If you are considering installing solar panels and a home battery, it is important to choose between AC or DC connected battery systems. This choice affects the efficiency and functionality of your system. In this article you get insight into:
- The characteristics of an AC connected (retrofit) home battery, including the advantages and disadvantages, and for whom this system is ideal.
- The properties of a DC-connected (hybrid) home battery, with the associated plus and minus points, and the suitability for different users.
- Guidelines for linking different types of batteries with specific converters, and tips for comparing these systems.
This information helps you to make an informed decision about which type of battery system best suits your situation.
What is the concept of an AC-connected home battery? #
An AC-connected home battery, also known as retrofit, combines a home battery with a separate or integrated battery inverter, managed by a smart meter. In this system, the direct current (DC) of solar panels is first converted to AC for domestic use. The excess solar power charges the battery, while the battery is first used in case of shortages before the power is reduced.
This configuration includes multiple energy conversions:
- DC of solar panels is converted to AC.
- AC from the meter cabinet is converted back to DC for battery storage.
- For use in the home, DC from the battery is converted to AC.
With three conversions there can be efficiency loss, which can be significant. For example, with an estimated efficiency of 98% per conversion, this results in a total efficiency of about 94%, meaning that there is about 6% energy loss.
Advantages of an AC connected home battery setup #
- Compatible with Existing PV Systems: Can be added to any already installed PV system.
- Brand-Agnostic: Provides freedom to choose from different brands and types of battery inverters and home batteries, including combinations with brands other than the PV converter or battery converter.
Malfunctions of an AC connected home battery setup #
- More Energy Conversions: Increased conversions from DC to AC and vice versa, resulting in higher conversion losses.
- Accurate Design and Installation Needed: A well-designed gauge cabinet and professional installation are crucial, considering the potential danger of merging flows of the grid, PV installation and home battery.
- Additional AC Connection Required: Needs an additional AC connection (security) in the meter cabinet.
- Compatibility problems: Possible need of multiple apps if the equipment is of different brands.
- Higher initial costs: Increased investment for the customer, since a battery converter needs to be purchased.
- Space: Takes more physical space because of the larger number of components.
- PV-Possible Loss: By power switching on the PV converter, PV power can be lost before it can be transferred to the home battery.
When is an AC connected home battery the most appropriate choice? #
An AC-coupled system is most useful for households that already have a working PV installation with an active PV converter, which is still subject to several years of warranty. Two retrofit options are available for this situation:
- You can choose a battery converter with an integrated home battery (all-in-one).
- An alternative is a loose battery converter to which you can connect the battery pack with power cables.
With a retrofit, the customer's existing PV system remains completely unchanged. This may be beneficial, especially if a third party has installed the PV installation, as no adjustments to the installation of third parties are required and the installer has no responsibility for this.
What exactly is a DC-connected home battery? #
A DC-connected home battery is a configuration that includes a home battery and a hybrid converter, both connected to the PV installation and to the home battery. Both the PV and battery power come together on the DC side of the hybrid converter.
As with an AC connected home battery, a DC connected home battery also uses a corresponding smart meter to control the system. This smart meter ensures that the battery is charged when there is excess solar power and that the battery is discharged before buying power from the grid.
The main difference between an AC-connected and a DC-connected configuration is that at the latter the current goes directly from the solar panels to the home battery. The hybrid converter converts the DC current to AC current that can be used in the home.
This only converts the power once, resulting in less conversion losses for the customer compared to an AC-connected battery. Moreover, the power from PV to battery does not even need to be converted, hence the name "DC-connected battery system."
The advantages of a DC-connected configuration include: #
- No additional investment required for a loose battery converter.
- Only one AC connection (security) needed in the meter cabinet.
- No conversion of PV current (DC) to battery current (DC).
- Only one conversion from DC to AC, resulting in significantly less conversion losses.
- Only one app is needed to view all real-time data.
- Lower purchase price compared to an AC-coupled system and a separate PV converter.
- Takes less space, both physically and in the meter cabinet, than an AC-coupled system.
The disadvantages of a DC-connected configuration include: #
- The choice of batteries for your customer is determined by the brand of the inverter.
- The hybrid converter has a higher purchase price than a standard PV converter.
- The PV converter reduces the power the home battery can deliver.
When is a DC-connected home battery the best choice? #
A DC-connected system is the most suitable solution for households that do not yet have a PV installation or for those whose warranty on the PV converter will expire soon.
Instead of installing a hybrid converter, smart meter and home battery directly, you can choose to install the first two components and add the battery later. As a result, the customer is ready to charge and fully prepared for the installation of a home battery.
Which brand of inverter can be combined with which home battery? #
It can sometimes be challenging to determine which brand inverter is compatible with which brand battery, especially given the constant introduction of new converters and batteries. At Verdasol we understand that it can be difficult for people to see the forest through the trees. That is why our advisors are ready to give free advice and help to make the right choice.
