Factories/Industries – How much solar (in KW) can be installed at the roof?

Thursday, 23 August, 2018

Solar installer in nature and the factories, cold storages, warehouses, commercial buildings, Malls etc can plan to install solar panels (KW) as per their requirements.

To understand the solar plant sizing, let us assume a hypothetical case where in an industry located in Kundali, Sonipat (Haryana), and

    • has a roof made of metal shed and has an area of 3000sqmeters,
  • has a contract load of 1,500 KW,
  • has an average monthly electricity consumption of 70,000 units or kWh
  • is connected to a distribution transformer of 2,000KVA.

Following factors should be taken into consideration while designing the solar system for your roof –

    1. Roof Size determines the maximum capacity of the solar plant that can be installed:
      1. Each panel has an area size of roughly 2 sq meter (1 meter X 2 meter) with a capacity of around 325 watts. So broadly, 3 panels can make 1 KW of solar installation which implies 1 KW can be installed in 6 sq meter of roof areain ideal conditions.
      2. However, space is required to be left between the panel rows to avoid shadow on the panels. As the panel structures are raised to provide inclination and thus the better exposure to sunlight, the shadow free area further decreases.
      3. Typically, on concrete roofs, 10 sq meter would be a good estimate for 1 KW of solar panels. For inclined metal sheds and asbestos roofs, the area required to install 1 KW of solar panels would decrease based on the direction of the shed. A South facing shed can accommodate more solar panels than the one facing north.
      4. For the roof in the above example, a solar plant of 300-350 KW (=3000 /10) can be installed based on the size and inclination of roof.


    1. Solar Plant size in KWs cannot be more than the Contract Load. In Haryana, Delhi, Uttar Pradesh, Rajasthan and other states, the size of solar plant is constraint by the Contract Load of the Building as per the Discom’s regulations. So, in this case, the maximum size of the solar plant that can be installed on the roof is 1500 KW.


    1. Electricity bill is an important factor to determine the size of the plant. As the Net Metering facility is available in all the states in India, the annual electricity consumption of the industrial unit, factory, warehouse or the building should be considered while sizing the solar plant.
      1. In Haryana, UP and Delhi, consumers should consider a solar generation of 1400 kWh per KW of solar panels with 5 percent variation in the first year of the plant’s installation.
      2. In the above example, the factory has average monthly consumption of 70,000 units or annual consumption of 8,40,000 units (=70,000 X 12).
      3. To reduce the variable part of the electricity bill to zero, the industrial unit should install 600 KW (=8,40,000 / 1,400) of solar panels on the roof or within the campus.


  1. Availability of Distribution Transformer capacity is important for the solar plant.

All the state regulators and Discoms have specified the maximum capacity of solar plants that can be connected to a Distribution transformer. For example, Haryana allows only 15% of the distribution transformer capacity that can be used by the solar plant while Delhi allows 20% of the transformer capacity and Uttar Pradesh allows 25% of transformer capacity.

In the example above, the transformer has a capacity of 2000 KVA.So, a maximum of 300 KW (=15% of 2000) of solar panels can be connected to this transformer.

Discoms may consider the distribution transformer located in the premises of the industry also as the distribution transformer in spite of the transformer being owned by the consumer. Therefore, it is important to check with the Discom for the maximum solar capacity that can be installed and Net Metered with the Distribution Transformer.

So, going by the above 4 factors, namely (1) Roof Size (2) Contract Load (3) Electricity Bill (4) Distribution Transformer capacity, the Kundali consumer in this example can plan for a solar plant of only 300 KW. In this case, the size of distribution transformer and the roof size are constraining factors.