Why AC coupling matters: Hoymiles Micro Storage technology explained


Key takeaways

  • Hoymiles Micro Storage (MS) is the world’s first AC-coupled balcony solar storage solution, compatible with all microinverter brands and simplifying installation.
  • The system integrates a 2.24 kWh battery and offers off-grid mode, ensuring reliable backup power and reducing dependency on the main grid.
  • It’s designed for small spaces like balconies but can be installed on walls, courtyards, or rooftops, making solar energy accessible even in limited residential areas.
  • Balcony solar systems with Hoymiles MS can significantly lower energy bills and provide a sustainable, efficient energy solution for homeowners.

Table of Contents


Hoymiles is revolutionizing the world of solar energy storage with the introduction of Hoymiles Micro Storage (MS), the world’s very first AC-coupled balcony solar storage solution.

This innovative technology simplifies installation and ensures compatibility across all microinverter brands. By leveraging AC coupling, Hoymiles MS offers unmatched flexibility and efficiency, making it a relative game-changer for residential solar systems.

Let’s explore why AC coupling matters and how Hoymiles MS can help transform your approach to solar energy.

What is balcony solar storage?

Balcony solar storage systems are primarily designed for balconies, but they can also be installed in other areas such as on walls, in courtyards, or even on rooftops.

They’re the perfect solutions for residential areas where space is at a premium as they allow homeowners to take advantage of the benefits of solar energy even in small settings.

Commonly known as plug-in solar systems or plug-and-play solar systems, balcony power plants feed generated power directly into the home grid. This is done through an electrical socket, making installation an easy and straightforward process.

Equipped with storage facilities, these systems help to provide a reliable source of backup power, which in turn helps you to reduce your energy bills and have a solid source of electricity in the case of emergencies.

Why does balcony solar matter?

Balcony solar systems are gaining popularity across the world due to their simplicity and efficiency in harnessing solar energy within limited residential spaces.

For instance, balcony solar has seen rapid growth in Germany in recent years. From the end of 2022 to the end of August 2023, the number of balcony PV plants surged by more than 200,000, totaling 260,000 for the whole of 2023.

These systems reduce people’s dependency on the grid and can make a big difference in lowering energy bills. However, the one issue is that they only function when the sun is shining.

In order to extend their functionality and make the most out of these systems, integrating energy storage is key, a process that often requires people to retrofit their existing system.

How does a typical balcony solar storage work?

Balcony solar storage systems incorporate several key components that work together to harness and store solar energy efficiently.

Wiring and components

In a typical setup, balcony solar storage systems involve several components:

  • PV modules: These photovoltaic (PV) modules, or solar panels, capture solar energy by converting sunlight into direct current (DC) electricity.
  • Energy storage system: This component stores the DC electricity generated by the PV modules. Some may not include a battery and users will set up battery storage themselves.
  • Microinverter: The microinverter plays a pivotal role in converting the DC electricity captured by the PV module into alternating current (AC) electricity. This is then ready to be used by households or fed back into the grid.
  • Home grid connection: This connection allows the AC electricity produced by the microinverter to be fed directly into the home’s electrical system, providing daily power and reducing reliance on the main power grid.

The transformation process

The original balcony solar setup is like this: You connect the solar panels with your microinverter and then insert the Schuko plug into the socket.

A typical balcony solar system using two solar panels and one Hoymiles microinverter
A typical balcony solar system using two solar panels and one Hoymiles microinverter

In order for you to integrate energy storage into a balcony solar system, you need to follow these steps:

  1. Remove the input of the original microinverter: Remove the input connection from the PV modules to the original microinverter.
  2. Connect the original PV modules to the input side of the energy storage system: Attach the PV modules to the input side of the energy storage system, allowing the captured solar energy to be stored.
  3. Connect the output of the energy storage system to the input of the microinverter: Link the output of the energy storage system to the input of the microinverter, enabling the stored energy to be converted to AC power.
  4. Plug the output of the microinverter into the home socket to connect to the grid: Finally, connect the output of the microinverter to the home socket, allowing the AC electricity to be used within the home or fed back into the grid.
A typical DC-coupled solar energy storage system for small home installations using Hoymiles microinverter
A typical DC-coupled solar energy storage system for small home installations using Hoymiles microinverter

Depending on the manufacturer, the battery can either be integrated into the storage system or installed separately. This configuration ensures that solar energy is efficiently captured, stored, and utilized, maximizing the benefits of your balcony solar system.

This is what we call a DC-coupled solution.

What are the challenges of a typical solar storage system?

There are two main challenges that you may bump into with DC-coupled systems:

  • Compatibility issues: DC-coupled systems face compatibility problems as different microinverter brands have unique MPPT algorithms. The simulated I-V Curves of energy storage are unlikely to be exactly the same as PV panels in order to work well with your original microinverter, so pairing tests are needed. This requires precise matching, which is often challenging and not always successful. Therefore, it’s likely that your balcony energy storage will only be able to achieve a 99% matching rate with microinverters.
  • Limited energy use: Mainstream DC-coupled systems don’t support bi-directional energy use, meaning they can only export power to the grid and not import it to charge the battery. On top of this, they often don’t support off-grid backup during power outages, meaning they can’t be relied upon when the grid breaks down.

What is Hoymiles’ AC-coupled solution?

Hoymiles has addressed the challenges of traditional solar storage systems by developing an innovative AC-coupled solution. This approach helps to simplify the integration process and enhance compatibility and efficiency, making it a superior choice for residential solar energy storage.

Hoymiles’ system wiring is like this: You plug the microinverter cable into MS, and then connect the output cable of MS to your home socket. It’s as easy as that.

What is Hoymiles’ AC-coupled solution?

Why Hoymiles adopts AC coupling

Hoymiles MS uses AC coupling, where the microinverter transmits AC power that’s already inverted from DC by PV modules to the energy storage equipment.

This is due to the fact that microinverters all put out 230V/50Hz AC power, so AC coupling wouldn’t have the same compatibility issues, although AC coupling is more technically challenging for R&D.

This unique approach eliminates compatibility issues associated with different MPPT algorithms, ensuring seamless integration with all microinverter brands.

The practical benefits of Hoymiles’ AC-coupled solution

  • Easy installation: Hoymiles MS features a built-in pre-installation design. This simplifies the process to just unplugging one connector and inserting three plugs, making it an accessible process, even for people with no practical installation experience.
  • A built-in battery: Hoymiles’ 2.24 kWh battery stores excess solar energy, providing a backup power supply for emergencies and reducing dependency on the grid.
  • Off-grid mode: This mode can be used as a home emergency power supply, offering an uninterrupted power supply even when the grid is down – which in turn enhances energy security.
  • Portable Power Supply:  Hoymiles MS itself can act as an independent power bank. You can plug devices into it when you, for example, go camping.

The future of balcony solar storage with Hoymiles

With Hoymiles’ Micro Storage system, you get unparalleled flexibility, ease of installation, and full compatibility. You can enjoy reliable energy storage, reduced energy bills, and be safe in the knowledge that you’re prepared for emergencies.

This system marks a significant step forward in making solar energy more accessible, simple, and efficient for residential use, all while contributing to a more sustainable future for all.