Hybrid Inverters vs Modular Solar Systems

What are the advantages and disadvantages of today's widely used hybrid inverters compared with systems that use separate battery and solar inverters? Hybrid inverters have become one of the most popular inverter types in recent years. This article explains the concept and when a modular system can be the better alternative.

Introduction and development

Grid-tied solar inverters have been widely used for decades. They convert the DC electricity from the solar panels into AC electricity that can be used directly. Batteries cannot normally be connected directly to a conventional grid-tied solar inverter, and the inverter stops producing when the public grid fails.

Battery inverters, on the other hand, are designed to charge and discharge batteries and can create their own AC grid. They can therefore continue operating when the public grid fails, manage the battery system and, depending on the system design, also feed electricity into the public grid.

Falling battery prices, the desire to use solar energy outside daylight hours and the wish for greater independence during grid failures have driven the popularity of hybrid inverters. In simplified terms, a hybrid inverter combines a grid-connected solar inverter and a battery inverter in one housing.

Characteristics, advantages and disadvantages of hybrid inverters

Combining two functions in one unit can save space, cost and installation effort, and commissioning can also be simpler. The trade-off is that functions, settings and display options can be more limited than in a modular system. In many hybrid designs, the solar-inverter and battery-inverter sections have similar power ratings, for example 10 kW.

The article explains that larger hybrid inverters are normally three-phase. In a 10 kW three-phase example, the available power may be distributed across the three phases. Some models can provide a greater share on one phase while reducing power on the others, but the exact asymmetric-load capability depends on the model.

This means that even a 10 kW hybrid inverter can be overloaded in backup-power operation if large loads are concentrated on one phase. Connecting an entire house indiscriminately to the backup output is therefore not always the best choice. A suitable bypass or transfer switch can be useful so that loads can be supplied from the public grid if the inverter is unavailable.

The article notes that many customers choose hybrid inverters, but argues that they are not the best solution in every case. For systems requiring greater flexibility, a combination of a battery inverter with one or more grid-tied solar inverters and/or charge controllers can be advantageous. This is the modular-system approach.

The modular-system concept

A modular system uses one or more battery inverters together with charge controllers and/or grid-tied solar inverters. The article highlights systems from SMA and Victron Energy, which can be designed for off-grid-capable operation and can create a stable local AC grid when configured appropriately.

Grid-tied inverters and charge controllers

Victron systems can integrate compatible grid-tied solar inverters from different manufacturers into the overall energy system. They can also combine many different Victron MPPT charge controllers.

With a charge controller, the solar panels feed DC power directly towards the battery system. Because batteries operate on DC, this avoids an additional AC conversion step during charging and can provide very high charging efficiency. Charge controllers are available for systems ranging from only a few modules to much larger PV arrays, and each controller provides its own MPPT tracking.

If a Victron MultiPlus-II battery inverter is combined with a grid-tied solar inverter, direct daytime consumption can be supplied efficiently by the solar inverter. The battery and its conversion losses are then bypassed whenever solar power is consumed directly. Charge controllers and grid-tied inverters therefore each have their own strengths.

For example, a business that charges vehicles mainly in the evening may benefit from strong DC charging into the battery via charge controllers. A site with high direct daytime consumption may benefit more from grid-tied solar inverters combined with the battery inverter.

Diagram: possible combinations of solar inverters and charge controllers with the VE MultiPlus-II.

The article also refers to an inutec three-phase Victron system in Schladen that combines two solar inverters with three 5 kW Victron MPPT charge controllers. The stated aim is to combine the advantages of both approaches.

Tip for existing systems

If you already have a solar system without battery storage and one or more reasonably modern grid-tied string inverters, adding a separate battery inverter such as a MultiPlus-II can allow the existing solar inverters to remain in use. This can be simpler and more economical than replacing the existing inverter equipment with a new hybrid inverter.

Who are the main manufacturers of modular systems?

The article highlights the European manufacturers SMA and Victron Energy. It describes SMA Sunny Island systems as particularly suitable for larger projects and Victron systems as especially flexible for homes and end customers.

Victron MultiPlus-II units include the switching functions required for suitable backup/off-grid configurations, so a correctly designed system can disconnect from the public grid and continue supplying selected loads.

Which is cheaper: a hybrid inverter or a modular system?

The article states that the purchase costs of modular systems and hybrid-inverter systems can be comparable. One potential cost advantage of some SMA and Victron configurations is the use of 48 V low-voltage batteries such as the Pylontech US series. Depending on the battery system, the battery-management electronics can already be integrated into the modules, reducing the need for a separate external BMS.

Conclusion

• If you want a relatively simple solar system with battery storage, the wide range of available hybrid inverters can be a good solution.
• If you want to combine differently oriented panel groups, add more PV fields later, use extensive software and configuration options, or build a system that can operate independently of the public grid, a modular system with separate battery inverter, solar inverter and/or charge controllers can offer more flexibility, albeit with greater installation and configuration effort.

If you buy a Victron system, technical support for system configuration is available remotely. Get free advice.