Battery storage is often presented as a natural companion to solar, and sometimes it is. But a battery is a specific answer to a specific problem: a gap between when a property generates electricity and when it uses it. Where that gap is small, a battery has less to do.
The question a battery actually answers
Solar panels generate mostly around midday. If a property's demand also peaks around midday, most of that generation is used as it is produced, and a battery has comparatively little surplus left to store.
If a property's demand peaks in the evening or overnight, a significant share of daytime generation would otherwise be exported. A battery captures part of that surplus and releases it later, when the property is actually drawing power.
Residential and commercial cases usually differ
A household that is out during the day and home in the evening is a common example of a real gap. A business that operates mainly during the hours it also generates, such as many offices, retail units and workshops, is a common example of a small gap.
Hospitality is more mixed: a restaurant open mainly for dinner service has a clear gap; a hotel with continuous daytime occupancy and daytime laundry or kitchen loads may not.
Backup power is a separate question
Storing surplus generation for later use is a different function from keeping the lights on during a power cut. Backup requires specific equipment and wiring, usually covers only selected circuits, and is not automatic just because a battery is installed. If backup matters to you, say so explicitly during the assessment.
Sizing follows the gap, not the roof
Where a battery is worthwhile, its capacity should be set against the energy the property draws in its gap period on a typical day, not against the peak output of the array. Sizing for the best generating day of the year usually leaves the battery under-used most of the time.
Questions worth asking before adding one
- How large is the gap between our generation hours and our demand hours?
- Is that gap consistent across the week, or does it vary by day?
- Do we want backup during a power cut, and does the proposed system actually provide it?
- Would reserving capacity for a battery now, without buying one yet, be the more sensible first step?
Related: Battery Storage
This article is general, technical background written for the Solara Energy demonstration website. It is not project-specific advice.
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