AC vs DC Solar Battery Storage
When you decide to go off-grid, then, It is time to look for solar storage options.
However, net metering provides an efficient way to go solar without going off-grid completely.
But, for an off-grid system, you need to install battery storage to get a continuous electricity supply.
When you decide to add battery storage to your solar installation, the first comparison that is considered is AC vs DC Solar battery storage.
Before jumping into that, let’s first know what AC power and DC power are.
What is AC Power?
“AC” refers to Alternating Current, which is the electricity flowing first in one direction and then the other.
This electrical current is used on the grid and in most of the household appliances.
What is DC Power?
“DC” refers to Direct Current.
It flows in one direction only. This electrical current is generated by the solar panels and stored by home solar batteries.
Do you know How solar panels work??
When the sunlight hits the surface of solar panels, it produces DC power.
That DC power passed to the inverter to convert it into AC so that we can use it for our home appliances.
As solar panels only generate electricity during the day time. So, for later use, we use batteries as backup storage.
We have two types of solar batteries available :
- AC Solar Batteries
- DC Solar Batteries
All batteries are DC, that is, they store DC power.
The only thing that matters is how does the battery charge from solar panels?
Let’s begin with the DC solar batteries, how do they charge from solar panels?
DC-coupled Batteries for Solar
DC-coupled systems are used in off-grid solar installations and also in remote power systems.
Like, in small capacity automotive/boating power systems.
The most common DC-coupled systems use solar regulators to charge a battery directly from solar and since the home appliances use AC power, then a battery inverter is used to supply AC power to the household appliances.
Let’s have a look at both pros and cons of DC Solar battery system:
- As solar panels produce DC power. Thus, in DC batteries, power is only converted from AC to DC once that is when it is supplied to the home appliances. This reduces energy loss.
- A DC battery system requires only one inverter which will lead to reducing the cost of your solar power system.
- Reduction in the energy loss will give very high efficiency: up to 99% battery charging efficiency (using MPPT).
- Low-cost setup for off-grid systems.
- In this system, fewer components are used, and hence it is easy to add additional panels and controllers if required.
- DC loads are easily added to this type of battery system.
- It will be a more complex option if you want to add a DC battery to an already installed PV system
- More complex to set up systems above 6kW as often multiple strings are required in parallel, plus string fusing.
- It becomes expensive to add DC batteries in large solar power systems (usually greater than 6kW). It is so because you have to install multiple solar charge controllers for a stable output.
- Some solar controllers are not compatible with DC batteries and it creates problems.
AC-coupled Batteries for Solar
As we discussed above, all batteries are DC, so the batteries attached in the AC solar battery System also stores DC power.
So, let’s see how batteries in AC battery systems charge from solar panels?
In an AC-coupled system, first DC power flows from solar panels to a solar inverter that converts the Direct Current to Alternating current.
You can power your home appliances with this AC electricity, or store this electricity in a battery system.
But, since the battery stores the DC electricity, so you need to pass this AC electricity through another inverter that transforms the electricity back to DC for storing in a battery system.
In this way, in these systems, any electricity that is stored in the battery system needs to be inverted three separate times before use.
Since every energy inversion leads to some energy loss, so, they are slightly less efficient (90-94%) compared to DC-coupled systems (98%).
However, these systems perform efficiently at high AC loads during the day.
AC coupled systems provide more advanced multi-mode inverter/chargers, generator controls, and energy management features.
- Compared to DC systems, these systems provide more flexibility, as, in these systems, the solar component’s location can be adjusted as per the requirement.
- Works with all kinds of solar inverters, even with micro inverters.
- If you want to add a battery to an already installed PV system, then this will be a more cost-effective way.
- AC battery Systems have higher efficiency when used to power AC appliances during the day such as air-conditioning, pool pumps, and hot water systems.
- These systems can use multiple string solar inverters in multiple locations (AC coupled micro-grids).
- Advanced AC systems can use a combination of AC and DC coupling.
- Because of 3 energy inversion before usage, there is more energy loss than DC systems and hence AC battery systems have slightly lower efficiency to charge a solar battery compared to DC ones.
- Having more than one inverter and equipment in different locations may increase the risk of system failure.
- These systems give lower efficiency when you want to power DC loads during the day.
Which is better for your needs?
As we have seen till now, both AC and DC battery system has its advantages and disadvantages.
So, how will you decide which one is the best choice for your use?
Well, it depends!
If you already have a solar panel system installed on your property and are looking to add battery storage, then an AC system is best for you.
This is because rewiring for a DC system is a complicated process that can increase your installation costs.
And, if you are installing a solar panel system and battery setup at the same time, then, a DC system will be the better way.
However, the installation time for systems is usually longer than for AC systems, so it’s important to consider in what way it will impact your installation cost.
Below infographic will describe the comparison in a better way:
We have seen both AC and DC Solar battery storage systems and considered their positive sides without leaving the downsides.
However, the DC system has the advantage of being more efficient than AC- systems.
But, these systems are more complicated to install, which can increase upfront costs and installation time.
So, it’s better to consider your budget and scale of usage before purchasing one.
Also, along with the batteries, you should not forget to do some real research on solar inverters before installing it.
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