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  Aug 6, 2021   

On-Grid Solar Energy System: Design Guide

On-Grid Solar Energy System: Design Guide

On-grid solar energy systems are the popular choice in places with conventional grid connectivity.
Grid-connected solar energy systems offer consumers an opportunity to be prosumers i.e. to produce, use and export the surplus generated solar energy to the local utility grid connected.

Consumers are often amused about “Whether this grid-connected solar energy system is sufficient enough to cater for our needs”? 
Can we export the surplus energy produced to the utility grid-connected? 
The answer to the above query is “YES”.  The solar energy system is capable enough to cater to our energy needs and to export the surplus energy generated using a net metering system.
The only requirement to fulfil this is an effective design solution that can meet our energy demand.
To avail of the series of economic benefits, the solar energy system offers in its 25 years lifespan is an effective design solution and little maintenance against the environmental factors!

ON-Grid Solar Energy System: Components

To start with designing steps, first let us understand the major components of the grid connected solar system.

  1. Solar panel
  2. Inverter
  3. Module mounting structure
  4. AC distribution box
  5. Earthing & lightning arrestor system
  6. Cables and other BoS items
  7. Net metering system
ON-Grid Solar Energy System: Components

Rooftop On-Grid Solar Energy System – Design Criteria:

Rooftop On-Grid Solar Energy System - Design Criteria

1. Available rooftop area:
Before installing a solar plant at your location, one must check the shadow-free area available.  According to the thumb rule, 1 kWp of solar PV plant requires approximately 100Sqft of shadow-free area. 

How can I calculate the shadow-free area at my location?
Don’t worry, our sales team will help you out with the site survey report, satellite image and measurements on the hand sketch and calculate the feasible area available.
For example, if the roof is 20 ft * 15ft then the area is 300 square feet. For this 300 Sq ft. area, we can install a ~ 3 kWp solar plant.
For a high capacity monocrystalline solar module, a shadow-free area of 80 Sq ft is sufficient for a 1kWp plant.

2. Energy requirement of the house/building:
Once you identify the feasible shadow-free rooftop area, the next step is to calculate your energy requirement. 
One can analyse the previous 12 months of electricity bills to identify the energy needs.

Follow the below steps to calculate the energy requirement:

  • Note down the monthly unit consumption of the house for the previous 12 months. 
  • Calculate the average of these 12 months.
Energy Requirement Calculator

Why do we need to calculate the average?

As we know, our energy requirement varies with the season. In summer the cooling appliances work all day long, whereas on the winter/rainy days they will be slightly in operation. 
During the winter season, one might need an air heater but most of the regions in India (except the extremely cold parts) don’t need an air heater.
So, if we calculate the solar plant capacity based on the season(summer/winter/rainy), it will not be a feasible option.

Let us take two cases:

  1. If we install a solar plant considering summer energy requirements, then a higher energy capacity solar plant will be estimated which is not an economically feasible option during the rainy/winter seasons. (As we know during the rainy/winter season energy requirement is generally less)
  2. If we consider installing a solar energy plant by considering the energy needs of the winter/rainy season then a lower capacity solar plant will be installed and this won’t be a feasible option during the summer season. (As energy requirement is high during summer).

Hence the average number of units is to be considered for optimum operation.
Now, the average consumption we have estimated as per the energy bills is 383 units.

  • Days in a month = 30
  • Daily consumption = 383/30 = 12.76 units.
  • We know 1 kWp solar plant generates average 4 units/day,
  • Solar plant capacity required = 12.76 /4 =3.19 kWp

Hence as per the estimated energy requirement of 383 units, a 3.19kWp of solar energy plant is sufficient for the particular location.

3. Sanctioned load:
Now, the next step is to identify the sanctioned load for the particular residential/commercial consumers.
Sanctioned load: This is the load allotted to the particular consumer by the local DISCOM and is mentioned in the electricity bill.
Before going for solar installation in a particular area, one needs to identify the sanctioned load as DISCOM in various states follows different policies.
For example, in states like Maharashtra and Delhi, solar plants cannot be installed beyond the sanctioned load capacity whereas in some states like Punjab it is 80% of the sanctioned load.
Now, according to our case study, the sanctioned load for the house is 3KW (The customer can install a higher capacity load plant by taking permission from the DISCOM).

4. Check the phase connection:
The next step is to determine the phase of the house i.e single or three-phase.
We need to check the phase of the house to select the proper inverter capacity, in the market single-phase inverter is available for the capacity of up to 5kW and a three-phase inverter above 5kW

Rooftop On-grid Solar Energy  System: Design Steps

Once all the criteria as discussed above are followed, the next step is to design a grid-tied solar energy system for the particular location.

The below six steps are followed to design an efficient grid connected solar energy system:

Grid Connected Solar Energy System

1. Panel Placing and Shadow Analysis:

  • One needs to do 3D shadow analysis using software like SolarLabs, SketchUp, Helioscope etc. to identify the obstructions on the building or in the surrounding that might cast shadows on the solar panels.
  • The next step is to design a solar energy system as per the estimated dimensions.
  • Once the design is ready, the next step is to identify the shadow-free area and install the solar panels accordingly.
  • Before installing the solar panel, one must ensure that no shadow falls on the location where panels are to be installed during the solar peak hours from 9 a.m to 4 p.m 
  • Install the panels in landscape or portrait mode and make sure sufficient space is left between the rows to avoid inter-row shading i.e. one panel does not cast any shadow on the panel behind and is easy for maintenance.
  • Determine the height of the structure as per the shadow-free space available. If modules come under the shadow area, then adjust the height accordingly to overcome it.
  • Now for the solar plant with a 3 kWp capacity, if we consider 335 Wp modules then,
  • No. of modules = 3000/335 = 8.955 i.e., 9 modules are needed.

Now, the next step is to install these 9 solar modules at the location. Here, we can connect 9 modules in series i.e. one string.

2. Inverter Selection: 

The  Solar inverter plays an important role in converting the direct current(DC) generated from the solar panel into the alternating current(AC). 
Most of the appliances at our home/building and the utility grid-connected operate on AC supply, hence selecting a proper size of the inverter to cater for our energy needs is an essential requirement.
String inverters prove to be an economical option for residential and commercial applications.
Suggestion: Choose an inverter from a reputed brand with a remote monitoring facility and inbuilt protection devices.
Here for our 3 kWp solar plant, we can use a 3 kW inverter.

FAQ: Can we connect a higher capacity solar plant with a lower capacity inverter? Do we need an inverter and solar plant of the same rating?
Yes, we can connect a solar plant with an inverter with a capacity less than solar panel capacity. 
As per the manufacturer recommendation, overloading up to 40% is permissible.
For example, solar energy systems with a 6 kWp capacity can be connected with a 5 kW inverter as 20 % overloading is permissible.

3. ACDB(AC Distribution Box):

The next task is to install an AC Distribution board (ACDB) with necessary SPDs, MCB and terminations.Make sure the box has sufficient Ingress Protection rating , for example for outdoors , IP65 is recommended.

4. Module Mounting Structure (MMS):

The mounting structure needs to resist environmental threats such as dust, rain etc., hence selecting a proper module mounting structure is an important task so as to keep the promise of operation of the solar panel for a long 25 year lifespan.

One must keep in mind the following point:

  1. Choose a structure that is strong enough and chemically operated well to avoid corrosion.
  2. For module mounting structure a galvanized iron is preferred
  3. Choose an MMS such that it can withstand a wind speed of 150km/hr.

 5. Cables:

To connect all the installed components a conventional cable selection is necessary:

  1. DC Cables selected must be tinned copper cross-linked polyolefin (XLPO) with sufficient current-carrying capacity.
  2. AC cables can be Copper/Aluminum cross-linked polyethylene cable (XLPE) cables depending on the losses and site conditions.
  3. The cable must be selected in such a way that losses incurred are below 2%.

6. Earthing and Lightning Arrestor:

As solar panels are installed on rooftops or in open space, solar panels are susceptible to various environmental threats. Especially in the rainy seasons, solar panels come in direct/indirect contact with lightning. To prevent the solar panels from these environmental threats following steps must be taken:

  1. Maintenance-free earthing pits to be planned for the solar panels, inverter and lightning arrestor.
  2. Find the topmost point on the building to install the LA. Make sure the down conductor of the LA is connected to the earth pit.

Here for our case study, 2 pits are sufficient for a 3kWp system. 

7. Net Metering: 

Solar net metering allows bidirectional flow of electricity i.e. one can export and import energy to the utility grid connected.
Don’t worry our technical team will guide you through all the solar net metering policies before installing a solar energy plant at your location.

Tips: Before installing solar panels

  1. Check for the government subsidies to avail maximum out of the solar installation.
  2. Depending on the grid availability and location, decide the type of solar energy system suitable for your energy requirement 
  3. If going for rooftop solar installation check rooftop capacity and shadow free area to install the required number of solar panels.
  4. To get optimum results, shading analysis must be done in order to ensure that solar panels installed are not covered with shadow from neighbouring trees/buildings or other factors.
  5. Choose your installer wisely and make sure they follow all precautionary measures so that you can enjoy the benefits of solar for a long 25 years.

If you are planning to install a solar panel system at your location and still have some doubts, contact us. Our technical team will guide you with the best possible solution and assist you with all government related formalities.

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