Image credit: Sunworks Energy

How can I calculate how much Solar rooftop power capacity I need?

You can use our Solar Calculator to get a rough estimate for how much it would cost and what capacity you need.

Here are some key pieces of information that are used in this calculation. The benchmarks vary for Residential and Commercial users.

For Residential systems:

Ideally, we can install 100% of Contracted Load

(LT — 1 and HT VI categories — this can be found on your electricity bill)

There are three kinds of options for residential systems: On-grid, Hybrid and Off-grid

On-grid system is the most common system. It is a system that is linked to the electricity grid of your area and when you are equipped with net metering capability, you can sell the surplus back to your electricity provider by feeding it in the grid.

When it comes to net metering — normally production of 85% of monthly units recommended. For example. For a residential home with 150 units of electricity consumption per month, we can place a 1 KW system, this would generate 120 units per month — which is 80% of the 150 unit requirement (benchmark used: Each 1 KW solar system generates 120 units per month)

To calculate this more accurately, we need the following details —
Monthly units consumed for the past 12 months, Available Roof area, Obstacles, Buildings around the location to understand shade patterns throughout the year.

Off-grid system — These systems are not connected to the grid. These solutions are usually best suited for areas where common electricity providers are not currently available to provide electricity. The only way to have electricity during times without sun or solar power generation is to use a battery backup.

After getting the Shadow free area and Roof space, we can approximately estimate that we can install 1 KW per 10 Sq Mtr.

To calculate this more accurately, we need the following details — Number of hours for which back up electricity is needed for the system, Available Roof area, Obstacles, Buildings around the location.

Hybrid system — These systems are a combination of off-grid and on-grid. They have a battery backup.
To calculate this more accurately, we need the following details — backup power needed for how many hours, Monthly units, Available Roof area, Obstacles, Buildings around the location, especially the south side since solar energy capture is the highest when panels are faced southward.

For a Commercial System:

We can install 50% of the Transformer Capacity (need to check the nearest transformer serving the commercial business) and 80% of Contracted Load (listed on electricity bills)

  1. On-grid system with Net metering — For a solar system that is connected to the grid and equipped to sell excess to the utility company, we can install 80% of the transformer capacity and 100% of the contract load.

To calculate this more accurately, we need the following details — Monthly units, Available area, Obstacles, Buildings around the location.

2. A solar system with Diesel Generator Integration and net metering —

Some customers prefer having a Diesel Generator (DG) for back up power. Normally this system is recommended for larger plants where the consumer will needs to use a DG every day due to power cuts.

We can run a solar power plant with a DG using a controller. Normally, solar will take reference supply from the main incomer. When power failure happens, when DG starts solar also switch on using the controller. But load should be more than 30% of DG capacity as per standards. If we run at zero percent, there will be reverse flow chances and DG efficiency will decrease.

To calculate this more accurately we need the following details — Monthly units, Available area, Obstacles, Buildings around the location.

3.Zero export —

In this type of system, there is no energy export to the grid. All the energy generated by the solar plant is used by the customer.

We can approximately install 1 KW per 10 Sq Mtr of roof area.

To calculate this more accurately we need the following details — the Roof space and Shadow free area, monthly consumption needs.

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