Design and installation of Solar PV Systems
Today our modern world needs energy for various day to day applications such as industrial manufacturing, heating, transport, agricultural, lightning applications, etc. Most of our energy need is usually satisfied by non-renewable sources of energy such as coal, crude oil, natural gas, etc. But the utilization of such resources has caused a heavy impact on our environment.
Also, this form of energy resource is not uniformly distributed on the earth. There is an uncertainty of market prices such as in the case of crude oil as it depends on production and extraction from its reserves. Due to the limited availability of non-renewable sources, the demand for renewable sources has grown in recent years.
Solar energy has been at the center of attention when it comes to renewable energy sources. It is readily available in an abundant form and has the potential to meet our entire planet&#;s energy requirement. The solar standalone PV system as shown in fig 1 is one of the approaches when it comes to fulfilling our energy demand independent of the utility. Hence in the following, we will see briefly the planning, designing, and installation of a standalone PV system for electricity generation.
Planning of a Standalone PV system
Site assessment, surveying & solar energy resource assessment:
Since the output generated by the PV system varies significantly depending on the time and geographical location it becomes of utmost importance to have an appropriate selection of the site for the standalone PV installation. Thus, the following points must be considered for the assessment and selection of locations for installation.
Minimum Shade: It must be made sure that the selected site either at rooftop or ground should not have shades or should not have any structure that intercepts the solar radiation falling on the panels to be installed. Also, make sure that there won&#;t be any structural construction soon surrounding the installation that might cause the problem of shading.
Surface Area: The surface area of the site at which the PV installation is intended should be known, to have an estimation of the size and number of panels required to generate the required power output for the load. This also helps to plan the installation of inverter, converts, and battery banks.
Rooftop: In the case of the rooftop installation the type of roof and its structure must be known. In the case of tilt roofs, the angle of tilt must be known and necessary mounting must be used to make the panels have more incidents of solar radiation i.e. ideally the radiation angle must be perpendicular to the PV panel and practically as close as to 90 degrees.
Routes: Possible routes for the cables from an inverter, battery bank, charge controller, and PV array must be planned in a way that would have minimum utilization of cables and lower voltage drop in cables. The designer should choose between the efficiency and the cost of the system.
To estimate the output power the solar energy assessment of the selected site is of foremost significance. Insolation is defined as the measure of the sun&#;s energy received in a specified area over a period of time. You can find this data using a pyranometer, however, it is not necessary as you can find the insolation data at your nearest meteorological station. While assessing the solar energy the data can be measured in two ways as follows:
Kilowatt-hours per square meter per day (KWh/m2/day): It is a quantity of energy measured in kilowatt-hours, falling on square meter per day.
Daily Peak Sun Hours (PSH): Number of hours in a day during which irradiance averages to W/m2.
Peak sun hours are most commonly used as they simplify the calculations. Do not get confused with the &#;Mean Sunshine Hours&#; and &#;Peak Sun Hours&#; which you would collect from the meteorological station. The &#;Mean sunshine hours&#; indicates the number of hours the sunshine&#;s were as the &#;Peak sun hours&#; is the actual amount of energy received in KWh/m2/day. Amongst all months over a period of year use the lowest mean daily insolation value as it will make sure that the system will operate in a more reliable way when the sun is least due to unsuitable weather conditions.
Considerations for Standalone PV system
Calculation of Energy Demand
The size of the standalone PV system depends on the load demand. The load and its operating time vary for different appliances, therefore special care must be taken during energy demand calculations. The energy consumption of the load can be determined by multiplying the power rating (W) of the load by its number of hours of operation. Thus, the unit can be written as watt × hour or simply Wh.
Energy demand Watt-hour = Power rating in Watt × Duration of operation in hours.
Thus, the daily total energy demand in Wh is calculated by adding the individual load demand of each appliance per day.
Total energy demand Watt-hour = &#; (Power rating in Watt × Duration of operation in hours).
A system should be designed for the worst-case scenario i.e. for the day when the energy demand is highest. A system designed for the highest demand will ensure that the system is reliable. If the system meets the peak load demand it will meet the lowest demand. But designing the system for the highest demand will increase the overall cost of the system. On the other hand, the system will be fully utilized only during the peak load demand. So, we have to choose between cost and reliability of the system.
Inverter & Converter (Charge Controller) Ratings
For choosing the proper inverter both the input and output voltage and current rating should be specified. The inverter&#;s output voltage is specified by the system load, it should be able to handle the load current and the current taken from the battery bank. Based on the total connected load to the system the inverter power rating can be specified.
Let&#;s consider 2.5 kVA in our case, hence an inverter with power handling capacity having a size of 20-30% higher than the power running the load should be chosen from the market. In the case of motor load, it should be 3-5 times higher than the power demand of such an appliance. In the case of the converter, the charge controller is rated in current and voltage. Its current rating is calculated by using the short-circuit current rating of the PV module. The value of voltage is the same as the nominal voltage of batteries.
Converter and Charge Controller Sizing
The charge controller rating should be 125% of the photovoltaic panel short circuit current. In other words, It should be 25% greater than the short circuit current of solar panel.
Size of solar charge controller in amperes = Short-circuit current of PV × 1.25 (Safety factor).
For example, we need a 6 numbers each of 160W solar panels for our system. Following are the related date of PV panel.
Suppose the PV module specification are as follow.
PM = 160 WPeak
VM = 17.9 VDC
IM = 8.9 A
VOC = 21.4 A
ISC = 10 A
The required rating of solar charge controller is = (4 panels x 10 A) x 1.25 = 50 A
Now, a 50A charge controller is needed for the 12V DC system configuration.
Note: This formula is not applicable on MPPT Solar chargers. Please refer to the user manual or check the nameplate data rating for proper sizing.
Inverter Sizing
The size of Inverter should be 25% bigger than the total load due to losses and efficiency problem in the inverter. In other words, It should be rated 125% than the total load required in watts. For example, if the required wattage is W, than the size of inverter should be:
W x 125%
W x 1.25
Watts.
So we need a 3kW of inverter in case of W load.
Daily Energy Supplied to Inverter
Let us consider in our case the daily energy consumption by the load is Wh. Note that the inverter has its efficiency, thus the energy supplied to the inverter should be more than the energy used by the load, so the losses in the inverter can be compensated. Assuming 90% efficiency in our case, the total energy supplied by the battery to the inverter would be given as;
Energy supplied by the battery to the inverter input = / 0.90 = Wh/per day.
System Voltage
The inverter input voltage is referred to as the system voltage. It is also the overall battery pack voltage. This system voltage is decided by the selected individual battery voltage, line current, maximum allowable voltage drop, and power loss in the cable. Usually, the voltage of the batteries is 12 V so will be the system voltage. But if we need higher voltage it should be multiples of 12 V. i.e. 12 V, 24 V, 36 V, and so on.
By decreasing the current, power loss and voltage drop in the cable can be reduced, this can be done by increasing the system voltage. This will increase the number of batteries in the series. Therefore, one must choose between power loss and system voltage. Now for our case let us consider the system voltage of 24 V.
Sizing of the Batteries
While sizing the battery some parameters are needed to be considered as follows:
Depth of Discharge (DOD) of the battery.
Voltage and ampere-hour (Ah) capacity of the battery.
The number of days of autonomy (It is the number of days required to power up the whole system (backup power) without solar panels in case of full shading or rainy days. We will cover this part in our upcoming article) to get the needed Ah capacity of batteries.
Let us consider we have batteries of 12 V, 100 Ah with DOD of 70%. Thus, the usable capacity of the is 100 Ah × 0.70 = 70 Ah. Therefore, the charged capacity that is required is determined as follows;
Required charge capacity = energy supplied by the battery to the inverter input/system voltage
Required charge capacity = Wh/ 24 V = 125 Ah
From this, the number of batteries required can be calculated as;
No. of batteries required = Required charge capacity / (100 × 0.7)
No. of batteries required = 125 Ah / (100 × 0.7) = 1.78 (round off 2 batteries)
Thus, 2 batteries of 12 V, 100 Ah are required. But due to round off 140 Ah instead of 125 Ah is required.
Required charge capacity = 2 × 100Ah × 0.7 = 140 Ah
Therefore, two 12 V, 100 Ah batteries in parallel to meet the above charge capacity. But as the individual battery is of 12 V, 100 Ah only and the system voltage requirement is of 24 V we need to connect two batteries in series to get the system voltage of 24 V as shown in figure 2 below:
So, in total there will be four batteries of 12 V, 100 Ah. Two connected in series and two connected in parallel.
Also, the required capacity of batteries can be found by the following formula.
Sizing of the PV Array
Different sizes of PV modules available in the market produce a different level of output power. One of the most common way to determine the sizing of the PV array is to use the lowest mean daily insolation (Solar irradiance) in peak sun hours as follows;
The total size of PV array (W) = (Energy demand per day of a load (Wh) / TPH) × 1.25
Where TPH is the lowest daily average peak sun hours of a month per year & 1.25 is the scaling factor. With this the number of PV modules Nmodules required can be determined as;
Nmodules = Total size of the PV array (W) / Rating of selected panels in peak-watts.
Suppose, in our case the load is Wh/per day. To know the needed total WPeak of a solar panel capacity, we use PFG factor i.e.
Total WPeak of PV panel capacity = / 3.2 (PFG)
= 931 WPeak
Now, the required number of PV panels are = 931 / 160W = 5.8.
This way, we need 6 numbers of solar panels each rated for 160W. You can find the exact number of solar panels by dividing the WPeak by other rating i.e. 100W, 120W 150W etc based on the availability.
Note: The value of PFG (Panel Generation Factor) is varying (due to climate and temperature changes) in different regions e.g, PFG in USA = 3.22, EU = 293, Thailand = 3.43 etc.
Moreover, the additional losses should be considered to find the exact panel generation factor (PGF). These losses (in %) occur due to :
Sunlight not striking the solar panel straight on (5%)
Not receiving energy at the maximum power point (excluded in case of MPPT charge controller). (10%)
Dirt on solar panels (5%)
PV panels aging and below specification (10%)
Temperature above 25°C (15%)
Related Post Types of Solar Panels and Which Solar Panel Type is Best?
Sizing of the Cables
The sizing of the cables depends on many factors such as maximum current carrying capacity. It should have a minimum voltage drop and have minimum resistive losses. As the cables would be placed in the outdoor environment it should be water-resistant and ultraviolet.
The cable must behave minimum voltage drop typically less than 2% as there is an issue of voltage drop in low voltage system. Under sizing of the cables will result in energy loss and sometimes can even lead to accidents. whereas the oversizing is not economically affordable. The cross-sectional area of the cable is given as;
A = (ρIML / VD) × 2
Where
ρ is the resistivity of the conducting wire material (ohm-meters).
L is the length of cable.
VD is the maximum permissible voltage drop.
IM is the maximum current carried by the cable.
In addition, you may use this cable and wire size calculator. Also, use the proper sized circuit breaker and rated plugs and switches.
Lets have a solved example for the above example.
Example:
Suppose we have the following electrical load in watts where we need a 12V, 120W solar panel system design and installation.
An LED lamp of 40W for 12 Hours per day.
A refrigerator of 80W for 8 Hours per day.
A DC Fan of 60W for 6 Hours per day.
Now let&#;s find the number of solar panels, rating and sizing of charge controller, inverter and batteries etc.
Finding the Total Load
Total Load in Wh / day
= (40W x 12 hours) + (80W x 8 hours) + (60W x 6 hours)
= Wh / per day
The required wattage by Solar Panels System
= Wh x 1.3 &#; (1.3 is the factor used for energy lost in the system)
= Wh/day
Finding the Size and No. of Solar Panels
WPeak Capacity of Solar Panel
= Wh /3.2
= 601.25 WPeak
Required No of Solar Panels
= 601.25 / 120W
No of Solar Panels = 5 Solar Panel Modules
This way, the 5 solar panels each of 120W will capable to power up our load requirements.
Find the Rating and Size of Inverter
As there is only AC loads in our system for specific time (i.e. no additional & direct DC load connected to the batteries) and our total required wattage is:
= 40W + 80W + 60W
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= 180W
Now, the rating of inverter should be 25% greater than the total load due to losses in the inverter.
= 180W x 2.5
Inverter Rating & Size = 225 W
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Find the Size, Rating & No of Batteries
Our load wattage and operational time in hours
= (40W x 12 hours) + (80W x 8 hours) + (60W x 6 hours)
Nominal Voltage of Deep Cycle Battery = 12V
Required Days of Autonomy (Power by batteries without solar panel power) = 2 days.
[(40W x 12 hours) + (80W x 8 hours) + (60W x 6 hours) / (0.85 x 0.6 x 12V)] x 2 days
The required capacity of batteries in Ampere-hour = 483.6 Ah
This way, we need a 12V 500Ah battery capacity for 2 days of autonomy.
In this case, we may use 4 number of batteries each of 12 V, 125Ah connected in parallel.
If the available battery capacity is 175Ah, 12 V, we may use 3 number of batteries. You can get the exact number of batteries by dividing the required capacity of batteries in Ampere-hour by the available battery Ah rating.
Required Number of batteries = Required capacity of batteries in Ampere-hour / Available battery Ah rating
Find The Rating and Size of Solar Charge Controller
The charge controller should be 125% (or 25% greater) than the solar panel short circuit current.
Size of solar charge controller in Amp = Short circuit current of PV × 1.25
PV module specification
PM = 120 WPeak
VM = 15.9 VDC
IM = 7.5 A
VOC = 19.4 A
ISC = 8.8 A
The required rating of solar charge controller is = (5 panels x 8.8 A) x 1.25 = 44 A
So you can use the next nearest rated charge controller which is 45A.
Note that this method can&#;t be used to find the exact size of MPPT solar chargers. Please refer to the user manual provided by the manufacturer or see the nameplate rating printed on it.
Finding the Cable, CB, Switches & Plug Ampacity
Use the following tools and explanatory posts with charts to find the exact amperage rating of wire and cables, switches & plugs and circuit breakers.
Conclusion
The standalone PV system is an excellent way to utilize the readily available eco-friendly energy of the sun. Its design and installation are convenient and reliable for small, medium, and large-scale energy requirements. Such a system makes the availability of electricity almost anywhere in the world, especially in remote areas. It makes the energy consumer independent of the utility and other sources of energy such as coal, natural gas, etc.
Such a system can have no negative impact on our environment and can provide energy for long periods after its installation. The above systematic design and installation provide useful guidelines for our need for clean and sustainable energy in the modern world.
By: M. Phansopkar
Updated By: Electrical Technology
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Designing a solar system is a complex task that involves various challenges, such as accurately determining the energy demand, selecting appropriate components, choosing the right solar panels, and optimising the system for efficiency and affordability. Getting the design right is crucial for the system's performance, safety, and economic viability.
If you&#;ve been wondering where to start with solar panels for your home or business, This article will guide you through the essential steps and considerations of how to design a solar PV system.
A solar photovoltaic system (PV system), or solar power system, is a 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 renewable energy sources.
It&#;s a reliable and clean source of electricity that can suit a wide range of applications such as residence, industry, agriculture, livestock, etc.
The first thing to know when answering &#;What solar panel system do I need?&#; is learning about the individual components that constitute it. A solar PV system consists of several components, each serving a specific function to harness solar energy, convert it into usable electrical power, and deliver it for use or storage.
Understanding the different solar system components and their roles is essential when designing one for your unique needs. It helps in selecting the appropriate equipment, optimising the solar system for maximum efficiency, and ensuring its smooth operation.
Solar panels, or photovoltaic modules, are the primary components that convert sunlight into direct current (DC) electricity. Each panel consists of multiple solar cells made of semiconductor materials, usually silicon, that generate electric charges when exposed to sunlight.
Critical considerations for solar panels include their efficiency, capacity (measured in watts peak, Wp), and the panel generation factor (actual electrical output vs. potential output), which varies by location. New design solar panels can reach efficiencies of 23%.
The solar charge controller regulates the voltage and current coming from the solar panels to the battery and prevents overcharging, reverse current flow, and battery drainage, thus prolonging the battery life and ensuring the safety and efficiency of the solar system.
Critical considerations for the solar charge controller include its capacity (measured in amperes), type (PWM or MPPT), and compatibility with the PV array and battery voltage.
The inverter converts the DC output of the PV panels or battery into alternating current (AC) suitable for AC appliances or feeding back into the grid. It&#;s a vital component as most household appliances and the grid operate on AC power.
Critical considerations for the inverter include its capacity (measured in watts), efficiency, and compatibility with the system voltage and grid requirements.
The battery stores energy generated by the solar panels for use when there is a demand, such as at night or during cloudy periods. Deep cycle batteries are recommended for solar PV systems as they are designed for repeated charge and discharge cycles. Depending on your exact location, batteries could be a vital component of your solar system in countries like the UK with inclement weather.
Critical considerations for the battery include its capacity (measured in ampere-hours, Ah), voltage, depth of discharge, efficiency, cycle life and maximal charging discharging power, and days of autonomy (the number of days the system can operate without solar power).
Auxiliary energy sources, such as diesel generators or other renewable energy sources, provide backup power when the solar PV system cannot meet the demand. They ensure continuous power supply during extended cloudy periods or peak demand times.
Critical considerations for auxiliary energy sources include their capacity, fuel efficiency, and integration with the solar PV system.
To design an efficient and effective solar PV system, it&#;s essential to accurately determine the energy demand that will be required.
Simply, this involves calculating the total power and energy consumption of all the loads that need to be supplied by the solar PV system. However, it may be more complex than you expect at first. The following will provide you with a complete breakdown of what to consider:
1. Calculate Total Watt-hours per Day for Each Appliance Used:
List all the appliances and devices that will be powered by the solar PV system and determine their total power consumption per day in watts. To be safe, you should design your system with the worst-case scenario, i.e., when demand will be at its highest.
This will ensure you&#;ll never be stranded without enough power for your needs.
Multiply the power consumption rating of each appliance (power rating in W) by its daily usage hours to get the watt-hours per day for each appliance. Add the watt-hours needed for all appliances together to get the total watt-hours per day, which must be delivered to the appliances.
Watt-hours per appliance (Wh) = power rating (W) × hours (h)
Total Energy Demand Watt-hour = Sum Wh for all appliances
2. Calculate the total watt-hours per day needed from the PV modules:
To be safe, you need to compensate for the potential energy loss in the system due to minor inefficiencies or environmental conditions. Typically, a factor of 1.3 is used as a rule of thumb. So, multiply the total appliance watt-hours by this amount to get the total energy required from the PV system.
In reality, this factor is determined by the efficiency of your panels, temperature, shading, dust & debris, conversion/transmission losses, and battery charging/discharging losses.
For example, if a household has the following appliances:
Appliance
Power Rating (W)
Duration of Operation (Hours)
LED Light
10
5
Refrigerator
150
24
TV
100
4
Fan
50
6
The total energy demand watt-hour would be calculated as follows:
Total Energy Demand Watt-hour = (10W * 5h) + (150W * 24h) + (100W * 4h) + (50W * 6h) = 50Wh + Wh + 400Wh + 300Wh = Wh or 4.35kWh
Therefore, the daily energy demand for this household is 4.35kWh. To account for energy loss in the system, multiply by 1.3:
Total Watt-hours per Day Needed from PV Modules = 4.35kWh * 1.3 = 5.655kWh
It's essential to select an inverter with a power rating that suits the system's needs, typically being 25-30% larger than the total wattage of appliances and three times the capacity for motors or compressors.
Different types of inverters include on-grid, off-grid, and microinverters, each suitable for different applications. For grid-tied systems, the inverter's input rating should match the PV array rating. Advanced 'smart inverters' allow two-way communication between the inverter and the electrical utility, which can help balance supply and demand, reduce costs, and ensure grid stability.
Lastly, it's essential to include proper protection mechanisms, such as fuses, RCDs (Residual Current Devices), and MCBs (Miniature Circuit Breakers), to ensure the system's safety.
To select an appropriate charge controller, you must consider the total wattage of your solar power system and the battery bank voltage. For this, we can use the formula Amps x Volts = Watts, derived from Ohm's law.
For instance, a 4,000-watt solar panel system combined with a 24V battery bank results in 166.67 amps. This is the minimum amperage that your charge controller should be able to handle, but it&#;s always a good idea to choose a higher-amp model to have a margin of safety.
Typically, charge controllers are rated based on their amperage and voltage capacities. Ensure that the chosen charge controller matches the PV array and battery voltages and can handle the PV array's current. For series charge controllers, the size depends on the total PV input current delivered to the controller and the PV panel configuration (series or parallel).
As a rule of thumb, the solar charge controller rating can be calculated by taking the PV array's total short circuit current (Isc) and multiplying it by 1.3:
Solar charge controller rating = Total short circuit current of PV array x 1.3
For example, if the total short circuit current of your PV installation array is 20A, the solar charge controller rating should be 20A x 1.3 = 26A. Therefore, a charge controller rated at least 26A would be suitable for this application.
You can get the total short circuit of your PV array by checking the individual Isc of each panel and multiplying it by the total number of strings panels.
Sizing the battery for an off-grid solar PV system is crucial to ensure there is enough power to run the required load for 24 hours, as well as fully recharge the battery each day. It&#;s recommended to use deep cycle batteries, which are designed for repeated discharging and recharging.
To size the battery, follow these steps:
Calculate the total Watt-hours used by appliances daily.
Adjust for battery loss by dividing the total Watt-hours by 0.85.
Adjust for depth of discharge by dividing the result from step 2 by 0.6.
Divide the result from Step 3 by the nominal battery voltage.
Multiply the result from step 4 by the days of autonomy (the number of days the system needs to operate without power from the PV panels) to get the required Ampere-hour (Ah) capacity.
Formula:
Battery Capacity (Ah) = (Total Watt-hours per day x Days of autonomy) / (0.85 x 0.6 x nominal battery voltage)
As the crux of your solar PV system, correctly sizing the PV array is perhaps the single most important factor. The PV array size can be determined using the lowest mean daily insolation in peak sun hours and the energy demand per day.
The formula for calculating the total size of the PV array (W) is:
Total size of PV array (W) = (Energy demand per day (Wh) / TPH) × 1.25
Where TPH is the lowest daily average peak sun hours of a month per year, and 1.25 is the scaling factor. The number of PV modules required can be determined by dividing the total size of the PV array (W) by the rating of the selected panels in peak watts. Typical solar panels today have a peak wattage of between 300W and 450W per panel.
The number of modules = Total size of the PV array (W) / Rating of selected panels in peak-watts
Additional losses due to factors like sunlight angle, dirt on panels, temperature above 25°C, and panel aging should be considered to find the exact panel generation factor (PGF).
For example, if your daily energy need is Wh, then:
Total WPeak of PV panel capacity = Energy demand per day / PGF = Wh / 2.4 = WPeak
Where 2.4 is a typical PGF value for the UK.
If you consider using 400W panels, then:
Number of panels = WPeak / 400W = 4 panels (rounded up).
Optimal cable sizing is crucial for maintaining minimum voltage drop and resistive losses while ensuring safety and economic affordability.
The cable cross-sectional area (A) can be calculated using the formula: A = (ρIML / VD) × 2
Where:
ρ is the wire material resistivity
I is the maximum current
M is the maximum current carried by the cable
L is the cable length
VD is the maximum permissible voltage drop.
It's also essential to select the proper size circuit breaker, rated plugs, and switches to avoid energy loss and accidents. You&#;ll find online calculators that may help you make precise calculations.
While many think designing a solar system is as simple as finding the best solar panel, it&#;s a process that actually requires meticulous planning and a comprehensive understanding of various components and factors. A well-designed system ensures efficiency, safety, and cost-effectiveness. Following the guidelines and considerations discussed in this article, you can design a solar panel system that meets your unique needs and contributes to a more sustainable future.
If you are looking for more details, kindly visit Customized PV Module.