Efficiency Mppt

Efficiency Mppt

« Previous12345Next »

Guide Manual of design PV Solar System

PV Solar 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 system are solar regulator, solar power inverter, battery bank, auxiliary energy sources and loads (appliances).
  •   solar panel – converts sunlight into DC electricity.
  •   solar regulator – regulates the voltage and current coming from the PV panels going to
      battery and prevents battery overcharging and prolongs the battery life.
  •   solar power inverter – converts DC output of PV panels or wind turbine into a clean AC current for AC
      appliances or fed back into grid line.
  •   Battery – stores energy for supplying to electrical appliances when there is a demand.
  •   Load – is electrical appliances that connected to solar PV system such as lights, radio, TV, computer,
      refrigerator, etc.
  •   Auxiliary energy sources – is diesel generator 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 total Watt-hours per day needed from the solar panels.
            Multiply the total appliances 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 solar panels
Different size of solar panels will produce different amount of power. To find out the sizing of solar panel, the total peak watt produced needs. The peak watt (Wp) produced depends on size of the solar panel and climate of site location. We have to consider "panel generation factor" which is different in each site location. For Thailand, the panel generation factor is 3.43. To determine the sizing of solar panels, calculate as follows:
     2.1 Calculate the total Watt-peak rating needed for solar panels
           Divide the total Watt-hours per day needed from the solar panels (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 solar panels available
           to you. Increase any fractional part of result to the next highest full number and that will be the
           number of solar panels required.
Result of the calculation is the minimum number of PV panels. If more solar panels are installed, the system will perform better and battery life will be improved. If fewer solar panels are used, the system may not work at all during cloudy periods and battery life will be shortened.

3. solar power inverter sizing
An solar power inverter is used in the system where AC power output is needed. The input rating of the solar power inverter should never be lower than the total watt of appliances. The solar power inverter must have the same nominal voltage as your battery.
For stand-alone systems, the solar power inverter must be large enough to handle the total amount of Watts you will be using at one time. The solar power inverter size should be 25-30% bigger than total Watts of appliances. In case of appliance type is motor or compressor then solar power inverter size should be minimum 3 times the capacity of those appliances and must be added to the solar power inverter capacity to handle surge current during starting.
For grid tie systems or grid connected systems, the input rating of the solar power inverter should be same as PV array rating to allow for safe and efficient operation.

4. PV Solar System Battery sizing
The battery type recommended for using in solar PV system is deep cycle battery. Deep cycle battery is specifically designed for to be discharged to 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 cloudy days. To find out the size of 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 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 regulator sizing
The solar regulator is typically rated against Amperage and Voltage capacities. Select the solar regulator to match the voltage of PV array and batteries and then identify which type of solar regulator is right for your application. Make sure that solar regulator has enough capacity to handle the current from PV array.
For the series charge controller type, the sizing of 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 solar regulator is to take the short circuit current (Isc) of the PV array, and multiply it by 1.3
solar regulator rating = Total short circuit current of PV array x 1.3
Remark: For MPPT charge controller sizing will be different. (See Basics of MPPT Charge Controller)

Example: A house has the following electrical appliance usage:

One 18 Watt fluorescent lamp with electronic ballast used 4 hours per day.
One 60 Watt fan used for 2 hours per day.
One 75 Watt refrigerator that runs 24 hours per day with compressor run 12 hours and off 12 hours.
The system will be powered by 12 Vdc, 110 Wp solar panel.

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 modules
          So this system should be powered by at least 4 modules of 110 Wp solar panel.

3. solar power inverter sizing
    Total Watt of all appliances = 18 + 60 + 75 = 153 W
    For safety, the solar power inverter should be considered 25-30% bigger size.
    The solar power inverter size should be about 190 W or greater.

4. PV Solar System 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 regulator sizing
    solar panel specification
    Pm = 110 Wp
    Vm = 16.7 Vdc
    Im = 6.6 A
    Voc = 20.7 A
    Isc = 7.5 A
    solar regulator rating = (4 strings x 7.5 A) x 1.3 = 39 A
    So the solar regulator should be rated 40 A at 12 V or greater.

About the Author

Solar China

Solar powered shed setup UK - MPPT Upgrade