Modelling and analysis of an improved scheme for a 340kWp grid interactive PV system in Pakistan to enhance performance ratio and battery life

Modelling and analysis of an improved scheme for a 340kWp grid interactive PV system in Pakistan... A scheme has been proposed, modeled and simulated to show an improved system efficiency, battery life and payback period of a 340 kWp peak power grid interactive solar photovoltaic system. In this case, a conventional solar photovoltaic system capable to fulfill 66% energy demands has been modified to meet complete energy demands without an increase in system’s photovoltaic capacity. It has been shown via modelling and simulation on PVSyst that using direct current appliances instead of alternating current appliances, initial power demands are reduced by 58% and conversion losses (DC–AC–DC) of 9.6% are eliminated. These modifications result in an overall increase in the system’s performance ratio from 73.8 to 83.4%, with an increase in energy production from 469.6 to 557.9 MWh. As an outcome, battery life is increased by 1200 duty cycles as the depth of discharge is reduced from 35 to 26%. Keywords Solar photovoltaic · Performance ratio · Battery life · Converter losses Introduction in its DC form directly [7], to power electricity loads in buildings, rather than converting it to alternating current Evidently, over the last decade, a sustained and progressive (AC) first, as is the current practice [ 8]. growth in the development and adoption of solar systems Technology advancements have profoundly triggered has been observed [1] and relatively an increasing pub- an important factor that favors the use of DC, the reason lic interest and the advancement in the efficient and cost- being that the electric appliances that operate internally on effective solar technology as concerns over grid failure and DC are increasing more rapidly, and the fact that these new the depletion natural resources have intensified [ 2]. Solar DC-internal technologies tend to be more efficient than their photovoltaic (PV) has emerged as a potential resource for AC counterparts especially fans and light-emitting diodes addition and supplementation of grid power capacity [3, 4]. (LEDs) [9]. Technically, this supports the idea that energy Net-metered PV power systems [5], which have dominated savings could be achieved by directly coupling DC power on-site renewable energy supply in the buildings sector, are sources with DC appliances [10], thus avoiding DC–AC–DC a direct current (DC) power source, as are batteries, which power conversion losses and resultantly, an accompanied are the dominant energy storage technology used with such efficiency increase can be achieved [ 11]. Recent demon- systems [6]. A number of factors are driving the recent shift strations experimented with commercial data centers have in the interest of using DC power from solar electric systems shown that considerable energy savings can be achieved with DC power distribution supplied directly to DC loads, rather than utilizing AC power [12, 13]. In support of the undersigned research paper, a real-time- * Zaeem Aslam zaeem.aslam1@gmail.com based modeling of a PV solar-powered system is configured, which is an integral part for the development of a complete Center for Energy Research and Development, University grid interactive solar photovoltaic (GISP) simulation model of Engineering and Technology Lahore (UET Lahore), where converter losses have been minimized and perfor- Lahore 54000, Pakistan 2 mance ratio of the PV system has been maximized using Faculty of Information Technology, University of Central DC as a primary source. Technically, the process is achieved Punjab, Punjab 54000, Pakistan Vol.:(0123456789) 1 3 188 International Journal of Energy and Environmental Engineering (2018) 9:187–199 by integrating the DC power directly with the load keeping built-in charge controller (DC–DC conversion) and batter- it independent from the DC–AC converters. In this case, ies for energy storage purpose. The technical specifications the relative energy savings of ‘direct-DC’ power for loads of different system components being used which include which have primarily day time usage only are also assessed. Yingli Solar, YL255P-29B YGE 60 cell 40 mm series PV Among several PV modelling software [14, 15], one of the modules, Zigor HIT3C Inverters and SOPzS lead acid bat- most common is PVSyst (See website: http://www.pvsys teries [20] are shown in Tables 1, 2 and 3, respectively. t.com). Over the years, this software application has been widely used for PV modelling [16] and sizing the compo- Schematic diagram of the proposed system nents of the PV system [17, 18] or PV system assessment [19]. In connection with this paper, a solar power system The part of the schematic diagram marked in Fig. 2 high- is modeled and simulated in PVSyst. The results obtained lights the improvement being proposed to the existing solar after performing the simulations clearly show that the sys- system increasing system efficiency by ensuring maximum tem performance ratio has improved and the overall cost of direct utilization of DC power generated by PV modules. the installed system has reduced after eliminating DC–AC Power converter losses occurring due to DC to AC conver- converters. sion are minimized, enhancing the overall performance ratio of the solar plant. System description Proposed system components Schematic diagram for existing system Table 4 below shows the modifications made to the existing system and the additional components added altogether. As a demonstration, the schematic diagram for the system under consideration is shown in Fig. 1. For the operational purpose, inverter is utilized as a major component of the sys- Load profile tem to run the connected load by converting DC energy from PV modules to AC energy. During cloudy days or at night, Existing system the inverter uses grid to run the load and at the same time charging the batteries. On account of frequent load shed- The complete load demands for the facility are shown in ding and worse grid conditions (frequent low grid voltage, Table 5. The total accumulated load of the facility is 425 kW. electrical transients and surges), AC–DC–AC conversion is Table 6 shows only the essential load estimating around used. Consequently, this also ensures the real-time energy 280 kW has been connected and supported by solar system. sharing between the grid and the PV plant at the same time While segregating the 280 kW solar connected load, the improving the power quality at output. operational hours of 220 kW day-time load are from 08:00 to 15:00 h, whereas the working hours of 60 kW load operating Existing system components during night are from 16:00 to 08:00 h. Table 7 provides details of the load shedding, sunshine The complete PV system consists of solar PV modules and grid availability hours in a single day. Considering the (DC power generator), inverters (DC–AC conversion) with present local scenario, there are approximately 6 h of load shedding in one single complete day. Taking into account multiple factors which include frequent grid failures or non- availability occurring at random times during the day and Table 1 Specifications of PV modules Parameters Specification Rating Type of module Polycrystalline 1332 no. Individual power Unit norm power 255 Wp Array global power Nominal (STC) 339.6 kWp In series 18 No. of PV modules In parallel (strings) 74 Array operating character- U mpp 540 V istics (50 °C) I mpp 8.28 A Fig. 1 Existing solar power system schematic diagram 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 189 Table 2 Specifications of Parameters Subjects Rating inverter Input data Recommended DC power Greater than 157 kWp MPPT voltage range 420–700 V DC Input current 375 A DC Battery charging capacity 200 A Output data Nominal output power 300 kW (150 kW × 2) Nominal frequency 50 Hz Power factor > 0.99 at full load Voltage distortion at full load < 3% General data Max power efficiency including transformer > 96% MPPT efficiency 99% Internal consumption in operation < 1% at full load Table 5 Existing AC load for Table 3 Specifications of batteries Load description Power (kW) the facility Parameter Specification Rating Fans and lights 350 Type of battery SOPzS tubular plated 348 no. Air conditioners 40 Water pumps 27 Individual capacity Capacity at C10 rating 1525 AH Voltage Nominal voltage 2 V Refrigeration 8 Total 425 In series 174 No. of batteries In parallel 2 General characteristics Duty cycles at 50% 2500 DOD Table 6 Distribution of AC load for the facility Electrolyte Sulphuric acid with Distribution of AC load Power (kW) density 1.24 kg/ dm AC load connected and powered by solar system 280 AC load running on diesel genset 145 Maximum AC load running on solar system at day time 220 Maximum AC load running on solar system at night 60 time Table 7 Load shedding, grid and sunshine hours in 1 day Description Hours Daily load shedding (average) 6 Daily sunshine hours available 8 Daily grid usage 10 availability of 8 h of daily sunshine, all the calculations for Fig. 2 Proposed solar power system schematic diagram the battery usage are made for only 10 h of grid utiliza- tion. Since the main objective is to reduce dependency on Table 4 Proposed modifications to the existing system National Grid, the system has been designed not to use grid during the day time and also ensuring maximum 35% Depth Parameter Specification Rating of Discharge (DOD) for the batteries at the same time. DC voltage regulator DC/DC converter capable 6 no. of power handling up to Proposed system 50 kW DC fans and lights 48 V energy-efficient DC Total Retrofitting concept has been implemented for the pro- fans and LED lights capacity 175 kW posed system, while replacing AC load appliances of the 1 3 190 International Journal of Energy and Environmental Engineering (2018) 9:187–199 complete facility with energy-efficient DC load appliances, AH × V × E i.e. lighting and fan load, which would reduce the overall N = (2) DOD × S × P load by 50%, i.e. from 350 to 175 kW. The AC inductive load estimated around 75 kW remains independent. The where N is the no. of panels required, E efficiency of solar load demands have been distinctly altered for the proposed PV module at NOCT (nominal operating cell temperature), system as shown in Table 8. The load operated during the S number of sun shine hours, and P panel wattage at NOCT. day time is reduced to 210 kW (accumulating 135 kW of Efficiency of the solar PV module is considered at NOCT lighting and fans load through retrofitting of AC appliances specifications mentioned, which signifies the realistic value with DC appliances and 75 kW of inductive load) which of the PV module performance in real-time conditions, operates from 08:00 to 15:00 h daily and the load operated whereas SH are taken as the yearly average sunshine hours during night time is reduced to 40 kW having working hours present in Pakistan in one single day. In the proposed system, from 16:00 to 08:00 h while completely eliminating the use DOD is reduced from 35 to 26% which specifically indicates of diesel generator. that the battery usage is reduced. Following equation (Eq.  1) is applied to calculate the depth of discharge (DOD) for the batteries in the proposed system: Battery discharge behaviour W × B DOD = Existing system (1) V × AH where DOD is the depth of discharge, W load in watts, B bat- The overall energy production and consumption along tery backup hours, V system voltage, and AH is the capacity with the detailed battery discharge statistics for consecu- of battery. tive 3 days of the existing solar system is given in Table 9. The number of PV modules required to charge batteries Grid is used for 10 h per day to meet the complete energy during the day is calculated using Eq. 2. This would help to demands of the connected load on solar system. The maxi- determine the most appropriate value for the DOD of the mum battery DOD for the existing system is 35%. batteries for a given Solar PV system: The graph in Fig. 3 shows the energy produced and con- sumed by the existing system in a single day. It explains the hourly status of actual energy generation from the Solar Table 8 Load profile for the proposed system Array, the optimum energy consumption (hours) and energy variance to/from battery. Description Power (kW) The graph in Fig. 4 shows the maximum DOD achieved Total rated load of the facility (after retrofitting AC 250 by the battery bank. It demonstrates the hourly status of per- appliances with DC) centage discharge of the battery bank based on a 24-h cycle New lighting and fans load (DC) 175 of system operation. The graph shows that the battery is AC inductive load 75 being used up to 35% depth of discharge. The operational Load connected/shifted to solar system 250 timing has been assumed based on standard operations Load running on diesel genset 0 (working hours) as mentioned above. Table 9 Energy consumption for 3 days for the existing system Time 24Hrs 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:0011:00 12:0013:00 14:0015:00 16:0017:00 18:0019:00 20:0021:00 22:0023:00 energy consumption (kWh)6060606060606060220 220220 220220 220220 2206060606060606060 energy generation (kWh)7272727856220 182231 258271 258231 283119 12410727272 Difference kWh12-60 12 -6012-60 18 -4 0-38 11 38 51 38 11 63 59 64 -5012-60 12 -6012 Grid Usage (kWh)72727272101 10172727272 Energy for batt. bank with loss 11 -6011-60 11 -6016-40 -381034463410575459-50 11 -6011-60 11 Current to batt. Bank (A) 455 -2500 455 -2500455 -2500687 -159 7-1593 430143219341432430 2380 2236 2442 -2087 455-2500455 -2500455 Day 01 Available Batt. Bank (kWh) 905 845 856 796807 747763 759759 721732 766812 847857 905905 905855 866806 817757 767 Percantage Discharged 0% 7% 5% 12%11% 17%16% 16%16% 20%19% 15%10% 6% 5% 0% 0% 0% 6% 4% 11%10% 16%15% Consumed kWh Batt. Bank 06049109 98 158142 145145 184173 1399258480 00 50 39 99 88 148137 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 02 Available Batt. Bank (kWh) 778 718 729 669680 620637 633633 595605 640686 720731 788841 900850 861801 812752 763 Percantage Discharged 14% 21% 19%26% 25%31% 30%30% 30%34% 33%29% 24%20% 19%13% 7% 1% 6% 5% 11%10% 17%16% Consumed kWh Batt. Bank 126 186 175 235225 285268 272272 310300 265219 184174 117635 55 44 10493153 142 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 03 Available Batt. Bank (kWh) 775 715 726 666677 617633 629629 591601 636682 717727 784838 896846 857797 808748 759 Percantage Discharged 14% 21% 20%26% 25%32% 30%30% 30%35% 34%30% 25%21% 20%13% 7% 1% 6% 5% 12%11% 17%16% Consumed kWh Batt. Bank 130 190 179 239228 288272 276275 314303 269223 188178 121679 59 48 10897157 146 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 191 Fig. 3 Overall energy generation and consumption pattern for the existing system Fig. 4 Maximum battery bank discharge for the existing system Figure 5 illustrates the hourly status of the battery bank Array, the optimum energy consumption (hours) and energy available and the battery bank consumed based on the 24-h variation to/from battery. cycle of system operation for the existing system. It shows The graph in Fig. 7 confirms the maximum DOD achieved that the battery bank is still 65% full. by the battery bank. It demonstrates the hourly status of per- centage discharge of the battery bank based on a 24-h cycle Proposed system of system operation. The graph shows that the battery is being used up to 26% depth of discharge. The operational timing has The overall energy production and consumption along with been assumed based on standard operations (working hours) the detailed battery discharge statistics for 3 consecutive as mentioned above. days of the proposed solar system is given in Table 10. It Figure 8 shows the hourly status of the battery bank avail- can be clearly seen that the grid usage has been reduced to able and the battery bank consumed based on the 24-h cycle 6 h per day to meet the complete energy demands of the con- of system operation for the proposed system. It shows that the nected load on solar system. The maximum battery DOD for battery bank is still 74% full. the proposed system also reduces to 26% ensuring increase in battery life. The graph in Fig. 6 demonstrates the energy produced and consumed by the proposed system in a single day. It explains the hourly status of actual energy generation from the Solar 1 3 192 International Journal of Energy and Environmental Engineering (2018) 9:187–199 Fig. 5 Battery bank status for the existing system Table 10 Energy consumption for 3 days for the proposed system Time 24Hrs 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:0012:00 13:0014:00 15:0016:00 17:0018:00 19:0020:00 21:0022:00 23:00 energy consumption (kWh)4040404040404040210 210210 210210 210210 2104040404040404040 energy generation (kWh)727856119 182231 258271 258231 182119 76 10 72 72 72 Difference kWh-40 32 -40-40 -40-40 38 16 -91-28 21 48 61 48 21 -287936-30 32 -4032-40 32 Grid Usage (kWh)7272 20 72 72 72 Energy for batt. bank with loss -4029-40 -40-40 -403515-91 -281943564319-28 72 33 -3029-40 29 -4029 Current to batt. Bank (A) -1667 1213 -1667-1667 -1667-1667 1446614 -3793-1177 809 1811 2313 1811809 -1177 2994 1372-1254 1213-1667 1213-1667 1213 Day 01 Available Batt. Bank (kWh) 1004 1033 993953 913873 908923 832803 823866 922965 985956 1028 1044 1014 1043 1003 1032992 1021 Percantage Discharged 4% 1% 5% 9% 13%16% 13%12% 20%23% 21%17% 12%8%6%8%2%0%3%0%4%1%5%2% Consumed kWh Batt. Bank 40 11 51 91 131171 136121 212241 221178 122795988160 30 141125223 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 02 Available Batt. Bank (kWh) 981 1010 970930 890850 885900 809781 800843 899942 962934 1005 1038 1008 1037997 1027987 1016 Percantage Discharged 6% 3% 7% 11%15% 19%15% 14%23% 25%23% 19%14% 10%8%11% 4% 1% 3% 1% 4% 2% 6% 3% Consumed kWh Batt. Bank 63 34 74 114154 194159 144235 263244 201145 10282110 39 6367 47 17 57 28 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 03 Available Batt. Bank (kWh) 976 1005 965925 885845 879894 803775 794838 893937 956928 1000 1033 1003 1032992 1021981 1010 Percantage Discharged 7% 4% 8% 11%15% 19%16% 14%23% 26%24% 20%14% 10%8%11% 4% 1% 4% 1% 5% 2% 6% 3% Consumed kWh Batt. Bank 68 39 79 119159 199165 150241 269250 206151 10788116 44 11 41 12 52 23 63 34 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Fig. 6 Overall energy generation and consumption pattern for the proposed system 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 193 Fig. 7 Maximum battery bank discharge for the existing system Fig. 8 Battery bank status for the proposed system the proposed system in the PVSyst software. The regulator has the tendency to charge the batteries and run the load from both PV array, grid and generator, thus ensuring the reliable working of the system and increasing the robust- ness of the overall system [21]. The remaining AC induc- tive load runs on the already-installed inverters. PVsyst software V5.55 is used to run the computer simu- lations to evaluate the performance of the solar power plant. Existing system While running the simulations, the solar modules are placed at the south facing with 0° angle of azimuth. The modules are tilted at an angle of 30° with the horizontal. The mount- Fig. 9 Flow diagram for the proposed system ing structure is kept fixed which significantly reduces the initial and maintenance cost of the overall solar power plant as it eliminates the rotating and moving parts. Due to fixed System simulation structure, best average tilt angle of 30° is used which can yield maximum production throughout the year [22]. Fig- Figure 9 shows the flow diagram for the proposed system. ure 10 shows the simulation results of normalized produc- These parameters have been used to run the simulations for tion and performance ratio for the existing system. The PV 1 3 194 International Journal of Energy and Environmental Engineering (2018) 9:187–199 Fig. 10 Normalized production and performance ratio for existing system plant is producing 3.79 kWh of energy per peak watt per day being accumulated in batteries. This accounts for the signifi- on average basis in a year working at performance ratio of cant losses in the system up to 8.6% in the form of battery 73.8% over the year including cloudy, foggy and rainy days. efficiency loss, gassing current (electrolyte dissociation) and Table 11 shows the energy produced per month by the PV battery self-discharge currents. plant for its first-year operation at different irradiation and temperature levels. Solar system is producing 469.56 MWh of useful energy after calculating all the losses based on Proposed system average horizontal global irradiance of 1720 kWh/m and ambient temperature of 24.12 °C in 1 year. Figure  12 shows the simulation results of normalized Figure 11 is the detailed analysis of the losses present in production and performance ratio for the proposed sys- the existing solar system. Only 35% of energy from the PV tem. The PV plant is producing 4.5 kWh of energy per modules is directly used whereas 65% of energy is used after peak watt per day on average basis in a year working at Table 11 Relative production for the existing system Balances and main results GlobHor kWh/ T Amb (°C) Globlnc (kWh/ GlobEff (kWh/ EArray (MWh) E_Grid (MWh) EffArrR (%) EffSysR (%) 2 2 2 m m ) m ) January 89.0 12.70 123.4 119.9 35.47 33.43 12.04 11.35 February 111.0 15.00 142.4 138.6 39.80 37.55 11.71 11.05 March 153.0 20.00 172.8 167.8 46.96 44.31 11.39 10.74 April 167.0 26.10 169.4 164.3 44.28 41.76 10.95 10.33 May 190.0 30.90 176.3 170.4 44.95 42.33 10.69 10.06 June 191.0 33.30 170.4 164.5 43.00 40.49 10.57 9.95 July 171.0 32.00 157.0 151.6 40.34 37.94 10.76 10.12 August 172.0 31.10 167.1 161.8 42.84 40.37 10.74 10.12 September 163.0 29.60 176.9 171.7 45.67 43.11 10.81 10.21 October 130.0 25.20 158.1 153.5 42.40 40.01 11.24 10.61 November 97.0 18.80 131.9 128.3 36.63 34.58 11.64 10.98 December 86.0 14.20 126.4 122.8 35.74 33.68 11.84 11.16 Year 1720.0 24.12 1872.2 1815.2 498.08 469.56 11.15 10.51 GlobHor horizontal global irradiation, T Amb ambient temperature, Globlnc global incident in coll. plane, GlobEff effective global, corr. for IAM and shadings, EArray effective energy at the output of the array, E_Grid energy injected into grid, EffArrR effic. Eout array/rough area, EffSysR effic. Eout system/rough area 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 195 Fig. 11 Loss diagram for the first year for the existing system Fig. 12 Normalized production and performance ratio 1 3 196 International Journal of Energy and Environmental Engineering (2018) 9:187–199 performance ratio of 83.4% over the year including cloudy, Results and discussion foggy and rainy days. Table  12 shows the energy produced per month by The performance ratio improvement and energy production the PV plant for its first-year operation at different irra- attained for each respective month for the given irradiance diation and temperature levels. Solar system is produc- data for both existing and proposed solar system are given ing 557.90 MWh of useful energy after calculating all the in Table 13. The existing solar system working on perfor- losses based on average horizontal global irradiance of mance ratio of 73.80% produces 469.56 kWh units and the 1720  kWh/m and ambient temperature of 24.12  °C in proposed system working on 83.40% efficiency can produce 1 year. 557.9 MWh of energy in one complete year. Figure  14 shows the detailed analysis of the losses The month-wise performance ratio trend for the first year present in the proposed solar system. It shows that after of the existing and the proposed system can be observed in retrofitting of AC appliances with DC appliances the sig- Fig. 14. The trend shows an increase of 9.6% over the year. nificant losses associated with the batteries in the form of The increased production of energy in the new system due efficiency loss, gassing current (electrolyte dissociation) to increased efficiency of the system is presented in Fig.  15. and battery self-discharge current have been eliminated The computer simulation results show that efficiency of resulting in an increase in performance ratio and energy the system can be improved by 9.6% for its day time usage generation of the system. when solar is being directly utilized by the load. These The loss diagram for the PV system after modifications 9.6% are the minimum losses which are associated with and upgrading the existing system shows that 557.9 MWh DC–AC–DC convertor losses. These losses can be mini- is the useful energy available after calculating all the mized by direct utilization of DC power. As a result, the losses. There is 88.9 MWh increase in the units produced. overall performance ratio of the system can be increased The loss diagram in Fig.  13 shows that the overall bat- from 73.8 to 83.4%. For the remaining AC load of 75 kW, tery efficiency losses for the complete system are 9.6% the normal DC–AC conversion is applicable. The solar mod- out of which 3.1% are due to gassing current which is also ules installed can produce 557.9 MWh of electricity units defined as electrolytic dissociation and 0.2% due to battery annually, whereas existing system produces only 469 MWh. self-discharge current [23]. These losses due to battery The system which previously provides power to only 66.66% DC–AC conversion have been eliminated in the new sys- of total load can now run the complete 100% load at the tem resulting in improved efficiency by 9.6%. same time reducing daily grid usage from 10 to 6 h and Table 12 Relative production for the proposed system Atchison College Lahore Balances and main results GlobHor T Amb (°C) Globlnc GlobEff (kWh/m ) EArray (MWh) E_Grid (MWh) EffArrR (%) EffSysR (%) 2 2 (kWh/m ) (KWh/m ) January 89.0 12.70 136.1 132.0 43.54 41.29 13.41 12.71 February 111.0 15.00 154.7 150.0 48.63 46.13 13.17 12.49 March 153.0 20.00 183.0 176.5 56.03 53.16 12.83 12.17 April 167.0 26.10 175.2 168.3 51.70 49.02 12.36 11.72 May 190.0 30.90 178.4 170.0 50.91 48.21 11.96 11.33 June 191.0 33.30 170.8 162.3 48.08 45.52 11.80 11.17 July 171.0 32.00 158.9 151.6 45.31 42.87 11.95 11.30 August 172.0 31.10 171.2 163.9 49.20 46.64 12.04 11.41 September 163.0 29.60 185.7 178.7 54.22 51.46 12.24 11.61 October 130.0 25.20 170.0 164.4 51.26 48.65 12.63 11.99 November 97.0 18.80 144.9 140.6 45.01 42.73 13.02 12.36 December 86.0 14.20 140.6 136.5 44.52 42.22 13.26 12.58 Year 1720.0 24.12 1969.5 1894.7 588.42 557.90 12.52 11.87 GlobHor horizontal global irradiation, T Amb ambient temperature, Globlnc global incident in coll. plane, GlobEff effective global, corr. for IAM and shadings, EArray effective energy at the output of the array, E_Grid energy injected into grid, EffArrR effic. Eoutarray/rough area, Eff- SysR effic. Eout system/rough area 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 197 Fig. 13 Loss diagram for the first year Table 13 Month-wise Month Horizontal global irra- Existing system New system improvement of PR and kWh diation (kWh/m ) PR Energy (kWh) PR Energy (kWh) Jan 88.99 79.52 33.43 87.99 41.29 Feb 110.99 77.26 37.55 86.06 46.13 Mar 152.87 75.23 44.31 83.99 53.16 Apr 166.98 72.53 41.76 81.19 49.02 May 190.03 70.95 42.33 79.27 48.21 Jun 191.05 70.29 40.49 78.47 45.52 Jul 170.97 71.57 37.94 79.56 42.87 Aug 172.05 71.35 40.37 79.67 46.64 Sep 163.09 71.77 43.11 80.37 51.46 Oct 130.12 74.52 40.01 83.01 48.65 Nov 97.01 77.08 34.58 85.54 42.73 Dec 85.91 78.19 33.68 86.75 42.22 Total 1720 kWh/m 73.80% 469.56 83.40% 557.9 completely eliminating the use of diesel generator. The bat- tery life is also enhanced as the number of battery cycles increases from 3800 to 5000 due to reduction of DOD from 35 to 26%. 1 3 198 International Journal of Energy and Environmental Engineering (2018) 9:187–199 Compliance with ethical standards 0.95 0.9 Conflict of interest We declare that the manuscript has not been pub- 0.85 lished before nor submitted to another journal for the consideration 0.8 of publication. It is the sole work and property of all the mentioned authors and there is no conflict of interest with anyone. 0.75 0.7 0.65 Open Access This article is distributed under the terms of the Crea- tive Commons Attribution 4.0 International License (http://creat iveco mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- tion, and reproduction in any medium, provided you give appropriate Present System New System credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Fig. 14 Performance ratio graph for the first year Table 14 Actual energy generated by existing PV system in the year January 2016 to December 2016 Sr. no. Month Energy generated Performance ratio Present System by PV (kWh) New System 1 January 33,108 75.75 2 February 37,491 77.14 3 March 44,003 74.71 4 April 41,689 72.41 First Year 5 May 42,154 70.66 6 June 40,099 69.61 Fig. 15 Energy production graph for the first year 7 July 37,928 71.55 8 August 39,990 70.68 9 September 42,869 71.37 Conclusions 10 October 39,869 74.26 11 November 34,162 76.15 By replacing traditional AC appliances with energy-effi- 12 December 33,151 75.37 Total Year 1 466,513 73.30 cient DC appliances in the existing solar system, load is reduced by 58% of total load, i.e. from 425 to 250 kW. Fur- ther, by ensuring direct utilization of DC power to run DC appliances, DC–AC–DC power converter losses for 70% Appendix 1 load are reduced by 9.6%. For the remaining 30% load, the efficiency stays the same as a conventional hybrid system. Real-time energy generation data of existing system for one Hence, efficiency improvement for 70% load results in a complete year from January 2016 to December 2016 is given much quicker payback time due to improvement of per- below (Table 14): formance ratio to 83.4% for the overall system. 340 kWp of PV which previously provide power to only 66.66% load can now run the 100% load. Further, implementing this technique ensures uninterrupted power supply to the References complete load at much lesser rate. It also ensures the use of generator to the minimum extent. The overall life of the 1. Sampaio, P.G.V., González, M.O.A.: Renew. Sustain. Energy Rev. batteries is also prolonged due to direct utilization feature 74, 590 (2017) resulting in increased duty cycles, reduced operation and 2. Manju, S., Sagar, N.: Renew. Sustain. 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Faranda, R.S., Hafezi, H., Leva, S., Mussetta, M., Ogliari, E.: The able Energy Agency, Abu Dhabi (2015) optimum PV plant for a given solar DC/AC converter. Energies 7. Rauf, S., Wahab, A., Rizwan, M., Khan, N.: In application of 8(6), 4853–4870 (2015) dc-grid for efficient use of solar PV system in smart grid. In: 18. Dolara, A., et al.: Performance analysis of a single-axis tracking Shakshuki, E. (ed.) Procedia Computer Science, Proceedings of PV system. IEEE J. Photovolt. 2(4), 524–531 (2012) the 6th International Conference on Sustainable Energy Informa- 19. Mermoud, A., Lejeune, T.: Performance assessment of a simula- tion Technology, Madrid, 23–26 May 2016, pp. 902–906 (2016) tion model for PV modules of any available technology. 25th Eur. 8. Obi, M., Bass, R.: Renew. Sustain. Energy Rev. 58, 1082 (2016) PV Sol. Energy Conf., pp. 6–10 (2010) 9. Lucía, Ó., Cvetkovic, I., Sarnago, H., Boroyevich, D., Mattavelli, 20. Manimekalai, P., Harikumar, R., Raghavan, S.: Int. J. Comput. P., Lee, F.C.: IEEE J. Emerg. Sel. Top. Power Electron. 1, 315 Appl. 82, 29 (2013) (2013) 21. Cetin, E., Yilanci, A., Ozturk, H.K., Colak, M., Kasikci, I., Iplikci, 10. Vossos, V., Garbesi, K., Shen, H.: Energy Build. 68, 223 (2014) S.: Energy Build. 42, 1344 (2010) 11. Kim, Youngjin: Energies 10, 427 (2017) 22. Perez, R., Ineichen, P., Seals, R.: Solar Energy 44, 271 (1990) 12. Garbesi, K., Vossos, V., Shen, H., Taylor, J., Burch, G.: Catalog of 23. Moslehi, K.: IEEE Trans. 1(1), 57 (2014) DC Appliances and Power Systems. Berkeley National Laboratory in association with the US Department of Energy, Berkeley (2011) Publisher’s Note Springer Nature remains neutral with regard to 13. Dastgeer, F., Gelani, H.E.: Energy Build. 138, 648 (2017) urisdictional claims in published maps and institutional affiliations. 14. Crawley, D.B., Hand, J.W., Kummert, M., Griffith, B.T.: Contrast- ing the capabilities of building energy performance simulation programs. Build. Environ. 43(4), 661–673 (2008) 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Energy and Environmental Engineering Springer Journals

Modelling and analysis of an improved scheme for a 340kWp grid interactive PV system in Pakistan to enhance performance ratio and battery life

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Springer Berlin Heidelberg
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Copyright © 2018 by The Author(s)
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Engineering; Renewable and Green Energy
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2008-9163
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10.1007/s40095-018-0261-0
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Abstract

A scheme has been proposed, modeled and simulated to show an improved system efficiency, battery life and payback period of a 340 kWp peak power grid interactive solar photovoltaic system. In this case, a conventional solar photovoltaic system capable to fulfill 66% energy demands has been modified to meet complete energy demands without an increase in system’s photovoltaic capacity. It has been shown via modelling and simulation on PVSyst that using direct current appliances instead of alternating current appliances, initial power demands are reduced by 58% and conversion losses (DC–AC–DC) of 9.6% are eliminated. These modifications result in an overall increase in the system’s performance ratio from 73.8 to 83.4%, with an increase in energy production from 469.6 to 557.9 MWh. As an outcome, battery life is increased by 1200 duty cycles as the depth of discharge is reduced from 35 to 26%. Keywords Solar photovoltaic · Performance ratio · Battery life · Converter losses Introduction in its DC form directly [7], to power electricity loads in buildings, rather than converting it to alternating current Evidently, over the last decade, a sustained and progressive (AC) first, as is the current practice [ 8]. growth in the development and adoption of solar systems Technology advancements have profoundly triggered has been observed [1] and relatively an increasing pub- an important factor that favors the use of DC, the reason lic interest and the advancement in the efficient and cost- being that the electric appliances that operate internally on effective solar technology as concerns over grid failure and DC are increasing more rapidly, and the fact that these new the depletion natural resources have intensified [ 2]. Solar DC-internal technologies tend to be more efficient than their photovoltaic (PV) has emerged as a potential resource for AC counterparts especially fans and light-emitting diodes addition and supplementation of grid power capacity [3, 4]. (LEDs) [9]. Technically, this supports the idea that energy Net-metered PV power systems [5], which have dominated savings could be achieved by directly coupling DC power on-site renewable energy supply in the buildings sector, are sources with DC appliances [10], thus avoiding DC–AC–DC a direct current (DC) power source, as are batteries, which power conversion losses and resultantly, an accompanied are the dominant energy storage technology used with such efficiency increase can be achieved [ 11]. Recent demon- systems [6]. A number of factors are driving the recent shift strations experimented with commercial data centers have in the interest of using DC power from solar electric systems shown that considerable energy savings can be achieved with DC power distribution supplied directly to DC loads, rather than utilizing AC power [12, 13]. In support of the undersigned research paper, a real-time- * Zaeem Aslam zaeem.aslam1@gmail.com based modeling of a PV solar-powered system is configured, which is an integral part for the development of a complete Center for Energy Research and Development, University grid interactive solar photovoltaic (GISP) simulation model of Engineering and Technology Lahore (UET Lahore), where converter losses have been minimized and perfor- Lahore 54000, Pakistan 2 mance ratio of the PV system has been maximized using Faculty of Information Technology, University of Central DC as a primary source. Technically, the process is achieved Punjab, Punjab 54000, Pakistan Vol.:(0123456789) 1 3 188 International Journal of Energy and Environmental Engineering (2018) 9:187–199 by integrating the DC power directly with the load keeping built-in charge controller (DC–DC conversion) and batter- it independent from the DC–AC converters. In this case, ies for energy storage purpose. The technical specifications the relative energy savings of ‘direct-DC’ power for loads of different system components being used which include which have primarily day time usage only are also assessed. Yingli Solar, YL255P-29B YGE 60 cell 40 mm series PV Among several PV modelling software [14, 15], one of the modules, Zigor HIT3C Inverters and SOPzS lead acid bat- most common is PVSyst (See website: http://www.pvsys teries [20] are shown in Tables 1, 2 and 3, respectively. t.com). Over the years, this software application has been widely used for PV modelling [16] and sizing the compo- Schematic diagram of the proposed system nents of the PV system [17, 18] or PV system assessment [19]. In connection with this paper, a solar power system The part of the schematic diagram marked in Fig. 2 high- is modeled and simulated in PVSyst. The results obtained lights the improvement being proposed to the existing solar after performing the simulations clearly show that the sys- system increasing system efficiency by ensuring maximum tem performance ratio has improved and the overall cost of direct utilization of DC power generated by PV modules. the installed system has reduced after eliminating DC–AC Power converter losses occurring due to DC to AC conver- converters. sion are minimized, enhancing the overall performance ratio of the solar plant. System description Proposed system components Schematic diagram for existing system Table 4 below shows the modifications made to the existing system and the additional components added altogether. As a demonstration, the schematic diagram for the system under consideration is shown in Fig. 1. For the operational purpose, inverter is utilized as a major component of the sys- Load profile tem to run the connected load by converting DC energy from PV modules to AC energy. During cloudy days or at night, Existing system the inverter uses grid to run the load and at the same time charging the batteries. On account of frequent load shed- The complete load demands for the facility are shown in ding and worse grid conditions (frequent low grid voltage, Table 5. The total accumulated load of the facility is 425 kW. electrical transients and surges), AC–DC–AC conversion is Table 6 shows only the essential load estimating around used. Consequently, this also ensures the real-time energy 280 kW has been connected and supported by solar system. sharing between the grid and the PV plant at the same time While segregating the 280 kW solar connected load, the improving the power quality at output. operational hours of 220 kW day-time load are from 08:00 to 15:00 h, whereas the working hours of 60 kW load operating Existing system components during night are from 16:00 to 08:00 h. Table 7 provides details of the load shedding, sunshine The complete PV system consists of solar PV modules and grid availability hours in a single day. Considering the (DC power generator), inverters (DC–AC conversion) with present local scenario, there are approximately 6 h of load shedding in one single complete day. Taking into account multiple factors which include frequent grid failures or non- availability occurring at random times during the day and Table 1 Specifications of PV modules Parameters Specification Rating Type of module Polycrystalline 1332 no. Individual power Unit norm power 255 Wp Array global power Nominal (STC) 339.6 kWp In series 18 No. of PV modules In parallel (strings) 74 Array operating character- U mpp 540 V istics (50 °C) I mpp 8.28 A Fig. 1 Existing solar power system schematic diagram 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 189 Table 2 Specifications of Parameters Subjects Rating inverter Input data Recommended DC power Greater than 157 kWp MPPT voltage range 420–700 V DC Input current 375 A DC Battery charging capacity 200 A Output data Nominal output power 300 kW (150 kW × 2) Nominal frequency 50 Hz Power factor > 0.99 at full load Voltage distortion at full load < 3% General data Max power efficiency including transformer > 96% MPPT efficiency 99% Internal consumption in operation < 1% at full load Table 5 Existing AC load for Table 3 Specifications of batteries Load description Power (kW) the facility Parameter Specification Rating Fans and lights 350 Type of battery SOPzS tubular plated 348 no. Air conditioners 40 Water pumps 27 Individual capacity Capacity at C10 rating 1525 AH Voltage Nominal voltage 2 V Refrigeration 8 Total 425 In series 174 No. of batteries In parallel 2 General characteristics Duty cycles at 50% 2500 DOD Table 6 Distribution of AC load for the facility Electrolyte Sulphuric acid with Distribution of AC load Power (kW) density 1.24 kg/ dm AC load connected and powered by solar system 280 AC load running on diesel genset 145 Maximum AC load running on solar system at day time 220 Maximum AC load running on solar system at night 60 time Table 7 Load shedding, grid and sunshine hours in 1 day Description Hours Daily load shedding (average) 6 Daily sunshine hours available 8 Daily grid usage 10 availability of 8 h of daily sunshine, all the calculations for Fig. 2 Proposed solar power system schematic diagram the battery usage are made for only 10 h of grid utiliza- tion. Since the main objective is to reduce dependency on Table 4 Proposed modifications to the existing system National Grid, the system has been designed not to use grid during the day time and also ensuring maximum 35% Depth Parameter Specification Rating of Discharge (DOD) for the batteries at the same time. DC voltage regulator DC/DC converter capable 6 no. of power handling up to Proposed system 50 kW DC fans and lights 48 V energy-efficient DC Total Retrofitting concept has been implemented for the pro- fans and LED lights capacity 175 kW posed system, while replacing AC load appliances of the 1 3 190 International Journal of Energy and Environmental Engineering (2018) 9:187–199 complete facility with energy-efficient DC load appliances, AH × V × E i.e. lighting and fan load, which would reduce the overall N = (2) DOD × S × P load by 50%, i.e. from 350 to 175 kW. The AC inductive load estimated around 75 kW remains independent. The where N is the no. of panels required, E efficiency of solar load demands have been distinctly altered for the proposed PV module at NOCT (nominal operating cell temperature), system as shown in Table 8. The load operated during the S number of sun shine hours, and P panel wattage at NOCT. day time is reduced to 210 kW (accumulating 135 kW of Efficiency of the solar PV module is considered at NOCT lighting and fans load through retrofitting of AC appliances specifications mentioned, which signifies the realistic value with DC appliances and 75 kW of inductive load) which of the PV module performance in real-time conditions, operates from 08:00 to 15:00 h daily and the load operated whereas SH are taken as the yearly average sunshine hours during night time is reduced to 40 kW having working hours present in Pakistan in one single day. In the proposed system, from 16:00 to 08:00 h while completely eliminating the use DOD is reduced from 35 to 26% which specifically indicates of diesel generator. that the battery usage is reduced. Following equation (Eq.  1) is applied to calculate the depth of discharge (DOD) for the batteries in the proposed system: Battery discharge behaviour W × B DOD = Existing system (1) V × AH where DOD is the depth of discharge, W load in watts, B bat- The overall energy production and consumption along tery backup hours, V system voltage, and AH is the capacity with the detailed battery discharge statistics for consecu- of battery. tive 3 days of the existing solar system is given in Table 9. The number of PV modules required to charge batteries Grid is used for 10 h per day to meet the complete energy during the day is calculated using Eq. 2. This would help to demands of the connected load on solar system. The maxi- determine the most appropriate value for the DOD of the mum battery DOD for the existing system is 35%. batteries for a given Solar PV system: The graph in Fig. 3 shows the energy produced and con- sumed by the existing system in a single day. It explains the hourly status of actual energy generation from the Solar Table 8 Load profile for the proposed system Array, the optimum energy consumption (hours) and energy variance to/from battery. Description Power (kW) The graph in Fig. 4 shows the maximum DOD achieved Total rated load of the facility (after retrofitting AC 250 by the battery bank. It demonstrates the hourly status of per- appliances with DC) centage discharge of the battery bank based on a 24-h cycle New lighting and fans load (DC) 175 of system operation. The graph shows that the battery is AC inductive load 75 being used up to 35% depth of discharge. The operational Load connected/shifted to solar system 250 timing has been assumed based on standard operations Load running on diesel genset 0 (working hours) as mentioned above. Table 9 Energy consumption for 3 days for the existing system Time 24Hrs 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:0011:00 12:0013:00 14:0015:00 16:0017:00 18:0019:00 20:0021:00 22:0023:00 energy consumption (kWh)6060606060606060220 220220 220220 220220 2206060606060606060 energy generation (kWh)7272727856220 182231 258271 258231 283119 12410727272 Difference kWh12-60 12 -6012-60 18 -4 0-38 11 38 51 38 11 63 59 64 -5012-60 12 -6012 Grid Usage (kWh)72727272101 10172727272 Energy for batt. bank with loss 11 -6011-60 11 -6016-40 -381034463410575459-50 11 -6011-60 11 Current to batt. Bank (A) 455 -2500 455 -2500455 -2500687 -159 7-1593 430143219341432430 2380 2236 2442 -2087 455-2500455 -2500455 Day 01 Available Batt. Bank (kWh) 905 845 856 796807 747763 759759 721732 766812 847857 905905 905855 866806 817757 767 Percantage Discharged 0% 7% 5% 12%11% 17%16% 16%16% 20%19% 15%10% 6% 5% 0% 0% 0% 6% 4% 11%10% 16%15% Consumed kWh Batt. Bank 06049109 98 158142 145145 184173 1399258480 00 50 39 99 88 148137 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 02 Available Batt. Bank (kWh) 778 718 729 669680 620637 633633 595605 640686 720731 788841 900850 861801 812752 763 Percantage Discharged 14% 21% 19%26% 25%31% 30%30% 30%34% 33%29% 24%20% 19%13% 7% 1% 6% 5% 11%10% 17%16% Consumed kWh Batt. Bank 126 186 175 235225 285268 272272 310300 265219 184174 117635 55 44 10493153 142 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 03 Available Batt. Bank (kWh) 775 715 726 666677 617633 629629 591601 636682 717727 784838 896846 857797 808748 759 Percantage Discharged 14% 21% 20%26% 25%32% 30%30% 30%35% 34%30% 25%21% 20%13% 7% 1% 6% 5% 12%11% 17%16% Consumed kWh Batt. Bank 130 190 179 239228 288272 276275 314303 269223 188178 121679 59 48 10897157 146 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 191 Fig. 3 Overall energy generation and consumption pattern for the existing system Fig. 4 Maximum battery bank discharge for the existing system Figure 5 illustrates the hourly status of the battery bank Array, the optimum energy consumption (hours) and energy available and the battery bank consumed based on the 24-h variation to/from battery. cycle of system operation for the existing system. It shows The graph in Fig. 7 confirms the maximum DOD achieved that the battery bank is still 65% full. by the battery bank. It demonstrates the hourly status of per- centage discharge of the battery bank based on a 24-h cycle Proposed system of system operation. The graph shows that the battery is being used up to 26% depth of discharge. The operational timing has The overall energy production and consumption along with been assumed based on standard operations (working hours) the detailed battery discharge statistics for 3 consecutive as mentioned above. days of the proposed solar system is given in Table 10. It Figure 8 shows the hourly status of the battery bank avail- can be clearly seen that the grid usage has been reduced to able and the battery bank consumed based on the 24-h cycle 6 h per day to meet the complete energy demands of the con- of system operation for the proposed system. It shows that the nected load on solar system. The maximum battery DOD for battery bank is still 74% full. the proposed system also reduces to 26% ensuring increase in battery life. The graph in Fig. 6 demonstrates the energy produced and consumed by the proposed system in a single day. It explains the hourly status of actual energy generation from the Solar 1 3 192 International Journal of Energy and Environmental Engineering (2018) 9:187–199 Fig. 5 Battery bank status for the existing system Table 10 Energy consumption for 3 days for the proposed system Time 24Hrs 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:0012:00 13:0014:00 15:0016:00 17:0018:00 19:0020:00 21:0022:00 23:00 energy consumption (kWh)4040404040404040210 210210 210210 210210 2104040404040404040 energy generation (kWh)727856119 182231 258271 258231 182119 76 10 72 72 72 Difference kWh-40 32 -40-40 -40-40 38 16 -91-28 21 48 61 48 21 -287936-30 32 -4032-40 32 Grid Usage (kWh)7272 20 72 72 72 Energy for batt. bank with loss -4029-40 -40-40 -403515-91 -281943564319-28 72 33 -3029-40 29 -4029 Current to batt. Bank (A) -1667 1213 -1667-1667 -1667-1667 1446614 -3793-1177 809 1811 2313 1811809 -1177 2994 1372-1254 1213-1667 1213-1667 1213 Day 01 Available Batt. Bank (kWh) 1004 1033 993953 913873 908923 832803 823866 922965 985956 1028 1044 1014 1043 1003 1032992 1021 Percantage Discharged 4% 1% 5% 9% 13%16% 13%12% 20%23% 21%17% 12%8%6%8%2%0%3%0%4%1%5%2% Consumed kWh Batt. Bank 40 11 51 91 131171 136121 212241 221178 122795988160 30 141125223 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 02 Available Batt. Bank (kWh) 981 1010 970930 890850 885900 809781 800843 899942 962934 1005 1038 1008 1037997 1027987 1016 Percantage Discharged 6% 3% 7% 11%15% 19%15% 14%23% 25%23% 19%14% 10%8%11% 4% 1% 3% 1% 4% 2% 6% 3% Consumed kWh Batt. Bank 63 34 74 114154 194159 144235 263244 201145 10282110 39 6367 47 17 57 28 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Day 03 Available Batt. Bank (kWh) 976 1005 965925 885845 879894 803775 794838 893937 956928 1000 1033 1003 1032992 1021981 1010 Percantage Discharged 7% 4% 8% 11%15% 19%16% 14%23% 26%24% 20%14% 10%8%11% 4% 1% 4% 1% 5% 2% 6% 3% Consumed kWh Batt. Bank 68 39 79 119159 199165 150241 269250 206151 10788116 44 11 41 12 52 23 63 34 System Status ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON Fig. 6 Overall energy generation and consumption pattern for the proposed system 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 193 Fig. 7 Maximum battery bank discharge for the existing system Fig. 8 Battery bank status for the proposed system the proposed system in the PVSyst software. The regulator has the tendency to charge the batteries and run the load from both PV array, grid and generator, thus ensuring the reliable working of the system and increasing the robust- ness of the overall system [21]. The remaining AC induc- tive load runs on the already-installed inverters. PVsyst software V5.55 is used to run the computer simu- lations to evaluate the performance of the solar power plant. Existing system While running the simulations, the solar modules are placed at the south facing with 0° angle of azimuth. The modules are tilted at an angle of 30° with the horizontal. The mount- Fig. 9 Flow diagram for the proposed system ing structure is kept fixed which significantly reduces the initial and maintenance cost of the overall solar power plant as it eliminates the rotating and moving parts. Due to fixed System simulation structure, best average tilt angle of 30° is used which can yield maximum production throughout the year [22]. Fig- Figure 9 shows the flow diagram for the proposed system. ure 10 shows the simulation results of normalized produc- These parameters have been used to run the simulations for tion and performance ratio for the existing system. The PV 1 3 194 International Journal of Energy and Environmental Engineering (2018) 9:187–199 Fig. 10 Normalized production and performance ratio for existing system plant is producing 3.79 kWh of energy per peak watt per day being accumulated in batteries. This accounts for the signifi- on average basis in a year working at performance ratio of cant losses in the system up to 8.6% in the form of battery 73.8% over the year including cloudy, foggy and rainy days. efficiency loss, gassing current (electrolyte dissociation) and Table 11 shows the energy produced per month by the PV battery self-discharge currents. plant for its first-year operation at different irradiation and temperature levels. Solar system is producing 469.56 MWh of useful energy after calculating all the losses based on Proposed system average horizontal global irradiance of 1720 kWh/m and ambient temperature of 24.12 °C in 1 year. Figure  12 shows the simulation results of normalized Figure 11 is the detailed analysis of the losses present in production and performance ratio for the proposed sys- the existing solar system. Only 35% of energy from the PV tem. The PV plant is producing 4.5 kWh of energy per modules is directly used whereas 65% of energy is used after peak watt per day on average basis in a year working at Table 11 Relative production for the existing system Balances and main results GlobHor kWh/ T Amb (°C) Globlnc (kWh/ GlobEff (kWh/ EArray (MWh) E_Grid (MWh) EffArrR (%) EffSysR (%) 2 2 2 m m ) m ) January 89.0 12.70 123.4 119.9 35.47 33.43 12.04 11.35 February 111.0 15.00 142.4 138.6 39.80 37.55 11.71 11.05 March 153.0 20.00 172.8 167.8 46.96 44.31 11.39 10.74 April 167.0 26.10 169.4 164.3 44.28 41.76 10.95 10.33 May 190.0 30.90 176.3 170.4 44.95 42.33 10.69 10.06 June 191.0 33.30 170.4 164.5 43.00 40.49 10.57 9.95 July 171.0 32.00 157.0 151.6 40.34 37.94 10.76 10.12 August 172.0 31.10 167.1 161.8 42.84 40.37 10.74 10.12 September 163.0 29.60 176.9 171.7 45.67 43.11 10.81 10.21 October 130.0 25.20 158.1 153.5 42.40 40.01 11.24 10.61 November 97.0 18.80 131.9 128.3 36.63 34.58 11.64 10.98 December 86.0 14.20 126.4 122.8 35.74 33.68 11.84 11.16 Year 1720.0 24.12 1872.2 1815.2 498.08 469.56 11.15 10.51 GlobHor horizontal global irradiation, T Amb ambient temperature, Globlnc global incident in coll. plane, GlobEff effective global, corr. for IAM and shadings, EArray effective energy at the output of the array, E_Grid energy injected into grid, EffArrR effic. Eout array/rough area, EffSysR effic. Eout system/rough area 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 195 Fig. 11 Loss diagram for the first year for the existing system Fig. 12 Normalized production and performance ratio 1 3 196 International Journal of Energy and Environmental Engineering (2018) 9:187–199 performance ratio of 83.4% over the year including cloudy, Results and discussion foggy and rainy days. Table  12 shows the energy produced per month by The performance ratio improvement and energy production the PV plant for its first-year operation at different irra- attained for each respective month for the given irradiance diation and temperature levels. Solar system is produc- data for both existing and proposed solar system are given ing 557.90 MWh of useful energy after calculating all the in Table 13. The existing solar system working on perfor- losses based on average horizontal global irradiance of mance ratio of 73.80% produces 469.56 kWh units and the 1720  kWh/m and ambient temperature of 24.12  °C in proposed system working on 83.40% efficiency can produce 1 year. 557.9 MWh of energy in one complete year. Figure  14 shows the detailed analysis of the losses The month-wise performance ratio trend for the first year present in the proposed solar system. It shows that after of the existing and the proposed system can be observed in retrofitting of AC appliances with DC appliances the sig- Fig. 14. The trend shows an increase of 9.6% over the year. nificant losses associated with the batteries in the form of The increased production of energy in the new system due efficiency loss, gassing current (electrolyte dissociation) to increased efficiency of the system is presented in Fig.  15. and battery self-discharge current have been eliminated The computer simulation results show that efficiency of resulting in an increase in performance ratio and energy the system can be improved by 9.6% for its day time usage generation of the system. when solar is being directly utilized by the load. These The loss diagram for the PV system after modifications 9.6% are the minimum losses which are associated with and upgrading the existing system shows that 557.9 MWh DC–AC–DC convertor losses. These losses can be mini- is the useful energy available after calculating all the mized by direct utilization of DC power. As a result, the losses. There is 88.9 MWh increase in the units produced. overall performance ratio of the system can be increased The loss diagram in Fig.  13 shows that the overall bat- from 73.8 to 83.4%. For the remaining AC load of 75 kW, tery efficiency losses for the complete system are 9.6% the normal DC–AC conversion is applicable. The solar mod- out of which 3.1% are due to gassing current which is also ules installed can produce 557.9 MWh of electricity units defined as electrolytic dissociation and 0.2% due to battery annually, whereas existing system produces only 469 MWh. self-discharge current [23]. These losses due to battery The system which previously provides power to only 66.66% DC–AC conversion have been eliminated in the new sys- of total load can now run the complete 100% load at the tem resulting in improved efficiency by 9.6%. same time reducing daily grid usage from 10 to 6 h and Table 12 Relative production for the proposed system Atchison College Lahore Balances and main results GlobHor T Amb (°C) Globlnc GlobEff (kWh/m ) EArray (MWh) E_Grid (MWh) EffArrR (%) EffSysR (%) 2 2 (kWh/m ) (KWh/m ) January 89.0 12.70 136.1 132.0 43.54 41.29 13.41 12.71 February 111.0 15.00 154.7 150.0 48.63 46.13 13.17 12.49 March 153.0 20.00 183.0 176.5 56.03 53.16 12.83 12.17 April 167.0 26.10 175.2 168.3 51.70 49.02 12.36 11.72 May 190.0 30.90 178.4 170.0 50.91 48.21 11.96 11.33 June 191.0 33.30 170.8 162.3 48.08 45.52 11.80 11.17 July 171.0 32.00 158.9 151.6 45.31 42.87 11.95 11.30 August 172.0 31.10 171.2 163.9 49.20 46.64 12.04 11.41 September 163.0 29.60 185.7 178.7 54.22 51.46 12.24 11.61 October 130.0 25.20 170.0 164.4 51.26 48.65 12.63 11.99 November 97.0 18.80 144.9 140.6 45.01 42.73 13.02 12.36 December 86.0 14.20 140.6 136.5 44.52 42.22 13.26 12.58 Year 1720.0 24.12 1969.5 1894.7 588.42 557.90 12.52 11.87 GlobHor horizontal global irradiation, T Amb ambient temperature, Globlnc global incident in coll. plane, GlobEff effective global, corr. for IAM and shadings, EArray effective energy at the output of the array, E_Grid energy injected into grid, EffArrR effic. Eoutarray/rough area, Eff- SysR effic. Eout system/rough area 1 3 International Journal of Energy and Environmental Engineering (2018) 9:187–199 197 Fig. 13 Loss diagram for the first year Table 13 Month-wise Month Horizontal global irra- Existing system New system improvement of PR and kWh diation (kWh/m ) PR Energy (kWh) PR Energy (kWh) Jan 88.99 79.52 33.43 87.99 41.29 Feb 110.99 77.26 37.55 86.06 46.13 Mar 152.87 75.23 44.31 83.99 53.16 Apr 166.98 72.53 41.76 81.19 49.02 May 190.03 70.95 42.33 79.27 48.21 Jun 191.05 70.29 40.49 78.47 45.52 Jul 170.97 71.57 37.94 79.56 42.87 Aug 172.05 71.35 40.37 79.67 46.64 Sep 163.09 71.77 43.11 80.37 51.46 Oct 130.12 74.52 40.01 83.01 48.65 Nov 97.01 77.08 34.58 85.54 42.73 Dec 85.91 78.19 33.68 86.75 42.22 Total 1720 kWh/m 73.80% 469.56 83.40% 557.9 completely eliminating the use of diesel generator. The bat- tery life is also enhanced as the number of battery cycles increases from 3800 to 5000 due to reduction of DOD from 35 to 26%. 1 3 198 International Journal of Energy and Environmental Engineering (2018) 9:187–199 Compliance with ethical standards 0.95 0.9 Conflict of interest We declare that the manuscript has not been pub- 0.85 lished before nor submitted to another journal for the consideration 0.8 of publication. It is the sole work and property of all the mentioned authors and there is no conflict of interest with anyone. 0.75 0.7 0.65 Open Access This article is distributed under the terms of the Crea- tive Commons Attribution 4.0 International License (http://creat iveco mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- tion, and reproduction in any medium, provided you give appropriate Present System New System credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Fig. 14 Performance ratio graph for the first year Table 14 Actual energy generated by existing PV system in the year January 2016 to December 2016 Sr. no. Month Energy generated Performance ratio Present System by PV (kWh) New System 1 January 33,108 75.75 2 February 37,491 77.14 3 March 44,003 74.71 4 April 41,689 72.41 First Year 5 May 42,154 70.66 6 June 40,099 69.61 Fig. 15 Energy production graph for the first year 7 July 37,928 71.55 8 August 39,990 70.68 9 September 42,869 71.37 Conclusions 10 October 39,869 74.26 11 November 34,162 76.15 By replacing traditional AC appliances with energy-effi- 12 December 33,151 75.37 Total Year 1 466,513 73.30 cient DC appliances in the existing solar system, load is reduced by 58% of total load, i.e. from 425 to 250 kW. Fur- ther, by ensuring direct utilization of DC power to run DC appliances, DC–AC–DC power converter losses for 70% Appendix 1 load are reduced by 9.6%. For the remaining 30% load, the efficiency stays the same as a conventional hybrid system. Real-time energy generation data of existing system for one Hence, efficiency improvement for 70% load results in a complete year from January 2016 to December 2016 is given much quicker payback time due to improvement of per- below (Table 14): formance ratio to 83.4% for the overall system. 340 kWp of PV which previously provide power to only 66.66% load can now run the 100% load. Further, implementing this technique ensures uninterrupted power supply to the References complete load at much lesser rate. It also ensures the use of generator to the minimum extent. The overall life of the 1. Sampaio, P.G.V., González, M.O.A.: Renew. Sustain. Energy Rev. batteries is also prolonged due to direct utilization feature 74, 590 (2017) resulting in increased duty cycles, reduced operation and 2. Manju, S., Sagar, N.: Renew. Sustain. 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International Journal of Energy and Environmental EngineeringSpringer Journals

Published: Jan 24, 2018

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