The system which utilizes only solar electric energy as main source of energy is referred as standalone solar electrical system. There are many locations on this earth where no source of electricity is available. At these locations standalone solar electrical system can be the ideal source of electricity. The main advantage of this system is that it does not depend on grid or any other source of electricity.
As it does not have any connection with grid or other electric supply line, it is also known as off-grid Photovoltaic system. As the sun is the only source of energy in this system it should have some means to make it active even in night times. A storage battery system does the job. Therefore, a storage battery system is an essential component of standalone solar system. But, often this battery system can be omitted from the system if the system is dedicated for the load which to be operated in day times only. Popular examples of standalone solar system are solar lanterns, solar home lighting systems, solar water pumping systems, etc.
Types of Standalone Solar Systems
Depending upon the use and design there are different types of standalone solar systems.
- Standalone Solar (PV) system with only DC load
- Standalone Solar (PV) system with DC load and Electronics control circuitry
- Standalone Solar (PV) system with DC load, Electronics control circuitry and Battery
- Standalone Solar (PV) system with AC/DC load, Electronics control circuitry and Battery.
Standalone Solar (PV) System with only DC Load
This system is simplest among all the standalone solar system. Standalone Solar (PV) System with only DC Load requires only two main components one the solar module array where the electricity is generated and one or more DC loads where the electricity is consumed. This system serves only during sunny day times. The configuration of this system is quite simple as we told earlier here the solar module array is directly connected to the load no other arrangement is required in between. It is quite natural that the rate of production of electricity in this system varies throughout the day depending upon the intensity and incidence angle of the sunlight.
This makes the applications of Standalone Solar (PV) System with only DC Load limited to some specific electrical appliances where the precise operation is not essential. This standalone solar system can be successfully utilized for pumping drinking and irrigation water as in these both cases fixed amount of water is not required to lift every hour.
DC fan can be operated by this system when speed of the fan is not required to be constant throughout the day. In this system the speed of the fan is maximum when the intensity of sunlight is maximum. Hence, maximum pleasant air flow is achieved during maximum hot period of the day times.
Standalone Solar (PV) System with DC Load and Electronic Control Circuit
Standalone Solar (PV) System with only DC Load can be improved by adding an electronic control circuit. This added electronic control circuit to the system, improves the utilization of power generated by the solar module array. This electronic control circuit is normally an electronic solar charge controller (SCC) (voltage or current regulator) or a maximum power point tracker (MPPT). The main purpose of these circuits is to provide regulated current and voltage to the load. The MPPT circuit is used to extract maximum power from the solar modules under all conditions. Thus, it ensures the best utilization of solar PV modules.
Standalone Solar (PV) System with DC Load, Electronic Control Circuit and Battery
A standalone system can be more practical and usable if it is able to serve even in absence of sunlight that is in night times. This can be simply done by adding a storage battery in the system which stores electricity produced during day times. This stored electricity can be utilized when there is no sunlight and in night times. After adding a suitable rated battery, the system becomes a Standalone Solar (PV) System with DC Load, Electronic Control Circuit and Battery. It is needless to say that this standalone system has four basic components.
- Solar Module Array
- Electronics Control Circuit
- Storage Battery System and
- DC Load
Here solar module charges the battery during daytimes and the battery supplies the load both during day and night. The electronic control circuit plays a vital role here it actually controls the flow of charges into the battery and out of the battery depending upon the system conditions and demands. The control circuit also protects the battery from overcharging as well as over-discharging. This system is most commonly used in solar street light system in remote villages. LED based solar lanterns which nowadays widely available in the local market are popular examples of Standalone Solar (PV) System with DC Load, Electronic Control Circuit and Battery.
Standalone Solar (PV) System with AC/DC Load, Electronic Control Circuit and Battery
So far we have discussed about the standalone solar energy systems which can only be used for operating DC load but maximum numbers of equipments we use in our daily life are AC operated so some means is required to attach with the solar energy system so that we can run AC equipment as well with standalone solar system. Inverter is a device which converts DC to AC of specified voltage and frequency. Inverter is basically a DC to AC converter whose input is DC and output is AC of desired voltage and frequency. So if we connect an inverter across the DC output terminals of electronic control device along with the DC load then the system becomes able to run AC equipments as well. As this system can operate both DC and AC load, the system becomes most popular version of standalone solar energy system. Nearly all kinds of DC and AC load can be operated by this system such as AC/DC fan, computer, TV, tube lights, CFL, LED lamps etc. This system is most suitable as alternative of grid electric supply where limited grid electric supply is available.
It is needless to say that this standalone system has six basic components
- Solar Module Array
- Electronics Control Circuit
- Storage Battery System and
- DC Load
- Inverter
- AC Load.
