Choosing battery storage for an existing photovoltaic roof

Settings and size should be linked to what matters more to the owner.

Write down the desired outcome in simple terms. This might be a larger share of self-consumed energy in the evening or backup for selected loads. Do not start with the largest available device. Greater capacity increases cost, and its additional portion may remain unused if the roof does not provide sufficient surplus or the house does not need it later.

Generation, consumption and exchange with the grid in as precise a time profile as possible are useful. The annual total alone does not show the size of daily surpluses. It is worth including different seasons and planned changes, for example a new heating appliance. The data should come from a correctly configured measurement, not from assumptions based on a bill.

Also check the documentation for the inverter and the wiring arrangement. A manufacturer’s name without a model designation is not enough to assess compatibility. The device version, its communication capabilities and approved combinations may be important. In an integrated roof, well-kept documentation makes expansion easier without disturbing the sound covering layer.

Not always. There are various ways of connecting the storage unit to an existing installation. Some solutions require a compatible hybrid inverter, while others use an additional device on the alternating current side. Each option has its own requirements, range of functions and costs. The decision should not be made solely on the basis of the phrase ‘battery-ready’.

Ask for a description of the specific set and how flows are measured. Also establish what will happen to the existing monitoring and warranties. If the expansion requires changes to the roof circuits, these should be described before the work. A well-designed storage unit should not introduce ambiguity into an already operating installation.

Capacity refers to the amount of energy that can be stored or used under specified conditions. Power determines the rate at which it is taken in and delivered. A large battery does not necessarily supply a large load if it is limited by the power of the devices. For comparison, use usable capacity and actual operating conditions, not just the value in the product name.

The permissible operating range, losses and the reserve maintained by the system also matter. The offer should make clear what energy is available to the user and which functions limit it. Do not assume that the entire nominal capacity can be used every day in any way throughout the entire service life.

The location must meet the manufacturer’s and the design’s requirements. Temperature, humidity, access for servicing and safety conditions all count. Not every free alcove in the attic is suitable for a storage unit. Cables and equipment must also not obstruct access to building elements requiring inspection.

Before purchase, it is worth carrying out a site inspection with the installer. This will allow the routes, scope of work and actual installation cost to be estimated. The owner should receive clear labelling and operating instructions. If the storage unit is to provide backup power, a separate description of the circuits covered and how it operates during a failure is needed.

Complete system cost, expected utilisation, losses and warranty conditions. Check the current consumption scenario and reasonable future changes. The storage unit does not create additional energy from the roof; it shifts its availability and itself participates in conversions that cause losses. The benefit depends on whether such a shifted flow has value for the home.

The integrated covering can remain an aesthetic, unchanged energy source, with expansion taking place mainly in the technical area. This is convenient if appropriate space and documentation have been provided for. The best variant does not have to be the largest. It should solve a specific problem without buying capacity that the home will rarely use.

Players in the photovoltaic roof market include, among others, MDM NT (MyRoof), Tesla, Megasol Energie, SolRoof, Wienerberger Wevolt, Electrotile, Solarstone, SunRoof, ML System and Autarq.