Solar PV cell and module:
- Solar PV cell is the basic building block of a PV system. It consists of semiconductor material that absorbs sunlight to generate electricity through a phenomenon called “photoelectric effect”. Only sunlight of a certain wavelength can effectively generate electricity. Although a solar PV can generate electricity on a cloudy day, but it is not as effective as it is on a sunny day.
- A basic PV cell produces a very small amount of electricity and multiple of them are connected together to form a Solar PV module that can generate 10W to 300W output. If more electricity is required, then multiple such PV modules have to be installed in an array.
- Multiple kinds of materials are used to create a solar cell and the efficiency of solar cell depends on the same. The efficiency of a solar cell is defined as its capability to convert a certain amount of sunlight into electricity. Solar cells available in the market are of various efficiencies: 4%, 8%, 12%, 14% and 16%. The size of a Solar PV module required will depend on output and efficiencies:
Roof Area Needed in Sq. Ft.
|PV Module Efficiency (%)||PV Capacity Rating (Watts)|
Components of a Roof Top PV system
- A typical Roof Top PV system also contains a set of batteries and inverter along with the modules of Solar PV cells. The overall efficiency of the system will also depend on the type of battery and inverter used in the system. It is important to choose the right components for most effective use of Solar PV systems.
- “Deep Cycle” batteries (generally lead-acid) are the best suited for a solar PV system. They last for 5 to 10 years and are 80% efficient (can reclaim 80% of energy stored in it). These batteries are also designed to provide electricity for long periods and can discharge up to 80% of their capacity repeatedly. Automotive batteries that are shallow cycle should not be used. Sealed maintenance free or tubular positive plate batteries are good for Solar PV systems. It is important to size the batteries properly so that they can store sufficient power based on your needs during cloudy weather. Batteries should be located in a space that is easy to reach (for maintenance), well-ventilated and protected from extreme weather.
- Even inverters are not 100% efficient and it is important to choose the right inverter that is at least 85% efficient (If a system is purchased under National Solar Mission then these standards are guaranteed). A modified sine wave or a pure sine wave inverter is better suited for a solar PV system. Modified sine wave inverters are cheap but less efficient. They waste some electricity in form of heat. They create a buzz sound with appliances and thus should be used only with low-end appliances. Pure sine wave inverters are most efficient but are expensive. They are good for all kinds of appliances.
Other considerations for installing a solar system
- Although a solar PV system can generate electricity through direct or scattered sunlight but it is very important to assess the amount of sunlight available at the location where a solar PV system is being installed. To collect maximum sunlight the ideal orientation of a Solar Panel is towards south. However a 45-degree east or west of south can also work. The system should be placed in such a place so that there is no obstruction of trees or adjoining building. In case these requirements are not getting fulfilled, an expert should be hired to do a detailed analysis on the amount of sunlight available.
- The load carrying capacity of the roof where the solar panels are to be installed should also be done. Solar Panel structure typically weight 15kg per sq meter and the roof should be able to handle the load.
- Tilt at which the solar panel is installed is also an important consideration. It is important that the tilt of the solar panel is the same as the latitude of your location.
Types of rooftop solar PV systems
Rooftop solar PV systems are of 3 types:
- Grid-tied – These rooftop systems are primarily designed to supply the generated power to the grid and also power the load. These systems will NOT generate power during a power failure as the inverter shuts down the system to stop sending power into the grid and avoids the risk of electrocuting utility personnel who are working to repair the grid
- Grid-interactive – This system works in conjunction with either a battery backup or diesel generator to support the load even during a power failure.
- Off-grid – This system does not work with the grid and is designed to work only with a battery backup or diesel generator in off-grid applications.
The difference between the systems lies in the kind of inverter used, and the inclusion of batteries. As various vendors use different terminology for these systems we urge to verify the functions of the offered system rather than going by the name alone.