Can the UK grid actually handle it?

How much electricity does replacing every gas boiler actually need?

Before asking whether the grid can handle electrification, we need to know what electrification actually requires. The starting point is UK gas consumption for domestic heating, which is startlingly large. Gas is so embedded in how British homes are heated that most people have no intuitive sense of the scale of what it delivers — or what replacing it would demand.

The UK's domestic gas sector delivers roughly the same amount of energy as the entire electricity grid — but at very different efficiency. A gas boiler turns gas into heat at about 85–90% efficiency. A heat pump turns electricity into heat at 200–400% efficiency (the SCOP). The result is that replacing gas with heat pumps does not require replacing like-for-like in energy terms. The question is: how much less electricity is needed than the gas it replaces?

The gap between the best heat pumps and the typical one — and why it matters enormously

This is where the debate about heat pump electrification gets uncomfortable. There is not one answer to "what SCOP will the UK achieve?" There are several, and they differ dramatically depending on whether you use the best available evidence or the average real-world installation record.

The difference between SPF 3.86 and 2.81 is not academic. Across 28 million homes, it is the difference between needing an extra 80 TWh of electricity per year and needing an extra 110 TWh. That 30 TWh gap is larger than the entire output of all UK solar panels in a year. Get the installation quality wrong across the fleet and you need several new power stations. Get it right and you need considerably fewer.

The annual energy numbers, while large, are not the critical problem. The UK grid already knows how to build more generating capacity. More renewables, more storage, more interconnection. A 23–44% increase in annual demand is a planning and investment challenge, not a fundamental impossibility. The real problem is not how much electricity, but when it is needed.

Why simultaneous demand is the actual grid killer

The UK grid currently handles a winter peak demand of approximately 36–47 GW. That is the maximum the system ever has to serve — and it is served by 71.7 GW of total de-rated generation capacity, providing a reasonable margin. Now consider what happens on a cold January morning when 28 million British homes simultaneously demand heat from electric sources.

This is not a subtle problem. On a cold morning, under naive electrification without any demand management, the peak electricity demand from heating alone would exceed the entire current capacity of the UK grid. Adding EVs makes it worse. This is the number that opponents of electrification cite when they say the grid cannot handle it — and in the unmanaged scenario, they are arithmetically correct.

Electric cars — another 27–67 TWh, but when do they charge?

By 2030, the UK is targeting a near-complete switch to electric vehicle sales. There were 473,348 EVs sold in 2025, taking total UK EV numbers above 1.5 million. With 9 million EVs on the road by 2030 as NESO targets, and up to 37.4 million by 2050 when net zero is achieved, the electricity demand picture changes significantly — but not catastrophically if managed well.

The EV story is almost entirely a story about timing. The electrons required to run the UK's car fleet are not the problem — 67 TWh to electrify all 40 million cars is about 21% of current consumption, generated steadily overnight when the grid has spare capacity. The problem is 44 million people arriving home at 6pm, plugging in, and demanding 7 kW each simultaneously. That peaks at well over 30 GW of additional demand — on top of the existing evening peak, on top of heating demand. Unmanaged, it is a grid crisis. Smart-charged, it is a grid asset.

The 100-amp fuse — Britain's hidden electrification bottleneck

The grid as a whole can — with investment and smart management — handle electrification. But the grid as a whole is not the first thing that runs out of capacity when you add a heat pump, a ZEB, a Sunamp and an EV charger to a typical British home. The first thing that runs out of capacity is the 100-amp fuse in your meter cupboard.

A typical modern UK home is supplied at single-phase 230V with a 100-amp main fuse. That gives a theoretical maximum of 100A × 230V = 23 kW. Older homes (pre-1980s) often have 60A or 80A supplies, giving only 14–18.5 kW. Three-phase supplies — which provide three times the capacity at the same amperage — are standard for commercial premises and in most of continental Europe, but are rare in UK homes. When you start adding up the loads in a fully electrified British home, the 100-amp single-phase fuse becomes the binding constraint very quickly.

The load meter illustrates the core message: the single-phase 100-amp supply is not a barrier to an all-electric home — it is a barrier to running all electric loads simultaneously. The ZEB charges between midnight and 6am on cheap Agile electricity. The EV charges overnight. The Sunamp charges from curtailed wind via the Eddi. The heat pump runs steadily during the day. The electric shower uses hot water that was pre-heated by the Sunamp, so it never runs at peak grid demand. At any given moment, the house draws less than 35% of its theoretical maximum.

The older homes problem

The 100A fuse is a modern standard. Pre-1980s housing — roughly half of the UK's stock — was commonly supplied at 60A (14kW) or 80A (18.5kW). A 60A home running a heat pump (2kW), an EV charger (7kW) and a Sunamp simultaneously draws 11.8kW = 83A. It is technically within the 80A limit but has essentially no headroom for anything else. A 60A home with an EV charger and a Tepeo ZEB charging simultaneously would draw 16.3kW = 113A — the fuse blows. In these homes, either the supply must be upgraded to 100A (a DNO application process) or smart load management must prevent simultaneous high-draw operation. Both are solvable. Neither is simple at 28 million homes' scale.

The substation nobody talks about — the £40 billion distribution problem

Beyond the individual fuse, there is a second constraint that operates at neighbourhood scale: the distribution transformer. Every street in Britain is served by a ground-mounted or pole-mounted transformer that steps the grid's 11,000V or 33,000V down to the 230V domestic supply. A typical residential distribution transformer rated at 500kVA serves 50–100 homes on a single phase, providing approximately 5–10kW of capacity per home at current design loads.

This was sized for a world where most energy in homes came from gas. The peak electrical draw was for lighting, cooking, and appliances — averaging perhaps 3–4kW per home at the evening peak with substantial diversity (not everyone cooks at exactly 6pm). Gas handled the thermal load silently, outside the electricity system entirely.

£40.7 billion to reinforce the distribution network for 5.7 million heat pumps is a staggering number — and it represents only about one-fifth of the full electrification task. Scaling to 28 million homes implies a distribution infrastructure investment in the hundreds of billions. This is why Ofgem's RIIO-3 settlement (2026–2031), the ED3 framework (2028–2033), and the Great Grid Upgrade are all necessary simultaneously — and why their combined cost of roughly £90 billion in the current pipeline still falls short of what full electrification would require.

What is already funded and approved — and where the gaps remain

What thermal storage does to the grid equation — the numbers with ZEBs and Sunamps

The peak demand crisis dissolves almost entirely when thermal storage is introduced at scale. The fundamental insight is that heat demand is inflexible in time — you need your home warm at 7am — but the electricity that generates that heat can be drawn from the grid at any time in the preceding 8–12 hours. A ZEB charged between midnight and 6am stores 40 kWh of heat that keeps the house warm all day without calling on the grid again. A Sunamp charged during the low-cost night provides hot water all morning without the heat pump running a DHW cycle at peak demand time.

The numbers look very different through the lens of thermal storage and smart demand management. A peak addition of 20–35 GW overnight — at a time when wind is generating, solar is not consuming overnight generation, and demand is at its lowest — is a very different challenge from 78 GW of simultaneous demand at 7am. It requires grid upgrades. It requires more renewable generation. It requires distribution network reinforcement. But it does not require a grid of impossible scale. It requires a grid that is perhaps 50% larger than today's, operating smarter, over a longer charging window.

Should there be a grant to upgrade homes to three-phase supply?

The load meter analysis raises an obvious follow-up question. If single-phase 100A is the binding constraint on running a fully electrified home — ZEB, heat pump, EV charger, Sunamp — simultaneously, why not simply upgrade homes to three-phase supply? Three-phase gives approximately three times the capacity: 3 × 100A × 230V = 69 kW instead of 23 kW. You could run everything at once with room to spare. It is the standard for new builds in Germany and the Netherlands. Should the UK grant it?

What three-phase upgrade actually costs

The minimum cost charged by UK Power Networks for upgrading to three-phase is £1,800 inc VAT. However, 70% of upgrades cost £3,500–£6,000 (plus VAT) for the DNO work alone. Add internal rewiring — new consumer unit, load balancing across phases, new three-phase meter — and the total typically lands at £3,500–£12,000 for a proper 100A-per-phase upgrade. Real-world quotes on installer forums regularly come back at £8,000–10,000 just for the DNO component. At 28 million homes, a universal three-phase grant programme would cost somewhere between £100 and £280 billion. That number rules out a universal approach entirely.

The European comparison — why Germany is more expensive

In Germany, heat pumps with high-power heating elements of 6–9 kW require a 400V three-phase connection. Electrical connection costs in Germany range from €1,800 to €4,000. This is one of the reasons German heat pump installations are significantly more expensive than British ones — the three-phase requirement adds cost that the UK avoids by using single-phase supply with smart load management instead. The UK's approach is not backwards. It is a deliberate (if implicit) choice to solve the same problem more cheaply through software rather than infrastructure.

Smart load management — the same problem at a fraction of the cost

The case against a universal three-phase grant is that the problem it solves is already solved by smart devices at far lower cost. A survey from UKPN suggested that for most domestic cases 100A single phase is adequate including induction hob, PV, battery, EV charger and heat pump — because smart devices prevent simultaneous operation. The ZEB charges overnight when the EV is idle. The Eddi backs off the Sunamp when the ZEB is running. The Zappi reduces EV charging rate when the heat pump fires up. At any given moment, the home draws well within its 23 kW limit — not because it has more capacity, but because its devices are intelligent about when they demand power.

A smart load management device costs £400–850. Three-phase costs £5,000–12,000. The problem being solved is identical. The cheaper solution is available today, without planning applications, DNO approvals, road opening licences, or waiting lists.

Where targeted three-phase investment does make sense

The smartest version of a three-phase policy would cost very little. A simple amendment to Part P of the Building Regulations requiring three-phase supply in all new builds from 2027 costs approximately £300–500 per home at construction — negligible alongside the £350,000+ cost of a new home. It would mean that every house built from 2027 onwards is future-proofed for any combination of heat pump, EV charger, ZEB and Sunamp without load management constraints. Within 20 years, as the housing stock turns over, the single-phase constraint gradually disappears from the new build sector without any government grant expenditure at all.

For the existing stock, the honest answer is that smart management is the solution and should be treated as infrastructure — mandatory alongside heat pump and EV installations, funded through the schemes that already exist, recognised in SAP and the Home Energy Model. That single change — requiring a smart load management device as a condition of any BUS or ECO4 grant — would cost perhaps £400–850 per installation and would solve the 100A constraint for the vast majority of homes that will electrify in the next decade.