How to Design Solar PV System
What is solar PV system?
Solar photovoltaic system or Solar power system is one of renewable energy system which uses PV modules to convert sunlight into electricity. The electricity generated can be either stored or used directly, fed back into grid line or combined with one or more other electricity generators or more renewable energy source. Solar PV system is 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 system are solar charge controller, inverter, battery bank, auxiliary energy sources and loads (appliances).
PV module converts sunlight into DC electricity.
Solar charge controller regulates the voltage and current coming from the PV panels going to
battery and prevents battery overcharging and prolongs the battery life.
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 PV modules.
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 PV modules
Different size of PV modules will produce different amount of power. To find out the sizing of PV module, the total peak watt produced needs. The peak watt (Wp) produced depends on size of the PV module 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 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 result to the next highest full number and that will be the
number of PV modules required.
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 total Watts of appliances. In case of 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 same as PV array rating to allow for safe and efficient operation.
4. 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 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 PV array and batteries and then identify which type of solar charge controller is right for your application. Make sure that solar charge controller 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 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
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 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 modules
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.
How to Set Up a Solar Power Plant
Setting up a solar power system for your home or business involves many steps. The first phase is about making decisions. Begin by determining the size of the project and how much energy you need, then choosing an appropriate type of panel that will work best in your area. Next comes selecting where on your property you want to mount it, as well as what kind of mounting structure you’ll use. Finally, decide whether you’re going with grid-tied or off-the-grid systems.
The second phase includes designing the electrical wiring needed to connect all components. This can be done by hand using wire nuts and connectors, but most people prefer to hire professionals specializing in this field.
The third stage consists of installing panels at their chosen location. Once they are installed, panels must be connected to each other and the rest of the circuit through junction boxes. Panels should also have wires attached to them so they can be wired into the main breaker box.
After everything has been completed, panels must be tested before being hooked up to the utility company’s meter. If there are any problems during testing, panels may require additional repairs before installation can continue. Once the entire setup process is complete, panels begin producing electricity immediately.
The amount of time required to produce enough energy depends on several factors, including the number of panels used, the efficiency rating of those panels; the weather conditions; and the distance between panels and the sun. However, once production begins, panels usually generate more than enough energy to meet daily needs.
How Much Does It Cost to Build a Solar Power Plant?
Cost depends upon several factors such as location, design, materials, labor, financing options, incentives offered by government agencies, and utilities. The following is an overview of the costs associated with building a photovoltaic system:
Site preparation
This includes clearing land for construction, installing utility services if needed, grading roads or other access routes, etc. Costs vary depending on local regulations and requirements.
Design
Solar engineers will determine what type of PV technology best suits your needs. They may also recommend additional equipment that can be integrated into the design, including inverters, batteries, charge controllers, and controls systems. Depending on the size of the project, they may provide preliminary estimates of total installed capacity and annual energy production.
Materials
Cost of panels varies based on the manufacturer but typically ranges from $0.50-$5 per watt. The cost of mounting hardware and installation labor are included in this estimate. In addition, some manufacturers offer rebates and tax credits which reduce the overall price of the system.
Financing Options
Many different types of loans are available to finance projects, ranging from bank loans to leasing arrangements. Some companies specialize in providing these products, while others work directly with banks and credit unions. It’s essential to understand all of the terms involved before signing any contracts.
Utility Rebate Programs
Many states have programs explicitly designed to encourage homeowners to install renewable energy sources like solar. These programs usually include financial assistance along with technical support.
The average cost for installing and maintaining a residential photovoltaic system is $3.50 per watt installed. This includes labor, materials, permits, inspections, taxes, financing fees, etc., but excludes any incentives that may be available.
How Long Does It Take to Build a Solar Power Plant?
It generally takes about 6 months, but the time can vary, to construct a small-scale system. Large commercial projects can take anywhere from 12 – 18 months. Construction time includes planning, permitting, site preparation, hardware installation, wiring, plumbing, foundation, roofing, insulation, framing, drywall, painting, finishing touches like landscaping and fencing. Labor hours vary greatly based on region, type of material being used, the complexity of the job, and the number of workers involved.
Conclusion
The future of energy looks bright for solar power. As technology improves, prices drop, and demand increases, we expect this trend to continue. In fact, according to International Energy Agency, global investment in renewables has increased fivefold since 2000. By 2050, IEA expects total annual investment in clean technologies to reach US$400 billion annually. This would result in cumulative capacity additions of around 400 GW worldwide.
