On Thursday 22 October, I braved Storm Austen to attend People's Emergency Briefing #4000 at the Community Centre in my village, Princetown.

It was run by kind volunteers from Totnes, who know the town's Energy Local scheme, in which members buy power from local generators. The turnout of 40 to 50 was impressive. I'm not sure whether the storm or the Jackdaw announcement drew more people.

I work deep inside the energy sector, so it was interesting to hear from people outside it. They are frustrated with Government, with energy companies, and with landlords and owners. Wittingly or not, these have together left ordinary people with some of the most expensive, and least secure, energy bills in the world.

The politics in the room were predictable. Conservative governments, and our local MP, took most of the blame. (I have never seen quite so many Free Palestine badges outside the M25.) Labour was never named. It appeared only as "the Government", which had just decided this or that. There was an easy assumption that the Liberal Democrats, who now hold many seats across the South West, would do better. Reform and the Greens, the two parties with the loudest views on net zero, from opposite ends, were not mentioned at all.

The policy agenda was selective too. Jackdaw came up again and again. The newly legal plug-in solar did not, and nor did reports that ministers want to cut the heat pump grant.

To be fair to them, the effective ban on onshore wind in England was not a coalition policy. It came in June 2015, a month after the coalition ended, from the new Conservative majority government, and Labour lifted it in July 2024. Still, I pushed back a little on the Lib Dems. Backing a controversial wind farm or pylon line near the people who vote for you takes courage, whatever colour your rosette. As we'll see, the South West has mostly avoided that test, and it is paying for it.

If a People's Emergency Briefing comes to a village hall near you, go. It is the closest thing to a focus group on climate you'll ever get to attend.

Few of the facts surprised me. I would question how some were presented, for example the cost of offshore wind.

Four misunderstandings I keep meeting

1. Heating is most of the problem

People underestimate how much of our energy goes on heating.

In 2024 the UK used 1,473 TWh of energy at the point of use. 42% of it, 619 TWh, went on heat: warming rooms, heating water, cooking and industrial processes. Transport took 43%. Lights, appliances and machines, which is what most people picture when they think of "energy", took only 15%.

Two more details sharpen the point:

• Leave out international flights and heat becomes the largest use outright, at 47%.

• Only 12% of that heat comes from electricity. The rest is mostly gas burned in boilers. That is why, in a gas shortage, Britain would switch off its power stations before it cut off one gas boiler. On a cold morning, the gas grid delivers more energy to homes than the electricity grid does all day.

And the thing people still picture first when you say "saving energy" is switching off the lights. Lighting in UK homes used 4 TWh in 2024, about 1% of household energy and 4% of household electricity. That is down 72% since 2010, as LED bulbs replaced incandescent ones. Across homes, offices, shops and factories, lighting is under 2% of all the energy the UK uses. For every kilowatt-hour that lights a home, nearly 80 go on heating it and its hot water.

2. So solar can do less than people hope

A few hours before the storm hit, I took the dog out towards the temperate rainforest near the village, expecting a last look at the autumn leaves. I admire the wood from a distance: it gets more visitors than its mosses and lichens can take. Even from across the valley, the oaks were still almost entirely green in late October, unlike many trees lower down in southern England. The morning was bright and clear, the latest in what has been the sunniest year on record in south-west England, as I wrote recently.

Even so, sunshine and heating demand barely overlap.

3. Heat pumps matter more than people think

A heat pump doesn't burn anything. It moves heat from the outside air into the house, the way a fridge moves heat out of its box, so it delivers more heat than the electricity it uses. Mine sits in a postwar prefab at the top of Princetown, one of the highest villages in England. Over four and a half winters it has turned 9,800 kWh of electricity into 32,000 kWh of heat, a ratio of about 3.3 (more on that here). Metered data from hundreds of British homes shows that 3 to 4 is normal for a well-installed system.

Now scale that up. In 2024 the UK used 458 TWh of energy on space heating and hot water, mostly gas burned in boilers that turn about 85% of it into heat. Heat pumps working at a ratio of 3 would deliver the same heat from about 130 TWh of electricity. Heating would go from nearly a third of all the energy the UK uses to about a tenth.

This is the part people miss. Electrifying heat doesn't mean finding 458 TWh of new electricity. It means finding about 130 TWh, around half of what the UK uses today. That's a lot, but it can be done. The catch is that it is needed in winter, when there is more wind and much less sun.

The bigger catch is the upfront cost, and it is the part people miss most. A heat pump costs about £12,000 to £14,000 to install, against perhaps £3,000 for a new gas boiler. That money has to come from somewhere: the homeowner's savings, a loan, or a government grant paid for by taxpayers. Multiply the gap by the more than 20 million British homes heated by gas and it comes to roughly £200bn. That is nearly three times the transmission investment Ofgem has just approved.

The grant doesn't make that go away; it moves it. The Boiler Upgrade Scheme pays £7,500 per home and has £625m to spend this year: about 83,000 homes. At that rate, converting 20 million homes would take more than 200 years. And ministers are already reported to want to cut the grant to help pay for defence. You can't conjure £200bn from nowhere. Either households find it, or something else gets less.

4. Wind and solar are not "free"

There is no fuel to buy for a wind or solar farm, so it is natural to think the electricity they make is free. It isn't. On top of the wholesale price for the power they sell, we pay most of them a subsidy:

• Older farms get Renewables Obligation certificates for every unit they generate, whatever the wholesale price. I've argued before that this scheme now slows the transition it was meant to speed up.

• Newer farms hold Contracts for Difference. These top their income up to a fixed "strike price" when wholesale prices are low, and make them pay money back when prices are high, as many did in 2022.

So the subsidy bill moves the opposite way to wholesale prices. It is biggest on stormy days, when output is highest and power is cheapest: the "surplus" days in my five stereotypes of the grid, when prices go negative and wind farms are paid to switch off. (Newer contracts stop paying when prices go negative. Renewables Obligation certificates keep coming, which is why some older farms will pay to keep generating.)

Why pay a subsidy at all? Because almost all of the cost of a wind or solar farm is paid up front: the turbines and panels, the land, the cables, the finance. Spread that cost over every unit the farm will make in its life, the way a mortgage spreads the price of a house over 25 years, and you get a cost per unit. Economists call this the levelised cost. The strike prices wind and solar farms bid in government auctions are the best public guide to it.

One warning before the numbers: levelised cost is the cost at the farm gate, not the cost of getting the power to your house. It is not the full system cost. Wind farms in the North Sea or the north of Scotland are among the cheapest in Britain to build and run, but Dartmoor is more than 500 miles away. Some of their power is lost as heat on the way. Getting the rest here takes new pylons and subsea cables, which cost billions of pounds and are paid for through network charges. It also needs backup for when the wind drops. None of that appears in the figures below.

I tried this on the room, framed as an opportunity. A single large, modern wind turbine near the village (not a small one) could produce electricity for 10p per kWh or less at the "system gate", where it joins the grid. That is well under half the 26p we pay. If the village could buy that power directly, at a price fixed for 15 years, Princetown could have cheaper electricity than anywhere around it, and know what it would pay until 2040. A private wire straight from the turbine would come closest to 10p. A local energy club through the existing grid, like the Totnes scheme and the arrangements new industry rules are bringing in, would still pay for the local wires and a supplier, but not the levies: my estimate is about 13p delivered, still half today's price. People were astonished, and the idea went down well. (I've written about how this could work for rural Britain.)

Then came the harder part: why the 10p turns into 26p on the bill. Most of the gap is everything else in the bill: network charges, supplier costs and what is left of the levies. And some of the power simply never arrives. Princetown is fed by a 10 km, 11,000-volt line up the hill from Yelverton. On a cold winter evening, with everyone's heating on, I'd estimate that about 8% of the power sent up it is lost as heat in the wire.

There was also a widespread recognition in the room, unsurprising among people who have chosen to live in the middle of a national park, that Dartmoor itself is neither wild nor in particularly good condition after decades of intensive farming. That matters for any turbine debate. The landscape a turbine would "spoil" is already heavily shaped by people.

On that basis, wind and solar are sometimes cheaper than gas and sometimes dearer.

• Cheaper: in the government's latest auctions, solar farms won contracts at £65 per MWh, onshore wind at £72 and offshore wind at £91 (2024 prices). A new gas power station costs about £147, on the government's own assumption of cheap gas and the hours gas plants actually run. At late-October gas prices the fuel and carbon alone cost about £180, before paying for the power station.

• Dearer: floating offshore wind, the technology planned for the Celtic Sea off Devon and Cornwall, won contracts at £216, more than gas at almost any price.

• Gas is subsidised too: gas power stations are paid through the Capacity Market just for being available when needed. The last two auctions will cost £2.6bn and £1.1bn in their first delivery years, and gas won more than half the capacity.

• Not the whole bill: none of these figures include the cost of keeping the lights on when the wind drops (a Dunkelflaute): backup power, balancing and extra network. Sunshine has its own costs too: balancing the grid on hot, sunny days now costs seven times what it did in 2017. The government's most recent estimate, from 2020, adds roughly £12 to £31 per MWh to wind and solar. That is real money, but it doesn't change the order for onshore wind and solar farms.

Small and local is not cheaper

The instinct in a village hall is that small and local must be better. On cost, it is usually the other way round.

Rooftop solar costs a household about £1,550 per kW to install, against about £660 for a solar farm, and it makes less electricity per panel: a roof is rarely ideally angled. My rough estimate is that rooftop power costs £140 per MWh, about twice a solar farm.

Rooftop solar still pays for the household, because every unit used at home saves the full retail price: 26p per kWh, or £263 per MWh. Less than half of that is the cost of the electricity itself. The rest pays for the networks, supplier costs and policy schemes, and those costs don't go away when one house uses less. They are spread over everyone else's bills, including households with no roof of their own. Britain's energy levies are broken in similar ways. (Government moved most of the Renewables Obligation off bills in April 2026, and VAT on electricity is zero until the end of March 2027, so this is now mostly about networks rather than "green levies".)

There is a temptation to treat private savings as proof of public good. A friend with an electric car saved £1,500 on petrol last year. Another halved their energy bill with solar panels. Both are true, and both are welcome. But a saving on your bill is not the same as a benefit to the country, what economists call the system benefit. About half the price of petrol is tax, fuel duty plus VAT, so a good part of that £1,500 is tax the driver no longer pays, which has to be raised from someone else. Much of the solar household's saving is network and other costs moved onto their neighbours. The benefit to the country, less fuel burned and less carbon emitted, is real, but it is smaller than the savings suggest. Incentives are meant to change what people do. The trouble starts when we mistake the incentive for the benefit.

Small wind turbines are even more striking. A small turbine that bothers nobody is easy to like. But a turbine's output rises with the area its blades sweep and with the cube of the wind speed, and the wind is stronger higher up. A modern onshore machine with a 150 m rotor sweeps about 100 times the area of a 15 m small turbine, in wind about 30% faster at hub height. Small turbines cost several times more per kW and run at under 20% of their capacity on good rural sites, against 36% for a modern wind farm. Building-mounted ones manage under 10%. Scale is what makes wind cheap. If a village wants the benefit of local wind, a share in a big wind farm does far more than a small turbine of its own: my share of a Scottish wind farm shows how.

And then there are the wires

The hardest cost to explain is the network. Networks already make up about a quarter of a typical household energy bill. Ofgem's settlement for 2026–31 allows for over £70bn of electricity transmission investment, and expects network charges for an average household to rise by about £108 a year by 2031, with offsetting savings elsewhere. Wind farms are cheapest where the wind is, which is usually far from where people live, so cheap wind needs long, expensive wires. Britain built its power stations in the middle; the wind is at the edges. Solar has a network cost of its own: a solar farm holds its grid connection all year but only uses it to the full on sunny middays, while batteries and other projects queue for the same capacity.

What most people miss about network charges is that they are mostly the cost of money. Network companies borrow to build, and our bills repay that borrowing, with interest, over about 45 years. The value of what they have built also rises with inflation, so a burst of inflation lands on bills for decades. When interest rates rise, the same pylon costs more every year: £1bn of new network costs bill payers about £34m a year at a 2% real interest rate, and £56m at 5%.

The same principle runs through almost the whole energy transition. Wind farms, solar farms, heat pumps and electric cars all cost more to build and less to run than what they replace. A gas boiler or a petrol car is cheap to buy, and you pay for it as you go, through fuel. That makes the transition unusually sensitive to interest rates. Borrow the extra £10,000 for a heat pump over 15 years at 2% and it costs about £780 a year; at 7%, about £1,100. That difference alone can cancel out the running-cost savings. Cheap money in the 2010s flattered the numbers. Dearer money is a big part of why the transition now feels so expensive.

What this means for the South West

This is where the conversation in Princetown got most interesting.

The South West has built a lot of solar: 4.4 GW, more than any other English region. It has built almost no wind: 358 MW onshore and none offshore, after nine years in which new onshore wind in England was all but banned. And apart from the new line connecting Hinkley Point C, it has had no big pylon projects. Nothing major is planned for Devon or Cornwall.

Most people assume that leaves the region cleaner and better off. It doesn't.

• Our electricity got dirtier. In 2019 the South West had the cleanest electricity of any region in Great Britain, largely thanks to the Hinkley Point B nuclear station. Hinkley B closed in August 2022. So far in 2026 the region's electricity has been about twice as carbon-intensive as the national average: gas has gone from about a third of the local mix to almost two thirds.

• The grid is held up by paying gas plants. Grid operator NESO says most of its actions to keep voltage within safe limits are in the South West. Since Hinkley B closed, it has kept gas stations at Avonmouth, Plymouth and Southampton running for the region's voltage, and paid more than half a million pounds a day above market prices to do it. Part of the problem is the solar: on quiet, sunny days, local solar output with low demand pushes voltage up.

• Even community solar gets switched off. Derril Water, a 42 MW solar farm at Pyworthy owned by about 9,500 households and small businesses, was ordered offline in May and only came back at the end of September. The co-op says the cause was an area-wide voltage problem, made worse by works at Alverdiscott substation. The fixes the grid operator commissioned at Taunton and Exeter were due by the end of 2025 and slipped to this autumn. Its members lost around £2m, and because the farm is connected to the local network rather than the national grid, it does not expect any compensation.

• Local power cuts are the most frequent. In 2023/24, homes in the National Grid Electricity Distribution South West area had more interruptions than in any of Great Britain's 14 distribution areas.

• The fix is years away. NESO is now buying grid-stability services at Exeter and Indian Queens, for delivery from 2029.

None of this means the lights are about to go out. NESO keeps the system secure, and the cost turns up on everyone's bills rather than as blackouts. But a region that has, understandably, resisted turbines and pylons now relies on a few gas power stations, paid to keep running, more than anywhere else in the country. That surprises almost everyone I explain it to.

So what

The people in Princetown Community Centre were right to be angry. British households pay some of the highest electricity prices in the world, and much of that comes from decisions they had no say in. Their frustration was aimed at the government, energy companies and landlords, and some of it is deserved.

But there is no free option waiting behind them. Every route to cheaper, cleaner energy costs money up front, and someone always pays: homeowners, taxpayers, bill payers, or the neighbours who can't fit solar panels.

So the questions worth asking in a village hall are harder ones:

• Where is the energy actually going? Mostly on heat. A plan that doesn't deal with heating, and with who pays the £200bn for heat pumps, isn't a plan.

• What does it cost everyone, not just me? Rooftop solar and a small turbine feel cheap to the people who own them. Big wind and solar farms are cheaper for everyone.

• Who pays, and when? Subsidies, grants and network charges all land on someone. The costs nobody can see are the ones nobody fixes.

• What are we willing to have nearby? In the South West, saying no to turbines and pylons hasn't meant no cost. It has meant paying gas power stations to keep the grid steady.

That is a harder conversation than "it's free, and they're stopping us having it". It's also the one that gets bills down, and a village hall on a stormy night is a good place to start it.

A forecast that leans one way in spring and the other way in summer is worth a second look. So I went back to find out when it had flipped. It hadn't drifted. It changed overnight, on 18 May.

Two years of too little sun

Britain's official day-ahead forecast of solar output is published on Elexon's BMRS, alongside wind. The obvious thing to check it against is Sheffield Solar's PV_Live, which estimates what Britain's panels actually produced, and which NESO itself uses as its measure of solar outturn.

For two years the forecast was cautious. Across 2024 and 2025 it came in below what arrived in every month from March to September, typically by 5–15% over the day as a whole, and usually by most in the evening.

That caution showed up somewhere else, too. National demand, as NESO measures it, is what the transmission grid has to supply, so every rooftop panel shows up as demand that isn't there. Expect too little sun and you expect too much demand. Half-hour by half-hour at lunchtime, NESO's demand forecast missed in step with the solar forecast: for every gigawatt of sunshine the solar forecast failed to expect, demand came in between two-thirds and nine-tenths of a gigawatt below NESO's forecast. That's the lunchtime lean I'd seen in spring.

Overnight

Then, on 18 May, the forecast changed shape.

In the four weeks before, it was simply a bit low all day, by about the same amount morning, noon and evening. In the four weeks after, midday was spot on. The lunchtime shortfall had gone. But the curve had spread out at both ends: 14% too high between 6 and 10am, and 19% too high between 4 and 8pm. Over the whole day it went from about 11% too low to about 8% too high.

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Nscale calls it "this unfortunate London-wide grid issue". UKPN, which "would not discuss a single project", said many data centres connecting to its network are "awaiting works on the wider national electricity transmission network".

On Radio 4's Today programme the next morning, Adam Bell, energy partner at PF Global, was blunter: "it is about the grid, full stop." Bell's explanation is that the south-east has the demand while the generation is elsewhere, with gas in the Midlands and wind in Scotland and the North Sea. Getting that power south "means reinforcing connections, and it means doing so at scale". That work is "taking a very, very long time", slowed by a shortage of commissioning engineers and by decisions split across Ofgem, the system operator and the energy department.

He's right. The grid data backs him up, and it also shows there's a bit more to it.

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Correction, 24 October. After this was published I found that my heat pump's flow sensor had been set up with the wrong range, so the heat figures from my monitoring were 30–60% too low. Corrected, my Ecodan sits mid-table rather than near the bottom, and lesson 3 and several charts have been updated. The wet running in lesson 5 is unaffected: it still happens at the right flow rate. The long-run figures from Mitsubishi's own app never used the sensor. Thanks to Graham Hendra, whose comment about my low flow rate set me looking, and to John Ewbank, who had already flagged that my COPs looked suspiciously low.

Here’s the good news first, because there’s a lot of it.

In spring 2022, at the peak of the price shock that followed Russia’s invasion of Ukraine, I bought a heat pump with a £5,000 Boiler Upgrade Scheme grant. It went into a postwar prefab at the top of Princetown, one of the highest villages in England, on a moor that gets more weather than most of the country. Plenty of people would have told me that was the wrong house for a heat pump.

Four and a half winters later it has kept us warm at a lifetime efficiency of about 3.3: 32,000 kWh of heat for 9,800 kWh of electricity. This October the whole house, heat pump, hot water and two electric cars, cost about £40 in energy.

This summer I wrote about how I regret my heat pump lacks air conditioning. This is the winter sequel. It’s a happier one, though not entirely.

This autumn I found out that my heat pump has probably been running “wet” for years: letting liquid refrigerant into a compressor that’s meant to see only gas.

What should happen, then what mine does: a valve opens too far, and liquid floods the compressor.

No app showed it, no error code flagged it and no annual service would have caught it. And I didn’t find it on my own. I’m an economist; my education taught me far more about interest rates and trade balances than compressors and refrigerants. I found it thanks to a remarkable community of heat pump owners, engineers and tinkerers who share their data, tools and time for free.

So here are seven things I wish I’d known before I bought a heat pump, and who taught me each one. There’s a checklist at the end for anyone choosing one now.

1. It works, and you can prove it

Taught by: heatpumpmonitor.org

If you take one thing from this piece, make it this: heat pumps work, even in a draughty prefab on Dartmoor.

Each year mine has turned one unit of electricity into 3.2–3.6 units of heat. (2024/25 is missing because Mitsubishi’s cloud service dropped out.)

The way I know that, rather than just believing it, is heatpumpmonitor.org. It’s run by OpenEnergyMonitor, an open-source project founded by Trystan Lea and Glyn Hudson in North Wales, and it’s one of the best things to happen to heat pumps in Britain. Around 800 homes publish their real, metered performance for anyone to see, and there’s a free API that needs no key, which for someone like me is catnip. Mine is system 529. I’ve leaned on it before, in Heatpump Mythbusting, Heat pumps age like Bordeaux and I put 519 British heat pumps into the Balancing Mechanism.

Left: how much heat the house needed each day, in kWh and as an average kW. Right: how efficiently it was made.

The pattern is what you’d expect: the colder it gets, the more heat the house needs and the harder the heat pump works for each unit. It’s at its best on 6–10 °C days, at a COP of about 4, and drops to about 3 in a frost. What surprised me was the other end. Above about 12 °C, when the house barely needs heating, efficiency collapses. Which brings me to lesson two.

2. Bigger isn’t safer

Taught by: heatpumpmonitor.org’s data, and a few humbling charts

The survey for my house suggested a smaller unit than the 6 kW one I ended up with. Princetown gets properly cold, the installer suggested going bigger, and “better safe than sorry” felt sensible. I don’t blame the installer: plenty of professionals would have looked at a postwar prefab and assumed it needed all the help it could get. I went in with my eyes open.

Look at the right-hand scale on that last chart. Even the coldest day in four years, 9 January 2024, averaged only about 4 kW. Most heating days needed between half a kilowatt and two. A gas boiler simply turns down to match. A heat pump can only turn down so far, and mine can’t turn down very far at all.

heatpumpmonitor.org keeps owner-run tests of how low each model will go. The 6 kW R32 Ecodan bottoms out at about 3 kW, half its rating; only 6 of the 45 models tested do worse, and several 6 kW units from Nibe, Daikin and Grant get down to 1.1–1.5 kW. In practice the lowest mine actually runs is about 3.3 kW, more than half its rating. Here's how that compares with what the house needs:

On almost every heating day since 2022, the house needed less heat than my heat pump's lowest output.

Anyone who has worked on power markets will recognise this. A gas power station has a “minimum stable generation” level, about 55% of its maximum for the median British unit, and below that it has to switch off rather than turn down. My heat pump behaves the same way. On a mild day the house wants a trickle, the heat pump can only deliver a gush, so it runs, overshoots, stops and starts again.

16 October, a 10 °C day: the house needed about 0.7 kW on average. The heat pump started 13 times and sat idle 83% of the day.

On mild days mine starts about 16 times, against about 8 for a typical monitored system. My dashboard now flags these spells automatically; in the past week it found eight, all on 11–15 °C days. Every start costs a little efficiency and a little wear.

What I wish I’d asked: not “what’s the maximum output?” but “what’s the minimum, and how does it compare with what my house needs on a mild day?”

3. The brand matters, and you can check it

Taught by: the OpenEnergyMonitor team’s open data

When I bought mine, Mitsubishi billed itself as Britain’s biggest heat pump maker, and Ecodans have been built in Livingston, Scotland, since 2009. Both counted for me.

Since then I’ve noticed that when installers and enthusiasts recommend a brand, it’s more often Vaillant. There are no public market-share figures by brand, but heatpumpmonitor.org offers a clue.

One in seven of the first 200 or so systems published there was a Mitsubishi. Among recent arrivals it’s one in twenty.

That’s a self-selected group of well-informed enthusiasts, so it isn’t market share, but it’s an important signal. Is the preference fair? Across the 250 systems most like mine (air source, radiators, a full year of good data), it’s closer than I expected: Vaillant and Viessmann lead at a median COP of about 4.0, Ecodans sit mid-table at 3.9, ahead of Daikin and Samsung, and the spread within each brand is bigger than the gap between them.

So I compared my own unit with everyone else’s over the same weeks this autumn.

Of 273 comparable systems, mine came 123rd from the top, just above the median. Ten of the 17 other Ecodans did worse.

When I first published this, mine came 21st from the bottom, at a COP of 2.35. That turned out to be my monitoring, not the heat pump: the flow sensor had been set up with the wrong range and was under-reading. Corrected, it's 3.77 against a median of 3.69. What hasn't changed is that it starts and stops about four times as often as a typical system. So the brand isn't the problem, and overall nor is this heat pump; what's left is what happens each time it starts.

The clearest test is to split the weather. Across nearly 300 radiator systems on heatpumpmonitor.org, here’s how each brand does on cold days and on mild ones, with mine as the star:

Each dot is one heat pump’s typical day in that weather. My cold days come from four winters of Mitsubishi’s own figures; my mild days are metered.

On cold days, 0–5 °C, mine is bang on the Ecodan median, with a COP of about 3.4, and on cold days the brands are all much closer together. When the heat pump is working hard, there’s nothing wrong with it.

On mild days, 11–15 °C, the 18 other Ecodans hold their own at a median COP of about 4.9, alongside Grant and Samsung and not far behind Vaillant. Mine manages about 5.2, a little above them, despite starting about 16 times on a mild day against 6 or 7 for a typical Ecodan.

What does that add up to? My Home Assistant has now learned enough about the house, how fast it loses heat and how warm the radiators need to run, to estimate what this heat pump should use in any weather, at the efficiency mine already manages on cold days. Over the past year it used about 2,265 kWh against roughly 1,850 achievable: 22% more. Between 4 and 8 °C it's within 10%, and on the few days below 2 °C it used about 40% more. But nearly two-thirds of the waste comes outside December to February, on mild days and through the summer, when the heat pump is mostly heating water and stopping and starting. Above 12 °C it uses between one and a half and two and a half times what it should. One caveat: this uses Mitsubishi's own estimate of electricity, which on low-load days counts standby as heating and reads well above my meter, so the real gap is smaller, perhaps much smaller.

Each dot is one day. The blue line is my best guess at what this house should need: an estimate, not a guarantee.

Starting often isn’t the whole story, though. Vaillants start more often than any other brand here, about 10 times a day, and are still the most efficient. What matters is what happens each time mine starts, and that’s lesson 5.

Around then, at an industry conference, I nearly spat out my coffee when a senior figure from an energy company told me how far he’d had to go to get a Mitsubishi heat pump removed from his home because it performed so badly. I won’t say more, but what stuck with me was how hard he’d had to push before anyone accepted there was a problem.

4. Get the data from day one

Taught by: Phil Thomson (F1p) and the emoncms community

Mitsubishi’s MELCloud app shows a few temperatures and how much electricity you’ve used, and not much else. Since January 2022 it has had ten updates on the App Store; eight of them say only “Minor improvements and updates”. Owners have noticed. It’s rated 1.7 stars across Apple and Google, against 4.3–4.5 for the apps from Vaillant, Daikin, Viessmann and Panasonic. Mitsubishi’s newer replacement, MELCloud Home, does no better at 1.6, and only NIBE’s app scores lower. “The heat pump is fine, this app is not,” as one 2024 reviewer put it.

UK store ratings for each heat pump maker’s control app, October 2026.

You don’t have to live with the app, though. I run my heating through Home Assistant, which is free but takes some tinkering. If that’s not your idea of fun, Havenwise offers a much nicer app that works with Ecodans through Mitsubishi’s own cloud, so you don’t need any extra hardware. It can only see and change what Mitsubishi’s cloud lets it, though, so for the readings inside the refrigerant circuit you still need a bridge.

Mitsubishi’s MELCloud web app at 8pm on 17 October. It says 14 °C outside; the heat pump’s own sensor read 6–7 °C, and had last been at 14 °C four hours earlier. The building picture is a question mark.

Then I found a little Wi-Fi adapter made by Phil Thomson, known on the forums as F1p. I’ll call it the bridge. It plugs into a service port (CN105) on the heat pump’s controller and works a bit like an OBD reader for a car: every 30 seconds it reads what the controller knows, including readings from inside the refrigerant circuit that owners never normally see.

It costs £34.99 on eBay at the time of writing. That’s a rounding error on the cost of an installation, and about a ninth of what Mitsubishi charges for an engineer’s visit. The extra data it captures, compared with the manufacturer’s app, is invaluable. If I were having a Mitsubishi installed today, I’d ask for one on day one. (If the listing ever disappears, the design and software are open source.)

Because heatpumpmonitor.org runs on emoncms, which will store any time series you give it, I started logging everything the bridge could read: refrigerant temperatures, both expansion valves, fan and compressor speed, superheat and subcooling. All of it is now on an open, live dashboard at myheatpump.kilowatts.io.

The live diagram, shown in its running-wet state: liquid (cyan) is overflowing the accumulator into the compressor, and valve A is flagged as too open.

What I wish I’d done: fitted monitoring on day one, a heat meter or a bridge like this, and published it.

5. The fault you can’t see

Taught by: John Ewbank and the OpenEnergyMonitor forum

This is where I needed help. The raw readings were overwhelming, so I sent the data to John Ewbank, a data scientist who knows heat pumps. Within a day he’d spotted that a reading called superheat kept collapsing to zero. He knew what to look for thanks to John Cantor, Andrew Fuller and Graham Hendra, and Cantor had seen the same pattern on an Ecodan of his own. On the OpenEnergyMonitor forum I found “Anyone monitoring a new R32 Ecodan?”, a thread where early owners have been comparing notes since January 2022. Some of the sharpest people who took the plunge with Mitsubishi had been down this road before me.

Here’s what should happen, in plain English (the animation at the top shows it moving):

1. In the outdoor coil, cold liquid refrigerant soaks up heat from the air and boils into a gas.

2. The compressor squeezes that gas, making it much hotter.

3. In a heat exchanger the hot gas hands its heat to the radiator water and condenses back into liquid.

4. An expansion valve lets the liquid back into the coil at low pressure, and round it goes.

The valve’s job is to let in just enough refrigerant that all of it boils in the coil, so only gas reaches the compressor, a few degrees warmer than its boiling point: for R32, typically about 7 degrees, though it varies. That margin is the superheat. (Mitsubishi’s service manual doesn’t publish a target figure; the only number it gives is the alarm threshold I come to below.) My Ecodan doesn’t report this superheat directly. It reports the superheat of the gas leaving the compressor, which includes the heat of compression, so it runs higher: about 13–27 degrees on my healthy runs. Either way, zero is the warning sign. It means liquid is getting through.

Mine doesn’t. John’s tentative reading, based on the data we have so far, is that the valve doing the fine control “is too fast to open and too slow to close”. It opens too far, more refrigerant floods the coil than can boil, and liquid is carried through to the compressor. Superheat drops to zero, the compressor moves less heat for the same electricity, and it takes minutes for the valve to creep shut, before it overshoots again.

16 October, a hot water run: 14 minutes at zero superheat before the valve caught up.

On 16 October a hot water run sat at zero superheat for its first 14 minutes. While it was running wet it made about 1.6 units of heat per unit of electricity, not much better than an immersion heater; once the valve caught up, that roughly doubled, to about 3.2. It seems worst when the unit starts from cold: the same hot water run on a 16 °C afternoon went wet for only about a minute.

Then, at 2am on 18 October, came the worst case yet, spotted by John that morning. The controller started a hot water top-up although the tank was already at its target, and that run stayed wet for all 24 minutes, at an efficiency of about 1.3. By the end the valve had closed as far as it does in any of my data, and it still didn't dry out. It had started six minutes after a heating run that had itself been wet for most of its length.

2am, 18 October: a heating run that is wet for 11 minutes, then a hot water top-up that never dries out, even with the valve closed right down.

Across 6–16 October, superheat sat at zero for about 10% of heating run time and 22% of hot water run time. What does it cost? Less than I first thought. Comparing every wet half-minute since May with dry running at the same point in a run, it has added about 2% to the heat pump's electricity: about 3% on hot water and 1% on heating. Over a year that's roughly 40–50 kWh. For me that's about £1.50, because I pay an abnormally low 2.9p per kWh on average: I fixed my tariff before the Iran war, and a big home battery lets me buy almost all my electricity when it's cheapest. At a typical price-cap rate of 25–30p, it would be £10–15 a year. Individual runs can be much worse (the 2am top-up above managed 1.3 against about 3.5 for a dry run), and I don't yet have a winter's worth of data. But it isn't really an efficiency problem. The bigger worry is wear: compressors aren't designed to swallow liquid.

My first guess was the control software in the outdoor unit, which on mine is several years old, and it’s still a suspect. But the 2am run, wet even with the valve nearly shut, makes me less sure it’s the whole story: it could also mean there’s more liquid refrigerant in the system than the valve can manage. (On a monobloc like mine the refrigerant is sealed in at the factory, so that wouldn’t be the installer’s doing.) Checking the charge is now on the list. That’s a hypothesis, not a verdict.

See it for yourself. Everything here comes from my heat pump’s live data, open to anyone at myheatpump.kilowatts.io. There’s a diagram of the whole system with live readings (it lights up when the unit is running wet), charts you can pan and zoom, automatic warnings for every wet spell, valve hunt and bout of short cycling, a replay of each one exactly as it happened, and a download of every reading. If you’re an engineer, an installer or anyone else with an idea of what’s going on or how to fix it, I’d love to hear from you. The best ideas in this story so far came from people who looked at the data and got in touch.

The dashboard’s automatic warnings for a single day, 17 October. Click any one to replay it.

6. A clue for installers, not a complaint about them

Taught by: John Ewbank, again

This isn’t a story about a bad installer. As John put it to me, this level of refrigerant detail goes well beyond what most installers have ever had to get their heads around. Superheat and valve positions aren’t in Mitsubishi’s app, no error code fires, and nothing in a standard service asks anyone to look. By Mitsubishi’s own definition it isn’t even a fault: the unit’s protection only trips if superheat falls to −15 degrees for three minutes, and mine has never tripped it. That’s exactly why nobody notices.

That’s exactly why it’s worth sharing. If you’re an installer who’s been called back to an Ecodan that “just isn’t as efficient as it should be”, and you’ve checked the flow temperatures, the weather compensation, the pipework and the controls and found nothing wrong, this might be the missing piece. A unit can look fine on every reading you normally check and still be quietly running wet. A bridge, or the service tool during a hot water run, shows it within minutes.

What would actually fix it?

I’d like mine fixed without it costing my installer, or me, much more time. The data-gathering is done.

When I rang Mitsubishi, I think I rather overwhelmed the person on the other end. Their usual route for a performance problem is to send out an engineer, a visit they charge £318 for, to plug in a service tool and read the unit’s operating data. I already had that data, every reading every 30 seconds for weeks, from a £35 bridge. That’s no criticism of the helpline, which simply isn’t set up for a customer who arrives with their own diagnostics. But it shows how much changes when owners can see inside their own machines.

What’s left is a short list of fairly cheap steps:

1. A software update. The view from the community, including some very experienced engineers, is that it might improve things but probably won’t fix them completely. It’s still the obvious first step, and done at my installer’s routine visit on 5 November it adds little to their day.

   It does seem a shame, in 2026, that updating it means someone driving out with a laptop. My heat pump has been on the internet since the day it was installed. My phone, my car and my television update themselves overnight. A machine meant to run efficiently for 20 years, whose efficiency depends on its software, should be able to as well.

   There’s precedent. In summer 2025 Daikin wrote to some UK owners offering a free “software enhancement”, fitted by an engineer at no charge in about 20 minutes. Owners understood it to speed up how the expansion valve reacts at low output, which is exactly where mine struggles.

2. Ten minutes of watching a hot water run, with the service tool or my dashboard open, to confirm what the data shows and check the refrigerant charge.

3. Mitsubishi’s technical team. Mitsubishi have kindly offered to take the issue to them, which is where it belongs: whether the valve’s start-up behaviour can be changed is a question only the manufacturer can answer. The evidence is already packaged up, run by run.

Meanwhile I’m trying what I can on my own, starting with the hot water, since that’s where the worst episodes happen. Home Assistant, which already runs my heating, now does two new things:

• No more pointless top-ups. Once the tank has reached temperature, it lowers the target by ten degrees, so the controller has no reason to run again the way it did at 2am. If someone runs a bath, the normal target comes straight back. Over ten days, five of 29 hot water runs began with the tank already within a degree of its target.

• A pause after a wet run. For 20 minutes after any run that went wet, it holds off starting the hot water. At 2am a wet heating run was followed straight away by a hot water run that never dried out, while the midnight charge, which started after a dry run, was mostly fine. Two runs make a hunch, not a finding, so the dashboard’s warnings will tell me whether the pause helps.

Neither fixes the underlying problem, but both cost nothing and should cut the worst of it.

7. You don’t need to be an engineer any more

Taught by: all of the above, and a bit of help from AI

The other thing that made this possible was AI. I used Claude to read Mitsubishi’s 87-page service manual, decode the bridge’s data and build the dashboard. It didn’t replace the people above: every time it got ahead of itself, someone like John set it straight. But it let an economist ask much better questions of the people who know.

Live with it, or push?

So where does that leave me? Since the correction, leaning towards the worried well.

The case is stronger than when I first wrote this. Once my monitoring was measuring properly, this heat pump turned out to be mid-table this autumn, a little above the median and ahead of most other Ecodans, in a draughty prefab on one of the coldest hilltops in England, and the house has never been cold. The wet spells are real, but they cost about 2% of its electricity: a couple of pounds a year on my tariff, £10–15 for most people. If my neighbour told me all that about their boiler, I'd tell them to stop worrying.

What still nags is wear, not money. A compressor that regularly swallows liquid seems unlikely to last as long as one that doesn't, and if mine does this, others probably do too, mostly in homes where nobody is looking. That's a question for Mitsubishi rather than for me.

So I'm taking the cheapest path for everyone: the software update at the routine visit, a winter of watching the dashboard's warnings, and Mitsubishi's technical team looking at the evidence they've already offered to review. If the wet spells go away, brilliant. If not, I'll have the clearest possible evidence, collected for free, and a heat pump that is doing its job in the meantime.

There's a lesson in the correction too. The most misleading number in this story came from one setting on the controller that nobody, me included, had thought to check. John Ewbank, who has given this a remarkable amount of his time, had already spotted that my efficiency figures looked too low to be right, and it was Graham Hendra asking why my flow rate was so low that sent me to the controller to find out why. Opening up the data is what exposed the wet running; letting other people look at it is what caught my mistake.

What I do regret is not digging into any of this four and a half years ago. The data and the community were already there. I just didn’t know to look, which is the main reason I’ve written this.

Questions worth arguing about

Should manufacturers answer for how their units perform when the public has paid for them? Mine was installed with a £5,000 grant; the scheme now pays £7,500. Faults like this aren’t visible in the manufacturer’s app and aren’t part of a standard service, so who’s meant to find them? And when the fix is software, shouldn’t it arrive over the internet connection the unit already has, rather than at £318 a visit?

Is opening up this data good for heat pumps, or does it just make more worried well? My wife, a therapist, has a phrase for people who can afford to obsess over small symptoms. Are tools like AI turning heat pump owners like me into exactly that, chasing a few percent of efficiency and creating grief for installers and helpdesks? Or is opening up the data from inside heat pumps exactly what gets them performing at their potential, beating gas boilers on cost and easing the strain on the grid?

I still lean towards the second, even having just been a case study in the first. I'd love to hear from you, especially if you've ever looked at your own superheat. Tell me in the comments.

Before you buy: a checklist

• Look up the models you’re considering on heatpumpmonitor.org, filtered to systems like yours.

• Ask about the minimum output in kW, not just the maximum, and compare it with your house’s needs on a mild day.

• Resist oversizing. Ask to see the heat loss calculation.

• Budget for monitoring from day one: a heat meter or, for a Mitsubishi, F1p’s CN105 bridge.

• Ask whether the annual service includes software updates, and whether your installer can check refrigerant readings if performance seems low.

• Ask whether it can cool as well as heat. (Here’s why.)

And if you already own a heat pump, put it on heatpumpmonitor.org. The next person choosing one will thank you.

My heat pump’s live data, warts and all, is at myheatpump.kilowatts.io. Have a look, and if you can see how to fix it, tell me.

Over the same five years the number of company car drivers rose by 120,000, and the tax they paid fell by £1 billion.

This is the second piece in a pre-Budget sequence on who is about to pay for taking levies off energy bills. The first was about the heat pump grant, a cut that would fall on wealth. This one falls on income. The last piece adds up the bill.

It is also the larger of the two, and nobody is talking about it.

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"No, and I think it's r…

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Tuesday 23 June had two of those moments. First, NESO bought power across the Channel, only for the market to sell more of it straight back to France, where it fetched twice the price. Then, at 16:15, NESO tried to tell RTE (the French grid operator) that Britain could no longer offer France emergency help. According to NESO, the message reached Paris the other way round: that France would no longer be helping Britain. To me, to you.

Paul and Barry could at least point at the wardrobe. At 16:15, NESO had to describe it down a phone line: which way, from when, until when, and in the right order. Get one word the wrong way round and France thinks you're cancelling its help rather than yours.

Here's the evening, from NESO's own timeline. Six messages about emergency help, in a little over four hours:

1. 16:15, NESO to RTE. NESO meant to say it could no longer offer France help from 4:30 to 6:30pm, because of network constraints in the South East. According to NESO, it came across the other way round: help from France to Britain.

2. 16:46, RTE to NESO. France withdraws its emergency help to Britain for 7 to 8pm. Whether that was a reply to the first message, none of the reports says.

3. 18:30, NESO to RTE. Britain can send France 500 MW of help, 8 to 11pm. To you.

4. 19:48, NESO to RTE. Scrap that. Could France send Britain 500 MW, 8 to 9pm, instead? To me.

5. 20:00. France delivers. Exports to France drop by 500 MW, and Britain's frequency, low for more than an hour, recovers.

6. About 20:30, RTE to NESO. No more help until 1am. The hour Britain asked for is honoured, and that's it.

Nobody dropped the wardrobe. But it went up and down the stairs a few times.

In fairness to NESO, the French have long found the British hard to follow even when we say things the right way round. There's a well-worn guide to what Britons say and what they mean: "quite good" means disappointing, "I'll bear it in mind" means it's already forgotten, and "with the greatest respect" means something unprintable. Grid operators have their own dialect. "Margins are a little tight this evening" means please send help. "We may be able to offer some assistance" means please don't ask. RTE, to its credit, needed no translation at 20:30: no more help until 1am.

The price of help

Phil Hewitt put his finger on the market side of Tuesday evening. Reading NESO's timeline, he noticed that NESO thought it had secured the system by buying power over the interconnectors, "only to find that it is all traded away because the French market was willing to pay twice as much for power as GB": about £1,200/MWh in France against £600 in Britain. By 17:45 the plan for the 19:00 hour had swung from importing 3,528 MW from France to exporting 1,500 MW.

NESO spent the evening carrying the wardrobe upstairs. The market kept sliding it back down. It wasn't sabotage. It's just which way the stairs went. Defying gravity makes a great musical. It's a wicked way to balance a grid.

I can't help chuckling at the imperfect. At 16:15 NESO meant nous allions vous aider, "we were going to help you", as in, we won't now. What reached Paris was the other way round. Lost in the Channel. Past imperfect, present tense, future haute tension, which is what the French call high voltage.

France, it turned out, had something up its sleeve. Fittingly, the French call the Channel la Manche: "the sleeve". At 20:00 it played its cards: reactors at Gravelines and on the Rhône already climbing back from the heat, then pumped storage at Grand'Maison and Montézic and reservoir stations across the Alps and the Massif Central, switched on in waves at 20:01, 20:06 and 20:17. About 2.25 GW of French plant came up within the hour, and Britain's frequency recovered in 191 seconds. (I told that story in The Night France Saved the British Grid.)

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1. Stop gas exports to mainland Europe. "If we were exporting, they would be your largest load and they would go first." Not Ireland, which is never cut.

2. Shut down gas-fired power stations, "the next set of large loads".

3. Isolate sections of the local gas networks, cutting off homes.

Electricity has a room like it, and it is also secret. NESO kindly gave me a tour of its electricity control room after I published the kilowatts.io dashboard last December. ITN filmed inside it on the day in 2024 that Britain's last coal power station closed. One fun fact from the tour: the wall-wide circuit map shows Britain on its side, with east at the top and west at the bottom.

I went to the data to see how much gas sits on each rung. The answer changes what the ladder means. The first rung is empty on the days it would be needed, there are rungs missing, and the order itself says something uncomfortable about which energy customers Britain protects.

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So I went through every outage notice published for a gas power station since mid-2017, every revision of each one, every availability plan generators have given the market since 2021, and the half-hourly output of every unit since 2019, to see which of those hold up.

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Three weeks ago I put an air quality monitor in there. It measures CO2, particulates, volatile organic compounds, humidity and, because we live on Dartmoor granite, radon. I already log the house's electricity every ten seconds. So when the in-laws came for Sunday lunch on 27 September, the roast was the best-instrumented meal I have ever cooked. The one sensor missing from the record is the one that was actually in the chicken: the Meater probe talks to my phone, not to Home Assistant.

I had a plan for it, too.

The plan

Our house is all-electric. There is no gas hob, no gas oven and no boiler: a heat pump, an induction hob, an electric oven and two electric cars. Every unit of energy that goes into a meal comes off the grid, which means I can choose how dirty that energy is by choosing when I cook.

So: chicken, not beef. Lunch, not dinner. The oven went on at about half past eleven, into a South West grid that was sliding from 150 grams of CO2 per kilowatt-hour towards its low for the day. It was a blustery Sunday, with wind supplying a quarter of the region's power, and when the sun finally came out after one o'clock the grid dropped to 70 g/kWh at half past two.

It worked. The kitchen used 6.5 kWh between eleven and half past three, at an average of 112 g/kWh. Call it 0.7 kg of CO2. The same cooking at that evening's 297 g/kWh would have been 1.9 kg. (Autumn is a good time to try this: there is still enough sun to dig a hole in the middle of the day.)

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The same high pressure that switched off the rain switched on the sun. Princetown has just had its sunniest summer in 36 years. That set me wondering whether 2026 was Britain's sunniest year on record.

It isn't. And the reason why turned into a bigger story than the record itself.

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I held Friday back on purpose. Monday's story could be told from data published on the day: boundary limits, outage notices, interconnector flows. Friday's could not. Friday had something Monday did not, a frequency excursion, and that told me the whole system had been short of power for a few minutes. It could not tell me who was short. The answer is in Elexon's settlement data, which records what every metered generator actually produced in each half-hour, and which is only published a few working days after the event. The first run for Friday, the Initial Interim run of the P114 files, arrived at 06:45 on Wednesday 14 October. This piece is built on it. It points somewhere I did not expect to be looking.

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On the government's own figures, they have a point. More than half the households that received a heat pump grant in the scheme's first two years lived in a home with four or more bedrooms. Among all households in England and Wales the figure is one in five.

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Emergency Assistance is the instrument of last resort between neighbouring system operators. It is what you reach for when the ordinary tools have run out.

At 1,200 MW this was the largest Emergency Assistance on a British interconnector since at least May 2023, which is as far back as the published warnings go. The last time NESO asked for emergency imports on any scale was the evening of 23 June, when it took 500 MW for one hour. Monday peaked at more than twice that and delivered roughly 1,200 MWh against 500.

Here is the odd part. Britain was not short of electricity. In both half-hours of the emergency, the national system was long: there was more generation than demand. The shortage was local. It was in the South East.

System frequency says the same thing: it stayed between 49.83 and 50.18 Hz all day, inside the normal operating band, and the only wobble around the emergency was the usual swing as the interconnectors changed schedule on the hour.

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At home, 3.6 million households heat with heat pumps. Six million electric cars charge overnight on time-of-use tariffs, read by the smart meter every home has had since 2025. Solar panels are a niche: about 3 GW, mostly on roofs. Nobody has built a grid battery.

This is not science fiction. It is Gone Green, the flagship scenario in National Grid's first UK Future Energy Scenarios, published in 2011. It was the only scenario the report modelled in full detail, and the one it was built around.

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I started with no view. I have ended with a list of things that point one way, a list that points the other, and a short list of things nobody outside the companies can measure. All three are below.

Everything here comes from public data: Elexon's half-hourly records for all 83 gas units on the system, NESO's constraint cost figures, and published gas and carbon prices. It describes who owns what and when it runs. It says nothing about how anyone prices or bids, and I have not looked.

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At 8pm on 24 July 2026, Britain's grid operator did something it had not done all year. Margins were tight, so NESO cut the capacity Britain could offer for export to France, Belgium, the Netherlands, Denmark and Norway to zero. At the same moment, about a gigawatt was flowing the other way across the Irish Sea, to the island of Ireland, as it does in almost every hour of the year.

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