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Sizing a 2 kWh off-grid solar power system for Mumbai, India

India is a country which is excellent for solar power. In contrast to Sweden, where I am located, it is definitely feasible to live off-grid the whole year.

In this article I describe the sizing of an off-grid solar power system in Mumbai, India. It should be able to supply 2 kWh of electrical energy to a household everyday during the months of September to December. This is enough to power an 80 Watt TV for 24 hours (you can calculate the daily energy need for your household devices here).

The solar power system should be well-functioning during a period when 10 “days of bad weather” occur, which means that the solar irradiance (power in the sunlight) is only 10 percent of the irradiance during an average day. The battery should get fully charged again if these bad days are followed by 1 “day of good weather”, with average solar irradiance.

In order to calculate how many solar panels and batteries I need, I go to Sunny off-grid and order a Solar Energy Calculation under the Store subpage. I then fill out the form Specify your order the following way:

Off-grid solar power system specification

The name of your location: Mumbai

Latitude: 19.22

Longitude: 72.91

Daily electricity consumption you need [Wh]: 2000

First month of the year when your solar power system should be well-functioning: September

Last month of the year when your solar power system should be well-functioning: December

How many days of bad weather should the battery last before it is discharged: 10

How many days of good weather should the battery need before it is charged full again: 1

When all the fields are filled out, I place my order and wait for the finished Solar Energy Calculation to appear in my email inbox (it may take a few days).

Sunny off-grid runs a simulation and sizes the off-grid solar power system, based on statistics of solar irradiance and temperature for the specific location. In the Solar Energy Calculation I was advised to install the following off-grid solar power system.

Results for how many solar panels and batteries are needed

Necessary solar panel power: 3.6 kW
For example 16 solar panels with 200 W power.

Necessary battery energy: 25 kWh
Corresponding to the battery capacity 2083 Ah for 12 V lead acid batteries. This can for example be fixed by connecting 29 batteries with the capacity of 72 Ah and voltage 12 V in parallel.

Simulations to motivate the results

The number of solar panels and batteries have been chosen so that the battery bank’s state-of-charge should never fall below 50%, which is important for lead acid batteries (otherwise the batteries may get damaged).

In the graphs below you can see how the solar power system has been simulated between September and December. In the simulation it has been assumed that the solar panels are aligned towards the south  (azimuth angle), with the tilt angle of 20 degrees, which is a suitable tilt angle for solar panels in Mumbai. It has also been assumed that monocrystalline solar panels are used.

The graphs show that the worst performing month is September, when the solar irradiance is the lowest. The state-of-charge level (SoC) goes down to 50% after the 10 days of bad weather, but then goes up to 90% again after 1 day of average solar irradiance. During the other months of the year, the SoC is far above 50%, so there is no risk of discharging the battery bank.

Off-grid solar power system block diagram

In the block diagram below you can see how the solar power system can be connected together.

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