Home battery: store your solar energy

A home battery stores the electricity your photovoltaic panels produce in excess during the day so it can be used in the evening or at night, when production is nil and consumption picks up again. It increases your self-consumption share, but it does not generate any electricity itself: without a photovoltaic installation upstream, or if production is already fully used during the day, it brings no benefit.

It is also not a substitute for a generator or an industrial uninterruptible power supply. A standard grid-tied battery discharges into the home according to the settings defined, but not every configuration keeps the house powered during a grid outage: this backup function must be explicitly requested, wired separately, and checked at handover.

The right capacity follows from your evening and night consumption compared with the residual output of your panels at those hours, not from a standard product range offered by a manufacturer. A household that mostly consumes between 6pm and 11pm has different needs from one that charges an electric vehicle overnight or heats electrically.

Ask the installer to document this analysis: typical hourly consumption, expected solar output hour by hour, and the coverage rate the battery is meant to achieve. An oversized capacity costs more without added benefit once the evening need is covered, since the surplus that will never be used at night is still exported to the grid as if the battery did not exist.

A battery is housed in a technical room, utility room or garage, sheltered from frost and high heat: the operating temperature range specified by the manufacturer determines its location and its actual service life. A minimum level of room ventilation is generally required, and access must stay clear for maintenance.

The fire safety rules that apply to this type of equipment, including the clearance to be kept from combustible materials and any requirement for a nearby smoke detector, must be confirmed by the installer before installation. They vary with the battery technology and power rating and fall under the installer's professional responsibility, not a judgement made on site.

Connecting a battery to the distribution board and the inverter involves dedicated protective devices, cable sizing adapted to the charge and discharge power, and often an update to the inverter configuration or the addition of a hybrid inverter. This work falls to an electrical company holding a business permit for that trade.

Backup operation, where included, requires a separate circuit that isolates part of the home from the public grid during an outage: this technical point must appear explicitly in the quote, since not every battery or inverter offers it as standard.

A battery's service life is expressed in charge and discharge cycles and in the residual capacity guaranteed after a given number of years; both figures are set out in the manufacturer's warranty and should be requested in writing before purchase. Capacity that gradually declines with use is a normal phenomenon, not a defect.

The Klimabonus Wunnen, which replaced the former PRIMe House programme in 2022, includes a dedicated component for a battery coupled to a residential photovoltaic installation. The eligibility conditions, in particular the link to the solar installation, and the amounts applicable at the time of your application are published on guichet.lu.

A complete quote states the usable capacity in kilowatt-hours, the charge and discharge power, compatibility with your existing inverter or the planned replacement, whether a backup function is included, the electrical protective devices installed, the installation conditions in the technical room, the product warranty and the residual capacity guarantee, and the timeline for installation and commissioning.

Check that the company holds a business permit for electrical work and professional liability insurance; these are public details you can have confirmed before signing.