Storage that earns its place, sized to your load.

Commercial storage pays in more than one way, and the value stacks: a lower metered peak, cheaper energy shifted from off-peak, more of your own solar used on site, and sometimes income from grid services. Which of those matters most depends entirely on your load and your tariff, so the design starts with your half-hourly data, not a per-kWh rule of thumb.

These pages orient you before the survey: how a commercial battery works, how it is sized and costed, the bankable makers we specify from, and the jobs a battery can do. The tax treatment of standalone storage is not settled, so we are careful with the numbers and point you to your own adviser.

What is a commercial battery storage system, and where does its value come from?

A commercial battery energy storage system, or BESS, is a block of lithium cells, power-conversion electronics and control software that sits between your incoming supply, your solar array and your loads. It charges when power is cheap or your panels are generating more than the building can use, and it discharges when power is expensive or your demand spikes. On a site over 50 kWp the unit is rarely a single wall box. It is a rack, a cabinet or a row of cabinets, with its own protection, metering and an energy-management layer deciding moment by moment what to do.

The reason a commercial battery earns its keep is that its value stacks: no single one of those jobs usually justifies the capital on its own, but together, against the right load and tariff, they can. The starting point is always how the equipment behaves, which we set out plainly in how commercial battery storage works. Everything after that is a question of which parts of the value stack your specific site can actually reach.

AC-coupled or DC-coupled, and how the architecture is chosen?

The coupling decides where the battery sits relative to your inverters. A DC-coupled system shares an inverter with the solar array and stores energy on the DC side before it is ever converted to AC. That keeps round-trip losses down when the battery is mostly soaking up surplus solar, and it suits a new-build where panels and storage are designed together. An AC-coupled system has its own inverter and connects on the AC side, alongside the existing supply. It is the natural choice for retrofit, for storage that has to work independently of the solar, and for sites where the battery's main job is tariff arbitrage or peak shaving rather than catching PV surplus.

Most commercial projects end up as a considered mix. A large site may run DC-coupled storage on a new PV block and AC-coupled storage to handle the wider load, governed by one control system. We choose the topology from what the site has to do, how much solar is involved, whether it is retrofit or new, and how the connection is configured, rather than from whichever arrangement a brochure happens to show. The hardware that ties it together is covered in how it works, and the brain that coordinates it is the subject of EMS software.

How is a commercial battery sized, and why does the job set the number?

Sizing follows the job the battery has to do, and a per-kWh rule of thumb cannot capture that. A battery is described by two figures that are easy to confuse: power, measured in kW, which is how hard it can push or pull at any instant, and energy, measured in kWh, which is how long it can sustain that. The right ratio between them depends entirely on what you are asking the battery to do. Peak shaving is a power problem first: you need enough kW to flatten the spike and enough kWh to cover how long the spike lasts. Arbitrage and self-consumption are energy problems: you need the capacity to hold a meaningful block of cheap or solar-generated power and release it later. Backup is sized on the critical load you must keep alive and the hours you need to ride through.

That is why we will not put a figure on a battery from a phone call. We size from your half-hourly consumption data and your solar generation profile, read against the specific outcome you are buying. A unit sized for backup may be wrong for arbitrage, and a unit sized to shave a short sharp peak may be far smaller than one sized to shift energy across a whole evening. The method, and the data we ask for, is set out in full on battery sizing.

Which battery brands do we specify, and what does bankable actually mean here?

We are brand-agnostic, and bankable here is an engineering test rather than a marketing tier. Solar modules have a recognised tiering scheme. Batteries do not, so we never describe a BESS as Tier 1, because the phrase belongs to PV modules and means nothing for storage. For a battery, bankable comes down to four hard questions. Is the manufacturer large enough and established enough that the warranty will still be honoured in ten years? Does it have a real track record at the scale you are buying? Is the warranty written in terms you can actually rely on, with a stated cycle life and capacity retention? And is the product certified to the standards that matter, IEC 62619 for the cells and modules and IEC 62933 for the system?

Judged that way, we specify from the makers we supply through UK distribution, led by Sigenergy and including Sunsynk, Solis, SolaX, Fox ESS, SolarEdge and JA Solar. The one we choose follows the project, its scale and your appetite for risk, with the warranty terms confirmed before contract rather than assumed. Where each brand sits relative to its capital is part of the picture on battery costs.

What jobs does a commercial battery actually do day to day?

Four jobs cover most of the load-side value, and the right design usually combines them. Peak shaving targets the half-hours when your demand spikes and your capacity or demand charges are set, holding the metered peak down by discharging through it; we cover the mechanics on peak shaving. Time-of-use arbitrage charges the battery when energy is cheap and discharges it when it is dear, turning a tariff spread into avoided cost, which is the subject of time-of-use arbitrage.

Solar self-consumption is often the quiet workhorse on a site with panels: instead of exporting surplus generation for a low rate, the battery stores it and feeds it back into the building later, so more of your own clean power offsets an expensive import. We set that out on solar self-consumption. Backup power is the job that has nothing to do with saving money and everything to do with continuity, keeping a defined critical load running through an outage, which we cover on backup power. Which of these dominates is a property of your load and tariff, and it is exactly what the survey is there to find.

Can a battery earn revenue from the grid, and how honest should that case be?

It can, and this is the part of the value stack where we are most careful with language. Beyond cutting your own costs, a battery can be paid to support the network: providing fast frequency response and other balancing services, holding capacity available for the system operator, or being pooled with other assets and dispatched by a third party. We describe each route on grid services, the Capacity Market, and aggregators and VPPs.

The income from these routes is modelled and market-dependent, and we never present it as promised. The rates move with auctions and with a fast-changing market, eligibility carries technical and contractual conditions, and a route that pays well this year may not next. So we put no fabricated per-kW-year or per-MWh figure on a page. Where revenue stacking is part of a business case, we model it against current market conditions, flag it as a variable rather than a guarantee, and let your own financial adviser sign off the assumptions. Treated that way it can be a genuine part of the return, and we will not write it up as a fixed promise.

What chemistry, safety and standards sit behind a system we would specify?

For commercial storage we specify LFP chemistry as the default. Lithium iron phosphate trades a little energy density for a markedly better thermal and safety profile and a long cycle life, which is the right balance for a fixed asset that has to cycle daily for many years. NMC has its place where space is tight, but for most yard and plant-room installations LFP is the sensible choice, and we explain the trade in full on LFP vs NMC.

Safety is engineered in layers. The cells and modules should meet IEC 62619 and the system IEC 62933, with the battery management and energy-management software watching cell voltages and temperatures continuously and shutting down before a fault propagates; the control layer is covered on EMS software. Around the hardware sit fire detection, separation distances, ventilation and the early-warning monitoring we set out on fire safety. For larger or outdoor deployments a containerised BESS brings its own fire suppression, thermal management and enclosure rating as an engineered package, which simplifies siting on a constrained yard.

What does planning and the grid connection actually involve?

The connection is usually the longest pole in the tent, so we plan it at the start of the project. A storage system that can export to the network needs a G99 connection agreement with the distribution network operator, which across our region is Northern Powergrid. The application sets out how much the site can import and export and under what conditions, and the operator's response can shape the size and even the viability of the scheme. On a constrained part of the network the offer can carry a cost or a curtailment condition, and the timescale is measured in months, not weeks. We cover the realities of the queue in the guide on the grid connection queue.

Planning is the other gate. A wall-mounted or indoor battery often sits within permitted development, but a sizeable outdoor or containerised installation can need full planning permission, with fire-service consultation, environmental and acoustic considerations and siting constraints to satisfy. We set out what to expect on planning. Both processes run in parallel with the design, and we sequence them deliberately so the connection offer and any planning condition are known before you commit capital.

What does a commercial battery cost, and how is the return worked out?

We do not publish a from-price, because an honest battery figure cannot come from a brochure. The capital depends on the power and energy you actually need, the coupling and connection, the brand specified, the civils and the connection conditions, and those only become real after a survey. So the cost is survey-led, and the number you receive is yours rather than a headline designed to win a click. How the capital breaks down, and how brand and scale move it, is set out on battery costs.

The return is modelled the same way. We take your half-hourly load and your solar profile, apply the jobs the battery will do on your site, and produce a business case grounded in your own data. Any saving, payback or ROI we show is modelled and market-dependent rather than guaranteed, because tariffs and grid-service rates move. You can see how the levers interact on the ROI calculator. One further caveat we will not paper over: the capital-allowances treatment of standalone storage is not settled in public HMRC guidance, so we give you the engineering and the indicative figures and leave the tax position to your accountant.