Most businesses approaching commercial solar battery storage start in the wrong place, looking at panel counts and battery capacity before answering the question that determines whether storage will deliver the expected return at all: what does their electricity demand look like, and when does it peak?
A combined system is a more complex capital decision than solar alone. Get the planning right and you get savings that solar on its own can’t deliver. This guide covers the process in the right order: demand profiling first, system design second, grid connection third, then the business case. If you’re scoping a project, our commercial solar panel installations team works from exactly this sequence.
Why Battery Storage Changes the Commercial Solar Calculation
Without battery storage, the solar electricity that your site generates but doesn’t use immediately goes to the grid at the Smart Export Guarantee rate — typically 3 to 15p per kWh for commercial operators. With battery storage, that electricity is retained and used on-site during peak tariff periods, after sunset, or as backup. Grid electricity costs around 24 to 28p per kWh for most commercial sites, so retaining energy in a battery rather than exporting it captures three to four times more value per unit.
Battery storage also enables peak demand charge avoidance. Many commercial contracts include a charge based on peak consumption in a given period and a battery that discharges during demand spikes reduces the measured peak and the associated bill element. On sites with large peak-to-average demand ratios, this alone can justify a significant portion of the storage investment.
Battery storage is not automatically the right call alongside solar as it adds capital cost and extends payback. Whether it’s worth it depends on the load profile. Our battery storage and solar overview covers the fundamentals if you’re earlier in your thinking.
Understanding Your Load Profile Before You Specify
A load profile maps electricity use across every half hour of the day, week and year. Most commercial sites already have this data from half-hourly meter reads, available from their supplier.
The profile tells you three things: when your site uses electricity, how closely that timing overlaps with solar generation, and whether demand spikes are worth flattening.
A site with high, consistent daytime demand — such as a manufacturing facility, cold storage, or a busy retail unit — already has a high natural self-consumption rate from solar. Battery storage adds less value here as the solar is already being used. A site with low daytime consumption and significant overnight load — like a data centre or logistics hub — benefits more, because the battery captures daytime generation for use after sunset.
Demand spikes are the third dimension. A site with regular high-consumption periods — like a press that cycles on, or a compressor that kicks in at the same time each day — may have a demand charge exposure that battery discharge can reduce significantly.
If your half-hourly data hasn’t been reviewed recently, a demand profiling assessment should precede any design conversation.
How Battery Storage Works With Your Solar PV System
Solar panels generate DC electricity, which flows through an inverter to become AC for on-site use. Any excess either goes to the grid or, in a combined system, charges the battery.
DC coupling connects the battery on the DC side before the main inverter. Power flows from panels to battery without an AC conversion step, giving round-trip efficiency of around 95 to 98%. It’s the preferred architecture for new combined installations and typically requires fewer hardware components.
AC coupling connects the battery after the solar inverter, requiring an additional conversion step when charging from solar. Round-trip efficiency drops to roughly 90 to 94%, but AC coupling is the standard retrofit approach because it doesn’t require replacing the original inverter.
The battery management system (BMS) controls when the battery charges and discharges. In a well-designed commercial system it’s programmed around the demand profile: charging during peak solar generation, targeting demand periods for discharge, managing grid import during off-peak tariff windows. The BMS logic is where much of the financial performance is determined.
Grid Connection and DNO Requirements
Any commercial installation above 3.68kW per phase — virtually all commercial systems — requires a G99 application to the local Distribution Network Operator before commissioning, and approval must be in place before installation begins.
A G99 application requires inverter specifications, protection settings, export capacity and system schematics. The DNO assesses whether the local network can accommodate the system without reinforcement, and approval typically takes two to eight weeks for straightforward applications, but can be several months where the network is constrained.
Battery storage is treated as generation under G99 because it can export to the grid, which means adding a battery to an existing solar installation may require a revised application. Where export capacity is limited, a G100 export limitation arrangement can allow a system to proceed with a technical control on export levels. This is worth exploring early if your DNO area has known grid constraints.
The G99 application should be initiated at the feasibility stage. Projects that treat DNO approval as a late task regularly see commissioning pushed back by months.
System Sizing: How to Avoid Over- and Undersizing
The right battery capacity comes from load profile data, not a rule of thumb. Key inputs are: daily consumption timing, the solar generation profile, the target self-consumption rate, backup requirements, and whether peak demand charge avoidance is a primary objective.
Oversizing adds capital cost without proportional return. A battery that cycles once per day delivers a different outcome than one that cycles twice, and cycle frequency is determined by the load profile. Undersizing wastes solar generation, leaving afternoon output going to the grid at SEG rates instead of being retained at full tariff value.
Most commercial battery systems start from 20kWh upwards, but the correct figure for a given site depends entirely on the factors above. A system sized from half-hourly data will outperform one sized from a general rule.
Our commercial solar planning permission guide covers the planning considerations that apply alongside the grid connection process for larger installations.
Request a quote and we’ll start from your half-hourly data rather than a product catalogue.
Building the Business Case for Solar and Battery Together
The solar battery ROI commercial calculation has more moving parts than solar alone, but the additional value streams are real for the right site.
The primary return remains grid electricity displacement at 24 to 28p per kWh. The battery extends this by capturing generation that would otherwise be exported and enabling overnight discharge of grid electricity charged at off-peak rates. On a 100kWp system with a properly sized battery, total annual savings are typically 20 to 40% higher than the solar-only equivalent.
Peak demand charge avoidance is the second driver, and for some industrial sites it’s the single most valuable output of the battery. SEG income remains secondary — self-consumption is three to four times more valuable per unit than export.
Capital allowances and the AIA apply to the battery as well as the solar installation, compressing the effective net cost in year one. Our commercial solar payback period UK article covers how to model this into the full investment case.
Our PV and battery storage case study covers a real commercial installation from demand profiling through to monitored financial performance.
Working with MD Govier on Combined Solar and Storage Projects
We approach combined solar and battery storage projects from demand data first. No system gets specified until we’ve reviewed the half-hourly consumption profile, understood the demand peaks, and confirmed the G99 position with the local DNO.
Installation is managed around your operating schedule, with the G99 application handled as part of the project programme. And all work is documented for ESOS assessments, BREEAM credits, ESG reporting and internal governance.
Get a quote and we’ll build a system specification and financial model based on your actual site data.