Battery Energy Storage for Office & Business Centres: Pre-Design Survey Checklist

The Physics of the Problem: Why Offices Are Not Factories

An office building's demand is dominated by lift motors (reactive power spikes up to 3x rated current during acceleration), tenant server rooms (constant 24/7 load, sensitive to voltage dips), and lighting/access control that must stay on even during a grid fault. These loads create short, high-power peaks that set your contracted capacity, not the average load.

At 0.4 kV, a 400 kW peak lasts only seconds (lift starting, chiller inrush). The grid connection is sized for that peak, so you pay demand charges for capacity used 1% of the time. A BESS shaves that peak, letting you lower contracted capacity without touching the building's behaviour.

What to Measure: Load Profile and Power Quality

You need a 1-minute interval load profile for at least one full week, ideally a month that includes a working day and a weekend. Record active power (kW), reactive power (kVAr), and voltage (V) at the main LV switchboard.

• Measure lift motor starting current (use a power quality analyser with 1-second logging).
• Log server room load separately – it is often 30-40% of the total.
• Check voltage sags: if you see dips below 90% of nominal, the BESS must have a fast response (<50 ms).

Without this data, any sizing figure is a guess. For a 60-400 kW building, you need at least 7 days of data to catch the peak that occurs only on a hot Thursday afternoon.

Documents to Pull: Bills, Single-Line Diagram, and Grid Contract

Get the last 12 months of electricity bills – they show the actual contracted capacity, demand charges, and energy tariffs. The single-line diagram (SLD) tells us the voltage level, transformer rating, and how the backup loads (lifts, security, comms) are wired.

Check the grid connection agreement: some DSOs (e.g., DTEK Kyiv) charge for exceeding contracted capacity by UAH 50-100 per kW per month. Also verify if the building has a standby diesel generator – if yes, the BESS can be smaller, covering only the transition time.

If the building is fed at 10 kV, we will need a transformer – that changes the solution. At 0.4 kV, we can connect directly to the LV busbar.

Rough Sizing Method: Power and Capacity for This Profile

Power (kW) = the peak you want to shave minus the new contracted capacity. For an office, start with the highest 15-minute average peak (from your load profile). Set the new contracted capacity to the 95th percentile of the load – that usually cuts 15-25% of the peak. The BESS power rating must be at least that difference.

Capacity (kWh) = power × duration. For office peaks, 15 minutes is enough for most shaving, but for backup of lifts and server rooms, you need at least 30 minutes of autonomy. Example: if the peak to shave is 150 kW, a 150 kW/75 kWh system (0.5C) gives 30 minutes of backup.

A common error is sizing for the average load, not the peak. That undersizes the inverter and the system trips during a lift start.

What Happens When Sizing Is Wrong: Failures and Costs

If the BESS is undersized on power, it will hit its inverter limit during a lift start – the output voltage sags, the UPS in the server room kicks in, and the lift controller may fault. Tenant complaints follow, and the system is useless for demand charge reduction.

If undersized on energy, the battery depletes before the peak period ends (e.g., evening cooling load) – you still pay the demand charge. Oversizing is a waste of capital; the payback stretches beyond 7 years.

Worst case: a system that cannot switch to island mode fast enough causes a blackout during a grid fault – access control fails, car-park lights go out, and you have a liability issue.