One of the most common household applications of Solar power
system here in Nepal has been AC Mains-Solar Hybrid System. These systems are
generally the choice of customers suffering from load shedding in areas with
electricity supply through national grid. Although there is some connection
with grid in such kind of system, this is totally off-grid system. The Grid current
is only used for charging the battery bank along with solar charging unlike
supplying the load.
We are trying to design a charging unit with two inputs with
intelligent charging control that can be used in AC Mains Solar hybrid system
installed as backup to continue the electrical interruption due to regular and routine
power outage (loadshedding) in Nepal with utility grid supply.
The topology of currently found solar hybrid system is as
shown:
 |
| Fig 1 |
As we can see that there is no control over amount of grid
charging or solar charging in the current system. Hybrid Solar system are designed
to charge the battery bank with only half energy supply from solar but the
current system doesn’t guarantee this idea of 50% charging from solar as there
is no control mechanism from grid charging. If both sun and grid charging are
available then the battery will be automatically charged from both the inputs
with their full potential without any regards to what and how the system is supposed
to work.
The topology of most used commercial solar hybrid system is
given below (Fig 2):
 |
| Fig 2 |
We can also find some power conditioning equipment with solar charge controller incorporated inside the same casing along with AC-DC Charger and Inverter. They are generally marketed as Solar Hybrid Inverter. Its general topology is as shown in Fig 3.
 |
| Fig 3 |
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