FLATLINE

What if your home's energy system was clever enough to heat the house, charge the battery, and top up the hot water tank — all before anyone else on the street woke up, at a fraction of the usual cost, without you lifting a finger? That's what FLATLINE set out to prove was not just technically possible, but commercially viable at scale.

The UK's largest domestic Demand Side Response trial, FLATLINE was an 18-month BEIS-funded project, invented and led via Sero with PassivSystems that demonstrated a radical new energy model for residential homes: fixed, predictable bills that are dramatically lower than average, delivered through intelligent coordination of home energy technologies — all without asking residents to change a thing about how they live.

The win:win:win proposition

What it delivered

The project trialled its methodology across two new-build pilot sites: 56 homes at Parc Eirin in Tonyrefail, and 3 homes at The Mill in Cardiff. These homes were built to a higher thermal specification than industry average — and critically, the build was monitored from foundations up to eliminate the "Performance Gap," the 27% deviation between design intent and construction reality that blights much of UK housing.

The technology

Each home was fitted with a coordinated suite of smart energy technologies, managed by the Building Energy Engine (BEE) — the intelligent hub developed by Sero and PassivSystems that sits at the heart of the system:

The BEE connects each home to a cloud-based control system that draws on metered data, weather forecasts, grid carbon intensity, and energy tariff pricing to optimise every home's behaviour in real time. It knows when to charge the battery from cheap overnight grid electricity, when to pre-heat the house before the expensive evening period, and when to let solar generation take over — all without any input from the resident.

How it works in practice

During the dDSR trials, the project tested two tariff approaches: a Carbon Saving tariff (which concentrated electrical import during cheap overnight periods) and the Octopus Agile tariff (which exploited a wider range of price windows throughout the day). In both cases, the outcome was the same: near-zero grid import during peak evening hours.

The intelligent technologies built into the fabric of their home anticipate and act upon demand — delivering the lowest-cost, cleanest energy whilst supporting the National Grid's decarbonisation.

In winter, the battery charges fully overnight, discharges through the morning, recharges ahead of the expensive evening period, and powers the home through peak hours without touching the grid. In summer, the system adapts: it charges only as much as needed overnight, then defers to solar generation as soon as it becomes available, saving battery capacity for the valuable evening window. Space heating drops away entirely, since the high-performance thermal envelope maintains comfort without it.

The resident experience

Residents were onboarded onto the Sero Life platform as part of the new-build handover process. Rather than asking them to manage a complex energy system, Sero's team built bespoke heating schedules around each household's existing routines: when they wake, when they leave for work, when they return, when they go to bed. From those inputs, the system forecasts annual energy demand and sets a fixed monthly bill accordingly.

The Sero Life App gives residents full visibility and control: adjusting temperatures or schedules takes a single tap. But for most residents, there's simply nothing to do — the system handles everything, and the bills are lower than they've ever been.

Scale and legacy

The active dDSR trials concluded in January 2021, but FLATLINE's most important outcome is what came after: the model became business as usual. All 225 homes at the full Parc Eirin development are now being fitted with the FLATLINE technology — far beyond the original 56-home trial. The same Parc Eirin site also served as a test bed for the sister VALUER project, which demonstrated that homes built and operated to this standard command measurable premiums in the property market.

The project established that domestic DSR is not a theoretical proposition. It works. It saves money. Residents love it. And it opens the door to a new model for how the UK's housing stock can participate in — rather than simply draw from — the energy system.

The consortium

Project documents