Battery storage for commercial solar: is it worth the extra capital?

Battery storage has become the default upsell on a commercial solar quote. It’s bundled in almost automatically, and installers often pitch it with a line about “avoiding peak charges.” However, that reasoning doesn’t hold up as well as it used to.

Sometimes storage is genuinely the right call. Often, on a straight numbers basis, it isn’t. Specifically, the honest answer depends on your export tariff, your load profile, and what your network charges actually look like. It doesn’t depend on whether an installer has a battery in stock.

What a commercial battery actually costs right now

Installed cost is the first thing to get straight. It varies more by system size than most quotes make clear. Fixed costs don’t shrink at the same rate on a small system. The grid connection, controls, fire safety measures, and integration with the existing inverter cost about the same regardless of size. As a result, per-kWh pricing falls sharply as capacity rises:

System size	Typical installed cost
Up to 50kWh	£400–£800 per kWh
~100kWh	£200–£400 per kWh
200–500kWh	£300–£500 per kWh
500kWh+ (containerised)	£140–£240 per kWh

So a modest 100kWh system might land anywhere from £20,000 to £40,000. However, a 500kWh containerised unit, despite holding five times the energy, could come in under £100,000.

Site-specific factors move these figures further. A straightforward indoor installation with spare switchboard capacity is cheap. However, a site needing a new transformer, an external enclosure, or extra fire compartmentation is not.

This capital sits on top of the panels. It therefore needs its own business case, not a free ride on the solar payback.

When storage genuinely earns its keep

Storage tends to pay for itself when one or more of these apply:

• Your export rate is weak relative to what you’d otherwise pay for power. Smart Export Guarantee rates vary hugely by supplier. Commonly quoted fixed rates run from around 3p to 15p per kWh, occasionally higher on bundled or conditional tariffs. If your export rate sits well below your import rate, that changes the maths. Storing surplus generation and using it later becomes worth more than selling it back at a low fixed price.
• You carry real exposure to peak-time network charges. Most DNOs charge under a red/amber/green DUoS structure. The red band applies during weekday peak hours — commonly 4pm to 7pm. DNOs price it well above the green (off-peak) rate. If your site draws heavily from the grid in that window, discharging stored solar power instead of importing pays off. It’s a genuine, recurring saving.
• You have a real resilience requirement. Cold storage, server rooms, security and life-safety systems, and livestock or irrigation infrastructure are the clearest cases. Here, downtime costs far more than the battery’s price. The case for resilience can stand alone, independent of the energy-arbitrage numbers.
• Your load profile is mismatched with generation. A site with heavy early-morning or evening demand, paired with a midday generation peak, wastes a meaningful share of its solar output. Storage bridges that gap. Examples include some retail units, schools with after-hours use, and certain shift patterns.

When it’s usually just added cost

Storage is harder to justify when:

• Self-consumption is already high. Many warehouses, factories and cold stores have heavy, steady daytime process loads. These sites may already use 70–80% or more of what the panels generate in real time. That leaves simply less surplus to store.
• The export tariff is already reasonable. If you’ve secured a decent SEG rate, you’re not wasting exported power at a token price. That weakens the case for storing it instead.
• Peak-charge exposure is minor. Smaller sites on lower-voltage connections can carry a much smaller DUoS red-band burden. In that case, there’s less to save by shifting consumption.
• There’s no real resilience need. A short interruption to supply is an inconvenience, not a cost. In that case, you’re arguably better off spending the capital elsewhere — on a larger array, efficiency measures, or simply banking it.

A myth worth correcting: “avoiding Triad charges”

Older battery pitches still reference “Triad avoidance.” This means shifting demand away from the three half-hours of highest annual system demand, to cut transmission charges. That strategy is largely obsolete, however.

Under Ofgem’s Targeted Charging Review, most of that residual transmission charge (TNUoS) moved onto fixed, capacity-based charges rather than usage at peak times. Distribution charges followed this shift from 2022; as a result, the old Triad system effectively wound down by 2023.

If a battery quote leans heavily on Triad savings as its main financial case, that’s worth challenging. The real, still-live saving comes from DUoS red-band charges instead. These are a separate, distribution-level mechanism, and they remain genuinely time-of-use.

Running the actual numbers

However, none of the above is a substitute for modelling your own site. Several variables decide whether storage pays back. They include your half-hourly load profile, your actual export rate, your exposure to red-band hours, the battery’s round-trip efficiency, and its warranted life before capacity degrades. These all interact in ways a generic rule of thumb can’t capture.

That’s exactly what our energy and ROI modelling work does. We run the solar-only case and the solar-plus-storage case side by side, on your real consumption data. As a result, you can see whether the extra capital earns its return or whether it’s better banked.

Where the answer is genuinely marginal, a short feasibility study is usually the cheaper option. It helps you find that out before committing to either. Still, we have no battery to sell you, so the recommendation goes whichever way the numbers point — including, sometimes, “not yet.”