The System Constraint
Peak energy demand is shaping the economics of heat electrification in the UK. As buildings transition away from gas to fully electric plantrooms, synchronised heating patterns risk transferring directly onto the electricity network, increasing pressure on generation and local grid capacity.
There is a fundamental distinction between the gas and electricity grids: the gas grid both stores and transports energy, whereas the electricity grid only transports it. Peak capacity was therefore embedded within the gas network. Electricity systems, in contrast, must balance supply and demand in real time. Large-scale electrical storage exists, but it remains capital-intensive and constrained at the scale required to buffer national heat demand.
Managing peak demand is therefore essential if electrification is to avoid disproportionate grid reinforcement.
The First Generation Response
Electrification has often been implemented as a heat pump-led exercise, with generation sized directly to peak conditions. Plantrooms have been configured around the characteristics of first generation units: low flow temperature operation, fixed flow rates, and limited temperature uplift per pass. More significantly, water has often been stored at low temperatures, or not stored in meaningful quantities at all.
Although high delta T storage was technically possible, most first generation units could only raise water temperature by 5–10 K per pass. Achieving a larger temperature spread within a thermal store therefore required high circulation rates and repeated charging cycles, often reducing stratification and limiting the effective delta T across the store.
Where temperature differentials are small, usable stored energy is limited. The store provides only short-duration buffering, and generation remains sized to real-time peak conditions. This outcome is not inherent to heat pump technology; it reflects the constraints of the first generation available to the UK market.
The Second Generation Opportunity
Second generation heat pumps are now available. They can achieve higher flow temperatures, operate at high delta T (30–40 K), and deliver variable volume performance. This allows the heat pump to function as one heat source within a broader system, rather than the defining constraint, and to charge thermal stores across a wider temperature range, increasing usable stored energy without increasing volume.
The shift enables a return to principles familiar from well-designed gas hybrid plantrooms: storage-led operation, peak decoupling, and rationalised installed capacity.
Second generation capability does not remove peak demand; it removes the constraint that previously limited how storage could be used. When significant thermal storage is combined with flexible hybrid energy centres and variable electricity tariffs, heat can be generated when electricity is lower cost and lower carbon, then stored for later use. This allows energy centres to materially reduce generation during peak periods and, where storage capacity permits, avoid operating at peak entirely. Electrical demand is therefore reshaped, rather than simply met in real time.
The Design Shift
The opportunity is therefore to redesign energy centres so that generation is decoupled from instantaneous demand, using thermal storage deliberately to absorb and release energy in response to system conditions.
At the level of a single building, this moderates site demand and reduces reliance on peak-period generation. Applied consistently across portfolios and regions, however, distributed thermal storage becomes a system-level intervention, reshaping aggregate demand and reducing pressure on national infrastructure.
Electrification cannot simply replace boilers with heat pumps and expect the system to behave as before. Peak demand must be managed deliberately, and storage must become integral to energy centre design.
This article forms the first part of a series examining peak demand in electrified heating systems. Subsequent pieces will address peak reduction strategies, plant sizing, and the economic case for pocket energy centres.
