Should I get a modular solar battery?

What is a modular solar battery?

A modular solar battery allows users to expand capacity or voltage by connecting multiple battery units in parallel or series, much like stacking LEGO bricks. These energy storage systems consist of smaller, interchangeable modules that can be combined to create a larger, customisable power solution.

Sometimes referred to as ‘hot-swappable modules’, these systems enable users to replace or upgrade individual units without disrupting the entire system. This ensures uninterrupted operation during maintenance or expansion. As demand for flexible home energy storage grows, more manufacturers are designing modular systems to offer adaptability, easier repairs, and future-proofing, effectively providing multiple solutions within a single product.

Modular vs. monolith: the trade-off between design and flexibility

Monolith batteries, like the Tesla Powerwall 3, are non-modular, meaning their battery packs cannot be replaced or expanded without affecting the entire system. These units come in fixed capacities and are typically heavier—often exceeding 100 kg—requiring multiple people for installation. The only way to scale up a monolith system is by connecting another unit in parallel to the existing one, as shown below:

At first glance, modular batteries may seem like the obvious choice. However, the table below provides a comprehensive comparison of advantages and disadvantages, ensuring you have a well-rounded perspective before making your decision:

Expanding a modular system offers superior energy management, with optimised energy flow, unified battery management, and efficient charge distribution, resulting in minimal energy losses. In contrast, expanding a monolith system requires separate power electronics and inverters for each unit, leading to imbalanced charging, higher conversion losses, and reduced efficiency in grid exports. This makes modular batteries a more flexible and efficient choice for those who anticipate that their energy needs change in the future.

Which batteries are modular and monolith?

Below is a high-level breakdown of popular home battery models available in the UK, including some key technical specifications:

If you only need an extra 5 kWh of storage, a modular system like Instagen allows you to expand gradually without overspending or over-sizing your system. In contrast, with a monolith system like the Tesla Powerwall, you'd have to add another full 13.5 kWh unit, which may be far more than what you need.

Modular batteries offer more precise scalability, making them a better choice for smaller incremental expansions. However, if you’re looking for an all-in-one solution with higher efficiency and don’t plan on expanding in small steps, a monolith system might still be worth considering.

Conclusion

In most cases, a modular battery offers a more flexible, cost-effective, and scalable solution. However, if space constraints, aesthetics, or specific software features are a priority, a monolith battery may still be a viable option.

If you anticipate higher electricity consumption in the future, a modular battery ensures easy, cost-effective expansion without the need for costly system overhauls.

Ultimately, the best choice depends on your current and future energy needs, available space, and personal preferences. If you're considering home battery storage and need guidance on the right system, complete the quick survey below to receive a tailored recommendation: