What Is DC Coupled Battery Storage?
In a DC-coupled system, Direct Current from your solar panels goes to a charge controller that is connected to the battery system.
This means that any energy generated by your solar panels will be converted only once into AC power, ensuring greater efficiency.
Additionally, this type of system is ideal for those with time-of-use (TOU) rates, as you can store solar power generated during off-peak hours to use during peak times – when energy rates are higher.
DC Coupled Battery Storage System
The components that make up a DC Coupled Battery Storage System are:
- Solar panels/PV array
- Multimode inverter
- Payback meter
- Batteries/Energy storage
- Off-grid cut off switch
- The national grid
Solar panels/PV array
Similar to an AC system, the energy comes from your solar panels or PV array.
The only difference is that, in a DC-coupled system, the energy goes directly to the batteries – through a charge controller – instead of being converted into AC first.
This is the key component in a DC Coupled System as it enables two-way power flow.
Not only does it convert DC power from your solar panels into AC power to be used in your home, but it can also reverse the process – converting stored energy in the batteries back into DC power to charge them.
This is known as ‘battery to grid’ functionality and is a key advantage of DC Coupled systems, as you can sell stored energy back to the grid when energy prices are high.
This is a device that is multi-directional and measures how much energy is being generated by your solar panels, how much is being used in your home and how much is being stored in the batteries.
It’s important to have a payback meter installed as it will enable you to see how much money you’re saving by generating and storing your own energy.
In a DC-coupled system, the batteries are connected to an energy storage disconnect unit which in turn is connected to the charge controller.
The type of batteries you’ll need will depend on the size of your solar PV array and how much energy you want to store.
Lead-acid batteries are the most common type used in DC-coupled systems, however, lithium-ion batteries are becoming increasingly popular as they offer a longer lifespan and higher efficiency.
Off-grid cut off switch
Not only does the system have an energy storage disconnect, it also has a separate PV system disconnect connected to the PV array.
This is for safety reasons and to ensure that the system can be disconnected from the grid if necessary.
The national grid
In a DC Coupled system, the batteries are connected to the inverter which is in turn connected to the national grid.
This means that, if there’s a power outage, you’ll still have access to electricity as the batteries will provide power to the inverter.
It also means that you can sell stored energy back to the grid when energy prices are high.
Advantages Of DC Coupling A Solar Battery
- More power
Since the both the battery and the panels share the same inverter, DC-coupled systems are generally more affordable than their AC-coupled counterparts.
This because the hardware costs are reduced, as you only need to purchase one inverter instead of two.
As DC-coupled systems only require one conversion from DC to AC power, they are more efficient than AC-coupled systems – which require two conversions.
This means that you’ll lose less power to heat, ensuring that more of the solar energy your panels generate is stored in the battery.
Oversizing is possible with a DC-coupled battery system. When the amount of solar energy produced is greater than the inverter’s rating, as it may be in certain locations, oversizing occurs.
As a result, you can add more solar panels to your roof to produce more power and utilize the same inverter. The extra solar energy will be stored in the battery for later use.
In ac-coupled systems, low battery voltages can develop. If too much energy is extracted from the battery bank in an outage, it may cascade throughout the system, shutting down the multimode inverter, then the interactive inverter and the PV array.
When there is no direct connection between the solar array and the batteries, consumers have to wait for grid power to return before their system can begin operating again.
A dc-coupled system, on the other hand, can send power from the PV array to the ESS at any time (during daylight hours).
The unimpeded route between the PV array and battery bank allows for a higher battery voltage, allowing the multitwist inverter to turn back on and provide electricity to the uninterruptible power supply.
This, in turn, provides power to the loads until grid power is restored.
Disadvantages Of DC Coupling A Solar Battery
- The initial cost
- Less flexible
The initial cost
The Energy Saving Trust claims that DC systems are unable to charge from the grid. Additionally, DC systems require batteries with a higher voltage rating, which can also add to the initial cost.
When you’re connecting a DC battery system, you’ll notice that there’s less flexibility because the batteries must be close to the inverter. Because they aren’t linked to the inverter in an AC-coupled system, the batteries may be placed further away.
Additionally, if you want to add more panels or batteries to a DC-coupled system at a later date, this may not be possible as the inverter may not have the capacity to handle the extra power.