The Client
A property investment company with a portfolio of three commercial office buildings in the Thames Valley, totalling 18,000m². The buildings were constructed between 2005 and 2015 and had D- to C-rated EPCs. The portfolio's annual energy costs were £680,000, with £240,000 driven by peak demand charges. The company had a 2030 net-zero target and needed to improve the EPC ratings to meet MEES regulations.
The Challenge
The portfolio's peak demand was 2.8MW, triggered by the simultaneous startup of HVAC systems across all three buildings at 7am. The capacity charge was £85/kW per year, meaning the portfolio paid £238,000 in peak demand charges alone. The buildings also had aging gas boilers (60% efficiency) and no renewable energy generation.
The company wanted a portfolio-wide solution that would reduce costs, improve EPC ratings, and meet the net-zero target. The solution also had to be replicable — the company planned to acquire 5 more buildings in the next 3 years and wanted a standardised approach.
The Skyline Approach
We analysed 12 months of half-hourly data from all three buildings. The data revealed a clear pattern: the peak demand was 2.8MW for 45 minutes each morning, but the baseload was only 1.2MW. The HVAC systems were the peak driver, and they were controlled independently — each building's BMS started at 7am without coordination.
- Peak demand 2.8MW for 45 min/day — battery could absorb the entire peak
- HVAC systems uncoordinated — staggered startup reduced peak by 400kW
- Aging gas boilers across all three buildings — heat pump standardised heating
- Battery + heat pump hybrid cut peak charges and eliminated gas bills
The key insight was that the portfolio's problem was not a lack of generation — it was a lack of coordination. The battery absorbed the HVAC startup peak, and the heat pumps replaced the gas boilers. The combined system cut the peak demand from 2.8MW to 1.6MW, and eliminated the gas bill entirely.
The Solution
1.2MWh BESS
Central battery system serving all three buildings via private wire. The battery discharges 1.2MW during the 7am HVAC startup, reducing the grid peak from 2.8MW to 1.6MW. The battery also provides arbitrage savings by charging overnight at 12p/kWh and discharging during peak hours at 78p/kWh. Annual peak demand charge reduction: £168,000.
800kW Heat Pump Array
Air-source heat pumps across all three buildings, with a total capacity of 800kW and a COP of 3.2. The system replaces the gas boilers and provides heating and hot water. Annual heat output: 4,200MWh. Annual electricity consumption: 1,300MWh. The gas bill of £180,000 is eliminated.
The Results
| Metric | Before | After |
|---|---|---|
| Peak demand | 2.8 MW | 1.6 MW (-43%) |
| Peak demand charges | £238,000/year | £52,000/year (-78%) |
| Gas consumption | 4,200 MWh/year | 0 MWh/year |
| Average EPC rating | C (68) | B (45) |
| CO₂ emissions | 1,100 tonnes | 520 tonnes (-53%) |
The Peak Shaving Effect
The most significant financial impact was the peak demand charge reduction. Before the battery, the portfolio's demand profile showed a 2.8MW spike at 7am every day. After the battery, the spike was 1.6MW. The battery discharged 1.2MW during the startup window, and the grid only saw 1.6MW. The capacity charge dropped from £238,000 to £52,000 — a saving of £186,000 per year.
The battery also provided arbitrage savings. It charged overnight at 12–15p/kWh and discharged during the evening peak at 78p/kWh. The daily cycle was 1,000kWh, and the average price spread was 60p/kWh. The daily arbitrage was £600, or £150,000 per year. The battery cost £320,000, so the arbitrage alone pays for the battery in 2.1 years.
The Portfolio-Wide Impact
The property investment company now has a standardised energy solution for all new acquisitions. The battery + heat pump configuration is designed to be modular, with a standard 400kWh battery unit and a 200kW heat pump unit per 6,000m² of floor space. The company has applied this to two new buildings in 2026, with identical results.
The EPC rating improvement was also significant. The average EPC across the portfolio improved from C (68) to B (45), which increased the property value by an estimated £1.2m (based on a 5% cap rate premium for B-rated buildings). The energy savings were £310,000 per year, but the property value uplift was an additional £1.2m.
The Technology-Agnostic Approach
The key to this project was recognising that the portfolio's problem was coordination, not generation. The battery handled the peak, the heat pump replaced the gas, and the combined system was modular and replicable. A solar array would have been a poor fit — the buildings had limited roof space and the peak demand was the primary cost driver.
If you manage a portfolio of commercial buildings with high peak demand charges and aging heating systems, a battery-plus-heat-pump system may be the right answer. We offer free feasibility studies that model your portfolio's specific load profile and heating demand.