Sunday, September 28, 2014

Typical AC Mains Solar Hybrid System in Nepal

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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