Frequently asked questions about solar systems



Q. How much space on my roof do I need for a solar PV installation?


The grid connected system of 1KW peak power capacity occupies about 10 square metres on the rooftop.



Q. How much electricity does a PV system output?


For every kW peak power installed on a South facing roof, the system will generate around 1200 units in a year. This reduces by around 15 to 20% for an East or West facing roof.



Q. How much does a Solar PV system cost?


The cost of the system varies depending on the capacity and configuration of the system, which ranges approximately between Rs.80, 000 to Rs.1, 30,000 per KW.



Q. Do I need plan permission from the Municipal Authorities?


The roof mounted systems do not need any permissions from Muncipal Authorities.



Q. Will my roof be strong enough?


Most roofs are strong enough to take a solar installation without any reinforcement. However, in case of larger systems, it is suggested to obtain the opinion of a qualified Structural Engineer.



Q. How many solar panels do I need to install for solar system?


No of solar panels depends on the particular system requirement and space availability. For example for a 1 KW (1000 W) system, four no’s of 250 W solar panels will be used or 5 no’s of 200W Solar panels will be used. The selection of these solar panels depends on commercial availability of particular solar panel and space availability at project location.



Q. Do Solar Panels generate even in cloudy condition?


Usually solar panels generation will fall under cloudy conditions and the generation depends on the extent of cloudy conditions.



Q. How does the generation of a solar panel vary throughout the day?


As shown in the above figure, considering the example of a 1KW system, the system starts generating in the early morning 7 am and will stop generating in the evening around 6 PM. As shown in the above figure we can observe that the system generates to its peak capacity in the afternoon around 12PM. The profile of the curve is same throughout the year but peak generation and average generation values may vary depending on the season.



The above shown figure indicates shows the estimated generation of 1Kw solar system throughout the year. From the above figure we can observe that the generation is maximum in the month of March and other summer months and lowest in the month of July (Rainy season). Considering the average over 12 months, estimated energy generation will be around 4.6 units/day per 1KW capacity of solar system.



Q. What appliances and how many appliances can I connect to my solar system?


The average wattage consumption of each appliance, those we typically use in our daily life are listed in the above table. For designing a solar system inverter, first we should consider the number of appliances to be connected to the inverter. We should decide the inverter capacity based on the number of appliances to be connected. The total aggregated load (no of appliances) should never cross the maximum capacity rating of the inverter.


The above table gives some example load profiles of a particular system size. For example for a 1KW system as mentioned in the above table we can connect 4 Tube lights, 3 Ceiling Fans, 1 Television & 1 Refrigerator. Or in alternative to this we can connect 3 Tube lights, 2 Ceiling Fans, 1 Television, 1 Computer & 1 Refrigerator. In any case total connected capacity must not cross the maximum inverter capacity rating (i.e 1KW in this case). In similar way for 2KW & 3KW systems also different load profiles are mentioned in the above table.


For Designing Off-Grid or Hybrid System we should follow above designing criteria. But in case of Grid-Tie (Net-Meter Based) system, as inverter output is directly synchronized to Utility power lines we need not to consider about the amount of total appliances connected in the building. Total generated power will be injected into the lines and the appliances connected to the same power lines will consume the generated solar power. Depending the load requirement solar inverter & utility power lines will work in coordination automatically to share the load giving the first priority to the generated solar power.



Q. What are the general maintenance requirements for a solar systems?


Generally solar systems require very minimum maintenance. Major maintenance required in solar system is for batteries. In case if batteries are flooded type they needed to be filled fresh distilled water for every 3-6 months based on charge and discharge cycle. And inverter doesn’t need any maintenance except that it needed to be maintained free from dust or any other deposits on it. And finally solar panels also needed very minimal maintenance. They needed to be cleaned regularly like once in month depending on dust deposited over panels.



Q. Do I need to inform Power Utility (DISCOM)?


Prior permission is to be taken from DISCOM to install the SPV system based on net metering.



Q. Is there ANY application?


The application shall be made in prescribed format to the Divisional Engineer/ Operation/DISCOM along with a fee of Rs.1,000/-. The consumer can download Solar net metering rooftop application from official websites of  corresponding DISCOMs.



Q. What is the difference between monocrystalline and polycrystalline PV panels?


Monocrystalline solar electricity panels tend to be slightly more expensive than polycrystalline panels, however monocrystalline panels are regarded as having a higher output per kW peak power installed. Polycrystalline wafer has a dark blue colour, monocrystalline wafer is black.



Q. How much do the solar PV panels weigh?


Normally about 13kg per m2.



Q. Are the solar PV panels fragile?


Solar PV panels are very robust and can withstand the normal stresses subjected by nature.



Q. What is a PV system?


PV technology produces electricity directly from electrons freed by the interaction of sunlight with a solar panel made of semiconductor material. The power provided is direct current (DC) electricity. The basic building block is known as a cell. Many cells put together are known as a module, and many modules assembled together form an array. A PV system will consist of an array of modules generating DC electricity, an inverter, and sometimes battery storage back up with charge controller.



Q. What is an inverter?


There are two kinds of electricity, DC and AC. Homes that are connected to utility power use AC electricity. Flashlights, small radios and automobiles use DC electricity. In to use solar power to operate the appliances in your home, an inverter will convert PV power from DC to AC. Inverters can be further classified as units that use batteries (UPS) and those that use the utility grid as power storage (Grid-tied). Inverters are now required to possess meters that will indicate their performance and some manufacturer’s supply remote display units that can be mounted inside the home. It is important to check on your inverter regularly to become acquainted with its operation and performance.



Q. What is a “grid-tie” PV system?


You may connect your solar system directly into the wires of your utility. Since the “Net Metering” allows you to do this you will actually be spinning your meter backwards when your system is generating more power than you are consuming. When you generate excess electricity (more power than you are using) it will enter the grid. Your meter will tally the excess and credit to your account.



Q. Are there any technical standards for various components of the system?


Yes. The various components of SPV system shall have IEC/ISI/BIS Certification and confirm to technical standards specified by MNRE/APTRANSCO/DISCOMs.



Q. How the billing and payments are made in net metering scheme?


(i) The consumer shall receive a net import/export bill indicating either net export to the grid or net import from the grid.


(ii) In case of net import bill, consumer shall settle the same as per existing norms. If it is a net export bill, then credit amount shall be carry forward to next month for adjustment against next month import bill. No interest will be payable on this credit forward amount. Net credit available in his account will be refunded twice in a year based on June and December Month bills of each year. Net Credit amount payable will be deposited by DISCOM in consumer’s bank account bearing a/c number provided by consumer at the stage of application, by June and December month end as the case may be. The amount payable for net export of energy will be based on pooled cost decided by APERC for that year.