EQUINOX — Equitable Novel Flexibility Exchange — was the first project funded by Ofgem's Network Innovation Competition to address one of the core challenges of the energy transition: what happens to the electricity grid as hundreds of thousands of heat pumps come online simultaneously at peak demand?
Via Sero, our role was in helping to establish the bid that brought this project to life, and then delivered the most technically exacting part of the trial: automated remote control of domestic heat pumps, with a Resident participation rate that no one in the industry had achieved before.
The challenge: heat pumps and the peak demand problem
Heat pumps are a cornerstone of the UK's decarbonisation strategy. But a large-scale shift from gas boilers to heat pumps creates a new pressure on electricity networks: concentrated demand at peak times, particularly cold winter evenings when heating loads are highest and grid capacity is most constrained.
The conventional response to this — building more network capacity — is slow and expensive. EQUINOX set out to test a different approach: could heat pump owners be incentivised or enabled to shift their demand away from peak periods, providing network flexibility while being fairly compensated and without any meaningful loss of comfort?
The Sero trial: automated, seamless, 100% retained
Sero's contribution to EQUINOX was delivered through its Building Energy Engine (BEE) — a cloud-based platform that monitored and managed energy systems in real homes at Aspen Grove in Cardiff, a development of EPC A zero-carbon homes built by Wates in partnership with Cardiff Council, each equipped with batteries, solar panels, and ground source heat pumps.
During EQUINOX events — typically two-hour windows between 5pm and 7pm, occurring two to three times a week — BEE responded to signals from National Grid Electricity Distribution and remotely turned off participants' heat pumps. Customers could opt out before or during any event, or leave the trial entirely at any point.
None did. The 100% retention rate across Sero's cohort throughout the entire trial was, to our knowledge, unprecedented in a project of this kind.
At an outdoor temperature of around 0°C, indoor temperatures dropped by just 0.25°C during the two-hour event periods. At 10°C, there was no measurable indoor temperature reduction at all. The homes' insulation was doing exactly what it should — making flexibility invisible to occupants.
What Trial 1 proved
The first trial ran from December 2022 to March 2023. Across 22 two-hour flexibility events involving 386 heat pump households from all EQUINOX partners, the project delivered a total turndown of 10.8 MWh — equivalent to 630 hours of flexibility. The average participation rate across all partners was 82%, with Sero's cohort achieving the full 100%.
Feedback was, in National Grid's own words, "overwhelmingly positive." Ninety-two per cent of participants reported being moderately or extremely satisfied with their experience. The early results indicated that well-insulated homes with heat pumps could provide meaningful network flexibility even during the coldest weather, without occupants noticing any disruption.
Trial 2 and the road to scale
A second trial ran from December 2023 to April 2024, with a target recruitment pool of approximately 5,600 customers across Octopus Energy, Sero, and Scottish Power — aiming to grow the cohort to 1,000 participant households, nearly three times the scale of the first. EQUINOX was designed from the outset to be a stepping stone towards national tariff design: demonstrating not just that heat pump flexibility works, but that it can be delivered equitably and at volume.
- National Grid Electricity Distribution
- Sero
- Octopus Energy
- Passiv UK
- SP Energy Networks
- Welsh Government
- West Midlands Combined Authority
- National Energy Action
- Scottish Power Retail
- Guidehouse