What happens in case of power outage?
When you lose the connection to the utility due to an outage, the grid-tied system shuts down. This is a safety regulation that cushions solar panels from accidentally powering the grid which may result in damage. However, it is possible to have electricity even when there is a power outage. For that to happen, you need to incorporate a power storage battery
into the system.
When you integrate batteries to a grid-tied system, it becomes a grid-hybrid. You can as well incorporate a generator that will produce backup energy for essential items in the house.
Battery storage in a grid-tied system can draw energy from the grid or the solar panel system. Therefore, you have a guarantee of backup power in case of an outage.
A battery storage connection in a grid-tied usually consists of an automatic transfer switch. This allows a grid-interactive and an isolated mode. The system works like a conventional standby generator. When there is a power outage in the utility, connections in your house switch off. This means that you have no access to electricity. However, the battery storage system senses the outage and detaches your house from the utility. After that, the backup power system supplies energy to your house.
Having battery storage for your grid-tied system is vital in maximization of solar production and storage of the extra power. When your system is producing excess power during the peak hours of the day, you can have the surplus energy stored in your batteries. When the cost of electricity is high in surging demand, you use your stored power. Therefore, you rely less on the grid during high demand evening hours. At such times the cost of energy is higher than normal. Therefore, you save a lot when you have your backup power.
Approaches to incorporate battery storage in a grid-tied system
If you wish to have battery storage in your grid-tied system, there are three approaches you can use.
- AC Coupling
- DC Coupling
- Use of a storage-ready inverter
Grid-tied inverters require the grid power to function. They frequently detect grid voltage and frequency and switch off if it goes below the range.
In a system with an AC coupling, the grid-tied inverter usually pairs to an off-grid one and a battery. The off-grid inverter acts as a second source of energy. It deceives the grid-tied inverter into remaining active. Through that, it is possible to charge the batteries and operate vital appliances when there is a blackout.
Advantage of AC Coupling:
AC coupling is the easiest and most convenient way, especially if it is a micro-inverter system.
Disadvantage of AC Coupling:
There is a challenge when it comes to sizing due to stringent requirements for inverter and size of the battery. In case the battery bank or inverter is undersize, the system might function poorly or entirely fail. Besides, an AC Coupled system might be expensive in case the present grid-tied inverter is big.
In these systems, a charge controller connects the solar panel array to the battery. Basically, it is the mode of function for off-grid systems. It is possible to incorporate a grid-tied system where the central inverter is 600 volts.
There is a manual switch to shift between off-grid and grid-tie modes. The drawback with DC coupling is that you cannot program it. To charge the battery, you have to turn the switch physically.
Although the inverter on the battery switches on and power essential appliances automatically, the solar array can’t charge the batteries unless you manually turn the switch. Therefore, you should be around to turn on; otherwise, the batteries might drain such that you can’t recharge from the solar.
Advantage of DC coupling:
Unlike the AC coupling, this type functions with an extensive range of off-grid inverters and size of the battery bank.
The disadvantage of DC coupling:
The major downside of DC coupling is that you have to be around to start the charging. The system still provides back up power when you are not there, but there won’t be any recharge from the panels.
Replacing the grid-tie inverter
Replacement of the present inverter with a storage ready one is the most expensive option. However, it is the most flexible too. It is compatible with all grid-tie systems.
Most of the times, homeowners wish to replace the current inverter with a type that can utilize a similar wiring array. Besides, they want one that is of the same size.
Replacement of the inverter is a better option than the use of DC or DC. The design from the manufacturer considers energy storage and is thus best for the purpose. This tactic is not convenient when it comes to micro inverters. Removing the old ones and incorporating a new one in every panel is tough. Besides, the cost of labor is higher, and the process takes more time. Therefore, for the sake of micro-inverter systems, AC coupling is more convenient.
Advantages of grid-tied inverter replacement:
This approach is compatible with any system. Additionally, the storage ready inverters have several extra features.
Disadvantages of grid-tied inverter replacement:
The drawback is the high cost of labor, especially in a system that uses micro-inverters.
It makes sense for an average household to maintain a connection to the utility grid. But having a battery backup is even more convenient. That is more so if the compensation policy by the utility company is not that good. Some utilities do not offer net metering at a retail rate; therefore, you won’t get the full credit amount for the power that you generate and send to the utility grid.