Many industries in Delhi/NCR (Kundali, Sonipat, Faridabad, Bahudargarh, Manesar, Bawal, Ghaziabad, Greater Noida etc) have to still depend on the Diesel Generator sets for running factories for few hours daily. What happens if the discom supply is disrupted during the sunny hours when the sun is still out generating the power? Grid tied solar plants or On-grid solar systems will run when the Discom power is available as the solar inverters have in built feature which commands the solar system to generate power when it can sense that the supply is available from other sources. Such a feature is built in solar inverters as the solar power is an intermittent source of electricity supply which provides variable output depending on the solar intensity at that moment. Hence if suddenly the clouds cover the sun, the solar generation will dip making the system unstable. Therefore, solar has to always run in conjunction with any other dependable and stable source of supply like Discom power, DG power or the batteries. As the batteries are quite expensive and need to be replaced periodically, most factories depend on the DGs for the back up power. Solar can be connected to the DG panel directly as it is connected to the LT panel of the Discom supply in the factories. Certain protections require to be built in based on the DG sizing however. Also, the factory load that can be served by solar should never be more than the DG supply which means that the primary supply source will always remain the DG. So, the size of solar plant cannot be more than that of the DG size as the solar alone cannot take the factory or plant’s load. Solar will help to reduce the diesel consumption during the DG hours as the DG will run at lower loads and even idle loads depending on the system design. For the system to work smoothly, if there are multiple DGs, they should be synchronized (manually or automatically) before they are put in sync with the rooftop solar system.