ChatGPT & DALL-E generated panoramic image of a pile of supersaturated sodium acetate (Hot Ice) hand warmers on a steel barge on the Thames.

Barges Of Giant Hand Warmers Likely Won’t Be Heating London

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This morning Dave Borlace of YouTube Just Have a Think fame reached out to ask me about a scheme to capture waste heat from a trash burning electricity plant, put it in thermal storage on barges and tow it 28 kilometers upriver to displace gas burning boilers in a district heating scheme. It’s all very Rube Goldberg-y, with the same chemicals used in hand warmers stuffed in shipping containers and a couple of big barges a day taking 56-kilometer round trips. But does it pencil out?

The chemical mixture, per the company’s published, peer-reviewed paper, is sodium acetate trihydrate and water, with a couple of trace elements added to prevent stuff from precipitating out of the liquid and ruining performance. Unlike hand warmers, it’s reusable thousands of times. The stuff is safe enough, although you wouldn’t want to drink it or spend any time around larger concentrations of the polymer. If the barge sank, it wouldn’t be a big deal.

The energy density appears to be 60 Wh/kg (218 kJ/kg) of thermal energy, so not electricity nor expected to be, a common excess of thermal energy storage solution claims. Given the low temperature of 58° Celsius for the molten liquid, that’s completely useless for making electricity, so the units are imperfect, but useful for comparisons. This is basically molten salt, but much lower temperature than the molten salts used in experimental nuclear reactors or dead-end concentrating solar power plants like the one that failed recently in Morocco. That’s good, because when that stuff ‘freezes’ into a solid, it tends to expand and rupture tanks, as well as having to be chipped out manually. The high temperature variants are also very corrosive, which this stuff seems to avoid.

Because it’s exploiting phase change energy characteristics — solid to liquid and back with the very high energy requirements of just the phase change — it’s not worth heating it much above 58° C because the vast majority of the energy comes from changing phase. It’s like water that stays at 0° Celsius for quite a long time before changing to ice, and vice versa. It’s the same thermodynamic party trick that we use to keep our iced tea cold.

The biggest Thames barges are 1,650 metric tons in capacity, so ignoring the pesky containers, that’s just under 100 MWh of low-temperature heat storage. They are asserting two barges with 120 MWh between them, so that pencils out as viable.

A 28 km river trip twice daily for the two very large barges is worth exploring for costs and carbon debt. That’s 3-4 hours one way upriver, and 2-3 hours downriver. Upriver would likely require a MWh of energy. Downriver a third of that probably. Diesel has an energy density of 12.6 kWh/kg and tugs are maybe 30% efficient, so that’s about 300 kg of diesel, so almost a ton of carbon dioxide per round trip or two tons a day. (Any mistakes are mine from Googling for tugboat power requirements, but it doesn’t appear material if I’m off a bit.)

That’s a tug and crew making two trips each way fully loaded over eight hours every day. Probably 4-5 people in the crew with a labor cost of perhaps £60k per person annual labor costs. Plus insurance, operational costs of tugs, etc. Calling it £1,500 per day in operational costs wouldn’t be out of line.

The sodium acetate trihydride costs around £500 per ton, and 120 MWh would require about 2,000 tons of the stuff. So that’s a £1 million just for the storage medium. Reusable up to 10,000 times they say. In theory that’s just under 30 years. Probably another million for the barges. In practice, let’s amortize it over 20 years. That makes it quite cheap actually, only about £300 per day. The heat capture facility at the source of heat might cost another £1.5 million per extrapolation from this study, so another £200 per day amortized.

So, 120 MWh of low temperature heat for operational costs of £2,000 or perhaps £17 per MWh. Two tons of carbon dioxide or 17 kg per MWh.

Of course, they are burning waste for energy to make this heat and that means they are burning plastics. That means that they are turning durably sequestered carbon into atmospheric carbon inefficiently. Every ton of municipal solid waste emits over a ton of carbon dioxide. The electricity turns out to be about 540 grams CO2e/kWh, which is to say it sucks. Also, lots of the waste could be recycled and the biomass should be ending up in compost or other biomass utilization schemes.

So transporting the stored heat isn’t particularly high emissions, but making it certainly is. If the heat were being captured with 100% efficiency at the waste burning plant, 120 MWh of heat would equate to perhaps 60 MWh of electricity. But it’s likely only 50% efficient, so it’s probably one to one. That 120 MWh of heat shares the 540 grams CO2e/kWh, so call it 270 for each. That means the heat has a carbon intensity of 270 kg per MWh and a day has a carbon intensity of over 32 tons of CO2. That’s about 12 million tons of CO2 per year.

Seems a bit Rube Goldberg-y for low temperature heat. You could just sink a geothermal shaft and put in an industrial heat pump that turns electricity in heat very efficiently with no one looking at it. No crew. No diesel. No dealing with tides. Decarbonizing electricity too.

A ground source industrial heat pump with a COP of 3 (normal for heating, with cooling being higher), would require 40 MWh of electricity for the same heat every day. At 162 grams CO2e per kWh in London in 2023, that’s about 6.5 tons of CO2 a day or 2.4 million tons per year. That goes down annually, of course.

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The 40 MWh per day at London commercial rates would cost perhaps £4,400 per day. A 2 MW heat pump (40 MWh/24 hours rounded up) and a bit of thermal storage to balance higher demand periods might cost £2 million as well, about the same as tugs and the heat storage material, so £300 or so there. Round that to £5,000 per day including maintenance and the like.

It actually seems to pencil out economically, assuming you have ‘free’ waste heat 28 km up river and there is no cost of carbon. And assuming my quickly Googled source of operational costs for Thames tugboats make any sense.

But let’s price carbon in for fun. The current UK carbon price is £64.90 per ton of CO2e. The waste heat plant at 540 grams CO2e per kWh, 0.54 tons per MWh, should be paying £35 per MWh in carbon fees. That turns into perhaps another £2,100 per day for the barges of hand warmers, sharing the cost with the electricity. For the heat pump solution, the carbon price is included in the electricity, so it’s not paying that.

How does this net out?

  • Barges of hand warmers about £4,100 per day
  • Ground source heat pump  about £5,000 per day

But that’s in 2024. The likelihood is that the UK will track the EU’s emissions trading scheme closely per policy guidance and communications, but it’s not formally linked yet, apparently.

EU ETS budgetary guidance for business cases kicks in at that point, and when I say kick, it’s going to kick like a mule.

Comparison table of net present value of US/Canadian social cost of carbon to EU carbon price budgetary guidance
Comparison table of net present value of US/Canadian social cost of carbon to EU carbon price budgetary guidance, chart by author

Those are USD, so conversion is required. US$203 in 2030 is about £162 per ton. That turns the waste heat’s share of the generator’s carbon price into £5,200 per day. In 2040 it will be £9,300.

All of a sudden, that heat pump is looking better and better. The likelihood that the waste-burning electricity generating unit will continue to be profitable with increases in carbon pricing and lots of low carbon wind energy and grid storage hanging around is very low. I expect that if they actually started delivering waste heat from the plant, it would be a scheme that wouldn’t last much beyond 2030, throwing all of the amortization calculations out the window. If it doesn’t show a solid return on investment by 2030, it never will.

Burning municipal trash can’t be lower carbon. If you bolt on carbon capture, it becomes much more expensive. If you pay for the carbon dioxide emissions it becomes much more expensive. As the UK continues to build massive HVDC interconnections to jurisdictions sometimes thousands of kilometers away to share North Sea wind with Morocco, European hydro with the UK, and Moroccan sunshine with the UK, the ability for a trash-burning plant to compete is disappearing rapidly.

My guess is that the trash-burning electricity plant will stop operating sometime between 2030 and 2035, and as a result, won’t be producing waste heat. This is the same old story for the district heating facility, so they should be aware of this risk. After all, they only have gas boilers because they had to replace the heat from the Battersea Power Station, which shut down in 1983, then finally is being renovated into mixed residential and commercial space with Malaysian investors, with part of the facility re-opening in 2022.

Surely the district heating facility will see the carbon pricing trap and dodge the bullet, and the barges of hand warmers running laps up and down the Thames will remain an interesting idea. Or maybe not. It’s not like the UK has a recent history of great public decisionmaking, especially where water is concerned.

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Michael Barnard

is a climate futurist, strategist and author. He spends his time projecting scenarios for decarbonization 40-80 years into the future. He assists multi-billion dollar investment funds and firms, executives, Boards and startups to pick wisely today. He is founder and Chief Strategist of TFIE Strategy Inc and a member of the Advisory Board of electric aviation startup FLIMAX. He hosts the Redefining Energy - Tech podcast ( , a part of the award-winning Redefining Energy team.

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