“DESIGN OF GRID-CONNECTED PV SYSTEM” Oleh TUNKU MUHAMMAD NIZAR BIN TUNKU MANSUR PPK SISTEM ELEKTRIK

METHODOLOGY 1 2 3 4 Undertaking a thorough site audit Determining the system sizing Selecting and matching the individual components Determining location for installation of the components 4 Grid-Connected PV System EET433 Renewable Energy System

UNDERTAKING SITE SURVEY To determine the solar access for the site. To determine whether any shadowing will occur and estimating its effect on the system Estimating the solar resource for the site. To determine the available space for the PV array. To determine whether the roof is suitable for mounting the PV array. To determine how the modules are mounted on the roof. To determine where the switchboard is located, where the inverter, and junction boxes will be installed, cabling route and therefore estimate the lengths of the cable runs. Grid-Connected PV System EET433 Renewable Energy System

SOLAR ACCESS TO THE SITE The solar access could be reduced due to: Natural landscapes such as mountains or hills. Trees or other vegetation. Other buildings. Parts of the actual building where the system will be located such sections of roof, TV aerials. Needs to consider future development of the site that may block the solar access. Grid-Connected PV System EET433 Renewable Energy System

SOLAR RESOURCES AT THE SITE This irradiation varies as a result of: Tilt Angle of the array. Direction the array is facing. Shading effect of objects. Grid-Connected PV System EET433 Renewable Energy System

HOW PV ARRAY ARE MOUNTED ON THE ROOF Retrofit Building Intergrated Grid-Connected PV System EET433 Renewable Energy System

AVAILABLE SPACE ON THE ROOF Calculating available space area and number of PV module that could fit on the roof. Arrangement of PV Module either length-wise up or length-wise across. Length-wise Up Length-wise Across Grid-Connected PV System EET433 Renewable Energy System

CALCULATING MAXIMUM NUMBER OF PV MODULE THAT COULD BE INSTALLED BASED ON ARRANGEMENT Length-wise Across Grid-Connected PV System EET433 Renewable Energy System

CALCULATING MAXIMUM NUMBER OF PV MODULE THAT COULD BE INSTALLED BASED ON ARRANGEMENT Length-wise Up Grid-Connected PV System EET433 Renewable Energy System

Other factor to consider Gap spacing between PV modules. CALCULATING MAXIMUM NUMBER OF PV MODULE THAT COULD BE INSTALLED BASED ON ARRANGEMENT Other factor to consider Gap spacing between PV modules. Offset spacing for PV array from all edges of roof. Grid-Connected PV System EET433 Renewable Energy System

MATCHING THE INVERTER WITH THE PV ARRAY The PV array power output to the inverter power rating is calculated as Where Pnom_inv = inverter nominal power (W) Parray_stc = peak power rating of the PV array (W) k = de-rating factor The optimal size value of k is depends on the type of PV technology but regardless type of mounting structure. for crystalline PV array : 0.90 ≤ k ≤ 1.00 for thin film PV array : 1.10 ≤ k ≤ 1.30 Grid-Connected PV System EET433 Renewable Energy System

MATCHING THE INVERTER WITH THE PV ARRAY The minimum and maximum number of PV modules could be calculated based on optimal range of de-rating factor. Where Pnom_inv = inverter nominal power (W) Pmod_stc = peak power rating of the PV module (W) k1 = upper limit of de-rating factor k2 = lower limit of de-rating factor for crystalline PV array : k1 = 1.00, k2 = 0.90 for thin film PV array : k1 = 1.30, k2 = 1.10 Grid-Connected PV System EET433 Renewable Energy System

MATCHING THE INVERTER WITH THE PV ARRAY It is acceptable to design with a slightly oversized inverter than the recommended range. However, if the inverter is undersized, it will limit the power transferred to the grid and it is a waste of energy. Grid-Connected PV System EET433 Renewable Energy System

PV ARRAY SIZING BASED ON INVERTER INVERTER (AMBO CHART) Vmax_inv 0.95 × Vmax_inv Vmin_mpp_inv Vmax_mpp_inv 1.1 ×Vmin_mpp_inv Idc_inv INVERTER MPP VOLTAGE RANGE Grid-Connected PV System EET433 Renewable Energy System

MINIMUM NO. PV MODULES PER STRING The minimum MPP voltage of the module will occurs during the highest cell temperature normally at noon. Assign a voltage drop of 5% in cables from the array to the inverter DC input. Assume the inverter is located very close to the point of connection to grid. Hence the Minimum Effective Voltage from the module at the inverter DC input is: Grid-Connected PV System EET433 Renewable Energy System

MINIMUM NO. PV MODULES PER STRING (continue 1) Assign a Safety Margin of 10% above minimum window voltage of the inverter DC input to get the lowest allowable voltage input into the inverter. Hence the minimum no. of modules per string is determined by: Grid-Connected PV System EET433 Renewable Energy System

MAXIMUM NO. PV MODULES PER STRING In the early morning, the cell temperature will be low because the module still not heat up by the sun. The maximum open voltage of the module is given by Assign a safety margin of 5% below the maximum input voltage of the inverter. Since we are calculating maximum open circuit voltage, then there will be no current, hence no voltage drop between the array and the inverter. Grid-Connected PV System EET433 Renewable Energy System

MAXIMUM NO. PV MODULES PER STRING (continue 1) The minimum no. of modules per string is determined by: Grid-Connected PV System EET433 Renewable Energy System

MAXIMUM NO. OF PARALLEL STRING Normally grid-connected inverter has maximum allowed limit for DC current input. This data normally provided by the manufacturer in the datasheet. A oversized current factor of 1.25 is used as safety factor in the calculation as below. Where Np_max = maximum number of parallel string Idc_inv_max = maximum DC input current into inverter Isc_stc = short circuit current of a string at STC. Grid-Connected PV System EET433 Renewable Energy System

CHECKING THE DESIGN Check number of PV modules per string are within the maximum and minimum range calculated. Check number of parallel string is within the permissible range calculated. Determine the optimal array configuration. Check the PV array size is within the optimal range, k. Check the string voltage not exceeding the maximum system voltage of the PV module. Grid-Connected PV System EET433 Renewable Energy System

PREDICTION OF SYSTEM PERFORMANCE The estimation of the predicted performance of PV system that has been designed is a useful indicator for all parties involved in the PV system project. Normally system performance indicator used is as follow: Yield of the system Specific yield Performance ratio. Grid-Connected PV System EET433 Renewable Energy System

ENERGY YIELD Energy Yield (Esys) is the amount of energy generated by the PV system. It can be reported as an annual yield, monthly yield or even daily yield. Energy Yield is given by: where Esys = PV system yield (kWh) fdirt = dirt de-rating factor ƞpv_inv = cable efficiency ƞinv = inverter efficiency Grid-Connected PV System EET433 Renewable Energy System

ENERGY YIELD (continue 1) fmm = module mismatch or power tolerance factor PSHperiod = PSH value for the specified tilt angle over the period of interest (h) ftemp_avg = de-rating factor due to the temperature Where γPmp = temperature coefficient for Pmp (% per oC) Tcell_avg = average daily maximum cell temperature (oC) Tstc = cell temperature at STC (oC) Grid-Connected PV System EET433 Renewable Energy System

ENERGY YIELD (continue 2) In the context of predicting the energy yield, the calculation of Tcell_avg should be done as below. In the case of NOCT and irradiance value are available Where Tamb_avg_max = average daily maximum ambient temperature (oC) NOCT = given by the manufacturer (oC) Gamb_avg_max = average daily maximum solar irradiance (Wm-2) Grid-Connected PV System EET433 Renewable Energy System

ENERGY YIELD (continue 3) In the case of only average maximum ambient temperature Tamb_avg_max available Grid-Connected PV System EET433 Renewable Energy System

SPECIFIC YIELD Specific Yield (Yf) is another system performance indicator that normalizes the different system capabilities. Specific Yield is given by: The unit is in kWh per kWp, which represent the number of hours that PV array would need to operate at its rated power to provide energy Esys. For Malaysian climate, the acceptable value for Yf should be more than 1,000 kWh per kWp. Grid-Connected PV System EET433 Renewable Energy System

PERFORMANCE RATIO Performance ratio (PR) is system performance indicator that takes into account almost all factors involved. Performance ratio is given by: It is unitless and sometimes is represented in percentage. It indicates the overall effect of losses on the rated output. For Malaysian climate, the acceptable value for PR should be more than 70%. Grid-Connected PV System EET433 Renewable Energy System

ENERGY COST AND PAYBACK PERIOD With the implementation of the Feed-in Tariff (FiT), the PV energy producer known as Feed-in Approval Holder (FiAH) could enjoy selling their energy produced from the PV system to the utility (Distribution Licensee) such as TNB. The tariff rate is available at SEDA website and depends on the size of installation, where it is installed and either made locally or not. In general the components of the FiT rates are as follow: Basic rate Bonus rate Grid-Connected PV System EET433 Renewable Energy System

FiT RATES FOR SOLAR PV (INDIVIDUAL) Grid-Connected PV System EET433 Renewable Energy System

FiT RATES FOR SOLAR PV (NON-INDIVIDUAL) Grid-Connected PV System EET433 Renewable Energy System

EXAMPLE FOR 4kW PV SYSTEM Estimated current cost per 1kW of the system = RM10,000 Estimated available sun hours per day = 5 (average daily) For the installation of a 4kW system with installation in a building structure, the FiT rates will be: 1.0184 + 0.2153 =  RM 1.2337  per kWh. The investment is 4 kW x RM10,000 = RM40,000 The energy produced by the system per month is:  = 4kW x 5 hours of peak sun per day x 30 days per month  = 600 kWh per month Payment of FiT per month = 600kWh x RM 1.2337 per kWh   = RM 740 Number of month to payback = RM40,000 / RM740 = 54 months (around 5 years) In this example, the payback period is around 5 years. In 6th year, profit begins and enjoy until 21st year. Grid-Connected PV System EET433 Renewable Energy System