PV off Grid Design Eng. Laith Basha M.Sc Renewable Energy & Energy Efficiency Cairo- Egypt & Kassel- Germany Universities, 2012 B.Sc Electrical Engineering The University of Jordan, 2007 Laith.basha@rss.jo PV off Grid Design المــــركــز الوطنــــــي لبحــــــوث الطـــاقــــــة National Energy Research Center

Stand alone PV system component

LOAD DC/BATTEYR VOLTAGE Stand alone PV system Block diagram Operation Voltage DC INVERTER DC/AC CHARGE CONTROLLER Operation Voltage AC ~ = LOAD AC 230 VOLT/50HZ ~ BATTERY BANK PV PANELS = LOAD DC/BATTEYR VOLTAGE

PV modules, PV panels 1. The number of the modules 2. The connection way, series or parallel.

PV module specification

Charge controller Battery charge Controllers control the amount of current entering the battery and protect it from overcharging and from completely discharging. They can also measure battery voltage to detect the state of charge.

Charge controller specs

Inverters PV cells generate direct current (DC). Batteries store electricity as DC. In cases where you need AC power. an inverter is used to change low voltage DC (12, 24, 32, 36, 48, 96, 120) voltage to higher voltage AC (120, 60 Hz or 240,50 Hz). Some power is lost in the conversion as inverters are, on average, about 80- to 95-percent efficient . The capacity of the inverter must be greater than the load peak power, so as to take into consideration: 1. Starting current of some loads (like motors). 2. Future expansion.

Inverters features- 1 Many of today's inverters also come equipped with the following features: Metering: a display to provide volts input/output, frequency output, voltage and frequency of a fuel-fired generator. Grid-connected capability: The inverter can convert the DC output from the array to AC power that can be synchronized with the grid (utility). This feature makes it possible to reduce or even eliminate monthly utility bills.

Inverters features- 2 Charging capability: Inverters can draw power from either the grid or a fuel-fired generator to charge the battery bank while, at the same time, continuing to pass that power through to the electrical loads in your house. Stacking: Some inverters can be linked together, either to produce twice the output or to produce power that is out of phase from inverter to inverter in order to produce AC power.

Inverter data sheet

Battery

Battery size The number of amp-hours a battery can deliver, is simply the number of amps of current it can discharge, multiplied by the number of hours it can deliver that current. System designers use amp-hour specifications to determine how long the system will operate without any significant amount of sunlight to recharge the batteries. This measure of "days of autonomy" is an important part of design procedures. Theoretically, a 400 amp-hour battery should be able to deliver either 400 amps for one hour, 100 amps for 4 hours, 4 amps for 100 hours, or 2 amp for 200 hours.

Charge and Discharge Rates The rate of charge or discharge is defined as the total capacity divided by some number. For example, a discharge rate of C/20 means the battery is being discharged at a current equal to 1/20th of its total capacity. In the case of a 400 amp-hour battery, this would mean a discharge rate of 20 amps. Depth of discharge is a measure of how much energy has been taken from a battery. With the lead-acid deep cycle battery used in a solar electric system, there is more tolerance for discharging. You can discharge the battery of a solar energy system 50% to 80% with no damage to the battery. This makes it very different from a car battery. As an example, "shallow cycle" batteries are designed to discharge from 10% to 25% of their total amp-hour capacity during each cycle. In contrast, most "deep cycle" batteries designed for photovoltaic applications are designed to discharge up to 80% of their capacity without damage.

Depth of discharge (DOD) Even deep cycle batteries are affected by the depth of discharge. The deeper the discharge, the smaller the number of charging cycles the battery will last. They are also affected by the rate of discharge and their tempera ture.

Temperature Effect Manufacturers generally rate batteries at 25ºC. The battery’s capacity will decrease at lower temperatures and increase at higher temperatures. A battery at 0ºC may have only 65 to 85 percent of its fully rated capacity. A battery at -30 ºC will drop to 50 percent. Battery capacity is increased at higher temperatures. Higher operating temperatures decreases the lifetime of the battery, therefore manufacturers recommend not to exceed certain temperature.

Battery data sheet

12V Compatible PV Module

Component efficiencies/ Losses Charge Controller Inverter PV = = ~ Loads = η = 93%-97% η = 92% - 97% Battery η = 80% DOD = 75%

Solar PV System Sizing Procedure Determine power consumption demands: The first step in designing a solar PV system is to find out the total power and energy consumption of all loads that need to be supplied by the solar PV system as follows: - Calculate total Watt-hours per day for each appliance used: Add the Watt-hours needed for all appliances together to get the total Watt-hours per day which must be delivered to the appliances. W x h = Wh

Energy consumption per day

PV modules Sizing 2. PV modules Sizing : The peak watts (Wp) needed depends on size of the PV module and climate of site location. The climate of site location is represented by Peak Sun Hours (PSH) which is selected according to the location and application. For Amman, the month with the lowest PSH is December with 3.9h/day at 26°-27° tilt angle (optimum latitude tilt). To determine the sizing of PV modules, calculate as follows: 2.1 Divide the Total Energy (Wh) /day on multiplication of the inverter efficiency (inv .eff), the Battery efficiency (Bat. Eff.) and the charge controller efficiency (cc.eff). 2.2 Calculate the total Watt-peak rating needed for PV modules: Divide the total Watt-hours per day needed from the PV modules by PSH to find the total peak power of the PV array. 2.3 Multiply the calculated watt peaks by a specific safety factor (e.g. Safety Factor = 1.2- 1.3) to compensate power losses of the PV modules over years, Temperature losses, Dust effect losses. 2.4 Calculate the number of PV panels for the system: Divide the answer obtained in item 3.2 by the rated output Watt-peak of the selected PV module.

Solar charge controller sizing 3. Solar charge controller sizing: The solar charge controller is typically rated for Amperage and Voltage capacities. Select the solar charge controller to match the voltage of PV array and batteries and then identify which type of solar charge controller is the right for your application. Make sure that solar charge controller has enough capacity to handle the maximum current of PV array. The sizing of controller depends on the total PV output current which is delivered to the controller and also depends on PV panel configuration (series or parallel configuration). According to a common practice, the sizing of solar charge controller is to take the short circuit current (Isc) of the PV array, and multiply it by 1.2 Solar charge controller rating = Total short circuit current of PV array x 1.2

Battery sizing 4. Battery sizing: The battery type recommended for using in solar PV system is deep cycle battery. Deep cycle battery is specifically designed to be discharged to low energy levels and rapidly recharged (cyclic charging and discharging day after day for years). The battery should be large enough to store sufficient energy to operate the appliances at night and cloudy days. To find out the size of battery bank, calculate as follows: 4.1 Calculate total Watt-hours per day used by appliances. 4.2 Divide the answer obtained in item 4.1 by the inverter (Inv.Eff) 4.3 Divide the answer obtained in item 4.2 by the Battery efficiency Depth and (Batt.Eff) of Discharge (DOD). 4.4 Divide the answer obtained in item 4.3 by the nominal battery voltage. 4.5 Multiply the answer obtained in item 4.4 by days of autonomy (the number of days that you need the system to operate when there is no power produced by PV panels) to get the required Ampere-hour capacity of deep-cycle battery. Battery Capacity (Ah) = Total Watt-hours per day used by appliances x Days of autonomy (Inv.Eff xBatt.Eff xDOD x nominal battery voltage)

Inverter sizing 5. Inverter sizing: An inverter is used in the system where AC power output is needed. The output rating of the inverter should never be lower than the total watt of appliances. The inverter’s input voltage must have the same nominal voltage as the battery bank. Assumptions that are needed : 5.1.Inverter efficiency: It is a percentage that is less than one which is considered according to the loss inside the electronics components of the inverter. 5.2. Safety factor: For stand-alone systems, the inverter must be large enough to handle the total amount of Watts you will be using at one time. The inverter size should be 25% bigger than total Watts of appliances. In case of appliance type is motor or compressor, then the inverter should be capable to handle the surge current during starting.

Exercise A house has the following electrical appliance use: One15 Watt fluorescent lamp with electronic ballast used 6 hours per day. One 50 Watt fan used for 3 hours per day. One 80 Watt refrigerator that runs 24 hours per day with compressor run 16 hours and off 8 hours. The system will be powered by 12 Vdc, 130Wp PV module (Isc = 8.2 A @STC) Assumptions: Inverter efficiency = 0.9, safety factor = 1.25 Battery efficiency = 0.8 Depth of discharge = 0.75 Charge controller efficiency = 0.9, safety factor = 1.2 Safety factor of the PV modules = 1.2 PSH = 3.9 h/day

Energy consumption calculation Inverter design Determine power consumption demands: Total appliance use = (15 W x 6 hours) + (50 W x 3 hours) + (80 W x 16 hours)  = 1520 Wh/day 5. Inverter design: Total Watts of all appliances = 15 + 50 + 80 = 145W For safety, the inverter should be considered 25% bigger size. Therefore, Inverter size = 145*1.25 = 181.25W. The inverter size should be about 181.25W or greater according to the availability in the market. Therefore, a 200W inverter is chosen .

Battery sizing 4. Battery sizing Total appliance use = ((15 W x 6 hours)+(50 W x 3 hours)+(80 W x 16 hours) = 1520 Wh Daily energy (DC side), EBattery = Eload / (Inv.eff x Discharging Batt.eff) = 1520/(0.9x0.9) = 1876Wh Nominal battery voltage = 12 V Days of autonomy = 3 days Battery capacity = [1876/ (0.75 x 12)] x 3 = 625 Ah required.                                                 So, the battery bank should be rated at 12 V 625.5Ah for 3 days of autonomy. Using a battery unit rated at 12V 100 Ah, 7 battery units will be utilized to build the battery bank.

PV modules sizing 2. PV modules sizing Daily total energy needed from PV modules (EPV) = 1520/(0.9x0.8x0.9) = 2346Wh Total Wp of PV modules needed =EPV / PSH = 2346 / 3.9 = 606.2 W A safety factor of 1.2 is needed to compensate the module losses. Therefore, the total power is 606.2 x 1.2 = 727.44WP Number of PV modules needed = 727.44 / 130 = 5.6 modules. Actual requirement = 6 modules (there are no fractions in PV modules) Because the system voltage of each module is 12V and we have 12V battery. Therefore the 6 modules will be connected in parallel. So this system should be powered by at least 6 modules of 130 Wp/12V PV module with a total peak power of 780Wp.

The complete system = = ~ = Loads PV 12V/60A 12V/230V 50Hz 200W Charge Controller Inverter PV = = ~ Loads = 12V/60A 12V/230V 50Hz 200W 130W/12V X6 Battery 12V/700Ah

Q & A