On Grid, Off Grid & Hybrid Solar PV Plant
The position of the sun in the Sky keeps on changing through-out the day. Based on the position of the sun, the amount of sunlight falling on the solar modules varies. Thus, the output of the Solar Panel will also vary based on the above mentioned situation. Conclusively, a Solar Power Plant without any complementary or back up source is not suitable to supply constant power to load. In contrast, a Diesel/Gas Power Plant, is able to supply the peak rated power at any point of time.
The power generation characteristics of the solar modules is shown above.
The figure shows that the peak power production can be seen at noon (the time when the modules get maximum amount of electricity). The region before and after the peak do not have the maximum generation. The graph clearly shows that the generation has a variation over a period of time and is not suitable to supply a constant power to the load alone. The system needs additional component (On grid or battery).
In this blog, we will be discussing about three types of solar PV plant:
1. On Grid Solar Power Plant
The on-grid plant is also known by the name grid connected plant or grid tied plant. This is the most common type of photovoltaic system. Both the grid and the solar panels will provide the electricity if the demand is higher than the power produced by the solar panels. The grid will compensate for the shortfall. If the demand remains low, then the excess power produced will be sent to grid.
Many utilities of India have introduced net metering (explained in the next section), which will calculate the difference between units of electricity imported from the grid and units of electricity exported to the grid. The owner is then supposed to pay only for the difference. If the exported units are greater than the imported units, this data is carried forward to next month and so on until financial year closure. This system suits best for the location where power cuts are not frequent in daytime, while solar power plant is producing power.
Net Metering
Net metering is a system in which power exports are offset by imports, reducing the electricity bill by deducting electricity generated from total electricity consumed over a certain period of time. On a monthly, half-yearly, or annual basis, the adjustment might be made. A bidirectional ‘net meter’ typically accounts for both electricity input and export. If the exported power is more than the imported electricity, the surplus electricity put into the grid may or may not be reimbursed (depending on the state’s net metering rules).
Gross Metering
A consumer is compensated at a fixed feed-in-tariff for the total number of units of solar energy generated and exported to the grid (as measured by a unidirectional “gross meter”), and must pay the electricity distribution company (DISCOM) at the retail supply tariff for the electricity consumed from the grid. Feed-in tariffs and retail supply tariffs are usually not the same.
Advantages of Grid Tied Solar PV Plant
1. Cost effective
2. Efficient
3. Does not require expensive batteries or storage devices to store the excess power produced by the panels.
4. The grid behaves as virtual battery, as the excess power produced is sent directly to the grid.
5. With net metering, a lot of money can be saved as the excess power is sold out to the utility.
6. As there is no involvement of storage devices, the maintenance required is also low.
Disadvantages of Grid Tied Solar Power Plant
1. The major disadvantage of a grid tied system that it shuts down when the utility grid shuts down due to some fault. This is called “anti-islanding” requirement which means the inverter must stop feeding when the grid experiences an abnormal condition. This shut down is important for the protection and safety of the workers or professionals who would be trying to repair the grid.
2. Before installing this system, the person should get cleared with the net metering solar policies by the utilities. The person can consult experts in the field to get knowledge about the policy.
2. Off-Grid Solar Power Plant
This type of system is not connected to the utility grid, instead a battery bank or storage devices to store the solar power. In an off-grid system, the battery is charged through a charge controller/MPPT (Maximum Power Point Tracker) circuitry. The energy stored in the battery is fed to the inverter which in turn feeds the AC load. Thus, an off grid PV system can deliver power even during night with a condition that the battery has enough stored power. So, the system designed should be in such a way that it handles the peak load when the PV array is not able to produce that much amount of power ensuring that there will be continuous supply of power. This is called autonomy of the off grid system, and usually off grid systems are designed for 2 or 3 days autonomy backup, i.e. over sizing of the battery bank and Solar PV system to ensure enough power is available even when there is a week of over cloudy and hazy daylight. (monsoon & winters in India)
Advantages of Off-Grid Solar Power Plant
The system is suitable with:
1. The places with frequent power cuts and shortage of power.
2. In rural areas or underdeveloped communities, where the grid lines not present to export the excess amount of units produced by the solar PV array.
Disadvantages of Off-Grid Solar Power Plant
1. The installation of battery makes the system costlier for the first investment compared to Grid Tie system..
2. The efficiency of the system is low as compared to the on grid system. ( DC-AC-DC-AC conversion cycle)
2. Regular maintenance is required from the day of commissioning.
3. The batteries have relatively a pre decided life span and degrade over time depending on Depth of discharge and Charge cycle usage.
Varies for Different battery chemistries- lead acid, SMF, VRLA gel, Lithium ion, Lithium Ferro Phosphate etc….
3. Hybrid Solar Power Plant
Hybrid solar system combines best of both systems, i.e. grid-connected and off-grid solar Power systems. These systems can be seen as an off-grid solar system with utility backup power, or grid-connected solar with battery storage. The power generated from the solar PV array is used to charge up the batteries. This power can be used to run the home appliances and if the batteries are fully charged up and Solar Power is being Generated is higher than the amount of consumption, it is exported to the grid.
Advantages of Hybrid Solar Power Plant
1. The system is less expensive than complete off grid solar power plant.
2. The supply will be have uninterrupted solar power supply regardless of utility power cuts or severe weather conditions..
3. No worries of power generation as in the case of off grid solar plant.
4. Power can be stored at low cost.
5. Both on-grid and off-grid systems work in synchronization to complement each other.
Disadvantages of Hybrid Solar Power Plant
1. Costlier than grid-connected solar system
2. Battery life of 8-15 years.
3. Only Critical loads are to be supplied with back up power using hybrid solar system approach.
Conclusion
Many key factors are to be kept in mind while installing the solar PV system. Guidance from expert is required to see which type of system suits bests for the type of location & where the system is being installed.
If you are planning to install one, make sure to gain the right knowledge, so that the system works for longer periods with maximum efficiency.
SolarOcta can guide you in all these nitty gritty of things and make sure that solar power plants are designed in an optimized manner so you get maximum gain with minimum investments, thus ensuring quality is never compromised at any levels or at any step in the EPC (engineering, Procurement & commissioning) of a Solar Power Plant.
