How to Design Solar PV System
How to Design Solar PV System & What is a solar PV system?
A solar photovoltaic system or Solar power system is one renewable energy system that uses PV modules to convert sunlight into electricity. The electricity generated can be either stored or used directly, fed back into the grid line, or combined with one or more other electricity generators or more renewable energy sources. The solar PV system is a very reliable and clean source of electricity that can suit a wide range of applications such as residence, industry, agriculture, livestock, etc.
Major system components
Solar PV system includes different components that should be selected according to your system type, site location, and applications. The major components for solar PV systems are solar charge controllers, inverters, battery banks, auxiliary energy sources, and loads (appliances).
��� PV module � converts sunlight into DC electricity. ��� A solar charge controller � regulates the voltage and current coming from the PV panels going to the battery and prevents battery overcharging and prolongs the battery life. ��� The inverter � converts the DC output of PV panels or wind turbines into a clean AC current for AC appliances or fed back into the grid line. ��� Battery � stores energy for supplying to electrical appliances when there is a demand. ��� Load � is electrical appliances that are connected to solar PV systems such as lights, radio, TV, computer, refrigerator, etc. ��� Auxiliary energy sources - are diesel generators or other renewable energy sources.
Solar PV system sizing
1. 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:
1.1 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.
1.2 Calculate the total Watt-hours per day needed from the PV modules.
Multiply the total appliance Watt-hours per day times 1.3 (the energy lost in the system) to get the total Watt-hours per day which must be provided by the panels.
2. Size the PV modules
Different sizes of PV modules will produce different amounts of power. To find out the sizing of PV module, the total peak watt produced needs. The peak watt (Wp) produced depends on the size of the PV module and the climate of the site location. We have to consider �the panel generation factor� which is different in each site location. For Thailand, the panel generation factor is 3.43. To determine the sizing of PV modules, calculate as follows:
2.1 Calculate the total Watt-peak rating needed for PV modules
Divide the total Watt-hours per day needed from the PV modules (from item 1.2) by 3.43 to get the total Watt-peak rating needed for the PV panels needed to operate the appliances.
2.2 Calculate the number of PV panels for the system
Divide the answer obtained in item 2.1 by the rated output Watt-peak of the PV modules available to you. Increase any fractional part of the result to the next highest full number and that will be the a number of PV modules are required.
The result of the calculation is the minimum number of PV panels. If more PV modules are installed, the system will perform better and battery life will be improved. If fewer PV modules are used, the system may not work at all during cloudy periods and battery life will be shortened.
3. Inverter sizing
An inverter is used in the system where AC power output is needed. The input rating of the inverter should never be lower than the total watt of appliances. The inverter must have the same nominal voltage as your battery. 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 25-30% bigger than the total Watts of appliances. In the case of the appliance, type is motor or compressor then inverter size should be minimum 3 times the capacity of those appliances and must be added to the inverter capacity to handle surge current during starting. For grid-tie systems or grid-connected systems, the input rating of the inverter should be the same as the PV array rating to allow for safe and efficient operation.
4. Battery sizing
The battery type recommended for use in a solar PV system is a deep cycle battery. Deep cycle battery is specifically designed to be discharged to a low energy level and rapid recharged or cycle charged and discharged day after day for years. The battery should be large enough to store sufficient energy to operate the appliances at night and on cloudy days. To find out the size of the battery, calculate as follows:
4.1 Calculate total Watt-hours per day used by appliances. 4.2 Divide the total Watt-hours per day used by 0.85 for battery loss. 4.3 Divide the answer obtained in item 4.2 by 0.6 for depth of discharge. 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 with 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 the deep-cycle battery. Battery Capacity (Ah) = Total Watt-hours per day used by appliances x Days of autonomy (0.85 x 0.6 x nominal battery voltage)
5. Solar charge controller sizing
The solar charge controller is typically rated against Amperage and Voltage capacities. Select the solar charge controller to match the voltage of the PV array and batteries and then identify which type of solar charge controller is right for your application. Make sure that the solar charge controller has enough capacity to handle the current from the PV array.
The sizing of the controller depends on the total PV input current which is delivered to the controller and also depends on PV panel configuration (series or parallel configuration).
According to standard practice, the sizing of the solar charge controller is to take the short circuit current (Isc) of the PV array and multiply it by 1.3
Solar charge controller rating = Total short circuit current of PV array x 1.3
Example: A house has the following electrical appliance usage:
One 18 Watt fluorescent lamp with electronic ballast is used 4 hours per day. One 60 Watt fan is used for 2 hours per day. One 75 Watt refrigerator that runs 24 hours per day with a compressor run 12 hours and off 12 hours. The system will be powered by a 12 Vdc, 110 Wp PV module.
1. Determine power consumption demands
Total appliance use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 24 x 0.5 hours) = 1,092 Wh/day Total PV panels energy needed = 1,092 x 1.3 = 1,419.6 Wh/day.
2. Size the PV panel
2.1 Total Wp of PV panel capacity needed = 1,419.6 / 3.4 = 413.9 Wp 2.2 Number of PV panels needed = 413.9 / 110 = 3.76 modules Actual requirement = 4 module
So this system should be powered by at least 4 modules of 110 Wp PV module.
3. Inverter sizing
Total Watt of all appliances = 18 + 60 + 75 = 153 W For safety, the inverter should be considered 25-30% bigger size. The inverter size should be about 190 W or greater.
4. Battery sizing
Total appliances use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours) Nominal battery voltage = 12 V Days of autonomy = 3 days Battery capacity = [(18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours)] x 3 (0.85 x 0.6 x 12) Total Ampere-hours required 535.29 Ah
So the battery should be rated 12 V 600 Ah for 3-day autonomy. 5. Solar charge controller sizing
PV module specification Pm = 110 Wp Vm = 16.7 Vdc Im = 6.6 A Voc = 20.7 A Isc = 7.5 A Solar charge controller rating = (4 strings x 7.5 A) x 1.3 = 39 A
So the solar charge controller should be rated 40 A at 12 V or greater. Conclusion:- Install a solar system and save as much as 50% off the cost of electricity.