batteries of capacities about one and half times greater to provide yearly maximum load needed with a reasonable grid price.
Sharma et al. [19] stated that utilizing energy storage batteries can decrease the energy required as less load from the grid will be needed in that case. A method to determine the best battery capacity for a common net zero facility with PV is presented. Optimization predictions showed that with present battery storage prices and electricity tariff in South Australian, the adaption of battery storage energy is feasible. Different strategies to attain zero energy in rural regions in Australia and to determine their effects in zero net energy balance is examined by Miller et al. [20]. Predictions indicate that a combined monitored measurements and simulation software helped residents to attain about 50% enhancement in the thermal efficiency in addition to solar production of 19,600 Smart Grid and Renewable Energy Wh.
Hachem-Vermette et al. [21] investigated a combined residential and commercial/institutional buildings. A hybrid system combined of thermal energy storage and solar thermal collector is installed to examine the effect on the system total efficiency. Outcomes revealed that employing both energy efficiency and photovoltaic modules lead to satisfy about 70% of the energy demand. A residential house integrated with PV system is analysed by Vieira et al. [22]. The system is modelled utilizing available solar intensity and energy demand of a common residential home in Portugal. It is stated that the system installed was capable to significantly reduce the consumption provided by the electric grid and consequently the electricity bill supplied by the grid. A single-family building located in Italy installed to represent the weather conditions of Mediterranean is examined by Ascione et al. [23]. Daily energy consumption is calculated to verify the solar generation and battery influence on load requirements. A theoretical code appropriate for the evaluation of energy consumption is utilized to analyze studied building compared to other buildings. Passive building air conditioning is examined by Ascione [24] motivated by the significant increase in space cooling and consequently potential increase in unhealthy effect on surroundings. They concluded that integrated renewable systems should not be considered as the only option for providing energy needed for the building. So, other alternatives as decreasing the air conditioning energy consumption in the building should be considered.
Maurer et al. [25] presented measurements to characterize building integrated solar energy systems components. The significant price reduction attained in the studied buildings are explained, consequently a discussion for the situation of building integrated solar energy in the future is introduced and standards rules are reviewed. Life cycle costs and the environmental impacts of various options are outlined by Sandra et al. [26] to evaluate solar systems potential in increasing energy efficiency. They stated that most of yearly energy required for domestic hot water can be achieved with the integration of renewable systems in addition to the economic feasibility of such systems.  [36] subroutines to determine the efficiency and the energy output of both HCPV and ETC. Furthermore, the environmental effects of the integrated HCPV-ETC system are evaluated to judge the feasibility of such systems in Kuwait climate.

Theoretical Model of HCPV
Each sub cell utilizes 5 parameters: short circuit current (I sc ), series and shunt resistances R s,i and R sh,i, , saturation current (I o,i ) in addition to diode ideality factor (n i ). T is cell temperature, k B is Boltzmann constant, V is voltages, q is the charge of the electron, I i is the load current; and express junction (1 for upper cell, 2 for medium cell and 3 for lower cell). The main parameter impacting the value of V oc , is I 0 (reverse saturation current), that represents deficiency of minority carriers through p-n junction. According to the theory of Shockley diodes (n = 1), though n larger than unity is more adequate to include imperfections created in industrial arrangements. R s is regarded as the main factor aiding to obtain high concentrated cells with improved efficiency. R sh is a result of the leakage current in the p-n junction because of defects. The well-known Maple program is used to perform numerical model calculations. Ghoneim et al. [38] introduced a detailed numerical procedure to analyse and solve Equation (1). The introduced model is examined versus available experimental data provided by the manufacturer of AZURSPACE [37] high concentrated solar cells. The present predicted results agree well with the measurements recorded by AZURSPACE manufacturer. Grid connected HCPV system presented in Figure 1 is suggested for this work

Theoretical Model of ETC
The receiver of ETC is composed of U-tube copper contained in a vacuumed tube of glass. A cylindrical aluminum fin circles the copper tube to increase the area of heat transfer between the copper tube and the surface of inside absorber. The working fluid passes to the inlet pipe of the collector to be diffused to the U-tubes, absorbs heat to return to the header tube. The radiation is transmitted from the outer cylindrical glass to the inner glass tube to transfer thermal heat to the absorber fin. The energy converted to thermal energy is transferred by conduction to the copper pipe by the fin and sucked by the fluid. Evacuated tube collector is presumed to be integrated in building to provide building cooling demand. In the present research, evacuated tube optimized factors attained utilizing the numerical code is adapted to construct a proper resized thermal system to generate cooling requirement for the building under study. TRNSYS is adapted to evaluate collector area needed, energy output and solar fraction utilizing using Kuwait weather conditions. The system consists of evacuated tube collector, a single effect absorption chiller, auxiliary heater, controllers and storage tank. The absorption chiller is chosen to create chilled water with outlet temperature 7˚C. Figure 2 presents single-effect lithium bromide water absorption chiller operated by evacuated tube collector. The essential parts of the unit are: generator, absorber, evaporator condenser, and heat exchanger.
Lithium bromide in the absorber is pushed to the generator to be boiled. Cold water passes to the condenser through the absorber. Hot water is provided to air conditioner at a minimum temperature of 87˚C and a maximum temperature of 93˚C. If storage hot water is less than 87˚C, additional energy is provided to increase it. When stored water is less 77˚C, it is not utilized, instead auxiliary heater satisfies the total demand. Coefficient of performance (COP) represents the Smart Grid and Renewable Energy

Building Load
The proposed building for this study is the Department of Electronic Engineer- spectively. In present work, air-conditioning system and its components consumes 84% of overall building energy load. The rest of load is divided among lighting, 9%, and electronic devices, 7%.

Environmental Impact of HCPV-ETC System
Carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) are the most harmful gases of conventional sources of energy; but CO 2 is regarded as the principal parameter affecting worldwide global warming. That is why the effects of CO 2 emissions only are studied in this work. The quantity of carbon emission eliminated through the utilization of solar energy resource is related to conventional resource that is not utilized in addition to the conversion method employed to generate energy. Substituting a plant of larger CO 2 emission with a less emitting resource leads to a less CO 2 emission. This difference in emitted CO 2 is defined as the avoided CO 2 emission. The CO 2 emission decrease, or CO 2 avoided is typically specified as the change among emissions produced by traditional resources and that resulted during manufacturing the solar system through system lifetime which is usually twenty-five years. A simple mathematical expression is utilized to evaluate the avoided CO 2 emission accomplished when employing HCPV-ETC system instead of a conventional one. In this work, eliminated CO 2 emission (E A ) is primarily the emissions of CO 2 produced when utilizing traditional energy resources and is given by: where F E is the emission factor of the plant (tonneCO 2 /kWh) and P g is the generated power (kWh).
To calculate CO 2 avoided emission because of the utilization of HCPV system, it is necessary to specify the reference electricity system. Frequently this will necessitate identifying a traditional system and the corresponding fuel type. Conversion efficiencies of various fuel types and the standard emission factors are the model input.

Results and Discussions Building Integrated Solar Energy
The aim of the building integrated with high concentrated photovoltaic (HCPV) arrays and evacuated tube collectors is to supply the demand of building energy to transfer it to net-zero energy building (NZEB) or when produced energy is smaller than the required, the building is near net-zero energy building (nNZEB  This value is greater than the annual energy required for building lighting and equipment by about 42 MWh which can be exchanged back to the electrical grid.
This prediction let us conclude that energy generated from integrated HCPV can provide the entire building lighting load as well as equipment load.
The monthly generated energy of HCPV system is shown in Figure 4 along the monthly consumption energy required for building lighting and equipment.
It is obvious that HCPV generated in all months using HCPV system exceeds the building lighting and equipment consumption.
An emission factor of 6.9 × 10 −4 metric tons CO 2 /kWh e [40] is employed to determine the annual avoided CO 2 emission. Annual avoided CO 2 emission change versus HCPV modules slope is illustrated in Figure 5. The precise calculation of CO 2 avoided emissions due to utilizing HCPV modules, must consider CO 2 emission produced during the manufacturing of HCPV different components. Generally, the rate of CO 2 emissions from HCPV modules is much smaller than the CO 2 emission rate produced from traditional energy resources, therefore it is ignored in this work.
Energy payback times (EPT) can be employed to judge the advantage of BIHCPV systems over traditional energy systems. EPT of BIHCPV system is the time required for the energy delivered through the lifespan of the module is reimbursed by the HCPV energy. The variation of EPT for the proposed BIHCPV system against module slope for zero azimuth angle is illustrated in Figure 6. Utilizing module of orientation of 25˚ (i.e. array with tilt of 5˚ smaller    than Kuwait latitude) accomplishes the minimum EPT which is about 7.7 years.
This means that the BIHCPV system can generate free energy after running for 8 years.

2) Building Integrated Evacuated Tube Collectors (BIETC)
A code is formulated to resemble the function of a solar lithium bromide absorption system to satisfy building cooling load from March to November. TRNSYS is utilized to connect individual solar cooling parts. Figure 7 illustrates the change of yearly energy generation from ETC for different collector slopes. The orientation of the collector is varied from 0˚ to 60˚ (i.e. latitude ±30˚). Also, various angles of azimuth are investigated from 0˚ to 40˚. As figure shows, the energy generation varies against collector orientation and azimuth angle. It is clear that the peak collector output occurs at tilt angle 25˚ (i.e. latitude +5˚) and for collector facing south. Consequently, yearly maximum energy generation is obtained utilizing a collector of slope 25˚.
The most significant parameter judging the size of solar cooling capacity is solar collector area. Furthermore, collector area has a great influence on solar cooling system feasibility. The predominant parameter controlling solar system economic feasibility is the conventional fuel price. The feasibility analysis in this work utilizes life cycle savings (LCS) technique [41]. LCS over a traditional one is the discrepancy among the decrease in conventional fuel price and the extra costs due to extra expenses of the renewable energy system. So, life cycle saving (LCS) variation against collector area is analyzed to determine solar cooling system feasibility. Furthermore, solar fraction (F) and overall system efficiency (η) variation against collector area are examined. Solar fraction is the portion of energy supplied by solar energy and system efficiency is the system output energy divided by input energy. A TRNSYS appropriate code is introduced to calculate the change of system efficiency (η), solar fraction (F) and LCS against collector area for the solar cooling system shown in Figure 8. Figure 8 indicates   Yearly avoided CO 2 variation along collector tilt angle is shown in Figure 9, as indicated a maximum avoided CO 2 emission of 377 tonne/year can be obtained at the optimum tilt angle 25˚. Energy payback time (EPT) for solar cooling system Furthermore, the expenses expected when implementing the Kyoto Protocol, that applying penalties in the case of emissions of greenhouse effect must be included in the prices of fossil fuel sources. Though Kyoto Protocol is not at present applied in Kuwait, nevertheless regarding the use of this protocol will promote the cost effective and environmental impacts of HCPV arrays substantially. Additionally, solar collectors and HCPV modules prices have been reduced considerably lately and keep decreasing greatly which will improve environmental effects and feasibility of solar heating and cooling greatly. Hence, the present outcomes should inspire governments for wide set up of solar heating and cooling systems to reduce energy consumption of conventional fuel and decrease environmental pollution to maintain our community clean and healthy.

Conclusions
Current work assesses the results of energy generation, using high concentrated photovoltaic (HCPV) modules and evacuated tube collectors (ETC) to drive so- • Utilizing HCPV modules of orientation of 25˚ (i.e. array with tilt of 5˚ smaller than Kuwait latitude) accomplishes a minimum EPT in about 7.7 years. So, BIHCPV system can generate free energy after running for 8 years.
• Evacuated tube collectors of area 466 m 2 , with tilt of 25˚ for collector due south can provide 64% of air-conditioning requirement in the building which is considered a significant fraction of the building cooling demand.
• Approximately 360 MWh of the total building demand should be supplied by conventional energy sources.
• Payback period for solar cooling system is about 18 years which is relatively high due to the higher expenses of solar absorption system. • Annually LCS for solar cooling absorption system is about $2400 for the optimum conditions. • LCOE of solar absorption cooling is $0.21/kWh. Hence, the net price of solar system after subtracting the CO 2 emission cost will be close to the present • HCPV module prices are anticipated to be reduced significantly in near future. Furthermore, HCPV cells efficiency continue to be enhanced, so HCPV systems will be cost effective.
• Present results should inspire Kuwait government for extensive installment of renewable energy applications to preserve our environment clean and healthy.